1 \input texinfo @c -*-texinfo-*-
5 @c oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
7 @c GNAT DOCUMENTATION o
11 @c GNAT is maintained by Ada Core Technologies Inc (http://www.gnat.com). o
13 @c oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
15 @setfilename gnat_rm.info
18 Copyright @copyright{} 1995-2008, Free Software Foundation, Inc.
20 Permission is granted to copy, distribute and/or modify this document
21 under the terms of the GNU Free Documentation License, Version 1.2 or
22 any later version published by the Free Software Foundation; with no
23 Invariant Sections, with the Front-Cover Texts being ``GNAT Reference
24 Manual'', and with no Back-Cover Texts. A copy of the license is
25 included in the section entitled ``GNU Free Documentation License''.
29 @set DEFAULTLANGUAGEVERSION Ada 2005
30 @set NONDEFAULTLANGUAGEVERSION Ada 95
32 @settitle GNAT Reference Manual
34 @setchapternewpage odd
37 @include gcc-common.texi
39 @dircategory GNU Ada tools
41 * GNAT Reference Manual: (gnat_rm). Reference Manual for GNU Ada tools.
45 @title GNAT Reference Manual
46 @subtitle GNAT, The GNU Ada Compiler
50 @vskip 0pt plus 1filll
57 @node Top, About This Guide, (dir), (dir)
58 @top GNAT Reference Manual
64 GNAT, The GNU Ada Compiler@*
65 GCC version @value{version-GCC}@*
72 * Implementation Defined Pragmas::
73 * Implementation Defined Attributes::
74 * Implementation Advice::
75 * Implementation Defined Characteristics::
76 * Intrinsic Subprograms::
77 * Representation Clauses and Pragmas::
78 * Standard Library Routines::
79 * The Implementation of Standard I/O::
81 * Interfacing to Other Languages::
82 * Specialized Needs Annexes::
83 * Implementation of Specific Ada Features::
84 * Project File Reference::
85 * Obsolescent Features::
86 * GNU Free Documentation License::
89 --- The Detailed Node Listing ---
93 * What This Reference Manual Contains::
94 * Related Information::
96 Implementation Defined Pragmas
98 * Pragma Abort_Defer::
105 * Pragma Assume_No_Invalid_Values::
107 * Pragma C_Pass_By_Copy::
109 * Pragma Check_Name::
110 * Pragma Check_Policy::
112 * Pragma Common_Object::
113 * Pragma Compile_Time_Error::
114 * Pragma Compile_Time_Warning::
115 * Pragma Compiler_Unit::
116 * Pragma Complete_Representation::
117 * Pragma Complex_Representation::
118 * Pragma Component_Alignment::
119 * Pragma Convention_Identifier::
121 * Pragma CPP_Constructor::
122 * Pragma CPP_Virtual::
123 * Pragma CPP_Vtable::
125 * Pragma Debug_Policy::
126 * Pragma Detect_Blocking::
127 * Pragma Elaboration_Checks::
129 * Pragma Export_Exception::
130 * Pragma Export_Function::
131 * Pragma Export_Object::
132 * Pragma Export_Procedure::
133 * Pragma Export_Value::
134 * Pragma Export_Valued_Procedure::
135 * Pragma Extend_System::
137 * Pragma External_Name_Casing::
139 * Pragma Favor_Top_Level::
140 * Pragma Finalize_Storage_Only::
141 * Pragma Float_Representation::
143 * Pragma Implemented_By_Entry::
144 * Pragma Implicit_Packing::
145 * Pragma Import_Exception::
146 * Pragma Import_Function::
147 * Pragma Import_Object::
148 * Pragma Import_Procedure::
149 * Pragma Import_Valued_Procedure::
150 * Pragma Initialize_Scalars::
151 * Pragma Inline_Always::
152 * Pragma Inline_Generic::
154 * Pragma Interface_Name::
155 * Pragma Interrupt_Handler::
156 * Pragma Interrupt_State::
157 * Pragma Keep_Names::
160 * Pragma Linker_Alias::
161 * Pragma Linker_Constructor::
162 * Pragma Linker_Destructor::
163 * Pragma Linker_Section::
164 * Pragma Long_Float::
165 * Pragma Machine_Attribute::
167 * Pragma Main_Storage::
170 * Pragma No_Strict_Aliasing ::
171 * Pragma Normalize_Scalars::
172 * Pragma Obsolescent::
173 * Pragma Optimize_Alignment::
175 * Pragma Persistent_BSS::
177 * Pragma Postcondition::
178 * Pragma Precondition::
179 * Pragma Profile (Ravenscar)::
180 * Pragma Profile (Restricted)::
181 * Pragma Psect_Object::
182 * Pragma Pure_Function::
183 * Pragma Restriction_Warnings::
185 * Pragma Short_Circuit_And_Or::
186 * Pragma Source_File_Name::
187 * Pragma Source_File_Name_Project::
188 * Pragma Source_Reference::
189 * Pragma Stream_Convert::
190 * Pragma Style_Checks::
193 * Pragma Suppress_All::
194 * Pragma Suppress_Exception_Locations::
195 * Pragma Suppress_Initialization::
198 * Pragma Task_Storage::
199 * Pragma Thread_Local_Storage::
200 * Pragma Time_Slice::
202 * Pragma Unchecked_Union::
203 * Pragma Unimplemented_Unit::
204 * Pragma Universal_Aliasing ::
205 * Pragma Universal_Data::
206 * Pragma Unmodified::
207 * Pragma Unreferenced::
208 * Pragma Unreferenced_Objects::
209 * Pragma Unreserve_All_Interrupts::
210 * Pragma Unsuppress::
211 * Pragma Use_VADS_Size::
212 * Pragma Validity_Checks::
215 * Pragma Weak_External::
216 * Pragma Wide_Character_Encoding::
218 Implementation Defined Attributes
229 * Default_Bit_Order::
239 * Has_Access_Values::
240 * Has_Discriminants::
247 * Max_Interrupt_Priority::
249 * Maximum_Alignment::
254 * Passed_By_Reference::
268 * Unconstrained_Array::
269 * Universal_Literal_String::
270 * Unrestricted_Access::
276 The Implementation of Standard I/O
278 * Standard I/O Packages::
284 * Wide_Wide_Text_IO::
288 * Filenames encoding::
290 * Operations on C Streams::
291 * Interfacing to C Streams::
295 * Ada.Characters.Latin_9 (a-chlat9.ads)::
296 * Ada.Characters.Wide_Latin_1 (a-cwila1.ads)::
297 * Ada.Characters.Wide_Latin_9 (a-cwila9.ads)::
298 * Ada.Characters.Wide_Wide_Latin_1 (a-chzla1.ads)::
299 * Ada.Characters.Wide_Wide_Latin_9 (a-chzla9.ads)::
300 * Ada.Command_Line.Environment (a-colien.ads)::
301 * Ada.Command_Line.Remove (a-colire.ads)::
302 * Ada.Command_Line.Response_File (a-clrefi.ads)::
303 * Ada.Direct_IO.C_Streams (a-diocst.ads)::
304 * Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads)::
305 * Ada.Exceptions.Last_Chance_Handler (a-elchha.ads)::
306 * Ada.Exceptions.Traceback (a-exctra.ads)::
307 * Ada.Sequential_IO.C_Streams (a-siocst.ads)::
308 * Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads)::
309 * Ada.Strings.Unbounded.Text_IO (a-suteio.ads)::
310 * Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads)::
311 * Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO (a-szuzti.ads)::
312 * Ada.Text_IO.C_Streams (a-tiocst.ads)::
313 * Ada.Text_IO.Reset_Standard_Files (a-tirsfi.ads)::
314 * Ada.Wide_Characters.Unicode (a-wichun.ads)::
315 * Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads)::
316 * Ada.Wide_Text_IO.Reset_Standard_Files (a-wrstfi.ads)::
317 * Ada.Wide_Wide_Characters.Unicode (a-zchuni.ads)::
318 * Ada.Wide_Wide_Text_IO.C_Streams (a-ztcstr.ads)::
319 * Ada.Wide_Wide_Text_IO.Reset_Standard_Files (a-zrstfi.ads)::
320 * GNAT.Altivec (g-altive.ads)::
321 * GNAT.Altivec.Conversions (g-altcon.ads)::
322 * GNAT.Altivec.Vector_Operations (g-alveop.ads)::
323 * GNAT.Altivec.Vector_Types (g-alvety.ads)::
324 * GNAT.Altivec.Vector_Views (g-alvevi.ads)::
325 * GNAT.Array_Split (g-arrspl.ads)::
326 * GNAT.AWK (g-awk.ads)::
327 * GNAT.Bounded_Buffers (g-boubuf.ads)::
328 * GNAT.Bounded_Mailboxes (g-boumai.ads)::
329 * GNAT.Bubble_Sort (g-bubsor.ads)::
330 * GNAT.Bubble_Sort_A (g-busora.ads)::
331 * GNAT.Bubble_Sort_G (g-busorg.ads)::
332 * GNAT.Byte_Order_Mark (g-byorma.ads)::
333 * GNAT.Byte_Swapping (g-bytswa.ads)::
334 * GNAT.Calendar (g-calend.ads)::
335 * GNAT.Calendar.Time_IO (g-catiio.ads)::
336 * GNAT.Case_Util (g-casuti.ads)::
337 * GNAT.CGI (g-cgi.ads)::
338 * GNAT.CGI.Cookie (g-cgicoo.ads)::
339 * GNAT.CGI.Debug (g-cgideb.ads)::
340 * GNAT.Command_Line (g-comlin.ads)::
341 * GNAT.Compiler_Version (g-comver.ads)::
342 * GNAT.Ctrl_C (g-ctrl_c.ads)::
343 * GNAT.CRC32 (g-crc32.ads)::
344 * GNAT.Current_Exception (g-curexc.ads)::
345 * GNAT.Debug_Pools (g-debpoo.ads)::
346 * GNAT.Debug_Utilities (g-debuti.ads)::
347 * GNAT.Decode_String (g-decstr.ads)::
348 * GNAT.Decode_UTF8_String (g-deutst.ads)::
349 * GNAT.Directory_Operations (g-dirope.ads)::
350 * GNAT.Directory_Operations.Iteration (g-diopit.ads)::
351 * GNAT.Dynamic_HTables (g-dynhta.ads)::
352 * GNAT.Dynamic_Tables (g-dyntab.ads)::
353 * GNAT.Encode_String (g-encstr.ads)::
354 * GNAT.Encode_UTF8_String (g-enutst.ads)::
355 * GNAT.Exception_Actions (g-excact.ads)::
356 * GNAT.Exception_Traces (g-exctra.ads)::
357 * GNAT.Exceptions (g-except.ads)::
358 * GNAT.Expect (g-expect.ads)::
359 * GNAT.Float_Control (g-flocon.ads)::
360 * GNAT.Heap_Sort (g-heasor.ads)::
361 * GNAT.Heap_Sort_A (g-hesora.ads)::
362 * GNAT.Heap_Sort_G (g-hesorg.ads)::
363 * GNAT.HTable (g-htable.ads)::
364 * GNAT.IO (g-io.ads)::
365 * GNAT.IO_Aux (g-io_aux.ads)::
366 * GNAT.Lock_Files (g-locfil.ads)::
367 * GNAT.MD5 (g-md5.ads)::
368 * GNAT.Memory_Dump (g-memdum.ads)::
369 * GNAT.Most_Recent_Exception (g-moreex.ads)::
370 * GNAT.OS_Lib (g-os_lib.ads)::
371 * GNAT.Perfect_Hash_Generators (g-pehage.ads)::
372 * GNAT.Random_Numbers (g-rannum.ads)::
373 * GNAT.Regexp (g-regexp.ads)::
374 * GNAT.Registry (g-regist.ads)::
375 * GNAT.Regpat (g-regpat.ads)::
376 * GNAT.Secondary_Stack_Info (g-sestin.ads)::
377 * GNAT.Semaphores (g-semaph.ads)::
378 * GNAT.Serial_Communications (g-sercom.ads)::
379 * GNAT.SHA1 (g-sha1.ads)::
380 * GNAT.SHA224 (g-sha224.ads)::
381 * GNAT.SHA256 (g-sha256.ads)::
382 * GNAT.SHA384 (g-sha384.ads)::
383 * GNAT.SHA512 (g-sha512.ads)::
384 * GNAT.Signals (g-signal.ads)::
385 * GNAT.Sockets (g-socket.ads)::
386 * GNAT.Source_Info (g-souinf.ads)::
387 * GNAT.Spelling_Checker (g-speche.ads)::
388 * GNAT.Spelling_Checker_Generic (g-spchge.ads)::
389 * GNAT.Spitbol.Patterns (g-spipat.ads)::
390 * GNAT.Spitbol (g-spitbo.ads)::
391 * GNAT.Spitbol.Table_Boolean (g-sptabo.ads)::
392 * GNAT.Spitbol.Table_Integer (g-sptain.ads)::
393 * GNAT.Spitbol.Table_VString (g-sptavs.ads)::
394 * GNAT.SSE (g-sse.ads)::
395 * GNAT.SSE.Vector_Types (g-ssvety.ads)::
396 * GNAT.Strings (g-string.ads)::
397 * GNAT.String_Split (g-strspl.ads)::
398 * GNAT.Table (g-table.ads)::
399 * GNAT.Task_Lock (g-tasloc.ads)::
400 * GNAT.Threads (g-thread.ads)::
401 * GNAT.Time_Stamp (g-timsta.ads)::
402 * GNAT.Traceback (g-traceb.ads)::
403 * GNAT.Traceback.Symbolic (g-trasym.ads)::
404 * GNAT.UTF_32 (g-utf_32.ads)::
405 * GNAT.UTF_32_Spelling_Checker (g-u3spch.ads)::
406 * GNAT.Wide_Spelling_Checker (g-wispch.ads)::
407 * GNAT.Wide_String_Split (g-wistsp.ads)::
408 * GNAT.Wide_Wide_Spelling_Checker (g-zspche.ads)::
409 * GNAT.Wide_Wide_String_Split (g-zistsp.ads)::
410 * Interfaces.C.Extensions (i-cexten.ads)::
411 * Interfaces.C.Streams (i-cstrea.ads)::
412 * Interfaces.CPP (i-cpp.ads)::
413 * Interfaces.Packed_Decimal (i-pacdec.ads)::
414 * Interfaces.VxWorks (i-vxwork.ads)::
415 * Interfaces.VxWorks.IO (i-vxwoio.ads)::
416 * System.Address_Image (s-addima.ads)::
417 * System.Assertions (s-assert.ads)::
418 * System.Memory (s-memory.ads)::
419 * System.Partition_Interface (s-parint.ads)::
420 * System.Pool_Global (s-pooglo.ads)::
421 * System.Pool_Local (s-pooloc.ads)::
422 * System.Restrictions (s-restri.ads)::
423 * System.Rident (s-rident.ads)::
424 * System.Strings.Stream_Ops (s-ststop.ads)::
425 * System.Task_Info (s-tasinf.ads)::
426 * System.Wch_Cnv (s-wchcnv.ads)::
427 * System.Wch_Con (s-wchcon.ads)::
431 * Text_IO Stream Pointer Positioning::
432 * Text_IO Reading and Writing Non-Regular Files::
434 * Treating Text_IO Files as Streams::
435 * Text_IO Extensions::
436 * Text_IO Facilities for Unbounded Strings::
440 * Wide_Text_IO Stream Pointer Positioning::
441 * Wide_Text_IO Reading and Writing Non-Regular Files::
445 * Wide_Wide_Text_IO Stream Pointer Positioning::
446 * Wide_Wide_Text_IO Reading and Writing Non-Regular Files::
448 Interfacing to Other Languages
451 * Interfacing to C++::
452 * Interfacing to COBOL::
453 * Interfacing to Fortran::
454 * Interfacing to non-GNAT Ada code::
456 Specialized Needs Annexes
458 Implementation of Specific Ada Features
459 * Machine Code Insertions::
460 * GNAT Implementation of Tasking::
461 * GNAT Implementation of Shared Passive Packages::
462 * Code Generation for Array Aggregates::
463 * The Size of Discriminated Records with Default Discriminants::
464 * Strict Conformance to the Ada Reference Manual::
466 Project File Reference
470 GNU Free Documentation License
477 @node About This Guide
478 @unnumbered About This Guide
481 This manual contains useful information in writing programs using the
482 @value{EDITION} compiler. It includes information on implementation dependent
483 characteristics of @value{EDITION}, including all the information required by
484 Annex M of the Ada language standard.
486 @value{EDITION} implements Ada 95 and Ada 2005, and it may also be invoked in
487 Ada 83 compatibility mode.
488 By default, @value{EDITION} assumes @value{DEFAULTLANGUAGEVERSION},
489 but you can override with a compiler switch
490 to explicitly specify the language version.
491 (Please refer to @ref{Compiling Different Versions of Ada,,, gnat_ugn,
492 @value{EDITION} User's Guide}, for details on these switches.)
493 Throughout this manual, references to ``Ada'' without a year suffix
494 apply to both the Ada 95 and Ada 2005 versions of the language.
496 Ada is designed to be highly portable.
497 In general, a program will have the same effect even when compiled by
498 different compilers on different platforms.
499 However, since Ada is designed to be used in a
500 wide variety of applications, it also contains a number of system
501 dependent features to be used in interfacing to the external world.
502 @cindex Implementation-dependent features
505 Note: Any program that makes use of implementation-dependent features
506 may be non-portable. You should follow good programming practice and
507 isolate and clearly document any sections of your program that make use
508 of these features in a non-portable manner.
511 For ease of exposition, ``GNAT Pro'' will be referred to simply as
512 ``GNAT'' in the remainder of this document.
516 * What This Reference Manual Contains::
518 * Related Information::
521 @node What This Reference Manual Contains
522 @unnumberedsec What This Reference Manual Contains
525 This reference manual contains the following chapters:
529 @ref{Implementation Defined Pragmas}, lists GNAT implementation-dependent
530 pragmas, which can be used to extend and enhance the functionality of the
534 @ref{Implementation Defined Attributes}, lists GNAT
535 implementation-dependent attributes which can be used to extend and
536 enhance the functionality of the compiler.
539 @ref{Implementation Advice}, provides information on generally
540 desirable behavior which are not requirements that all compilers must
541 follow since it cannot be provided on all systems, or which may be
542 undesirable on some systems.
545 @ref{Implementation Defined Characteristics}, provides a guide to
546 minimizing implementation dependent features.
549 @ref{Intrinsic Subprograms}, describes the intrinsic subprograms
550 implemented by GNAT, and how they can be imported into user
551 application programs.
554 @ref{Representation Clauses and Pragmas}, describes in detail the
555 way that GNAT represents data, and in particular the exact set
556 of representation clauses and pragmas that is accepted.
559 @ref{Standard Library Routines}, provides a listing of packages and a
560 brief description of the functionality that is provided by Ada's
561 extensive set of standard library routines as implemented by GNAT@.
564 @ref{The Implementation of Standard I/O}, details how the GNAT
565 implementation of the input-output facilities.
568 @ref{The GNAT Library}, is a catalog of packages that complement
569 the Ada predefined library.
572 @ref{Interfacing to Other Languages}, describes how programs
573 written in Ada using GNAT can be interfaced to other programming
576 @ref{Specialized Needs Annexes}, describes the GNAT implementation of all
577 of the specialized needs annexes.
580 @ref{Implementation of Specific Ada Features}, discusses issues related
581 to GNAT's implementation of machine code insertions, tasking, and several
585 @ref{Project File Reference}, presents the syntax and semantics
589 @ref{Obsolescent Features} documents implementation dependent features,
590 including pragmas and attributes, which are considered obsolescent, since
591 there are other preferred ways of achieving the same results. These
592 obsolescent forms are retained for backwards compatibility.
596 @cindex Ada 95 Language Reference Manual
597 @cindex Ada 2005 Language Reference Manual
599 This reference manual assumes a basic familiarity with the Ada 95 language, as
600 described in the International Standard ANSI/ISO/IEC-8652:1995,
602 It does not require knowledge of the new features introduced by Ada 2005,
603 (officially known as ISO/IEC 8652:1995 with Technical Corrigendum 1
605 Both reference manuals are included in the GNAT documentation
609 @unnumberedsec Conventions
610 @cindex Conventions, typographical
611 @cindex Typographical conventions
614 Following are examples of the typographical and graphic conventions used
619 @code{Functions}, @code{utility program names}, @code{standard names},
626 @file{File names}, @samp{button names}, and @samp{field names}.
629 @code{Variables}, @env{environment variables}, and @var{metasyntactic
636 [optional information or parameters]
639 Examples are described by text
641 and then shown this way.
646 Commands that are entered by the user are preceded in this manual by the
647 characters @samp{$ } (dollar sign followed by space). If your system uses this
648 sequence as a prompt, then the commands will appear exactly as you see them
649 in the manual. If your system uses some other prompt, then the command will
650 appear with the @samp{$} replaced by whatever prompt character you are using.
652 @node Related Information
653 @unnumberedsec Related Information
655 See the following documents for further information on GNAT:
659 @xref{Top, @value{EDITION} User's Guide, About This Guide, gnat_ugn,
660 @value{EDITION} User's Guide}, which provides information on how to use the
661 GNAT compiler system.
664 @cite{Ada 95 Reference Manual}, which contains all reference
665 material for the Ada 95 programming language.
668 @cite{Ada 95 Annotated Reference Manual}, which is an annotated version
669 of the Ada 95 standard. The annotations describe
670 detailed aspects of the design decision, and in particular contain useful
671 sections on Ada 83 compatibility.
674 @cite{Ada 2005 Reference Manual}, which contains all reference
675 material for the Ada 2005 programming language.
678 @cite{Ada 2005 Annotated Reference Manual}, which is an annotated version
679 of the Ada 2005 standard. The annotations describe
680 detailed aspects of the design decision, and in particular contain useful
681 sections on Ada 83 and Ada 95 compatibility.
684 @cite{DEC Ada, Technical Overview and Comparison on DIGITAL Platforms},
685 which contains specific information on compatibility between GNAT and
689 @cite{DEC Ada, Language Reference Manual, part number AA-PYZAB-TK} which
690 describes in detail the pragmas and attributes provided by the DEC Ada 83
695 @node Implementation Defined Pragmas
696 @chapter Implementation Defined Pragmas
699 Ada defines a set of pragmas that can be used to supply additional
700 information to the compiler. These language defined pragmas are
701 implemented in GNAT and work as described in the Ada Reference Manual.
703 In addition, Ada allows implementations to define additional pragmas
704 whose meaning is defined by the implementation. GNAT provides a number
705 of these implementation-defined pragmas, which can be used to extend
706 and enhance the functionality of the compiler. This section of the GNAT
707 Reference Manual describes these additional pragmas.
709 Note that any program using these pragmas might not be portable to other
710 compilers (although GNAT implements this set of pragmas on all
711 platforms). Therefore if portability to other compilers is an important
712 consideration, the use of these pragmas should be minimized.
715 * Pragma Abort_Defer::
722 * Pragma Assume_No_Invalid_Values::
724 * Pragma C_Pass_By_Copy::
726 * Pragma Check_Name::
727 * Pragma Check_Policy::
729 * Pragma Common_Object::
730 * Pragma Compile_Time_Error::
731 * Pragma Compile_Time_Warning::
732 * Pragma Compiler_Unit::
733 * Pragma Complete_Representation::
734 * Pragma Complex_Representation::
735 * Pragma Component_Alignment::
736 * Pragma Convention_Identifier::
738 * Pragma CPP_Constructor::
739 * Pragma CPP_Virtual::
740 * Pragma CPP_Vtable::
742 * Pragma Debug_Policy::
743 * Pragma Detect_Blocking::
744 * Pragma Elaboration_Checks::
746 * Pragma Export_Exception::
747 * Pragma Export_Function::
748 * Pragma Export_Object::
749 * Pragma Export_Procedure::
750 * Pragma Export_Value::
751 * Pragma Export_Valued_Procedure::
752 * Pragma Extend_System::
754 * Pragma External_Name_Casing::
756 * Pragma Favor_Top_Level::
757 * Pragma Finalize_Storage_Only::
758 * Pragma Float_Representation::
760 * Pragma Implemented_By_Entry::
761 * Pragma Implicit_Packing::
762 * Pragma Import_Exception::
763 * Pragma Import_Function::
764 * Pragma Import_Object::
765 * Pragma Import_Procedure::
766 * Pragma Import_Valued_Procedure::
767 * Pragma Initialize_Scalars::
768 * Pragma Inline_Always::
769 * Pragma Inline_Generic::
771 * Pragma Interface_Name::
772 * Pragma Interrupt_Handler::
773 * Pragma Interrupt_State::
774 * Pragma Keep_Names::
777 * Pragma Linker_Alias::
778 * Pragma Linker_Constructor::
779 * Pragma Linker_Destructor::
780 * Pragma Linker_Section::
781 * Pragma Long_Float::
782 * Pragma Machine_Attribute::
784 * Pragma Main_Storage::
787 * Pragma No_Strict_Aliasing::
788 * Pragma Normalize_Scalars::
789 * Pragma Obsolescent::
790 * Pragma Optimize_Alignment::
792 * Pragma Persistent_BSS::
794 * Pragma Postcondition::
795 * Pragma Precondition::
796 * Pragma Profile (Ravenscar)::
797 * Pragma Profile (Restricted)::
798 * Pragma Psect_Object::
799 * Pragma Pure_Function::
800 * Pragma Restriction_Warnings::
802 * Pragma Short_Circuit_And_Or::
803 * Pragma Source_File_Name::
804 * Pragma Source_File_Name_Project::
805 * Pragma Source_Reference::
806 * Pragma Stream_Convert::
807 * Pragma Style_Checks::
810 * Pragma Suppress_All::
811 * Pragma Suppress_Exception_Locations::
812 * Pragma Suppress_Initialization::
815 * Pragma Task_Storage::
816 * Pragma Thread_Local_Storage::
817 * Pragma Time_Slice::
819 * Pragma Unchecked_Union::
820 * Pragma Unimplemented_Unit::
821 * Pragma Universal_Aliasing ::
822 * Pragma Universal_Data::
823 * Pragma Unmodified::
824 * Pragma Unreferenced::
825 * Pragma Unreferenced_Objects::
826 * Pragma Unreserve_All_Interrupts::
827 * Pragma Unsuppress::
828 * Pragma Use_VADS_Size::
829 * Pragma Validity_Checks::
832 * Pragma Weak_External::
833 * Pragma Wide_Character_Encoding::
836 @node Pragma Abort_Defer
837 @unnumberedsec Pragma Abort_Defer
839 @cindex Deferring aborts
847 This pragma must appear at the start of the statement sequence of a
848 handled sequence of statements (right after the @code{begin}). It has
849 the effect of deferring aborts for the sequence of statements (but not
850 for the declarations or handlers, if any, associated with this statement
854 @unnumberedsec Pragma Ada_83
863 A configuration pragma that establishes Ada 83 mode for the unit to
864 which it applies, regardless of the mode set by the command line
865 switches. In Ada 83 mode, GNAT attempts to be as compatible with
866 the syntax and semantics of Ada 83, as defined in the original Ada
867 83 Reference Manual as possible. In particular, the keywords added by Ada 95
868 and Ada 2005 are not recognized, optional package bodies are allowed,
869 and generics may name types with unknown discriminants without using
870 the @code{(<>)} notation. In addition, some but not all of the additional
871 restrictions of Ada 83 are enforced.
873 Ada 83 mode is intended for two purposes. Firstly, it allows existing
874 Ada 83 code to be compiled and adapted to GNAT with less effort.
875 Secondly, it aids in keeping code backwards compatible with Ada 83.
876 However, there is no guarantee that code that is processed correctly
877 by GNAT in Ada 83 mode will in fact compile and execute with an Ada
878 83 compiler, since GNAT does not enforce all the additional checks
882 @unnumberedsec Pragma Ada_95
891 A configuration pragma that establishes Ada 95 mode for the unit to which
892 it applies, regardless of the mode set by the command line switches.
893 This mode is set automatically for the @code{Ada} and @code{System}
894 packages and their children, so you need not specify it in these
895 contexts. This pragma is useful when writing a reusable component that
896 itself uses Ada 95 features, but which is intended to be usable from
897 either Ada 83 or Ada 95 programs.
900 @unnumberedsec Pragma Ada_05
909 A configuration pragma that establishes Ada 2005 mode for the unit to which
910 it applies, regardless of the mode set by the command line switches.
911 This mode is set automatically for the @code{Ada} and @code{System}
912 packages and their children, so you need not specify it in these
913 contexts. This pragma is useful when writing a reusable component that
914 itself uses Ada 2005 features, but which is intended to be usable from
915 either Ada 83 or Ada 95 programs.
917 @node Pragma Ada_2005
918 @unnumberedsec Pragma Ada_2005
927 This configuration pragma is a synonym for pragma Ada_05 and has the
928 same syntax and effect.
930 @node Pragma Annotate
931 @unnumberedsec Pragma Annotate
936 pragma Annotate (IDENTIFIER [,IDENTIFIER] @{, ARG@});
938 ARG ::= NAME | EXPRESSION
942 This pragma is used to annotate programs. @var{identifier} identifies
943 the type of annotation. GNAT verifies that it is an identifier, but does
944 not otherwise analyze it. The second optional identifier is also left
945 unanalyzed, and by convention is used to control the action of the tool to
946 which the annotation is addressed. The remaining @var{arg} arguments
947 can be either string literals or more generally expressions.
948 String literals are assumed to be either of type
949 @code{Standard.String} or else @code{Wide_String} or @code{Wide_Wide_String}
950 depending on the character literals they contain.
951 All other kinds of arguments are analyzed as expressions, and must be
954 The analyzed pragma is retained in the tree, but not otherwise processed
955 by any part of the GNAT compiler. This pragma is intended for use by
956 external tools, including ASIS@.
959 @unnumberedsec Pragma Assert
966 [, string_EXPRESSION]);
970 The effect of this pragma depends on whether the corresponding command
971 line switch is set to activate assertions. The pragma expands into code
972 equivalent to the following:
975 if assertions-enabled then
976 if not boolean_EXPRESSION then
977 System.Assertions.Raise_Assert_Failure
984 The string argument, if given, is the message that will be associated
985 with the exception occurrence if the exception is raised. If no second
986 argument is given, the default message is @samp{@var{file}:@var{nnn}},
987 where @var{file} is the name of the source file containing the assert,
988 and @var{nnn} is the line number of the assert. A pragma is not a
989 statement, so if a statement sequence contains nothing but a pragma
990 assert, then a null statement is required in addition, as in:
995 pragma Assert (K > 3, "Bad value for K");
1001 Note that, as with the @code{if} statement to which it is equivalent, the
1002 type of the expression is either @code{Standard.Boolean}, or any type derived
1003 from this standard type.
1005 If assertions are disabled (switch @option{-gnata} not used), then there
1006 is no run-time effect (and in particular, any side effects from the
1007 expression will not occur at run time). (The expression is still
1008 analyzed at compile time, and may cause types to be frozen if they are
1009 mentioned here for the first time).
1011 If assertions are enabled, then the given expression is tested, and if
1012 it is @code{False} then @code{System.Assertions.Raise_Assert_Failure} is called
1013 which results in the raising of @code{Assert_Failure} with the given message.
1015 You should generally avoid side effects in the expression arguments of
1016 this pragma, because these side effects will turn on and off with the
1017 setting of the assertions mode, resulting in assertions that have an
1018 effect on the program. However, the expressions are analyzed for
1019 semantic correctness whether or not assertions are enabled, so turning
1020 assertions on and off cannot affect the legality of a program.
1022 @node Pragma Assume_No_Invalid_Values
1023 @unnumberedsec Pragma Assume_No_Invalid_Values
1024 @findex Assume_No_Invalid_Values
1025 @cindex Invalid representations
1026 @cindex Invalid values
1029 @smallexample @c ada
1030 pragma Assume_No_Invalid_Values (On | Off);
1034 This is a configuration pragma that controls the assumptions made by the
1035 compiler about the occurrence of invalid representations (invalid values)
1038 The default behavior (corresponding to an Off argument for this pragma), is
1039 to assume that values may in general be invalid unless the compiler can
1040 prove they are valid. Consider the following example:
1042 @smallexample @c ada
1043 V1 : Integer range 1 .. 10;
1044 V2 : Integer range 11 .. 20;
1046 for J in V2 .. V1 loop
1052 if V1 and V2 have valid values, then the loop is known at compile
1053 time not to execute since the lower bound must be greater than the
1054 upper bound. However in default mode, no such assumption is made,
1055 and the loop may execute. If @code{Assume_No_Invalid_Values (On)}
1056 is given, the compiler will assume that any occurrence of a variable
1057 other than in an explicit @code{'Valid} test always has a valid
1058 value, and the loop above will be optimized away.
1060 The use of @code{Assume_No_Invalid_Values (On)} is appropriate if
1061 you know your code is free of uninitialized variables and other
1062 possible sources of invalid representations, and may result in
1063 more efficient code. A program that accesses an invalid representation
1064 with this pragma in effect is erroneous, so no guarantees can be made
1067 It is peculiar though permissible to use this pragma in conjunction
1068 with validity checking (-gnatVa). In such cases, accessing invalid
1069 values will generally give an exception, though formally the program
1070 is erroneous so there are no guarantees that this will always be the
1071 case, and it is recommended that these two options not be used together.
1073 @node Pragma Ast_Entry
1074 @unnumberedsec Pragma Ast_Entry
1079 @smallexample @c ada
1080 pragma AST_Entry (entry_IDENTIFIER);
1084 This pragma is implemented only in the OpenVMS implementation of GNAT@. The
1085 argument is the simple name of a single entry; at most one @code{AST_Entry}
1086 pragma is allowed for any given entry. This pragma must be used in
1087 conjunction with the @code{AST_Entry} attribute, and is only allowed after
1088 the entry declaration and in the same task type specification or single task
1089 as the entry to which it applies. This pragma specifies that the given entry
1090 may be used to handle an OpenVMS asynchronous system trap (@code{AST})
1091 resulting from an OpenVMS system service call. The pragma does not affect
1092 normal use of the entry. For further details on this pragma, see the
1093 DEC Ada Language Reference Manual, section 9.12a.
1095 @node Pragma C_Pass_By_Copy
1096 @unnumberedsec Pragma C_Pass_By_Copy
1097 @cindex Passing by copy
1098 @findex C_Pass_By_Copy
1101 @smallexample @c ada
1102 pragma C_Pass_By_Copy
1103 ([Max_Size =>] static_integer_EXPRESSION);
1107 Normally the default mechanism for passing C convention records to C
1108 convention subprograms is to pass them by reference, as suggested by RM
1109 B.3(69). Use the configuration pragma @code{C_Pass_By_Copy} to change
1110 this default, by requiring that record formal parameters be passed by
1111 copy if all of the following conditions are met:
1115 The size of the record type does not exceed the value specified for
1118 The record type has @code{Convention C}.
1120 The formal parameter has this record type, and the subprogram has a
1121 foreign (non-Ada) convention.
1125 If these conditions are met the argument is passed by copy, i.e.@: in a
1126 manner consistent with what C expects if the corresponding formal in the
1127 C prototype is a struct (rather than a pointer to a struct).
1129 You can also pass records by copy by specifying the convention
1130 @code{C_Pass_By_Copy} for the record type, or by using the extended
1131 @code{Import} and @code{Export} pragmas, which allow specification of
1132 passing mechanisms on a parameter by parameter basis.
1135 @unnumberedsec Pragma Check
1137 @cindex Named assertions
1141 @smallexample @c ada
1143 [Name =>] Identifier,
1144 [Check =>] Boolean_EXPRESSION
1145 [, [Message =>] string_EXPRESSION] );
1149 This pragma is similar to the predefined pragma @code{Assert} except that an
1150 extra identifier argument is present. In conjunction with pragma
1151 @code{Check_Policy}, this can be used to define groups of assertions that can
1152 be independently controlled. The identifier @code{Assertion} is special, it
1153 refers to the normal set of pragma @code{Assert} statements. The identifiers
1154 @code{Precondition} and @code{Postcondition} correspond to the pragmas of these
1155 names, so these three names would normally not be used directly in a pragma
1158 Checks introduced by this pragma are normally deactivated by default. They can
1159 be activated either by the command line option @option{-gnata}, which turns on
1160 all checks, or individually controlled using pragma @code{Check_Policy}.
1162 @node Pragma Check_Name
1163 @unnumberedsec Pragma Check_Name
1164 @cindex Defining check names
1165 @cindex Check names, defining
1169 @smallexample @c ada
1170 pragma Check_Name (check_name_IDENTIFIER);
1174 This is a configuration pragma that defines a new implementation
1175 defined check name (unless IDENTIFIER matches one of the predefined
1176 check names, in which case the pragma has no effect). Check names
1177 are global to a partition, so if two or more configuration pragmas
1178 are present in a partition mentioning the same name, only one new
1179 check name is introduced.
1181 An implementation defined check name introduced with this pragma may
1182 be used in only three contexts: @code{pragma Suppress},
1183 @code{pragma Unsuppress},
1184 and as the prefix of a @code{Check_Name'Enabled} attribute reference. For
1185 any of these three cases, the check name must be visible. A check
1186 name is visible if it is in the configuration pragmas applying to
1187 the current unit, or if it appears at the start of any unit that
1188 is part of the dependency set of the current unit (e.g., units that
1189 are mentioned in @code{with} clauses).
1191 @node Pragma Check_Policy
1192 @unnumberedsec Pragma Check_Policy
1193 @cindex Controlling assertions
1194 @cindex Assertions, control
1195 @cindex Check pragma control
1196 @cindex Named assertions
1200 @smallexample @c ada
1202 ([Name =>] Identifier,
1203 [Policy =>] POLICY_IDENTIFIER);
1205 POLICY_IDENTIFIER ::= On | Off | Check | Ignore
1209 This pragma is similar to the predefined pragma @code{Assertion_Policy},
1210 except that it controls sets of named assertions introduced using the
1211 @code{Check} pragmas. It can be used as a configuration pragma or (unlike
1212 @code{Assertion_Policy}) can be used within a declarative part, in which case
1213 it controls the status to the end of the corresponding construct (in a manner
1214 identical to pragma @code{Suppress)}.
1216 The identifier given as the first argument corresponds to a name used in
1217 associated @code{Check} pragmas. For example, if the pragma:
1219 @smallexample @c ada
1220 pragma Check_Policy (Critical_Error, Off);
1224 is given, then subsequent @code{Check} pragmas whose first argument is also
1225 @code{Critical_Error} will be disabled. The special identifier @code{Assertion}
1226 controls the behavior of normal @code{Assert} pragmas (thus a pragma
1227 @code{Check_Policy} with this identifier is similar to the normal
1228 @code{Assertion_Policy} pragma except that it can appear within a
1231 The special identifiers @code{Precondition} and @code{Postcondition} control
1232 the status of preconditions and postconditions. If a @code{Precondition} pragma
1233 is encountered, it is ignored if turned off by a @code{Check_Policy} specifying
1234 that @code{Precondition} checks are @code{Off} or @code{Ignored}. Similarly use
1235 of the name @code{Postcondition} controls whether @code{Postcondition} pragmas
1238 The check policy is @code{Off} to turn off corresponding checks, and @code{On}
1239 to turn on corresponding checks. The default for a set of checks for which no
1240 @code{Check_Policy} is given is @code{Off} unless the compiler switch
1241 @option{-gnata} is given, which turns on all checks by default.
1243 The check policy settings @code{Check} and @code{Ignore} are also recognized
1244 as synonyms for @code{On} and @code{Off}. These synonyms are provided for
1245 compatibility with the standard @code{Assertion_Policy} pragma.
1247 @node Pragma Comment
1248 @unnumberedsec Pragma Comment
1253 @smallexample @c ada
1254 pragma Comment (static_string_EXPRESSION);
1258 This is almost identical in effect to pragma @code{Ident}. It allows the
1259 placement of a comment into the object file and hence into the
1260 executable file if the operating system permits such usage. The
1261 difference is that @code{Comment}, unlike @code{Ident}, has
1262 no limitations on placement of the pragma (it can be placed
1263 anywhere in the main source unit), and if more than one pragma
1264 is used, all comments are retained.
1266 @node Pragma Common_Object
1267 @unnumberedsec Pragma Common_Object
1268 @findex Common_Object
1272 @smallexample @c ada
1273 pragma Common_Object (
1274 [Internal =>] LOCAL_NAME
1275 [, [External =>] EXTERNAL_SYMBOL]
1276 [, [Size =>] EXTERNAL_SYMBOL] );
1280 | static_string_EXPRESSION
1284 This pragma enables the shared use of variables stored in overlaid
1285 linker areas corresponding to the use of @code{COMMON}
1286 in Fortran. The single
1287 object @var{LOCAL_NAME} is assigned to the area designated by
1288 the @var{External} argument.
1289 You may define a record to correspond to a series
1290 of fields. The @var{Size} argument
1291 is syntax checked in GNAT, but otherwise ignored.
1293 @code{Common_Object} is not supported on all platforms. If no
1294 support is available, then the code generator will issue a message
1295 indicating that the necessary attribute for implementation of this
1296 pragma is not available.
1298 @node Pragma Compile_Time_Error
1299 @unnumberedsec Pragma Compile_Time_Error
1300 @findex Compile_Time_Error
1304 @smallexample @c ada
1305 pragma Compile_Time_Error
1306 (boolean_EXPRESSION, static_string_EXPRESSION);
1310 This pragma can be used to generate additional compile time
1312 is particularly useful in generics, where errors can be issued for
1313 specific problematic instantiations. The first parameter is a boolean
1314 expression. The pragma is effective only if the value of this expression
1315 is known at compile time, and has the value True. The set of expressions
1316 whose values are known at compile time includes all static boolean
1317 expressions, and also other values which the compiler can determine
1318 at compile time (e.g., the size of a record type set by an explicit
1319 size representation clause, or the value of a variable which was
1320 initialized to a constant and is known not to have been modified).
1321 If these conditions are met, an error message is generated using
1322 the value given as the second argument. This string value may contain
1323 embedded ASCII.LF characters to break the message into multiple lines.
1325 @node Pragma Compile_Time_Warning
1326 @unnumberedsec Pragma Compile_Time_Warning
1327 @findex Compile_Time_Warning
1331 @smallexample @c ada
1332 pragma Compile_Time_Warning
1333 (boolean_EXPRESSION, static_string_EXPRESSION);
1337 Same as pragma Compile_Time_Error, except a warning is issued instead
1338 of an error message. Note that if this pragma is used in a package that
1339 is with'ed by a client, the client will get the warning even though it
1340 is issued by a with'ed package (normally warnings in with'ed units are
1341 suppressed, but this is a special exception to that rule).
1343 One typical use is within a generic where compile time known characteristics
1344 of formal parameters are tested, and warnings given appropriately. Another use
1345 with a first parameter of True is to warn a client about use of a package,
1346 for example that it is not fully implemented.
1348 @node Pragma Compiler_Unit
1349 @unnumberedsec Pragma Compiler_Unit
1350 @findex Compiler_Unit
1354 @smallexample @c ada
1355 pragma Compiler_Unit;
1359 This pragma is intended only for internal use in the GNAT run-time library.
1360 It indicates that the unit is used as part of the compiler build. The effect
1361 is to disallow constructs (raise with message, conditional expressions etc)
1362 that would cause trouble when bootstrapping using an older version of GNAT.
1363 For the exact list of restrictions, see the compiler sources and references
1364 to Is_Compiler_Unit.
1366 @node Pragma Complete_Representation
1367 @unnumberedsec Pragma Complete_Representation
1368 @findex Complete_Representation
1372 @smallexample @c ada
1373 pragma Complete_Representation;
1377 This pragma must appear immediately within a record representation
1378 clause. Typical placements are before the first component clause
1379 or after the last component clause. The effect is to give an error
1380 message if any component is missing a component clause. This pragma
1381 may be used to ensure that a record representation clause is
1382 complete, and that this invariant is maintained if fields are
1383 added to the record in the future.
1385 @node Pragma Complex_Representation
1386 @unnumberedsec Pragma Complex_Representation
1387 @findex Complex_Representation
1391 @smallexample @c ada
1392 pragma Complex_Representation
1393 ([Entity =>] LOCAL_NAME);
1397 The @var{Entity} argument must be the name of a record type which has
1398 two fields of the same floating-point type. The effect of this pragma is
1399 to force gcc to use the special internal complex representation form for
1400 this record, which may be more efficient. Note that this may result in
1401 the code for this type not conforming to standard ABI (application
1402 binary interface) requirements for the handling of record types. For
1403 example, in some environments, there is a requirement for passing
1404 records by pointer, and the use of this pragma may result in passing
1405 this type in floating-point registers.
1407 @node Pragma Component_Alignment
1408 @unnumberedsec Pragma Component_Alignment
1409 @cindex Alignments of components
1410 @findex Component_Alignment
1414 @smallexample @c ada
1415 pragma Component_Alignment (
1416 [Form =>] ALIGNMENT_CHOICE
1417 [, [Name =>] type_LOCAL_NAME]);
1419 ALIGNMENT_CHOICE ::=
1427 Specifies the alignment of components in array or record types.
1428 The meaning of the @var{Form} argument is as follows:
1431 @findex Component_Size
1432 @item Component_Size
1433 Aligns scalar components and subcomponents of the array or record type
1434 on boundaries appropriate to their inherent size (naturally
1435 aligned). For example, 1-byte components are aligned on byte boundaries,
1436 2-byte integer components are aligned on 2-byte boundaries, 4-byte
1437 integer components are aligned on 4-byte boundaries and so on. These
1438 alignment rules correspond to the normal rules for C compilers on all
1439 machines except the VAX@.
1441 @findex Component_Size_4
1442 @item Component_Size_4
1443 Naturally aligns components with a size of four or fewer
1444 bytes. Components that are larger than 4 bytes are placed on the next
1447 @findex Storage_Unit
1449 Specifies that array or record components are byte aligned, i.e.@:
1450 aligned on boundaries determined by the value of the constant
1451 @code{System.Storage_Unit}.
1455 Specifies that array or record components are aligned on default
1456 boundaries, appropriate to the underlying hardware or operating system or
1457 both. For OpenVMS VAX systems, the @code{Default} choice is the same as
1458 the @code{Storage_Unit} choice (byte alignment). For all other systems,
1459 the @code{Default} choice is the same as @code{Component_Size} (natural
1464 If the @code{Name} parameter is present, @var{type_LOCAL_NAME} must
1465 refer to a local record or array type, and the specified alignment
1466 choice applies to the specified type. The use of
1467 @code{Component_Alignment} together with a pragma @code{Pack} causes the
1468 @code{Component_Alignment} pragma to be ignored. The use of
1469 @code{Component_Alignment} together with a record representation clause
1470 is only effective for fields not specified by the representation clause.
1472 If the @code{Name} parameter is absent, the pragma can be used as either
1473 a configuration pragma, in which case it applies to one or more units in
1474 accordance with the normal rules for configuration pragmas, or it can be
1475 used within a declarative part, in which case it applies to types that
1476 are declared within this declarative part, or within any nested scope
1477 within this declarative part. In either case it specifies the alignment
1478 to be applied to any record or array type which has otherwise standard
1481 If the alignment for a record or array type is not specified (using
1482 pragma @code{Pack}, pragma @code{Component_Alignment}, or a record rep
1483 clause), the GNAT uses the default alignment as described previously.
1485 @node Pragma Convention_Identifier
1486 @unnumberedsec Pragma Convention_Identifier
1487 @findex Convention_Identifier
1488 @cindex Conventions, synonyms
1492 @smallexample @c ada
1493 pragma Convention_Identifier (
1494 [Name =>] IDENTIFIER,
1495 [Convention =>] convention_IDENTIFIER);
1499 This pragma provides a mechanism for supplying synonyms for existing
1500 convention identifiers. The @code{Name} identifier can subsequently
1501 be used as a synonym for the given convention in other pragmas (including
1502 for example pragma @code{Import} or another @code{Convention_Identifier}
1503 pragma). As an example of the use of this, suppose you had legacy code
1504 which used Fortran77 as the identifier for Fortran. Then the pragma:
1506 @smallexample @c ada
1507 pragma Convention_Identifier (Fortran77, Fortran);
1511 would allow the use of the convention identifier @code{Fortran77} in
1512 subsequent code, avoiding the need to modify the sources. As another
1513 example, you could use this to parametrize convention requirements
1514 according to systems. Suppose you needed to use @code{Stdcall} on
1515 windows systems, and @code{C} on some other system, then you could
1516 define a convention identifier @code{Library} and use a single
1517 @code{Convention_Identifier} pragma to specify which convention
1518 would be used system-wide.
1520 @node Pragma CPP_Class
1521 @unnumberedsec Pragma CPP_Class
1523 @cindex Interfacing with C++
1527 @smallexample @c ada
1528 pragma CPP_Class ([Entity =>] LOCAL_NAME);
1532 The argument denotes an entity in the current declarative region that is
1533 declared as a record type. It indicates that the type corresponds to an
1534 externally declared C++ class type, and is to be laid out the same way
1535 that C++ would lay out the type. If the C++ class has virtual primitives
1536 then the record must be declared as a tagged record type.
1538 Types for which @code{CPP_Class} is specified do not have assignment or
1539 equality operators defined (such operations can be imported or declared
1540 as subprograms as required). Initialization is allowed only by constructor
1541 functions (see pragma @code{CPP_Constructor}). Such types are implicitly
1542 limited if not explicitly declared as limited or derived from a limited
1543 type, and an error is issued in that case.
1545 Pragma @code{CPP_Class} is intended primarily for automatic generation
1546 using an automatic binding generator tool.
1547 See @ref{Interfacing to C++} for related information.
1549 Note: Pragma @code{CPP_Class} is currently obsolete. It is supported
1550 for backward compatibility but its functionality is available
1551 using pragma @code{Import} with @code{Convention} = @code{CPP}.
1553 @node Pragma CPP_Constructor
1554 @unnumberedsec Pragma CPP_Constructor
1555 @cindex Interfacing with C++
1556 @findex CPP_Constructor
1560 @smallexample @c ada
1561 pragma CPP_Constructor ([Entity =>] LOCAL_NAME
1562 [, [External_Name =>] static_string_EXPRESSION ]
1563 [, [Link_Name =>] static_string_EXPRESSION ]);
1567 This pragma identifies an imported function (imported in the usual way
1568 with pragma @code{Import}) as corresponding to a C++ constructor. If
1569 @code{External_Name} and @code{Link_Name} are not specified then the
1570 @code{Entity} argument is a name that must have been previously mentioned
1571 in a pragma @code{Import} with @code{Convention} = @code{CPP}. Such name
1572 must be of one of the following forms:
1576 @code{function @var{Fname} return @var{T}}
1580 @code{function @var{Fname} return @var{T}'Class}
1583 @code{function @var{Fname} (@dots{}) return @var{T}}
1587 @code{function @var{Fname} (@dots{}) return @var{T}'Class}
1591 where @var{T} is a limited record type imported from C++ with pragma
1592 @code{Import} and @code{Convention} = @code{CPP}.
1594 The first two forms import the default constructor, used when an object
1595 of type @var{T} is created on the Ada side with no explicit constructor.
1596 The latter two forms cover all the non-default constructors of the type.
1597 See the GNAT users guide for details.
1599 If no constructors are imported, it is impossible to create any objects
1600 on the Ada side and the type is implicitly declared abstract.
1602 Pragma @code{CPP_Constructor} is intended primarily for automatic generation
1603 using an automatic binding generator tool.
1604 See @ref{Interfacing to C++} for more related information.
1606 Note: The use of functions returning class-wide types for constructors is
1607 currently obsolete. They are supported for backward compatibility. The
1608 use of functions returning the type T leave the Ada sources more clear
1609 because the imported C++ constructors always return an object of type T;
1610 that is, they never return an object whose type is a descendant of type T.
1612 @node Pragma CPP_Virtual
1613 @unnumberedsec Pragma CPP_Virtual
1614 @cindex Interfacing to C++
1617 This pragma is now obsolete has has no effect because GNAT generates
1618 the same object layout than the G++ compiler.
1620 See @ref{Interfacing to C++} for related information.
1622 @node Pragma CPP_Vtable
1623 @unnumberedsec Pragma CPP_Vtable
1624 @cindex Interfacing with C++
1627 This pragma is now obsolete has has no effect because GNAT generates
1628 the same object layout than the G++ compiler.
1630 See @ref{Interfacing to C++} for related information.
1633 @unnumberedsec Pragma Debug
1638 @smallexample @c ada
1639 pragma Debug ([CONDITION, ]PROCEDURE_CALL_WITHOUT_SEMICOLON);
1641 PROCEDURE_CALL_WITHOUT_SEMICOLON ::=
1643 | PROCEDURE_PREFIX ACTUAL_PARAMETER_PART
1647 The procedure call argument has the syntactic form of an expression, meeting
1648 the syntactic requirements for pragmas.
1650 If debug pragmas are not enabled or if the condition is present and evaluates
1651 to False, this pragma has no effect. If debug pragmas are enabled, the
1652 semantics of the pragma is exactly equivalent to the procedure call statement
1653 corresponding to the argument with a terminating semicolon. Pragmas are
1654 permitted in sequences of declarations, so you can use pragma @code{Debug} to
1655 intersperse calls to debug procedures in the middle of declarations. Debug
1656 pragmas can be enabled either by use of the command line switch @option{-gnata}
1657 or by use of the configuration pragma @code{Debug_Policy}.
1659 @node Pragma Debug_Policy
1660 @unnumberedsec Pragma Debug_Policy
1661 @findex Debug_Policy
1665 @smallexample @c ada
1666 pragma Debug_Policy (CHECK | IGNORE);
1670 If the argument is @code{CHECK}, then pragma @code{DEBUG} is enabled.
1671 If the argument is @code{IGNORE}, then pragma @code{DEBUG} is ignored.
1672 This pragma overrides the effect of the @option{-gnata} switch on the
1675 @node Pragma Detect_Blocking
1676 @unnumberedsec Pragma Detect_Blocking
1677 @findex Detect_Blocking
1681 @smallexample @c ada
1682 pragma Detect_Blocking;
1686 This is a configuration pragma that forces the detection of potentially
1687 blocking operations within a protected operation, and to raise Program_Error
1690 @node Pragma Elaboration_Checks
1691 @unnumberedsec Pragma Elaboration_Checks
1692 @cindex Elaboration control
1693 @findex Elaboration_Checks
1697 @smallexample @c ada
1698 pragma Elaboration_Checks (Dynamic | Static);
1702 This is a configuration pragma that provides control over the
1703 elaboration model used by the compilation affected by the
1704 pragma. If the parameter is @code{Dynamic},
1705 then the dynamic elaboration
1706 model described in the Ada Reference Manual is used, as though
1707 the @option{-gnatE} switch had been specified on the command
1708 line. If the parameter is @code{Static}, then the default GNAT static
1709 model is used. This configuration pragma overrides the setting
1710 of the command line. For full details on the elaboration models
1711 used by the GNAT compiler, see @ref{Elaboration Order Handling in GNAT,,,
1712 gnat_ugn, @value{EDITION} User's Guide}.
1714 @node Pragma Eliminate
1715 @unnumberedsec Pragma Eliminate
1716 @cindex Elimination of unused subprograms
1721 @smallexample @c ada
1723 [Unit_Name =>] IDENTIFIER |
1724 SELECTED_COMPONENT);
1727 [Unit_Name =>] IDENTIFIER |
1729 [Entity =>] IDENTIFIER |
1730 SELECTED_COMPONENT |
1732 [,OVERLOADING_RESOLUTION]);
1734 OVERLOADING_RESOLUTION ::= PARAMETER_AND_RESULT_TYPE_PROFILE |
1737 PARAMETER_AND_RESULT_TYPE_PROFILE ::= PROCEDURE_PROFILE |
1740 PROCEDURE_PROFILE ::= Parameter_Types => PARAMETER_TYPES
1742 FUNCTION_PROFILE ::= [Parameter_Types => PARAMETER_TYPES,]
1743 Result_Type => result_SUBTYPE_NAME]
1745 PARAMETER_TYPES ::= (SUBTYPE_NAME @{, SUBTYPE_NAME@})
1746 SUBTYPE_NAME ::= STRING_VALUE
1748 SOURCE_LOCATION ::= Source_Location => SOURCE_TRACE
1749 SOURCE_TRACE ::= STRING_VALUE
1751 STRING_VALUE ::= STRING_LITERAL @{& STRING_LITERAL@}
1755 This pragma indicates that the given entity is not used outside the
1756 compilation unit it is defined in. The entity must be an explicitly declared
1757 subprogram; this includes generic subprogram instances and
1758 subprograms declared in generic package instances.
1760 If the entity to be eliminated is a library level subprogram, then
1761 the first form of pragma @code{Eliminate} is used with only a single argument.
1762 In this form, the @code{Unit_Name} argument specifies the name of the
1763 library level unit to be eliminated.
1765 In all other cases, both @code{Unit_Name} and @code{Entity} arguments
1766 are required. If item is an entity of a library package, then the first
1767 argument specifies the unit name, and the second argument specifies
1768 the particular entity. If the second argument is in string form, it must
1769 correspond to the internal manner in which GNAT stores entity names (see
1770 compilation unit Namet in the compiler sources for details).
1772 The remaining parameters (OVERLOADING_RESOLUTION) are optionally used
1773 to distinguish between overloaded subprograms. If a pragma does not contain
1774 the OVERLOADING_RESOLUTION parameter(s), it is applied to all the overloaded
1775 subprograms denoted by the first two parameters.
1777 Use PARAMETER_AND_RESULT_TYPE_PROFILE to specify the profile of the subprogram
1778 to be eliminated in a manner similar to that used for the extended
1779 @code{Import} and @code{Export} pragmas, except that the subtype names are
1780 always given as strings. At the moment, this form of distinguishing
1781 overloaded subprograms is implemented only partially, so we do not recommend
1782 using it for practical subprogram elimination.
1784 Note that in case of a parameterless procedure its profile is represented
1785 as @code{Parameter_Types => ("")}
1787 Alternatively, the @code{Source_Location} parameter is used to specify
1788 which overloaded alternative is to be eliminated by pointing to the
1789 location of the DEFINING_PROGRAM_UNIT_NAME of this subprogram in the
1790 source text. The string literal (or concatenation of string literals)
1791 given as SOURCE_TRACE must have the following format:
1793 @smallexample @c ada
1794 SOURCE_TRACE ::= SOURCE_LOCATION@{LBRACKET SOURCE_LOCATION RBRACKET@}
1799 SOURCE_LOCATION ::= FILE_NAME:LINE_NUMBER
1800 FILE_NAME ::= STRING_LITERAL
1801 LINE_NUMBER ::= DIGIT @{DIGIT@}
1804 SOURCE_TRACE should be the short name of the source file (with no directory
1805 information), and LINE_NUMBER is supposed to point to the line where the
1806 defining name of the subprogram is located.
1808 For the subprograms that are not a part of generic instantiations, only one
1809 SOURCE_LOCATION is used. If a subprogram is declared in a package
1810 instantiation, SOURCE_TRACE contains two SOURCE_LOCATIONs, the first one is
1811 the location of the (DEFINING_PROGRAM_UNIT_NAME of the) instantiation, and the
1812 second one denotes the declaration of the corresponding subprogram in the
1813 generic package. This approach is recursively used to create SOURCE_LOCATIONs
1814 in case of nested instantiations.
1816 The effect of the pragma is to allow the compiler to eliminate
1817 the code or data associated with the named entity. Any reference to
1818 an eliminated entity outside the compilation unit it is defined in,
1819 causes a compile time or link time error.
1821 The intention of pragma @code{Eliminate} is to allow a program to be compiled
1822 in a system independent manner, with unused entities eliminated, without
1823 the requirement of modifying the source text. Normally the required set
1824 of @code{Eliminate} pragmas is constructed automatically using the gnatelim
1825 tool. Elimination of unused entities local to a compilation unit is
1826 automatic, without requiring the use of pragma @code{Eliminate}.
1828 Note that the reason this pragma takes string literals where names might
1829 be expected is that a pragma @code{Eliminate} can appear in a context where the
1830 relevant names are not visible.
1832 Note that any change in the source files that includes removing, splitting of
1833 adding lines may make the set of Eliminate pragmas using SOURCE_LOCATION
1836 It is legal to use pragma Eliminate where the referenced entity is a
1837 dispatching operation, but it is not clear what this would mean, since
1838 in general the call does not know which entity is actually being called.
1839 Consequently, a pragma Eliminate for a dispatching operation is ignored.
1841 @node Pragma Export_Exception
1842 @unnumberedsec Pragma Export_Exception
1844 @findex Export_Exception
1848 @smallexample @c ada
1849 pragma Export_Exception (
1850 [Internal =>] LOCAL_NAME
1851 [, [External =>] EXTERNAL_SYMBOL]
1852 [, [Form =>] Ada | VMS]
1853 [, [Code =>] static_integer_EXPRESSION]);
1857 | static_string_EXPRESSION
1861 This pragma is implemented only in the OpenVMS implementation of GNAT@. It
1862 causes the specified exception to be propagated outside of the Ada program,
1863 so that it can be handled by programs written in other OpenVMS languages.
1864 This pragma establishes an external name for an Ada exception and makes the
1865 name available to the OpenVMS Linker as a global symbol. For further details
1866 on this pragma, see the
1867 DEC Ada Language Reference Manual, section 13.9a3.2.
1869 @node Pragma Export_Function
1870 @unnumberedsec Pragma Export_Function
1871 @cindex Argument passing mechanisms
1872 @findex Export_Function
1877 @smallexample @c ada
1878 pragma Export_Function (
1879 [Internal =>] LOCAL_NAME
1880 [, [External =>] EXTERNAL_SYMBOL]
1881 [, [Parameter_Types =>] PARAMETER_TYPES]
1882 [, [Result_Type =>] result_SUBTYPE_MARK]
1883 [, [Mechanism =>] MECHANISM]
1884 [, [Result_Mechanism =>] MECHANISM_NAME]);
1888 | static_string_EXPRESSION
1893 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
1897 | subtype_Name ' Access
1901 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
1903 MECHANISM_ASSOCIATION ::=
1904 [formal_parameter_NAME =>] MECHANISM_NAME
1909 | Descriptor [([Class =>] CLASS_NAME)]
1910 | Short_Descriptor [([Class =>] CLASS_NAME)]
1912 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a
1916 Use this pragma to make a function externally callable and optionally
1917 provide information on mechanisms to be used for passing parameter and
1918 result values. We recommend, for the purposes of improving portability,
1919 this pragma always be used in conjunction with a separate pragma
1920 @code{Export}, which must precede the pragma @code{Export_Function}.
1921 GNAT does not require a separate pragma @code{Export}, but if none is
1922 present, @code{Convention Ada} is assumed, which is usually
1923 not what is wanted, so it is usually appropriate to use this
1924 pragma in conjunction with a @code{Export} or @code{Convention}
1925 pragma that specifies the desired foreign convention.
1926 Pragma @code{Export_Function}
1927 (and @code{Export}, if present) must appear in the same declarative
1928 region as the function to which they apply.
1930 @var{internal_name} must uniquely designate the function to which the
1931 pragma applies. If more than one function name exists of this name in
1932 the declarative part you must use the @code{Parameter_Types} and
1933 @code{Result_Type} parameters is mandatory to achieve the required
1934 unique designation. @var{subtype_mark}s in these parameters must
1935 exactly match the subtypes in the corresponding function specification,
1936 using positional notation to match parameters with subtype marks.
1937 The form with an @code{'Access} attribute can be used to match an
1938 anonymous access parameter.
1941 @cindex Passing by descriptor
1942 Passing by descriptor is supported only on the OpenVMS ports of GNAT@.
1943 The default behavior for Export_Function is to accept either 64bit or
1944 32bit descriptors unless short_descriptor is specified, then only 32bit
1945 descriptors are accepted.
1947 @cindex Suppressing external name
1948 Special treatment is given if the EXTERNAL is an explicit null
1949 string or a static string expressions that evaluates to the null
1950 string. In this case, no external name is generated. This form
1951 still allows the specification of parameter mechanisms.
1953 @node Pragma Export_Object
1954 @unnumberedsec Pragma Export_Object
1955 @findex Export_Object
1959 @smallexample @c ada
1960 pragma Export_Object
1961 [Internal =>] LOCAL_NAME
1962 [, [External =>] EXTERNAL_SYMBOL]
1963 [, [Size =>] EXTERNAL_SYMBOL]
1967 | static_string_EXPRESSION
1971 This pragma designates an object as exported, and apart from the
1972 extended rules for external symbols, is identical in effect to the use of
1973 the normal @code{Export} pragma applied to an object. You may use a
1974 separate Export pragma (and you probably should from the point of view
1975 of portability), but it is not required. @var{Size} is syntax checked,
1976 but otherwise ignored by GNAT@.
1978 @node Pragma Export_Procedure
1979 @unnumberedsec Pragma Export_Procedure
1980 @findex Export_Procedure
1984 @smallexample @c ada
1985 pragma Export_Procedure (
1986 [Internal =>] LOCAL_NAME
1987 [, [External =>] EXTERNAL_SYMBOL]
1988 [, [Parameter_Types =>] PARAMETER_TYPES]
1989 [, [Mechanism =>] MECHANISM]);
1993 | static_string_EXPRESSION
1998 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
2002 | subtype_Name ' Access
2006 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
2008 MECHANISM_ASSOCIATION ::=
2009 [formal_parameter_NAME =>] MECHANISM_NAME
2014 | Descriptor [([Class =>] CLASS_NAME)]
2015 | Short_Descriptor [([Class =>] CLASS_NAME)]
2017 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a
2021 This pragma is identical to @code{Export_Function} except that it
2022 applies to a procedure rather than a function and the parameters
2023 @code{Result_Type} and @code{Result_Mechanism} are not permitted.
2024 GNAT does not require a separate pragma @code{Export}, but if none is
2025 present, @code{Convention Ada} is assumed, which is usually
2026 not what is wanted, so it is usually appropriate to use this
2027 pragma in conjunction with a @code{Export} or @code{Convention}
2028 pragma that specifies the desired foreign convention.
2031 @cindex Passing by descriptor
2032 Passing by descriptor is supported only on the OpenVMS ports of GNAT@.
2033 The default behavior for Export_Procedure is to accept either 64bit or
2034 32bit descriptors unless short_descriptor is specified, then only 32bit
2035 descriptors are accepted.
2037 @cindex Suppressing external name
2038 Special treatment is given if the EXTERNAL is an explicit null
2039 string or a static string expressions that evaluates to the null
2040 string. In this case, no external name is generated. This form
2041 still allows the specification of parameter mechanisms.
2043 @node Pragma Export_Value
2044 @unnumberedsec Pragma Export_Value
2045 @findex Export_Value
2049 @smallexample @c ada
2050 pragma Export_Value (
2051 [Value =>] static_integer_EXPRESSION,
2052 [Link_Name =>] static_string_EXPRESSION);
2056 This pragma serves to export a static integer value for external use.
2057 The first argument specifies the value to be exported. The Link_Name
2058 argument specifies the symbolic name to be associated with the integer
2059 value. This pragma is useful for defining a named static value in Ada
2060 that can be referenced in assembly language units to be linked with
2061 the application. This pragma is currently supported only for the
2062 AAMP target and is ignored for other targets.
2064 @node Pragma Export_Valued_Procedure
2065 @unnumberedsec Pragma Export_Valued_Procedure
2066 @findex Export_Valued_Procedure
2070 @smallexample @c ada
2071 pragma Export_Valued_Procedure (
2072 [Internal =>] LOCAL_NAME
2073 [, [External =>] EXTERNAL_SYMBOL]
2074 [, [Parameter_Types =>] PARAMETER_TYPES]
2075 [, [Mechanism =>] MECHANISM]);
2079 | static_string_EXPRESSION
2084 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
2088 | subtype_Name ' Access
2092 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
2094 MECHANISM_ASSOCIATION ::=
2095 [formal_parameter_NAME =>] MECHANISM_NAME
2100 | Descriptor [([Class =>] CLASS_NAME)]
2101 | Short_Descriptor [([Class =>] CLASS_NAME)]
2103 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a
2107 This pragma is identical to @code{Export_Procedure} except that the
2108 first parameter of @var{LOCAL_NAME}, which must be present, must be of
2109 mode @code{OUT}, and externally the subprogram is treated as a function
2110 with this parameter as the result of the function. GNAT provides for
2111 this capability to allow the use of @code{OUT} and @code{IN OUT}
2112 parameters in interfacing to external functions (which are not permitted
2114 GNAT does not require a separate pragma @code{Export}, but if none is
2115 present, @code{Convention Ada} is assumed, which is almost certainly
2116 not what is wanted since the whole point of this pragma is to interface
2117 with foreign language functions, so it is usually appropriate to use this
2118 pragma in conjunction with a @code{Export} or @code{Convention}
2119 pragma that specifies the desired foreign convention.
2122 @cindex Passing by descriptor
2123 Passing by descriptor is supported only on the OpenVMS ports of GNAT@.
2124 The default behavior for Export_Valued_Procedure is to accept either 64bit or
2125 32bit descriptors unless short_descriptor is specified, then only 32bit
2126 descriptors are accepted.
2128 @cindex Suppressing external name
2129 Special treatment is given if the EXTERNAL is an explicit null
2130 string or a static string expressions that evaluates to the null
2131 string. In this case, no external name is generated. This form
2132 still allows the specification of parameter mechanisms.
2134 @node Pragma Extend_System
2135 @unnumberedsec Pragma Extend_System
2136 @cindex @code{system}, extending
2138 @findex Extend_System
2142 @smallexample @c ada
2143 pragma Extend_System ([Name =>] IDENTIFIER);
2147 This pragma is used to provide backwards compatibility with other
2148 implementations that extend the facilities of package @code{System}. In
2149 GNAT, @code{System} contains only the definitions that are present in
2150 the Ada RM@. However, other implementations, notably the DEC Ada 83
2151 implementation, provide many extensions to package @code{System}.
2153 For each such implementation accommodated by this pragma, GNAT provides a
2154 package @code{Aux_@var{xxx}}, e.g.@: @code{Aux_DEC} for the DEC Ada 83
2155 implementation, which provides the required additional definitions. You
2156 can use this package in two ways. You can @code{with} it in the normal
2157 way and access entities either by selection or using a @code{use}
2158 clause. In this case no special processing is required.
2160 However, if existing code contains references such as
2161 @code{System.@var{xxx}} where @var{xxx} is an entity in the extended
2162 definitions provided in package @code{System}, you may use this pragma
2163 to extend visibility in @code{System} in a non-standard way that
2164 provides greater compatibility with the existing code. Pragma
2165 @code{Extend_System} is a configuration pragma whose single argument is
2166 the name of the package containing the extended definition
2167 (e.g.@: @code{Aux_DEC} for the DEC Ada case). A unit compiled under
2168 control of this pragma will be processed using special visibility
2169 processing that looks in package @code{System.Aux_@var{xxx}} where
2170 @code{Aux_@var{xxx}} is the pragma argument for any entity referenced in
2171 package @code{System}, but not found in package @code{System}.
2173 You can use this pragma either to access a predefined @code{System}
2174 extension supplied with the compiler, for example @code{Aux_DEC} or
2175 you can construct your own extension unit following the above
2176 definition. Note that such a package is a child of @code{System}
2177 and thus is considered part of the implementation. To compile
2178 it you will have to use the appropriate switch for compiling
2179 system units. @xref{Top, @value{EDITION} User's Guide, About This
2180 Guide,, gnat_ugn, @value{EDITION} User's Guide}, for details.
2182 @node Pragma External
2183 @unnumberedsec Pragma External
2188 @smallexample @c ada
2190 [ Convention =>] convention_IDENTIFIER,
2191 [ Entity =>] LOCAL_NAME
2192 [, [External_Name =>] static_string_EXPRESSION ]
2193 [, [Link_Name =>] static_string_EXPRESSION ]);
2197 This pragma is identical in syntax and semantics to pragma
2198 @code{Export} as defined in the Ada Reference Manual. It is
2199 provided for compatibility with some Ada 83 compilers that
2200 used this pragma for exactly the same purposes as pragma
2201 @code{Export} before the latter was standardized.
2203 @node Pragma External_Name_Casing
2204 @unnumberedsec Pragma External_Name_Casing
2205 @cindex Dec Ada 83 casing compatibility
2206 @cindex External Names, casing
2207 @cindex Casing of External names
2208 @findex External_Name_Casing
2212 @smallexample @c ada
2213 pragma External_Name_Casing (
2214 Uppercase | Lowercase
2215 [, Uppercase | Lowercase | As_Is]);
2219 This pragma provides control over the casing of external names associated
2220 with Import and Export pragmas. There are two cases to consider:
2223 @item Implicit external names
2224 Implicit external names are derived from identifiers. The most common case
2225 arises when a standard Ada Import or Export pragma is used with only two
2228 @smallexample @c ada
2229 pragma Import (C, C_Routine);
2233 Since Ada is a case-insensitive language, the spelling of the identifier in
2234 the Ada source program does not provide any information on the desired
2235 casing of the external name, and so a convention is needed. In GNAT the
2236 default treatment is that such names are converted to all lower case
2237 letters. This corresponds to the normal C style in many environments.
2238 The first argument of pragma @code{External_Name_Casing} can be used to
2239 control this treatment. If @code{Uppercase} is specified, then the name
2240 will be forced to all uppercase letters. If @code{Lowercase} is specified,
2241 then the normal default of all lower case letters will be used.
2243 This same implicit treatment is also used in the case of extended DEC Ada 83
2244 compatible Import and Export pragmas where an external name is explicitly
2245 specified using an identifier rather than a string.
2247 @item Explicit external names
2248 Explicit external names are given as string literals. The most common case
2249 arises when a standard Ada Import or Export pragma is used with three
2252 @smallexample @c ada
2253 pragma Import (C, C_Routine, "C_routine");
2257 In this case, the string literal normally provides the exact casing required
2258 for the external name. The second argument of pragma
2259 @code{External_Name_Casing} may be used to modify this behavior.
2260 If @code{Uppercase} is specified, then the name
2261 will be forced to all uppercase letters. If @code{Lowercase} is specified,
2262 then the name will be forced to all lowercase letters. A specification of
2263 @code{As_Is} provides the normal default behavior in which the casing is
2264 taken from the string provided.
2268 This pragma may appear anywhere that a pragma is valid. In particular, it
2269 can be used as a configuration pragma in the @file{gnat.adc} file, in which
2270 case it applies to all subsequent compilations, or it can be used as a program
2271 unit pragma, in which case it only applies to the current unit, or it can
2272 be used more locally to control individual Import/Export pragmas.
2274 It is primarily intended for use with OpenVMS systems, where many
2275 compilers convert all symbols to upper case by default. For interfacing to
2276 such compilers (e.g.@: the DEC C compiler), it may be convenient to use
2279 @smallexample @c ada
2280 pragma External_Name_Casing (Uppercase, Uppercase);
2284 to enforce the upper casing of all external symbols.
2286 @node Pragma Fast_Math
2287 @unnumberedsec Pragma Fast_Math
2292 @smallexample @c ada
2297 This is a configuration pragma which activates a mode in which speed is
2298 considered more important for floating-point operations than absolutely
2299 accurate adherence to the requirements of the standard. Currently the
2300 following operations are affected:
2303 @item Complex Multiplication
2304 The normal simple formula for complex multiplication can result in intermediate
2305 overflows for numbers near the end of the range. The Ada standard requires that
2306 this situation be detected and corrected by scaling, but in Fast_Math mode such
2307 cases will simply result in overflow. Note that to take advantage of this you
2308 must instantiate your own version of @code{Ada.Numerics.Generic_Complex_Types}
2309 under control of the pragma, rather than use the preinstantiated versions.
2312 @node Pragma Favor_Top_Level
2313 @unnumberedsec Pragma Favor_Top_Level
2314 @findex Favor_Top_Level
2318 @smallexample @c ada
2319 pragma Favor_Top_Level (type_NAME);
2323 The named type must be an access-to-subprogram type. This pragma is an
2324 efficiency hint to the compiler, regarding the use of 'Access or
2325 'Unrestricted_Access on nested (non-library-level) subprograms. The
2326 pragma means that nested subprograms are not used with this type, or
2327 are rare, so that the generated code should be efficient in the
2328 top-level case. When this pragma is used, dynamically generated
2329 trampolines may be used on some targets for nested subprograms.
2330 See also the No_Implicit_Dynamic_Code restriction.
2332 @node Pragma Finalize_Storage_Only
2333 @unnumberedsec Pragma Finalize_Storage_Only
2334 @findex Finalize_Storage_Only
2338 @smallexample @c ada
2339 pragma Finalize_Storage_Only (first_subtype_LOCAL_NAME);
2343 This pragma allows the compiler not to emit a Finalize call for objects
2344 defined at the library level. This is mostly useful for types where
2345 finalization is only used to deal with storage reclamation since in most
2346 environments it is not necessary to reclaim memory just before terminating
2347 execution, hence the name.
2349 @node Pragma Float_Representation
2350 @unnumberedsec Pragma Float_Representation
2352 @findex Float_Representation
2356 @smallexample @c ada
2357 pragma Float_Representation (FLOAT_REP[, float_type_LOCAL_NAME]);
2359 FLOAT_REP ::= VAX_Float | IEEE_Float
2363 In the one argument form, this pragma is a configuration pragma which
2364 allows control over the internal representation chosen for the predefined
2365 floating point types declared in the packages @code{Standard} and
2366 @code{System}. On all systems other than OpenVMS, the argument must
2367 be @code{IEEE_Float} and the pragma has no effect. On OpenVMS, the
2368 argument may be @code{VAX_Float} to specify the use of the VAX float
2369 format for the floating-point types in Standard. This requires that
2370 the standard runtime libraries be recompiled. @xref{The GNAT Run-Time
2371 Library Builder gnatlbr,,, gnat_ugn, @value{EDITION} User's Guide
2372 OpenVMS}, for a description of the @code{GNAT LIBRARY} command.
2374 The two argument form specifies the representation to be used for
2375 the specified floating-point type. On all systems other than OpenVMS,
2377 be @code{IEEE_Float} and the pragma has no effect. On OpenVMS, the
2378 argument may be @code{VAX_Float} to specify the use of the VAX float
2383 For digits values up to 6, F float format will be used.
2385 For digits values from 7 to 9, G float format will be used.
2387 For digits values from 10 to 15, F float format will be used.
2389 Digits values above 15 are not allowed.
2393 @unnumberedsec Pragma Ident
2398 @smallexample @c ada
2399 pragma Ident (static_string_EXPRESSION);
2403 This pragma provides a string identification in the generated object file,
2404 if the system supports the concept of this kind of identification string.
2405 This pragma is allowed only in the outermost declarative part or
2406 declarative items of a compilation unit. If more than one @code{Ident}
2407 pragma is given, only the last one processed is effective.
2409 On OpenVMS systems, the effect of the pragma is identical to the effect of
2410 the DEC Ada 83 pragma of the same name. Note that in DEC Ada 83, the
2411 maximum allowed length is 31 characters, so if it is important to
2412 maintain compatibility with this compiler, you should obey this length
2415 @node Pragma Implemented_By_Entry
2416 @unnumberedsec Pragma Implemented_By_Entry
2417 @findex Implemented_By_Entry
2421 @smallexample @c ada
2422 pragma Implemented_By_Entry (LOCAL_NAME);
2426 This is a representation pragma which applies to protected, synchronized and
2427 task interface primitives. If the pragma is applied to primitive operation Op
2428 of interface Iface, it is illegal to override Op in a type that implements
2429 Iface, with anything other than an entry.
2431 @smallexample @c ada
2432 type Iface is protected interface;
2433 procedure Do_Something (Object : in out Iface) is abstract;
2434 pragma Implemented_By_Entry (Do_Something);
2436 protected type P is new Iface with
2437 procedure Do_Something; -- Illegal
2440 task type T is new Iface with
2441 entry Do_Something; -- Legal
2446 NOTE: The pragma is still in its design stage by the Ada Rapporteur Group. It
2447 is intended to be used in conjunction with dispatching requeue statements as
2448 described in AI05-0030. Should the ARG decide on an official name and syntax,
2449 this pragma will become language-defined rather than GNAT-specific.
2451 @node Pragma Implicit_Packing
2452 @unnumberedsec Pragma Implicit_Packing
2453 @findex Implicit_Packing
2457 @smallexample @c ada
2458 pragma Implicit_Packing;
2462 This is a configuration pragma that requests implicit packing for packed
2463 arrays for which a size clause is given but no explicit pragma Pack or
2464 specification of Component_Size is present. It also applies to records
2465 where no record representation clause is present. Consider this example:
2467 @smallexample @c ada
2468 type R is array (0 .. 7) of Boolean;
2473 In accordance with the recommendation in the RM (RM 13.3(53)), a Size clause
2474 does not change the layout of a composite object. So the Size clause in the
2475 above example is normally rejected, since the default layout of the array uses
2476 8-bit components, and thus the array requires a minimum of 64 bits.
2478 If this declaration is compiled in a region of code covered by an occurrence
2479 of the configuration pragma Implicit_Packing, then the Size clause in this
2480 and similar examples will cause implicit packing and thus be accepted. For
2481 this implicit packing to occur, the type in question must be an array of small
2482 components whose size is known at compile time, and the Size clause must
2483 specify the exact size that corresponds to the length of the array multiplied
2484 by the size in bits of the component type.
2485 @cindex Array packing
2487 Similarly, the following example shows the use in the record case
2489 @smallexample @c ada
2491 a, b, c, d, e, f, g, h : boolean;
2498 Without a pragma Pack, each Boolean field requires 8 bits, so the
2499 minimum size is 72 bits, but with a pragma Pack, 16 bits would be
2500 sufficient. The use of pragma Implciit_Packing allows this record
2501 declaration to compile without an explicit pragma Pack.
2502 @node Pragma Import_Exception
2503 @unnumberedsec Pragma Import_Exception
2505 @findex Import_Exception
2509 @smallexample @c ada
2510 pragma Import_Exception (
2511 [Internal =>] LOCAL_NAME
2512 [, [External =>] EXTERNAL_SYMBOL]
2513 [, [Form =>] Ada | VMS]
2514 [, [Code =>] static_integer_EXPRESSION]);
2518 | static_string_EXPRESSION
2522 This pragma is implemented only in the OpenVMS implementation of GNAT@.
2523 It allows OpenVMS conditions (for example, from OpenVMS system services or
2524 other OpenVMS languages) to be propagated to Ada programs as Ada exceptions.
2525 The pragma specifies that the exception associated with an exception
2526 declaration in an Ada program be defined externally (in non-Ada code).
2527 For further details on this pragma, see the
2528 DEC Ada Language Reference Manual, section 13.9a.3.1.
2530 @node Pragma Import_Function
2531 @unnumberedsec Pragma Import_Function
2532 @findex Import_Function
2536 @smallexample @c ada
2537 pragma Import_Function (
2538 [Internal =>] LOCAL_NAME,
2539 [, [External =>] EXTERNAL_SYMBOL]
2540 [, [Parameter_Types =>] PARAMETER_TYPES]
2541 [, [Result_Type =>] SUBTYPE_MARK]
2542 [, [Mechanism =>] MECHANISM]
2543 [, [Result_Mechanism =>] MECHANISM_NAME]
2544 [, [First_Optional_Parameter =>] IDENTIFIER]);
2548 | static_string_EXPRESSION
2552 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
2556 | subtype_Name ' Access
2560 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
2562 MECHANISM_ASSOCIATION ::=
2563 [formal_parameter_NAME =>] MECHANISM_NAME
2568 | Descriptor [([Class =>] CLASS_NAME)]
2569 | Short_Descriptor [([Class =>] CLASS_NAME)]
2571 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
2575 This pragma is used in conjunction with a pragma @code{Import} to
2576 specify additional information for an imported function. The pragma
2577 @code{Import} (or equivalent pragma @code{Interface}) must precede the
2578 @code{Import_Function} pragma and both must appear in the same
2579 declarative part as the function specification.
2581 The @var{Internal} argument must uniquely designate
2582 the function to which the
2583 pragma applies. If more than one function name exists of this name in
2584 the declarative part you must use the @code{Parameter_Types} and
2585 @var{Result_Type} parameters to achieve the required unique
2586 designation. Subtype marks in these parameters must exactly match the
2587 subtypes in the corresponding function specification, using positional
2588 notation to match parameters with subtype marks.
2589 The form with an @code{'Access} attribute can be used to match an
2590 anonymous access parameter.
2592 You may optionally use the @var{Mechanism} and @var{Result_Mechanism}
2593 parameters to specify passing mechanisms for the
2594 parameters and result. If you specify a single mechanism name, it
2595 applies to all parameters. Otherwise you may specify a mechanism on a
2596 parameter by parameter basis using either positional or named
2597 notation. If the mechanism is not specified, the default mechanism
2601 @cindex Passing by descriptor
2602 Passing by descriptor is supported only on the OpenVMS ports of GNAT@.
2603 The default behavior for Import_Function is to pass a 64bit descriptor
2604 unless short_descriptor is specified, then a 32bit descriptor is passed.
2606 @code{First_Optional_Parameter} applies only to OpenVMS ports of GNAT@.
2607 It specifies that the designated parameter and all following parameters
2608 are optional, meaning that they are not passed at the generated code
2609 level (this is distinct from the notion of optional parameters in Ada
2610 where the parameters are passed anyway with the designated optional
2611 parameters). All optional parameters must be of mode @code{IN} and have
2612 default parameter values that are either known at compile time
2613 expressions, or uses of the @code{'Null_Parameter} attribute.
2615 @node Pragma Import_Object
2616 @unnumberedsec Pragma Import_Object
2617 @findex Import_Object
2621 @smallexample @c ada
2622 pragma Import_Object
2623 [Internal =>] LOCAL_NAME
2624 [, [External =>] EXTERNAL_SYMBOL]
2625 [, [Size =>] EXTERNAL_SYMBOL]);
2629 | static_string_EXPRESSION
2633 This pragma designates an object as imported, and apart from the
2634 extended rules for external symbols, is identical in effect to the use of
2635 the normal @code{Import} pragma applied to an object. Unlike the
2636 subprogram case, you need not use a separate @code{Import} pragma,
2637 although you may do so (and probably should do so from a portability
2638 point of view). @var{size} is syntax checked, but otherwise ignored by
2641 @node Pragma Import_Procedure
2642 @unnumberedsec Pragma Import_Procedure
2643 @findex Import_Procedure
2647 @smallexample @c ada
2648 pragma Import_Procedure (
2649 [Internal =>] LOCAL_NAME
2650 [, [External =>] EXTERNAL_SYMBOL]
2651 [, [Parameter_Types =>] PARAMETER_TYPES]
2652 [, [Mechanism =>] MECHANISM]
2653 [, [First_Optional_Parameter =>] IDENTIFIER]);
2657 | static_string_EXPRESSION
2661 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
2665 | subtype_Name ' Access
2669 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
2671 MECHANISM_ASSOCIATION ::=
2672 [formal_parameter_NAME =>] MECHANISM_NAME
2677 | Descriptor [([Class =>] CLASS_NAME)]
2678 | Short_Descriptor [([Class =>] CLASS_NAME)]
2680 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
2684 This pragma is identical to @code{Import_Function} except that it
2685 applies to a procedure rather than a function and the parameters
2686 @code{Result_Type} and @code{Result_Mechanism} are not permitted.
2688 @node Pragma Import_Valued_Procedure
2689 @unnumberedsec Pragma Import_Valued_Procedure
2690 @findex Import_Valued_Procedure
2694 @smallexample @c ada
2695 pragma Import_Valued_Procedure (
2696 [Internal =>] LOCAL_NAME
2697 [, [External =>] EXTERNAL_SYMBOL]
2698 [, [Parameter_Types =>] PARAMETER_TYPES]
2699 [, [Mechanism =>] MECHANISM]
2700 [, [First_Optional_Parameter =>] IDENTIFIER]);
2704 | static_string_EXPRESSION
2708 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
2712 | subtype_Name ' Access
2716 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
2718 MECHANISM_ASSOCIATION ::=
2719 [formal_parameter_NAME =>] MECHANISM_NAME
2724 | Descriptor [([Class =>] CLASS_NAME)]
2725 | Short_Descriptor [([Class =>] CLASS_NAME)]
2727 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
2731 This pragma is identical to @code{Import_Procedure} except that the
2732 first parameter of @var{LOCAL_NAME}, which must be present, must be of
2733 mode @code{OUT}, and externally the subprogram is treated as a function
2734 with this parameter as the result of the function. The purpose of this
2735 capability is to allow the use of @code{OUT} and @code{IN OUT}
2736 parameters in interfacing to external functions (which are not permitted
2737 in Ada functions). You may optionally use the @code{Mechanism}
2738 parameters to specify passing mechanisms for the parameters.
2739 If you specify a single mechanism name, it applies to all parameters.
2740 Otherwise you may specify a mechanism on a parameter by parameter
2741 basis using either positional or named notation. If the mechanism is not
2742 specified, the default mechanism is used.
2744 Note that it is important to use this pragma in conjunction with a separate
2745 pragma Import that specifies the desired convention, since otherwise the
2746 default convention is Ada, which is almost certainly not what is required.
2748 @node Pragma Initialize_Scalars
2749 @unnumberedsec Pragma Initialize_Scalars
2750 @findex Initialize_Scalars
2751 @cindex debugging with Initialize_Scalars
2755 @smallexample @c ada
2756 pragma Initialize_Scalars;
2760 This pragma is similar to @code{Normalize_Scalars} conceptually but has
2761 two important differences. First, there is no requirement for the pragma
2762 to be used uniformly in all units of a partition, in particular, it is fine
2763 to use this just for some or all of the application units of a partition,
2764 without needing to recompile the run-time library.
2766 In the case where some units are compiled with the pragma, and some without,
2767 then a declaration of a variable where the type is defined in package
2768 Standard or is locally declared will always be subject to initialization,
2769 as will any declaration of a scalar variable. For composite variables,
2770 whether the variable is initialized may also depend on whether the package
2771 in which the type of the variable is declared is compiled with the pragma.
2773 The other important difference is that you can control the value used
2774 for initializing scalar objects. At bind time, you can select several
2775 options for initialization. You can
2776 initialize with invalid values (similar to Normalize_Scalars, though for
2777 Initialize_Scalars it is not always possible to determine the invalid
2778 values in complex cases like signed component fields with non-standard
2779 sizes). You can also initialize with high or
2780 low values, or with a specified bit pattern. See the users guide for binder
2781 options for specifying these cases.
2783 This means that you can compile a program, and then without having to
2784 recompile the program, you can run it with different values being used
2785 for initializing otherwise uninitialized values, to test if your program
2786 behavior depends on the choice. Of course the behavior should not change,
2787 and if it does, then most likely you have an erroneous reference to an
2788 uninitialized value.
2790 It is even possible to change the value at execution time eliminating even
2791 the need to rebind with a different switch using an environment variable.
2792 See the GNAT users guide for details.
2794 Note that pragma @code{Initialize_Scalars} is particularly useful in
2795 conjunction with the enhanced validity checking that is now provided
2796 in GNAT, which checks for invalid values under more conditions.
2797 Using this feature (see description of the @option{-gnatV} flag in the
2798 users guide) in conjunction with pragma @code{Initialize_Scalars}
2799 provides a powerful new tool to assist in the detection of problems
2800 caused by uninitialized variables.
2802 Note: the use of @code{Initialize_Scalars} has a fairly extensive
2803 effect on the generated code. This may cause your code to be
2804 substantially larger. It may also cause an increase in the amount
2805 of stack required, so it is probably a good idea to turn on stack
2806 checking (see description of stack checking in the GNAT users guide)
2807 when using this pragma.
2809 @node Pragma Inline_Always
2810 @unnumberedsec Pragma Inline_Always
2811 @findex Inline_Always
2815 @smallexample @c ada
2816 pragma Inline_Always (NAME [, NAME]);
2820 Similar to pragma @code{Inline} except that inlining is not subject to
2821 the use of option @option{-gnatn} and the inlining happens regardless of
2822 whether this option is used.
2824 @node Pragma Inline_Generic
2825 @unnumberedsec Pragma Inline_Generic
2826 @findex Inline_Generic
2830 @smallexample @c ada
2831 pragma Inline_Generic (generic_package_NAME);
2835 This is implemented for compatibility with DEC Ada 83 and is recognized,
2836 but otherwise ignored, by GNAT@. All generic instantiations are inlined
2837 by default when using GNAT@.
2839 @node Pragma Interface
2840 @unnumberedsec Pragma Interface
2845 @smallexample @c ada
2847 [Convention =>] convention_identifier,
2848 [Entity =>] local_NAME
2849 [, [External_Name =>] static_string_expression]
2850 [, [Link_Name =>] static_string_expression]);
2854 This pragma is identical in syntax and semantics to
2855 the standard Ada pragma @code{Import}. It is provided for compatibility
2856 with Ada 83. The definition is upwards compatible both with pragma
2857 @code{Interface} as defined in the Ada 83 Reference Manual, and also
2858 with some extended implementations of this pragma in certain Ada 83
2861 @node Pragma Interface_Name
2862 @unnumberedsec Pragma Interface_Name
2863 @findex Interface_Name
2867 @smallexample @c ada
2868 pragma Interface_Name (
2869 [Entity =>] LOCAL_NAME
2870 [, [External_Name =>] static_string_EXPRESSION]
2871 [, [Link_Name =>] static_string_EXPRESSION]);
2875 This pragma provides an alternative way of specifying the interface name
2876 for an interfaced subprogram, and is provided for compatibility with Ada
2877 83 compilers that use the pragma for this purpose. You must provide at
2878 least one of @var{External_Name} or @var{Link_Name}.
2880 @node Pragma Interrupt_Handler
2881 @unnumberedsec Pragma Interrupt_Handler
2882 @findex Interrupt_Handler
2886 @smallexample @c ada
2887 pragma Interrupt_Handler (procedure_LOCAL_NAME);
2891 This program unit pragma is supported for parameterless protected procedures
2892 as described in Annex C of the Ada Reference Manual. On the AAMP target
2893 the pragma can also be specified for nonprotected parameterless procedures
2894 that are declared at the library level (which includes procedures
2895 declared at the top level of a library package). In the case of AAMP,
2896 when this pragma is applied to a nonprotected procedure, the instruction
2897 @code{IERET} is generated for returns from the procedure, enabling
2898 maskable interrupts, in place of the normal return instruction.
2900 @node Pragma Interrupt_State
2901 @unnumberedsec Pragma Interrupt_State
2902 @findex Interrupt_State
2906 @smallexample @c ada
2907 pragma Interrupt_State
2909 [State =>] SYSTEM | RUNTIME | USER);
2913 Normally certain interrupts are reserved to the implementation. Any attempt
2914 to attach an interrupt causes Program_Error to be raised, as described in
2915 RM C.3.2(22). A typical example is the @code{SIGINT} interrupt used in
2916 many systems for an @kbd{Ctrl-C} interrupt. Normally this interrupt is
2917 reserved to the implementation, so that @kbd{Ctrl-C} can be used to
2918 interrupt execution. Additionally, signals such as @code{SIGSEGV},
2919 @code{SIGABRT}, @code{SIGFPE} and @code{SIGILL} are often mapped to specific
2920 Ada exceptions, or used to implement run-time functions such as the
2921 @code{abort} statement and stack overflow checking.
2923 Pragma @code{Interrupt_State} provides a general mechanism for overriding
2924 such uses of interrupts. It subsumes the functionality of pragma
2925 @code{Unreserve_All_Interrupts}. Pragma @code{Interrupt_State} is not
2926 available on OS/2, Windows or VMS. On all other platforms than VxWorks,
2927 it applies to signals; on VxWorks, it applies to vectored hardware interrupts
2928 and may be used to mark interrupts required by the board support package
2931 Interrupts can be in one of three states:
2935 The interrupt is reserved (no Ada handler can be installed), and the
2936 Ada run-time may not install a handler. As a result you are guaranteed
2937 standard system default action if this interrupt is raised.
2941 The interrupt is reserved (no Ada handler can be installed). The run time
2942 is allowed to install a handler for internal control purposes, but is
2943 not required to do so.
2947 The interrupt is unreserved. The user may install a handler to provide
2952 These states are the allowed values of the @code{State} parameter of the
2953 pragma. The @code{Name} parameter is a value of the type
2954 @code{Ada.Interrupts.Interrupt_ID}. Typically, it is a name declared in
2955 @code{Ada.Interrupts.Names}.
2957 This is a configuration pragma, and the binder will check that there
2958 are no inconsistencies between different units in a partition in how a
2959 given interrupt is specified. It may appear anywhere a pragma is legal.
2961 The effect is to move the interrupt to the specified state.
2963 By declaring interrupts to be SYSTEM, you guarantee the standard system
2964 action, such as a core dump.
2966 By declaring interrupts to be USER, you guarantee that you can install
2969 Note that certain signals on many operating systems cannot be caught and
2970 handled by applications. In such cases, the pragma is ignored. See the
2971 operating system documentation, or the value of the array @code{Reserved}
2972 declared in the spec of package @code{System.OS_Interface}.
2974 Overriding the default state of signals used by the Ada runtime may interfere
2975 with an application's runtime behavior in the cases of the synchronous signals,
2976 and in the case of the signal used to implement the @code{abort} statement.
2978 @node Pragma Keep_Names
2979 @unnumberedsec Pragma Keep_Names
2984 @smallexample @c ada
2985 pragma Keep_Names ([On =>] enumeration_first_subtype_LOCAL_NAME);
2989 The @var{LOCAL_NAME} argument
2990 must refer to an enumeration first subtype
2991 in the current declarative part. The effect is to retain the enumeration
2992 literal names for use by @code{Image} and @code{Value} even if a global
2993 @code{Discard_Names} pragma applies. This is useful when you want to
2994 generally suppress enumeration literal names and for example you therefore
2995 use a @code{Discard_Names} pragma in the @file{gnat.adc} file, but you
2996 want to retain the names for specific enumeration types.
2998 @node Pragma License
2999 @unnumberedsec Pragma License
3001 @cindex License checking
3005 @smallexample @c ada
3006 pragma License (Unrestricted | GPL | Modified_GPL | Restricted);
3010 This pragma is provided to allow automated checking for appropriate license
3011 conditions with respect to the standard and modified GPL@. A pragma
3012 @code{License}, which is a configuration pragma that typically appears at
3013 the start of a source file or in a separate @file{gnat.adc} file, specifies
3014 the licensing conditions of a unit as follows:
3018 This is used for a unit that can be freely used with no license restrictions.
3019 Examples of such units are public domain units, and units from the Ada
3023 This is used for a unit that is licensed under the unmodified GPL, and which
3024 therefore cannot be @code{with}'ed by a restricted unit.
3027 This is used for a unit licensed under the GNAT modified GPL that includes
3028 a special exception paragraph that specifically permits the inclusion of
3029 the unit in programs without requiring the entire program to be released
3033 This is used for a unit that is restricted in that it is not permitted to
3034 depend on units that are licensed under the GPL@. Typical examples are
3035 proprietary code that is to be released under more restrictive license
3036 conditions. Note that restricted units are permitted to @code{with} units
3037 which are licensed under the modified GPL (this is the whole point of the
3043 Normally a unit with no @code{License} pragma is considered to have an
3044 unknown license, and no checking is done. However, standard GNAT headers
3045 are recognized, and license information is derived from them as follows.
3049 A GNAT license header starts with a line containing 78 hyphens. The following
3050 comment text is searched for the appearance of any of the following strings.
3052 If the string ``GNU General Public License'' is found, then the unit is assumed
3053 to have GPL license, unless the string ``As a special exception'' follows, in
3054 which case the license is assumed to be modified GPL@.
3056 If one of the strings
3057 ``This specification is adapted from the Ada Semantic Interface'' or
3058 ``This specification is derived from the Ada Reference Manual'' is found
3059 then the unit is assumed to be unrestricted.
3063 These default actions means that a program with a restricted license pragma
3064 will automatically get warnings if a GPL unit is inappropriately
3065 @code{with}'ed. For example, the program:
3067 @smallexample @c ada
3070 procedure Secret_Stuff is
3076 if compiled with pragma @code{License} (@code{Restricted}) in a
3077 @file{gnat.adc} file will generate the warning:
3082 >>> license of withed unit "Sem_Ch3" is incompatible
3084 2. with GNAT.Sockets;
3085 3. procedure Secret_Stuff is
3089 Here we get a warning on @code{Sem_Ch3} since it is part of the GNAT
3090 compiler and is licensed under the
3091 GPL, but no warning for @code{GNAT.Sockets} which is part of the GNAT
3092 run time, and is therefore licensed under the modified GPL@.
3094 @node Pragma Link_With
3095 @unnumberedsec Pragma Link_With
3100 @smallexample @c ada
3101 pragma Link_With (static_string_EXPRESSION @{,static_string_EXPRESSION@});
3105 This pragma is provided for compatibility with certain Ada 83 compilers.
3106 It has exactly the same effect as pragma @code{Linker_Options} except
3107 that spaces occurring within one of the string expressions are treated
3108 as separators. For example, in the following case:
3110 @smallexample @c ada
3111 pragma Link_With ("-labc -ldef");
3115 results in passing the strings @code{-labc} and @code{-ldef} as two
3116 separate arguments to the linker. In addition pragma Link_With allows
3117 multiple arguments, with the same effect as successive pragmas.
3119 @node Pragma Linker_Alias
3120 @unnumberedsec Pragma Linker_Alias
3121 @findex Linker_Alias
3125 @smallexample @c ada
3126 pragma Linker_Alias (
3127 [Entity =>] LOCAL_NAME,
3128 [Target =>] static_string_EXPRESSION);
3132 @var{LOCAL_NAME} must refer to an object that is declared at the library
3133 level. This pragma establishes the given entity as a linker alias for the
3134 given target. It is equivalent to @code{__attribute__((alias))} in GNU C
3135 and causes @var{LOCAL_NAME} to be emitted as an alias for the symbol
3136 @var{static_string_EXPRESSION} in the object file, that is to say no space
3137 is reserved for @var{LOCAL_NAME} by the assembler and it will be resolved
3138 to the same address as @var{static_string_EXPRESSION} by the linker.
3140 The actual linker name for the target must be used (e.g.@: the fully
3141 encoded name with qualification in Ada, or the mangled name in C++),
3142 or it must be declared using the C convention with @code{pragma Import}
3143 or @code{pragma Export}.
3145 Not all target machines support this pragma. On some of them it is accepted
3146 only if @code{pragma Weak_External} has been applied to @var{LOCAL_NAME}.
3148 @smallexample @c ada
3149 -- Example of the use of pragma Linker_Alias
3153 pragma Export (C, i);
3155 new_name_for_i : Integer;
3156 pragma Linker_Alias (new_name_for_i, "i");
3160 @node Pragma Linker_Constructor
3161 @unnumberedsec Pragma Linker_Constructor
3162 @findex Linker_Constructor
3166 @smallexample @c ada
3167 pragma Linker_Constructor (procedure_LOCAL_NAME);
3171 @var{procedure_LOCAL_NAME} must refer to a parameterless procedure that
3172 is declared at the library level. A procedure to which this pragma is
3173 applied will be treated as an initialization routine by the linker.
3174 It is equivalent to @code{__attribute__((constructor))} in GNU C and
3175 causes @var{procedure_LOCAL_NAME} to be invoked before the entry point
3176 of the executable is called (or immediately after the shared library is
3177 loaded if the procedure is linked in a shared library), in particular
3178 before the Ada run-time environment is set up.
3180 Because of these specific contexts, the set of operations such a procedure
3181 can perform is very limited and the type of objects it can manipulate is
3182 essentially restricted to the elementary types. In particular, it must only
3183 contain code to which pragma Restrictions (No_Elaboration_Code) applies.
3185 This pragma is used by GNAT to implement auto-initialization of shared Stand
3186 Alone Libraries, which provides a related capability without the restrictions
3187 listed above. Where possible, the use of Stand Alone Libraries is preferable
3188 to the use of this pragma.
3190 @node Pragma Linker_Destructor
3191 @unnumberedsec Pragma Linker_Destructor
3192 @findex Linker_Destructor
3196 @smallexample @c ada
3197 pragma Linker_Destructor (procedure_LOCAL_NAME);
3201 @var{procedure_LOCAL_NAME} must refer to a parameterless procedure that
3202 is declared at the library level. A procedure to which this pragma is
3203 applied will be treated as a finalization routine by the linker.
3204 It is equivalent to @code{__attribute__((destructor))} in GNU C and
3205 causes @var{procedure_LOCAL_NAME} to be invoked after the entry point
3206 of the executable has exited (or immediately before the shared library
3207 is unloaded if the procedure is linked in a shared library), in particular
3208 after the Ada run-time environment is shut down.
3210 See @code{pragma Linker_Constructor} for the set of restrictions that apply
3211 because of these specific contexts.
3213 @node Pragma Linker_Section
3214 @unnumberedsec Pragma Linker_Section
3215 @findex Linker_Section
3219 @smallexample @c ada
3220 pragma Linker_Section (
3221 [Entity =>] LOCAL_NAME,
3222 [Section =>] static_string_EXPRESSION);
3226 @var{LOCAL_NAME} must refer to an object that is declared at the library
3227 level. This pragma specifies the name of the linker section for the given
3228 entity. It is equivalent to @code{__attribute__((section))} in GNU C and
3229 causes @var{LOCAL_NAME} to be placed in the @var{static_string_EXPRESSION}
3230 section of the executable (assuming the linker doesn't rename the section).
3232 The compiler normally places library-level objects in standard sections
3233 depending on their type: procedures and functions generally go in the
3234 @code{.text} section, initialized variables in the @code{.data} section
3235 and uninitialized variables in the @code{.bss} section.
3237 Other, special sections may exist on given target machines to map special
3238 hardware, for example I/O ports or flash memory. This pragma is a means to
3239 defer the final layout of the executable to the linker, thus fully working
3240 at the symbolic level with the compiler.
3242 Some file formats do not support arbitrary sections so not all target
3243 machines support this pragma. The use of this pragma may cause a program
3244 execution to be erroneous if it is used to place an entity into an
3245 inappropriate section (e.g.@: a modified variable into the @code{.text}
3246 section). See also @code{pragma Persistent_BSS}.
3248 @smallexample @c ada
3249 -- Example of the use of pragma Linker_Section
3253 pragma Volatile (Port_A);
3254 pragma Linker_Section (Port_A, ".bss.port_a");
3257 pragma Volatile (Port_B);
3258 pragma Linker_Section (Port_B, ".bss.port_b");
3262 @node Pragma Long_Float
3263 @unnumberedsec Pragma Long_Float
3269 @smallexample @c ada
3270 pragma Long_Float (FLOAT_FORMAT);
3272 FLOAT_FORMAT ::= D_Float | G_Float
3276 This pragma is implemented only in the OpenVMS implementation of GNAT@.
3277 It allows control over the internal representation chosen for the predefined
3278 type @code{Long_Float} and for floating point type representations with
3279 @code{digits} specified in the range 7 through 15.
3280 For further details on this pragma, see the
3281 @cite{DEC Ada Language Reference Manual}, section 3.5.7b. Note that to use
3282 this pragma, the standard runtime libraries must be recompiled.
3283 @xref{The GNAT Run-Time Library Builder gnatlbr,,, gnat_ugn,
3284 @value{EDITION} User's Guide OpenVMS}, for a description of the
3285 @code{GNAT LIBRARY} command.
3287 @node Pragma Machine_Attribute
3288 @unnumberedsec Pragma Machine_Attribute
3289 @findex Machine_Attribute
3293 @smallexample @c ada
3294 pragma Machine_Attribute (
3295 [Entity =>] LOCAL_NAME,
3296 [Attribute_Name =>] static_string_EXPRESSION
3297 [, [Info =>] static_EXPRESSION] );
3301 Machine-dependent attributes can be specified for types and/or
3302 declarations. This pragma is semantically equivalent to
3303 @code{__attribute__((@var{attribute_name}))} (if @var{info} is not
3304 specified) or @code{__attribute__((@var{attribute_name}(@var{info})))}
3305 in GNU C, where @code{@var{attribute_name}} is recognized by the
3306 compiler middle-end or the @code{TARGET_ATTRIBUTE_TABLE} machine
3307 specific macro. A string literal for the optional parameter @var{info}
3308 is transformed into an identifier, which may make this pragma unusable
3309 for some attributes. @xref{Target Attributes,, Defining target-specific
3310 uses of @code{__attribute__}, gccint, GNU Compiler Collection (GCC)
3311 Internals}, further information.
3314 @unnumberedsec Pragma Main
3320 @smallexample @c ada
3322 (MAIN_OPTION [, MAIN_OPTION]);
3325 [Stack_Size =>] static_integer_EXPRESSION
3326 | [Task_Stack_Size_Default =>] static_integer_EXPRESSION
3327 | [Time_Slicing_Enabled =>] static_boolean_EXPRESSION
3331 This pragma is provided for compatibility with OpenVMS VAX Systems. It has
3332 no effect in GNAT, other than being syntax checked.
3334 @node Pragma Main_Storage
3335 @unnumberedsec Pragma Main_Storage
3337 @findex Main_Storage
3341 @smallexample @c ada
3343 (MAIN_STORAGE_OPTION [, MAIN_STORAGE_OPTION]);
3345 MAIN_STORAGE_OPTION ::=
3346 [WORKING_STORAGE =>] static_SIMPLE_EXPRESSION
3347 | [TOP_GUARD =>] static_SIMPLE_EXPRESSION
3351 This pragma is provided for compatibility with OpenVMS VAX Systems. It has
3352 no effect in GNAT, other than being syntax checked. Note that the pragma
3353 also has no effect in DEC Ada 83 for OpenVMS Alpha Systems.
3355 @node Pragma No_Body
3356 @unnumberedsec Pragma No_Body
3361 @smallexample @c ada
3366 There are a number of cases in which a package spec does not require a body,
3367 and in fact a body is not permitted. GNAT will not permit the spec to be
3368 compiled if there is a body around. The pragma No_Body allows you to provide
3369 a body file, even in a case where no body is allowed. The body file must
3370 contain only comments and a single No_Body pragma. This is recognized by
3371 the compiler as indicating that no body is logically present.
3373 This is particularly useful during maintenance when a package is modified in
3374 such a way that a body needed before is no longer needed. The provision of a
3375 dummy body with a No_Body pragma ensures that there is no interference from
3376 earlier versions of the package body.
3378 @node Pragma No_Return
3379 @unnumberedsec Pragma No_Return
3384 @smallexample @c ada
3385 pragma No_Return (procedure_LOCAL_NAME @{, procedure_LOCAL_NAME@});
3389 Each @var{procedure_LOCAL_NAME} argument must refer to one or more procedure
3390 declarations in the current declarative part. A procedure to which this
3391 pragma is applied may not contain any explicit @code{return} statements.
3392 In addition, if the procedure contains any implicit returns from falling
3393 off the end of a statement sequence, then execution of that implicit
3394 return will cause Program_Error to be raised.
3396 One use of this pragma is to identify procedures whose only purpose is to raise
3397 an exception. Another use of this pragma is to suppress incorrect warnings
3398 about missing returns in functions, where the last statement of a function
3399 statement sequence is a call to such a procedure.
3401 Note that in Ada 2005 mode, this pragma is part of the language, and is
3402 identical in effect to the pragma as implemented in Ada 95 mode.
3404 @node Pragma No_Strict_Aliasing
3405 @unnumberedsec Pragma No_Strict_Aliasing
3406 @findex No_Strict_Aliasing
3410 @smallexample @c ada
3411 pragma No_Strict_Aliasing [([Entity =>] type_LOCAL_NAME)];
3415 @var{type_LOCAL_NAME} must refer to an access type
3416 declaration in the current declarative part. The effect is to inhibit
3417 strict aliasing optimization for the given type. The form with no
3418 arguments is a configuration pragma which applies to all access types
3419 declared in units to which the pragma applies. For a detailed
3420 description of the strict aliasing optimization, and the situations
3421 in which it must be suppressed, see @ref{Optimization and Strict
3422 Aliasing,,, gnat_ugn, @value{EDITION} User's Guide}.
3424 @node Pragma Normalize_Scalars
3425 @unnumberedsec Pragma Normalize_Scalars
3426 @findex Normalize_Scalars
3430 @smallexample @c ada
3431 pragma Normalize_Scalars;
3435 This is a language defined pragma which is fully implemented in GNAT@. The
3436 effect is to cause all scalar objects that are not otherwise initialized
3437 to be initialized. The initial values are implementation dependent and
3441 @item Standard.Character
3443 Objects whose root type is Standard.Character are initialized to
3444 Character'Last unless the subtype range excludes NUL (in which case
3445 NUL is used). This choice will always generate an invalid value if
3448 @item Standard.Wide_Character
3450 Objects whose root type is Standard.Wide_Character are initialized to
3451 Wide_Character'Last unless the subtype range excludes NUL (in which case
3452 NUL is used). This choice will always generate an invalid value if
3455 @item Standard.Wide_Wide_Character
3457 Objects whose root type is Standard.Wide_Wide_Character are initialized to
3458 the invalid value 16#FFFF_FFFF# unless the subtype range excludes NUL (in
3459 which case NUL is used). This choice will always generate an invalid value if
3464 Objects of an integer type are treated differently depending on whether
3465 negative values are present in the subtype. If no negative values are
3466 present, then all one bits is used as the initial value except in the
3467 special case where zero is excluded from the subtype, in which case
3468 all zero bits are used. This choice will always generate an invalid
3469 value if one exists.
3471 For subtypes with negative values present, the largest negative number
3472 is used, except in the unusual case where this largest negative number
3473 is in the subtype, and the largest positive number is not, in which case
3474 the largest positive value is used. This choice will always generate
3475 an invalid value if one exists.
3477 @item Floating-Point Types
3478 Objects of all floating-point types are initialized to all 1-bits. For
3479 standard IEEE format, this corresponds to a NaN (not a number) which is
3480 indeed an invalid value.
3482 @item Fixed-Point Types
3483 Objects of all fixed-point types are treated as described above for integers,
3484 with the rules applying to the underlying integer value used to represent
3485 the fixed-point value.
3488 Objects of a modular type are initialized to all one bits, except in
3489 the special case where zero is excluded from the subtype, in which
3490 case all zero bits are used. This choice will always generate an
3491 invalid value if one exists.
3493 @item Enumeration types
3494 Objects of an enumeration type are initialized to all one-bits, i.e.@: to
3495 the value @code{2 ** typ'Size - 1} unless the subtype excludes the literal
3496 whose Pos value is zero, in which case a code of zero is used. This choice
3497 will always generate an invalid value if one exists.
3501 @node Pragma Obsolescent
3502 @unnumberedsec Pragma Obsolescent
3507 @smallexample @c ada
3510 pragma Obsolescent (
3511 [Message =>] static_string_EXPRESSION
3512 [,[Version =>] Ada_05]]);
3514 pragma Obsolescent (
3516 [,[Message =>] static_string_EXPRESSION
3517 [,[Version =>] Ada_05]] );
3521 This pragma can occur immediately following a declaration of an entity,
3522 including the case of a record component. If no Entity argument is present,
3523 then this declaration is the one to which the pragma applies. If an Entity
3524 parameter is present, it must either match the name of the entity in this
3525 declaration, or alternatively, the pragma can immediately follow an enumeration
3526 type declaration, where the Entity argument names one of the enumeration
3529 This pragma is used to indicate that the named entity
3530 is considered obsolescent and should not be used. Typically this is
3531 used when an API must be modified by eventually removing or modifying
3532 existing subprograms or other entities. The pragma can be used at an
3533 intermediate stage when the entity is still present, but will be
3536 The effect of this pragma is to output a warning message on a reference to
3537 an entity thus marked that the subprogram is obsolescent if the appropriate
3538 warning option in the compiler is activated. If the Message parameter is
3539 present, then a second warning message is given containing this text. In
3540 addition, a reference to the eneity is considered to be a violation of pragma
3541 Restrictions (No_Obsolescent_Features).
3543 This pragma can also be used as a program unit pragma for a package,
3544 in which case the entity name is the name of the package, and the
3545 pragma indicates that the entire package is considered
3546 obsolescent. In this case a client @code{with}'ing such a package
3547 violates the restriction, and the @code{with} statement is
3548 flagged with warnings if the warning option is set.
3550 If the Version parameter is present (which must be exactly
3551 the identifier Ada_05, no other argument is allowed), then the
3552 indication of obsolescence applies only when compiling in Ada 2005
3553 mode. This is primarily intended for dealing with the situations
3554 in the predefined library where subprograms or packages
3555 have become defined as obsolescent in Ada 2005
3556 (e.g.@: in Ada.Characters.Handling), but may be used anywhere.
3558 The following examples show typical uses of this pragma:
3560 @smallexample @c ada
3562 pragma Obsolescent (p, Message => "use pp instead of p");
3567 pragma Obsolescent ("use q2new instead");
3569 type R is new integer;
3572 Message => "use RR in Ada 2005",
3582 type E is (a, bc, 'd', quack);
3583 pragma Obsolescent (Entity => bc)
3584 pragma Obsolescent (Entity => 'd')
3587 (a, b : character) return character;
3588 pragma Obsolescent (Entity => "+");
3593 Note that, as for all pragmas, if you use a pragma argument identifier,
3594 then all subsequent parameters must also use a pragma argument identifier.
3595 So if you specify "Entity =>" for the Entity argument, and a Message
3596 argument is present, it must be preceded by "Message =>".
3598 @node Pragma Optimize_Alignment
3599 @unnumberedsec Pragma Optimize_Alignment
3600 @findex Optimize_Alignment
3601 @cindex Alignment, default settings
3605 @smallexample @c ada
3606 pragma Optimize_Alignment (TIME | SPACE | OFF);
3610 This is a configuration pragma which affects the choice of default alignments
3611 for types where no alignment is explicitly specified. There is a time/space
3612 trade-off in the selection of these values. Large alignments result in more
3613 efficient code, at the expense of larger data space, since sizes have to be
3614 increased to match these alignments. Smaller alignments save space, but the
3615 access code is slower. The normal choice of default alignments (which is what
3616 you get if you do not use this pragma, or if you use an argument of OFF),
3617 tries to balance these two requirements.
3619 Specifying SPACE causes smaller default alignments to be chosen in two cases.
3620 First any packed record is given an alignment of 1. Second, if a size is given
3621 for the type, then the alignment is chosen to avoid increasing this size. For
3624 @smallexample @c ada
3634 In the default mode, this type gets an alignment of 4, so that access to the
3635 Integer field X are efficient. But this means that objects of the type end up
3636 with a size of 8 bytes. This is a valid choice, since sizes of objects are
3637 allowed to be bigger than the size of the type, but it can waste space if for
3638 example fields of type R appear in an enclosing record. If the above type is
3639 compiled in @code{Optimize_Alignment (Space)} mode, the alignment is set to 1.
3641 Specifying TIME causes larger default alignments to be chosen in the case of
3642 small types with sizes that are not a power of 2. For example, consider:
3644 @smallexample @c ada
3656 The default alignment for this record is normally 1, but if this type is
3657 compiled in @code{Optimize_Alignment (Time)} mode, then the alignment is set
3658 to 4, which wastes space for objects of the type, since they are now 4 bytes
3659 long, but results in more efficient access when the whole record is referenced.
3661 As noted above, this is a configuration pragma, and there is a requirement
3662 that all units in a partition be compiled with a consistent setting of the
3663 optimization setting. This would normally be achieved by use of a configuration
3664 pragma file containing the appropriate setting. The exception to this rule is
3665 that units with an explicit configuration pragma in the same file as the source
3666 unit are excluded from the consistency check, as are all predefined units. The
3667 latter are compiled by default in pragma Optimize_Alignment (Off) mode if no
3668 pragma appears at the start of the file.
3670 @node Pragma Passive
3671 @unnumberedsec Pragma Passive
3676 @smallexample @c ada
3677 pragma Passive [(Semaphore | No)];
3681 Syntax checked, but otherwise ignored by GNAT@. This is recognized for
3682 compatibility with DEC Ada 83 implementations, where it is used within a
3683 task definition to request that a task be made passive. If the argument
3684 @code{Semaphore} is present, or the argument is omitted, then DEC Ada 83
3685 treats the pragma as an assertion that the containing task is passive
3686 and that optimization of context switch with this task is permitted and
3687 desired. If the argument @code{No} is present, the task must not be
3688 optimized. GNAT does not attempt to optimize any tasks in this manner
3689 (since protected objects are available in place of passive tasks).
3691 @node Pragma Persistent_BSS
3692 @unnumberedsec Pragma Persistent_BSS
3693 @findex Persistent_BSS
3697 @smallexample @c ada
3698 pragma Persistent_BSS [(LOCAL_NAME)]
3702 This pragma allows selected objects to be placed in the @code{.persistent_bss}
3703 section. On some targets the linker and loader provide for special
3704 treatment of this section, allowing a program to be reloaded without
3705 affecting the contents of this data (hence the name persistent).
3707 There are two forms of usage. If an argument is given, it must be the
3708 local name of a library level object, with no explicit initialization
3709 and whose type is potentially persistent. If no argument is given, then
3710 the pragma is a configuration pragma, and applies to all library level
3711 objects with no explicit initialization of potentially persistent types.
3713 A potentially persistent type is a scalar type, or a non-tagged,
3714 non-discriminated record, all of whose components have no explicit
3715 initialization and are themselves of a potentially persistent type,
3716 or an array, all of whose constraints are static, and whose component
3717 type is potentially persistent.
3719 If this pragma is used on a target where this feature is not supported,
3720 then the pragma will be ignored. See also @code{pragma Linker_Section}.
3722 @node Pragma Polling
3723 @unnumberedsec Pragma Polling
3728 @smallexample @c ada
3729 pragma Polling (ON | OFF);
3733 This pragma controls the generation of polling code. This is normally off.
3734 If @code{pragma Polling (ON)} is used then periodic calls are generated to
3735 the routine @code{Ada.Exceptions.Poll}. This routine is a separate unit in the
3736 runtime library, and can be found in file @file{a-excpol.adb}.
3738 Pragma @code{Polling} can appear as a configuration pragma (for example it
3739 can be placed in the @file{gnat.adc} file) to enable polling globally, or it
3740 can be used in the statement or declaration sequence to control polling
3743 A call to the polling routine is generated at the start of every loop and
3744 at the start of every subprogram call. This guarantees that the @code{Poll}
3745 routine is called frequently, and places an upper bound (determined by
3746 the complexity of the code) on the period between two @code{Poll} calls.
3748 The primary purpose of the polling interface is to enable asynchronous
3749 aborts on targets that cannot otherwise support it (for example Windows
3750 NT), but it may be used for any other purpose requiring periodic polling.
3751 The standard version is null, and can be replaced by a user program. This
3752 will require re-compilation of the @code{Ada.Exceptions} package that can
3753 be found in files @file{a-except.ads} and @file{a-except.adb}.
3755 A standard alternative unit (in file @file{4wexcpol.adb} in the standard GNAT
3756 distribution) is used to enable the asynchronous abort capability on
3757 targets that do not normally support the capability. The version of
3758 @code{Poll} in this file makes a call to the appropriate runtime routine
3759 to test for an abort condition.
3761 Note that polling can also be enabled by use of the @option{-gnatP} switch.
3762 @xref{Switches for gcc,,, gnat_ugn, @value{EDITION} User's Guide}, for
3765 @node Pragma Postcondition
3766 @unnumberedsec Pragma Postcondition
3767 @cindex Postconditions
3768 @cindex Checks, postconditions
3769 @findex Postconditions
3773 @smallexample @c ada
3774 pragma Postcondition (
3775 [Check =>] Boolean_Expression
3776 [,[Message =>] String_Expression]);
3780 The @code{Postcondition} pragma allows specification of automatic
3781 postcondition checks for subprograms. These checks are similar to
3782 assertions, but are automatically inserted just prior to the return
3783 statements of the subprogram with which they are associated (including
3784 implicit returns at the end of procedure bodies and associated
3785 exception handlers).
3787 In addition, the boolean expression which is the condition which
3788 must be true may contain references to function'Result in the case
3789 of a function to refer to the returned value.
3791 @code{Postcondition} pragmas may appear either immediate following the
3792 (separate) declaration of a subprogram, or at the start of the
3793 declarations of a subprogram body. Only other pragmas may intervene
3794 (that is appear between the subprogram declaration and its
3795 postconditions, or appear before the postcondition in the
3796 declaration sequence in a subprogram body). In the case of a
3797 postcondition appearing after a subprogram declaration, the
3798 formal arguments of the subprogram are visible, and can be
3799 referenced in the postcondition expressions.
3801 The postconditions are collected and automatically tested just
3802 before any return (implicit or explicit) in the subprogram body.
3803 A postcondition is only recognized if postconditions are active
3804 at the time the pragma is encountered. The compiler switch @option{gnata}
3805 turns on all postconditions by default, and pragma @code{Check_Policy}
3806 with an identifier of @code{Postcondition} can also be used to
3807 control whether postconditions are active.
3809 The general approach is that postconditions are placed in the spec
3810 if they represent functional aspects which make sense to the client.
3811 For example we might have:
3813 @smallexample @c ada
3814 function Direction return Integer;
3815 pragma Postcondition
3816 (Direction'Result = +1
3818 Direction'Result = -1);
3822 which serves to document that the result must be +1 or -1, and
3823 will test that this is the case at run time if postcondition
3826 Postconditions within the subprogram body can be used to
3827 check that some internal aspect of the implementation,
3828 not visible to the client, is operating as expected.
3829 For instance if a square root routine keeps an internal
3830 counter of the number of times it is called, then we
3831 might have the following postcondition:
3833 @smallexample @c ada
3834 Sqrt_Calls : Natural := 0;
3836 function Sqrt (Arg : Float) return Float is
3837 pragma Postcondition
3838 (Sqrt_Calls = Sqrt_Calls'Old + 1);
3844 As this example, shows, the use of the @code{Old} attribute
3845 is often useful in postconditions to refer to the state on
3846 entry to the subprogram.
3848 Note that postconditions are only checked on normal returns
3849 from the subprogram. If an abnormal return results from
3850 raising an exception, then the postconditions are not checked.
3852 If a postcondition fails, then the exception
3853 @code{System.Assertions.Assert_Failure} is raised. If
3854 a message argument was supplied, then the given string
3855 will be used as the exception message. If no message
3856 argument was supplied, then the default message has
3857 the form "Postcondition failed at file:line". The
3858 exception is raised in the context of the subprogram
3859 body, so it is possible to catch postcondition failures
3860 within the subprogram body itself.
3862 Within a package spec, normal visibility rules
3863 in Ada would prevent forward references within a
3864 postcondition pragma to functions defined later in
3865 the same package. This would introduce undesirable
3866 ordering constraints. To avoid this problem, all
3867 postcondition pragmas are analyzed at the end of
3868 the package spec, allowing forward references.
3870 The following example shows that this even allows
3871 mutually recursive postconditions as in:
3873 @smallexample @c ada
3874 package Parity_Functions is
3875 function Odd (X : Natural) return Boolean;
3876 pragma Postcondition
3880 (x /= 0 and then Even (X - 1))));
3882 function Even (X : Natural) return Boolean;
3883 pragma Postcondition
3887 (x /= 1 and then Odd (X - 1))));
3889 end Parity_Functions;
3893 There are no restrictions on the complexity or form of
3894 conditions used within @code{Postcondition} pragmas.
3895 The following example shows that it is even possible
3896 to verify performance behavior.
3898 @smallexample @c ada
3901 Performance : constant Float;
3902 -- Performance constant set by implementation
3903 -- to match target architecture behavior.
3905 procedure Treesort (Arg : String);
3906 -- Sorts characters of argument using N*logN sort
3907 pragma Postcondition
3908 (Float (Clock - Clock'Old) <=
3909 Float (Arg'Length) *
3910 log (Float (Arg'Length)) *
3916 Note: postcondition pragmas associated with subprograms that are
3917 marked as Inline_Always, or those marked as Inline with front-end
3918 inlining (-gnatN option set) are accepted and legality-checked
3919 by the compiler, but are ignored at run-time even if postcondition
3920 checking is enabled.
3922 @node Pragma Precondition
3923 @unnumberedsec Pragma Precondition
3924 @cindex Preconditions
3925 @cindex Checks, preconditions
3926 @findex Preconditions
3930 @smallexample @c ada
3931 pragma Precondition (
3932 [Check =>] Boolean_Expression
3933 [,[Message =>] String_Expression]);
3937 The @code{Precondition} pragma is similar to @code{Postcondition}
3938 except that the corresponding checks take place immediately upon
3939 entry to the subprogram, and if a precondition fails, the exception
3940 is raised in the context of the caller, and the attribute 'Result
3941 cannot be used within the precondition expression.
3943 Otherwise, the placement and visibility rules are identical to those
3944 described for postconditions. The following is an example of use
3945 within a package spec:
3947 @smallexample @c ada
3948 package Math_Functions is
3950 function Sqrt (Arg : Float) return Float;
3951 pragma Precondition (Arg >= 0.0)
3957 @code{Precondition} pragmas may appear either immediate following the
3958 (separate) declaration of a subprogram, or at the start of the
3959 declarations of a subprogram body. Only other pragmas may intervene
3960 (that is appear between the subprogram declaration and its
3961 postconditions, or appear before the postcondition in the
3962 declaration sequence in a subprogram body).
3964 Note: postcondition pragmas associated with subprograms that are
3965 marked as Inline_Always, or those marked as Inline with front-end
3966 inlining (-gnatN option set) are accepted and legality-checked
3967 by the compiler, but are ignored at run-time even if postcondition
3968 checking is enabled.
3972 @node Pragma Profile (Ravenscar)
3973 @unnumberedsec Pragma Profile (Ravenscar)
3978 @smallexample @c ada
3979 pragma Profile (Ravenscar);
3983 A configuration pragma that establishes the following set of configuration
3987 @item Task_Dispatching_Policy (FIFO_Within_Priorities)
3988 [RM D.2.2] Tasks are dispatched following a preemptive
3989 priority-ordered scheduling policy.
3991 @item Locking_Policy (Ceiling_Locking)
3992 [RM D.3] While tasks and interrupts execute a protected action, they inherit
3993 the ceiling priority of the corresponding protected object.
3995 @c @item Detect_Blocking
3996 @c This pragma forces the detection of potentially blocking operations within a
3997 @c protected operation, and to raise Program_Error if that happens.
4001 plus the following set of restrictions:
4004 @item Max_Entry_Queue_Length = 1
4005 Defines the maximum number of calls that are queued on a (protected) entry.
4006 Note that this restrictions is checked at run time. Violation of this
4007 restriction results in the raising of Program_Error exception at the point of
4008 the call. For the Profile (Ravenscar) the value of Max_Entry_Queue_Length is
4009 always 1 and hence no task can be queued on a protected entry.
4011 @item Max_Protected_Entries = 1
4012 [RM D.7] Specifies the maximum number of entries per protected type. The
4013 bounds of every entry family of a protected unit shall be static, or shall be
4014 defined by a discriminant of a subtype whose corresponding bound is static.
4015 For the Profile (Ravenscar) the value of Max_Protected_Entries is always 1.
4017 @item Max_Task_Entries = 0
4018 [RM D.7] Specifies the maximum number of entries
4019 per task. The bounds of every entry family
4020 of a task unit shall be static, or shall be
4021 defined by a discriminant of a subtype whose
4022 corresponding bound is static. A value of zero
4023 indicates that no rendezvous are possible. For
4024 the Profile (Ravenscar), the value of Max_Task_Entries is always
4027 @item No_Abort_Statements
4028 [RM D.7] There are no abort_statements, and there are
4029 no calls to Task_Identification.Abort_Task.
4031 @item No_Asynchronous_Control
4032 There are no semantic dependences on the package
4033 Asynchronous_Task_Control.
4036 There are no semantic dependencies on the package Ada.Calendar.
4038 @item No_Dynamic_Attachment
4039 There is no call to any of the operations defined in package Ada.Interrupts
4040 (Is_Reserved, Is_Attached, Current_Handler, Attach_Handler, Exchange_Handler,
4041 Detach_Handler, and Reference).
4043 @item No_Dynamic_Priorities
4044 [RM D.7] There are no semantic dependencies on the package Dynamic_Priorities.
4046 @item No_Implicit_Heap_Allocations
4047 [RM D.7] No constructs are allowed to cause implicit heap allocation.
4049 @item No_Local_Protected_Objects
4050 Protected objects and access types that designate
4051 such objects shall be declared only at library level.
4053 @item No_Local_Timing_Events
4054 [RM D.7] All objects of type Ada.Timing_Events.Timing_Event are
4055 declared at the library level.
4057 @item No_Protected_Type_Allocators
4058 There are no allocators for protected types or
4059 types containing protected subcomponents.
4061 @item No_Relative_Delay
4062 There are no delay_relative statements.
4064 @item No_Requeue_Statements
4065 Requeue statements are not allowed.
4067 @item No_Select_Statements
4068 There are no select_statements.
4070 @item No_Specific_Termination_Handlers
4071 [RM D.7] There are no calls to Ada.Task_Termination.Set_Specific_Handler
4072 or to Ada.Task_Termination.Specific_Handler.
4074 @item No_Task_Allocators
4075 [RM D.7] There are no allocators for task types
4076 or types containing task subcomponents.
4078 @item No_Task_Attributes_Package
4079 There are no semantic dependencies on the Ada.Task_Attributes package.
4081 @item No_Task_Hierarchy
4082 [RM D.7] All (non-environment) tasks depend
4083 directly on the environment task of the partition.
4085 @item No_Task_Termination
4086 Tasks which terminate are erroneous.
4088 @item No_Unchecked_Conversion
4089 There are no semantic dependencies on the Ada.Unchecked_Conversion package.
4091 @item No_Unchecked_Deallocation
4092 There are no semantic dependencies on the Ada.Unchecked_Deallocation package.
4094 @item Simple_Barriers
4095 Entry barrier condition expressions shall be either static
4096 boolean expressions or boolean objects which are declared in
4097 the protected type which contains the entry.
4101 This set of configuration pragmas and restrictions correspond to the
4102 definition of the ``Ravenscar Profile'' for limited tasking, devised and
4103 published by the @cite{International Real-Time Ada Workshop}, 1997,
4104 and whose most recent description is available at
4105 @url{http://www-users.cs.york.ac.uk/~burns/ravenscar.ps}.
4107 The original definition of the profile was revised at subsequent IRTAW
4108 meetings. It has been included in the ISO
4109 @cite{Guide for the Use of the Ada Programming Language in High
4110 Integrity Systems}, and has been approved by ISO/IEC/SC22/WG9 for inclusion in
4111 the next revision of the standard. The formal definition given by
4112 the Ada Rapporteur Group (ARG) can be found in two Ada Issues (AI-249 and
4113 AI-305) available at
4114 @url{http://www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs/AI-00249.TXT} and
4115 @url{http://www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs/AI-00305.TXT}
4118 The above set is a superset of the restrictions provided by pragma
4119 @code{Profile (Restricted)}, it includes six additional restrictions
4120 (@code{Simple_Barriers}, @code{No_Select_Statements},
4121 @code{No_Calendar}, @code{No_Implicit_Heap_Allocations},
4122 @code{No_Relative_Delay} and @code{No_Task_Termination}). This means
4123 that pragma @code{Profile (Ravenscar)}, like the pragma
4124 @code{Profile (Restricted)},
4125 automatically causes the use of a simplified,
4126 more efficient version of the tasking run-time system.
4128 @node Pragma Profile (Restricted)
4129 @unnumberedsec Pragma Profile (Restricted)
4130 @findex Restricted Run Time
4134 @smallexample @c ada
4135 pragma Profile (Restricted);
4139 A configuration pragma that establishes the following set of restrictions:
4142 @item No_Abort_Statements
4143 @item No_Entry_Queue
4144 @item No_Task_Hierarchy
4145 @item No_Task_Allocators
4146 @item No_Dynamic_Priorities
4147 @item No_Terminate_Alternatives
4148 @item No_Dynamic_Attachment
4149 @item No_Protected_Type_Allocators
4150 @item No_Local_Protected_Objects
4151 @item No_Requeue_Statements
4152 @item No_Task_Attributes_Package
4153 @item Max_Asynchronous_Select_Nesting = 0
4154 @item Max_Task_Entries = 0
4155 @item Max_Protected_Entries = 1
4156 @item Max_Select_Alternatives = 0
4160 This set of restrictions causes the automatic selection of a simplified
4161 version of the run time that provides improved performance for the
4162 limited set of tasking functionality permitted by this set of restrictions.
4164 @node Pragma Psect_Object
4165 @unnumberedsec Pragma Psect_Object
4166 @findex Psect_Object
4170 @smallexample @c ada
4171 pragma Psect_Object (
4172 [Internal =>] LOCAL_NAME,
4173 [, [External =>] EXTERNAL_SYMBOL]
4174 [, [Size =>] EXTERNAL_SYMBOL]);
4178 | static_string_EXPRESSION
4182 This pragma is identical in effect to pragma @code{Common_Object}.
4184 @node Pragma Pure_Function
4185 @unnumberedsec Pragma Pure_Function
4186 @findex Pure_Function
4190 @smallexample @c ada
4191 pragma Pure_Function ([Entity =>] function_LOCAL_NAME);
4195 This pragma appears in the same declarative part as a function
4196 declaration (or a set of function declarations if more than one
4197 overloaded declaration exists, in which case the pragma applies
4198 to all entities). It specifies that the function @code{Entity} is
4199 to be considered pure for the purposes of code generation. This means
4200 that the compiler can assume that there are no side effects, and
4201 in particular that two calls with identical arguments produce the
4202 same result. It also means that the function can be used in an
4205 Note that, quite deliberately, there are no static checks to try
4206 to ensure that this promise is met, so @code{Pure_Function} can be used
4207 with functions that are conceptually pure, even if they do modify
4208 global variables. For example, a square root function that is
4209 instrumented to count the number of times it is called is still
4210 conceptually pure, and can still be optimized, even though it
4211 modifies a global variable (the count). Memo functions are another
4212 example (where a table of previous calls is kept and consulted to
4213 avoid re-computation).
4216 Note: Most functions in a @code{Pure} package are automatically pure, and
4217 there is no need to use pragma @code{Pure_Function} for such functions. One
4218 exception is any function that has at least one formal of type
4219 @code{System.Address} or a type derived from it. Such functions are not
4220 considered pure by default, since the compiler assumes that the
4221 @code{Address} parameter may be functioning as a pointer and that the
4222 referenced data may change even if the address value does not.
4223 Similarly, imported functions are not considered to be pure by default,
4224 since there is no way of checking that they are in fact pure. The use
4225 of pragma @code{Pure_Function} for such a function will override these default
4226 assumption, and cause the compiler to treat a designated subprogram as pure
4229 Note: If pragma @code{Pure_Function} is applied to a renamed function, it
4230 applies to the underlying renamed function. This can be used to
4231 disambiguate cases of overloading where some but not all functions
4232 in a set of overloaded functions are to be designated as pure.
4234 If pragma @code{Pure_Function} is applied to a library level function, the
4235 function is also considered pure from an optimization point of view, but the
4236 unit is not a Pure unit in the categorization sense. So for example, a function
4237 thus marked is free to @code{with} non-pure units.
4239 @node Pragma Restriction_Warnings
4240 @unnumberedsec Pragma Restriction_Warnings
4241 @findex Restriction_Warnings
4245 @smallexample @c ada
4246 pragma Restriction_Warnings
4247 (restriction_IDENTIFIER @{, restriction_IDENTIFIER@});
4251 This pragma allows a series of restriction identifiers to be
4252 specified (the list of allowed identifiers is the same as for
4253 pragma @code{Restrictions}). For each of these identifiers
4254 the compiler checks for violations of the restriction, but
4255 generates a warning message rather than an error message
4256 if the restriction is violated.
4259 @unnumberedsec Pragma Shared
4263 This pragma is provided for compatibility with Ada 83. The syntax and
4264 semantics are identical to pragma Atomic.
4266 @node Pragma Short_Circuit_And_Or
4267 @unnumberedsec Pragma Short_Circuit_And_Or
4268 @findex Short_Circuit_And_Or
4271 This configuration pragma causes any occurrence of the AND operator applied to
4272 operands of type Standard.Boolean to be short-circuited (i.e. the AND operator
4273 is treated as if it were AND THEN). Or is similarly treated as OR ELSE. This
4274 may be useful in the context of certification protocols requiring the use of
4275 short-circuited logical operators. If this configuration pragma occurs locally
4276 within the file being compiled, it applies only to the file being compiled.
4277 There is no requirement that all units in a partition use this option.
4279 semantics are identical to pragma Atomic.
4280 @node Pragma Source_File_Name
4281 @unnumberedsec Pragma Source_File_Name
4282 @findex Source_File_Name
4286 @smallexample @c ada
4287 pragma Source_File_Name (
4288 [Unit_Name =>] unit_NAME,
4289 Spec_File_Name => STRING_LITERAL,
4290 [Index => INTEGER_LITERAL]);
4292 pragma Source_File_Name (
4293 [Unit_Name =>] unit_NAME,
4294 Body_File_Name => STRING_LITERAL,
4295 [Index => INTEGER_LITERAL]);
4299 Use this to override the normal naming convention. It is a configuration
4300 pragma, and so has the usual applicability of configuration pragmas
4301 (i.e.@: it applies to either an entire partition, or to all units in a
4302 compilation, or to a single unit, depending on how it is used.
4303 @var{unit_name} is mapped to @var{file_name_literal}. The identifier for
4304 the second argument is required, and indicates whether this is the file
4305 name for the spec or for the body.
4307 The optional Index argument should be used when a file contains multiple
4308 units, and when you do not want to use @code{gnatchop} to separate then
4309 into multiple files (which is the recommended procedure to limit the
4310 number of recompilations that are needed when some sources change).
4311 For instance, if the source file @file{source.ada} contains
4313 @smallexample @c ada
4325 you could use the following configuration pragmas:
4327 @smallexample @c ada
4328 pragma Source_File_Name
4329 (B, Spec_File_Name => "source.ada", Index => 1);
4330 pragma Source_File_Name
4331 (A, Body_File_Name => "source.ada", Index => 2);
4334 Note that the @code{gnatname} utility can also be used to generate those
4335 configuration pragmas.
4337 Another form of the @code{Source_File_Name} pragma allows
4338 the specification of patterns defining alternative file naming schemes
4339 to apply to all files.
4341 @smallexample @c ada
4342 pragma Source_File_Name
4343 ( [Spec_File_Name =>] STRING_LITERAL
4344 [,[Casing =>] CASING_SPEC]
4345 [,[Dot_Replacement =>] STRING_LITERAL]);
4347 pragma Source_File_Name
4348 ( [Body_File_Name =>] STRING_LITERAL
4349 [,[Casing =>] CASING_SPEC]
4350 [,[Dot_Replacement =>] STRING_LITERAL]);
4352 pragma Source_File_Name
4353 ( [Subunit_File_Name =>] STRING_LITERAL
4354 [,[Casing =>] CASING_SPEC]
4355 [,[Dot_Replacement =>] STRING_LITERAL]);
4357 CASING_SPEC ::= Lowercase | Uppercase | Mixedcase
4361 The first argument is a pattern that contains a single asterisk indicating
4362 the point at which the unit name is to be inserted in the pattern string
4363 to form the file name. The second argument is optional. If present it
4364 specifies the casing of the unit name in the resulting file name string.
4365 The default is lower case. Finally the third argument allows for systematic
4366 replacement of any dots in the unit name by the specified string literal.
4368 A pragma Source_File_Name cannot appear after a
4369 @ref{Pragma Source_File_Name_Project}.
4371 For more details on the use of the @code{Source_File_Name} pragma,
4372 @xref{Using Other File Names,,, gnat_ugn, @value{EDITION} User's Guide},
4373 and @ref{Alternative File Naming Schemes,,, gnat_ugn, @value{EDITION}
4376 @node Pragma Source_File_Name_Project
4377 @unnumberedsec Pragma Source_File_Name_Project
4378 @findex Source_File_Name_Project
4381 This pragma has the same syntax and semantics as pragma Source_File_Name.
4382 It is only allowed as a stand alone configuration pragma.
4383 It cannot appear after a @ref{Pragma Source_File_Name}, and
4384 most importantly, once pragma Source_File_Name_Project appears,
4385 no further Source_File_Name pragmas are allowed.
4387 The intention is that Source_File_Name_Project pragmas are always
4388 generated by the Project Manager in a manner consistent with the naming
4389 specified in a project file, and when naming is controlled in this manner,
4390 it is not permissible to attempt to modify this naming scheme using
4391 Source_File_Name pragmas (which would not be known to the project manager).
4393 @node Pragma Source_Reference
4394 @unnumberedsec Pragma Source_Reference
4395 @findex Source_Reference
4399 @smallexample @c ada
4400 pragma Source_Reference (INTEGER_LITERAL, STRING_LITERAL);
4404 This pragma must appear as the first line of a source file.
4405 @var{integer_literal} is the logical line number of the line following
4406 the pragma line (for use in error messages and debugging
4407 information). @var{string_literal} is a static string constant that
4408 specifies the file name to be used in error messages and debugging
4409 information. This is most notably used for the output of @code{gnatchop}
4410 with the @option{-r} switch, to make sure that the original unchopped
4411 source file is the one referred to.
4413 The second argument must be a string literal, it cannot be a static
4414 string expression other than a string literal. This is because its value
4415 is needed for error messages issued by all phases of the compiler.
4417 @node Pragma Stream_Convert
4418 @unnumberedsec Pragma Stream_Convert
4419 @findex Stream_Convert
4423 @smallexample @c ada
4424 pragma Stream_Convert (
4425 [Entity =>] type_LOCAL_NAME,
4426 [Read =>] function_NAME,
4427 [Write =>] function_NAME);
4431 This pragma provides an efficient way of providing stream functions for
4432 types defined in packages. Not only is it simpler to use than declaring
4433 the necessary functions with attribute representation clauses, but more
4434 significantly, it allows the declaration to made in such a way that the
4435 stream packages are not loaded unless they are needed. The use of
4436 the Stream_Convert pragma adds no overhead at all, unless the stream
4437 attributes are actually used on the designated type.
4439 The first argument specifies the type for which stream functions are
4440 provided. The second parameter provides a function used to read values
4441 of this type. It must name a function whose argument type may be any
4442 subtype, and whose returned type must be the type given as the first
4443 argument to the pragma.
4445 The meaning of the @var{Read}
4446 parameter is that if a stream attribute directly
4447 or indirectly specifies reading of the type given as the first parameter,
4448 then a value of the type given as the argument to the Read function is
4449 read from the stream, and then the Read function is used to convert this
4450 to the required target type.
4452 Similarly the @var{Write} parameter specifies how to treat write attributes
4453 that directly or indirectly apply to the type given as the first parameter.
4454 It must have an input parameter of the type specified by the first parameter,
4455 and the return type must be the same as the input type of the Read function.
4456 The effect is to first call the Write function to convert to the given stream
4457 type, and then write the result type to the stream.
4459 The Read and Write functions must not be overloaded subprograms. If necessary
4460 renamings can be supplied to meet this requirement.
4461 The usage of this attribute is best illustrated by a simple example, taken
4462 from the GNAT implementation of package Ada.Strings.Unbounded:
4464 @smallexample @c ada
4465 function To_Unbounded (S : String)
4466 return Unbounded_String
4467 renames To_Unbounded_String;
4469 pragma Stream_Convert
4470 (Unbounded_String, To_Unbounded, To_String);
4474 The specifications of the referenced functions, as given in the Ada
4475 Reference Manual are:
4477 @smallexample @c ada
4478 function To_Unbounded_String (Source : String)
4479 return Unbounded_String;
4481 function To_String (Source : Unbounded_String)
4486 The effect is that if the value of an unbounded string is written to a stream,
4487 then the representation of the item in the stream is in the same format that
4488 would be used for @code{Standard.String'Output}, and this same representation
4489 is expected when a value of this type is read from the stream. Note that the
4490 value written always includes the bounds, even for Unbounded_String'Write,
4491 since Unbounded_String is not an array type.
4493 @node Pragma Style_Checks
4494 @unnumberedsec Pragma Style_Checks
4495 @findex Style_Checks
4499 @smallexample @c ada
4500 pragma Style_Checks (string_LITERAL | ALL_CHECKS |
4501 On | Off [, LOCAL_NAME]);
4505 This pragma is used in conjunction with compiler switches to control the
4506 built in style checking provided by GNAT@. The compiler switches, if set,
4507 provide an initial setting for the switches, and this pragma may be used
4508 to modify these settings, or the settings may be provided entirely by
4509 the use of the pragma. This pragma can be used anywhere that a pragma
4510 is legal, including use as a configuration pragma (including use in
4511 the @file{gnat.adc} file).
4513 The form with a string literal specifies which style options are to be
4514 activated. These are additive, so they apply in addition to any previously
4515 set style check options. The codes for the options are the same as those
4516 used in the @option{-gnaty} switch to @command{gcc} or @command{gnatmake}.
4517 For example the following two methods can be used to enable
4522 @smallexample @c ada
4523 pragma Style_Checks ("l");
4528 gcc -c -gnatyl @dots{}
4533 The form ALL_CHECKS activates all standard checks (its use is equivalent
4534 to the use of the @code{gnaty} switch with no options. @xref{Top,
4535 @value{EDITION} User's Guide, About This Guide, gnat_ugn,
4536 @value{EDITION} User's Guide}, for details.
4538 The forms with @code{Off} and @code{On}
4539 can be used to temporarily disable style checks
4540 as shown in the following example:
4542 @smallexample @c ada
4546 pragma Style_Checks ("k"); -- requires keywords in lower case
4547 pragma Style_Checks (Off); -- turn off style checks
4548 NULL; -- this will not generate an error message
4549 pragma Style_Checks (On); -- turn style checks back on
4550 NULL; -- this will generate an error message
4554 Finally the two argument form is allowed only if the first argument is
4555 @code{On} or @code{Off}. The effect is to turn of semantic style checks
4556 for the specified entity, as shown in the following example:
4558 @smallexample @c ada
4562 pragma Style_Checks ("r"); -- require consistency of identifier casing
4564 Rf1 : Integer := ARG; -- incorrect, wrong case
4565 pragma Style_Checks (Off, Arg);
4566 Rf2 : Integer := ARG; -- OK, no error
4569 @node Pragma Subtitle
4570 @unnumberedsec Pragma Subtitle
4575 @smallexample @c ada
4576 pragma Subtitle ([Subtitle =>] STRING_LITERAL);
4580 This pragma is recognized for compatibility with other Ada compilers
4581 but is ignored by GNAT@.
4583 @node Pragma Suppress
4584 @unnumberedsec Pragma Suppress
4589 @smallexample @c ada
4590 pragma Suppress (Identifier [, [On =>] Name]);
4594 This is a standard pragma, and supports all the check names required in
4595 the RM. It is included here because GNAT recognizes one additional check
4596 name: @code{Alignment_Check} which can be used to suppress alignment checks
4597 on addresses used in address clauses. Such checks can also be suppressed
4598 by suppressing range checks, but the specific use of @code{Alignment_Check}
4599 allows suppression of alignment checks without suppressing other range checks.
4601 Note that pragma Suppress gives the compiler permission to omit
4602 checks, but does not require the compiler to omit checks. The compiler
4603 will generate checks if they are essentially free, even when they are
4604 suppressed. In particular, if the compiler can prove that a certain
4605 check will necessarily fail, it will generate code to do an
4606 unconditional ``raise'', even if checks are suppressed. The compiler
4609 Of course, run-time checks are omitted whenever the compiler can prove
4610 that they will not fail, whether or not checks are suppressed.
4612 @node Pragma Suppress_All
4613 @unnumberedsec Pragma Suppress_All
4614 @findex Suppress_All
4618 @smallexample @c ada
4619 pragma Suppress_All;
4623 This pragma can only appear immediately following a compilation
4624 unit. The effect is to apply @code{Suppress (All_Checks)} to the unit
4625 which it follows. This pragma is implemented for compatibility with DEC
4626 Ada 83 usage. The use of pragma @code{Suppress (All_Checks)} as a normal
4627 configuration pragma is the preferred usage in GNAT@.
4629 @node Pragma Suppress_Exception_Locations
4630 @unnumberedsec Pragma Suppress_Exception_Locations
4631 @findex Suppress_Exception_Locations
4635 @smallexample @c ada
4636 pragma Suppress_Exception_Locations;
4640 In normal mode, a raise statement for an exception by default generates
4641 an exception message giving the file name and line number for the location
4642 of the raise. This is useful for debugging and logging purposes, but this
4643 entails extra space for the strings for the messages. The configuration
4644 pragma @code{Suppress_Exception_Locations} can be used to suppress the
4645 generation of these strings, with the result that space is saved, but the
4646 exception message for such raises is null. This configuration pragma may
4647 appear in a global configuration pragma file, or in a specific unit as
4648 usual. It is not required that this pragma be used consistently within
4649 a partition, so it is fine to have some units within a partition compiled
4650 with this pragma and others compiled in normal mode without it.
4652 @node Pragma Suppress_Initialization
4653 @unnumberedsec Pragma Suppress_Initialization
4654 @findex Suppress_Initialization
4655 @cindex Suppressing initialization
4656 @cindex Initialization, suppression of
4660 @smallexample @c ada
4661 pragma Suppress_Initialization ([Entity =>] type_Name);
4665 This pragma suppresses any implicit or explicit initialization
4666 associated with the given type name for all variables of this type.
4668 @node Pragma Task_Info
4669 @unnumberedsec Pragma Task_Info
4674 @smallexample @c ada
4675 pragma Task_Info (EXPRESSION);
4679 This pragma appears within a task definition (like pragma
4680 @code{Priority}) and applies to the task in which it appears. The
4681 argument must be of type @code{System.Task_Info.Task_Info_Type}.
4682 The @code{Task_Info} pragma provides system dependent control over
4683 aspects of tasking implementation, for example, the ability to map
4684 tasks to specific processors. For details on the facilities available
4685 for the version of GNAT that you are using, see the documentation
4686 in the spec of package System.Task_Info in the runtime
4689 @node Pragma Task_Name
4690 @unnumberedsec Pragma Task_Name
4695 @smallexample @c ada
4696 pragma Task_Name (string_EXPRESSION);
4700 This pragma appears within a task definition (like pragma
4701 @code{Priority}) and applies to the task in which it appears. The
4702 argument must be of type String, and provides a name to be used for
4703 the task instance when the task is created. Note that this expression
4704 is not required to be static, and in particular, it can contain
4705 references to task discriminants. This facility can be used to
4706 provide different names for different tasks as they are created,
4707 as illustrated in the example below.
4709 The task name is recorded internally in the run-time structures
4710 and is accessible to tools like the debugger. In addition the
4711 routine @code{Ada.Task_Identification.Image} will return this
4712 string, with a unique task address appended.
4714 @smallexample @c ada
4715 -- Example of the use of pragma Task_Name
4717 with Ada.Task_Identification;
4718 use Ada.Task_Identification;
4719 with Text_IO; use Text_IO;
4722 type Astring is access String;
4724 task type Task_Typ (Name : access String) is
4725 pragma Task_Name (Name.all);
4728 task body Task_Typ is
4729 Nam : constant String := Image (Current_Task);
4731 Put_Line ("-->" & Nam (1 .. 14) & "<--");
4734 type Ptr_Task is access Task_Typ;
4735 Task_Var : Ptr_Task;
4739 new Task_Typ (new String'("This is task 1"));
4741 new Task_Typ (new String'("This is task 2"));
4745 @node Pragma Task_Storage
4746 @unnumberedsec Pragma Task_Storage
4747 @findex Task_Storage
4750 @smallexample @c ada
4751 pragma Task_Storage (
4752 [Task_Type =>] LOCAL_NAME,
4753 [Top_Guard =>] static_integer_EXPRESSION);
4757 This pragma specifies the length of the guard area for tasks. The guard
4758 area is an additional storage area allocated to a task. A value of zero
4759 means that either no guard area is created or a minimal guard area is
4760 created, depending on the target. This pragma can appear anywhere a
4761 @code{Storage_Size} attribute definition clause is allowed for a task
4764 @node Pragma Thread_Local_Storage
4765 @unnumberedsec Pragma Thread_Local_Storage
4766 @findex Thread_Local_Storage
4767 @cindex Task specific storage
4768 @cindex TLS (Thread Local Storage)
4771 @smallexample @c ada
4772 pragma Thread_Local_Storage ([Entity =>] LOCAL_NAME);
4776 This pragma specifies that the specified entity, which must be
4777 a variable declared in a library level package, is to be marked as
4778 "Thread Local Storage" (@code{TLS}). On systems supporting this (which
4779 include Solaris, GNU/Linux and VxWorks 6), this causes each thread
4780 (and hence each Ada task) to see a distinct copy of the variable.
4782 The variable may not have default initialization, and if there is
4783 an explicit initialization, it must be either @code{null} for an
4784 access variable, or a static expression for a scalar variable.
4785 This provides a low level mechanism similar to that provided by
4786 the @code{Ada.Task_Attributes} package, but much more efficient
4787 and is also useful in writing interface code that will interact
4788 with foreign threads.
4790 If this pragma is used on a system where @code{TLS} is not supported,
4791 then an error message will be generated and the program will be rejected.
4793 @node Pragma Time_Slice
4794 @unnumberedsec Pragma Time_Slice
4799 @smallexample @c ada
4800 pragma Time_Slice (static_duration_EXPRESSION);
4804 For implementations of GNAT on operating systems where it is possible
4805 to supply a time slice value, this pragma may be used for this purpose.
4806 It is ignored if it is used in a system that does not allow this control,
4807 or if it appears in other than the main program unit.
4809 Note that the effect of this pragma is identical to the effect of the
4810 DEC Ada 83 pragma of the same name when operating under OpenVMS systems.
4813 @unnumberedsec Pragma Title
4818 @smallexample @c ada
4819 pragma Title (TITLING_OPTION [, TITLING OPTION]);
4822 [Title =>] STRING_LITERAL,
4823 | [Subtitle =>] STRING_LITERAL
4827 Syntax checked but otherwise ignored by GNAT@. This is a listing control
4828 pragma used in DEC Ada 83 implementations to provide a title and/or
4829 subtitle for the program listing. The program listing generated by GNAT
4830 does not have titles or subtitles.
4832 Unlike other pragmas, the full flexibility of named notation is allowed
4833 for this pragma, i.e.@: the parameters may be given in any order if named
4834 notation is used, and named and positional notation can be mixed
4835 following the normal rules for procedure calls in Ada.
4837 @node Pragma Unchecked_Union
4838 @unnumberedsec Pragma Unchecked_Union
4840 @findex Unchecked_Union
4844 @smallexample @c ada
4845 pragma Unchecked_Union (first_subtype_LOCAL_NAME);
4849 This pragma is used to specify a representation of a record type that is
4850 equivalent to a C union. It was introduced as a GNAT implementation defined
4851 pragma in the GNAT Ada 95 mode. Ada 2005 includes an extended version of this
4852 pragma, making it language defined, and GNAT fully implements this extended
4853 version in all language modes (Ada 83, Ada 95, and Ada 2005). For full
4854 details, consult the Ada 2005 Reference Manual, section B.3.3.
4856 @node Pragma Unimplemented_Unit
4857 @unnumberedsec Pragma Unimplemented_Unit
4858 @findex Unimplemented_Unit
4862 @smallexample @c ada
4863 pragma Unimplemented_Unit;
4867 If this pragma occurs in a unit that is processed by the compiler, GNAT
4868 aborts with the message @samp{@var{xxx} not implemented}, where
4869 @var{xxx} is the name of the current compilation unit. This pragma is
4870 intended to allow the compiler to handle unimplemented library units in
4873 The abort only happens if code is being generated. Thus you can use
4874 specs of unimplemented packages in syntax or semantic checking mode.
4876 @node Pragma Universal_Aliasing
4877 @unnumberedsec Pragma Universal_Aliasing
4878 @findex Universal_Aliasing
4882 @smallexample @c ada
4883 pragma Universal_Aliasing [([Entity =>] type_LOCAL_NAME)];
4887 @var{type_LOCAL_NAME} must refer to a type declaration in the current
4888 declarative part. The effect is to inhibit strict type-based aliasing
4889 optimization for the given type. In other words, the effect is as though
4890 access types designating this type were subject to pragma No_Strict_Aliasing.
4891 For a detailed description of the strict aliasing optimization, and the
4892 situations in which it must be suppressed, @xref{Optimization and Strict
4893 Aliasing,,, gnat_ugn, @value{EDITION} User's Guide}.
4895 @node Pragma Universal_Data
4896 @unnumberedsec Pragma Universal_Data
4897 @findex Universal_Data
4901 @smallexample @c ada
4902 pragma Universal_Data [(library_unit_Name)];
4906 This pragma is supported only for the AAMP target and is ignored for
4907 other targets. The pragma specifies that all library-level objects
4908 (Counter 0 data) associated with the library unit are to be accessed
4909 and updated using universal addressing (24-bit addresses for AAMP5)
4910 rather than the default of 16-bit Data Environment (DENV) addressing.
4911 Use of this pragma will generally result in less efficient code for
4912 references to global data associated with the library unit, but
4913 allows such data to be located anywhere in memory. This pragma is
4914 a library unit pragma, but can also be used as a configuration pragma
4915 (including use in the @file{gnat.adc} file). The functionality
4916 of this pragma is also available by applying the -univ switch on the
4917 compilations of units where universal addressing of the data is desired.
4919 @node Pragma Unmodified
4920 @unnumberedsec Pragma Unmodified
4922 @cindex Warnings, unmodified
4926 @smallexample @c ada
4927 pragma Unmodified (LOCAL_NAME @{, LOCAL_NAME@});
4931 This pragma signals that the assignable entities (variables,
4932 @code{out} parameters, @code{in out} parameters) whose names are listed are
4933 deliberately not assigned in the current source unit. This
4934 suppresses warnings about the
4935 entities being referenced but not assigned, and in addition a warning will be
4936 generated if one of these entities is in fact assigned in the
4937 same unit as the pragma (or in the corresponding body, or one
4940 This is particularly useful for clearly signaling that a particular
4941 parameter is not modified, even though the spec suggests that it might
4944 @node Pragma Unreferenced
4945 @unnumberedsec Pragma Unreferenced
4946 @findex Unreferenced
4947 @cindex Warnings, unreferenced
4951 @smallexample @c ada
4952 pragma Unreferenced (LOCAL_NAME @{, LOCAL_NAME@});
4953 pragma Unreferenced (library_unit_NAME @{, library_unit_NAME@});
4957 This pragma signals that the entities whose names are listed are
4958 deliberately not referenced in the current source unit. This
4959 suppresses warnings about the
4960 entities being unreferenced, and in addition a warning will be
4961 generated if one of these entities is in fact referenced in the
4962 same unit as the pragma (or in the corresponding body, or one
4965 This is particularly useful for clearly signaling that a particular
4966 parameter is not referenced in some particular subprogram implementation
4967 and that this is deliberate. It can also be useful in the case of
4968 objects declared only for their initialization or finalization side
4971 If @code{LOCAL_NAME} identifies more than one matching homonym in the
4972 current scope, then the entity most recently declared is the one to which
4973 the pragma applies. Note that in the case of accept formals, the pragma
4974 Unreferenced may appear immediately after the keyword @code{do} which
4975 allows the indication of whether or not accept formals are referenced
4976 or not to be given individually for each accept statement.
4978 The left hand side of an assignment does not count as a reference for the
4979 purpose of this pragma. Thus it is fine to assign to an entity for which
4980 pragma Unreferenced is given.
4982 Note that if a warning is desired for all calls to a given subprogram,
4983 regardless of whether they occur in the same unit as the subprogram
4984 declaration, then this pragma should not be used (calls from another
4985 unit would not be flagged); pragma Obsolescent can be used instead
4986 for this purpose, see @xref{Pragma Obsolescent}.
4988 The second form of pragma @code{Unreferenced} is used within a context
4989 clause. In this case the arguments must be unit names of units previously
4990 mentioned in @code{with} clauses (similar to the usage of pragma
4991 @code{Elaborate_All}. The effect is to suppress warnings about unreferenced
4992 units and unreferenced entities within these units.
4994 @node Pragma Unreferenced_Objects
4995 @unnumberedsec Pragma Unreferenced_Objects
4996 @findex Unreferenced_Objects
4997 @cindex Warnings, unreferenced
5001 @smallexample @c ada
5002 pragma Unreferenced_Objects (local_subtype_NAME @{, local_subtype_NAME@});
5006 This pragma signals that for the types or subtypes whose names are
5007 listed, objects which are declared with one of these types or subtypes may
5008 not be referenced, and if no references appear, no warnings are given.
5010 This is particularly useful for objects which are declared solely for their
5011 initialization and finalization effect. Such variables are sometimes referred
5012 to as RAII variables (Resource Acquisition Is Initialization). Using this
5013 pragma on the relevant type (most typically a limited controlled type), the
5014 compiler will automatically suppress unwanted warnings about these variables
5015 not being referenced.
5017 @node Pragma Unreserve_All_Interrupts
5018 @unnumberedsec Pragma Unreserve_All_Interrupts
5019 @findex Unreserve_All_Interrupts
5023 @smallexample @c ada
5024 pragma Unreserve_All_Interrupts;
5028 Normally certain interrupts are reserved to the implementation. Any attempt
5029 to attach an interrupt causes Program_Error to be raised, as described in
5030 RM C.3.2(22). A typical example is the @code{SIGINT} interrupt used in
5031 many systems for a @kbd{Ctrl-C} interrupt. Normally this interrupt is
5032 reserved to the implementation, so that @kbd{Ctrl-C} can be used to
5033 interrupt execution.
5035 If the pragma @code{Unreserve_All_Interrupts} appears anywhere in any unit in
5036 a program, then all such interrupts are unreserved. This allows the
5037 program to handle these interrupts, but disables their standard
5038 functions. For example, if this pragma is used, then pressing
5039 @kbd{Ctrl-C} will not automatically interrupt execution. However,
5040 a program can then handle the @code{SIGINT} interrupt as it chooses.
5042 For a full list of the interrupts handled in a specific implementation,
5043 see the source code for the spec of @code{Ada.Interrupts.Names} in
5044 file @file{a-intnam.ads}. This is a target dependent file that contains the
5045 list of interrupts recognized for a given target. The documentation in
5046 this file also specifies what interrupts are affected by the use of
5047 the @code{Unreserve_All_Interrupts} pragma.
5049 For a more general facility for controlling what interrupts can be
5050 handled, see pragma @code{Interrupt_State}, which subsumes the functionality
5051 of the @code{Unreserve_All_Interrupts} pragma.
5053 @node Pragma Unsuppress
5054 @unnumberedsec Pragma Unsuppress
5059 @smallexample @c ada
5060 pragma Unsuppress (IDENTIFIER [, [On =>] NAME]);
5064 This pragma undoes the effect of a previous pragma @code{Suppress}. If
5065 there is no corresponding pragma @code{Suppress} in effect, it has no
5066 effect. The range of the effect is the same as for pragma
5067 @code{Suppress}. The meaning of the arguments is identical to that used
5068 in pragma @code{Suppress}.
5070 One important application is to ensure that checks are on in cases where
5071 code depends on the checks for its correct functioning, so that the code
5072 will compile correctly even if the compiler switches are set to suppress
5075 @node Pragma Use_VADS_Size
5076 @unnumberedsec Pragma Use_VADS_Size
5077 @cindex @code{Size}, VADS compatibility
5078 @findex Use_VADS_Size
5082 @smallexample @c ada
5083 pragma Use_VADS_Size;
5087 This is a configuration pragma. In a unit to which it applies, any use
5088 of the 'Size attribute is automatically interpreted as a use of the
5089 'VADS_Size attribute. Note that this may result in incorrect semantic
5090 processing of valid Ada 95 or Ada 2005 programs. This is intended to aid in
5091 the handling of existing code which depends on the interpretation of Size
5092 as implemented in the VADS compiler. See description of the VADS_Size
5093 attribute for further details.
5095 @node Pragma Validity_Checks
5096 @unnumberedsec Pragma Validity_Checks
5097 @findex Validity_Checks
5101 @smallexample @c ada
5102 pragma Validity_Checks (string_LITERAL | ALL_CHECKS | On | Off);
5106 This pragma is used in conjunction with compiler switches to control the
5107 built-in validity checking provided by GNAT@. The compiler switches, if set
5108 provide an initial setting for the switches, and this pragma may be used
5109 to modify these settings, or the settings may be provided entirely by
5110 the use of the pragma. This pragma can be used anywhere that a pragma
5111 is legal, including use as a configuration pragma (including use in
5112 the @file{gnat.adc} file).
5114 The form with a string literal specifies which validity options are to be
5115 activated. The validity checks are first set to include only the default
5116 reference manual settings, and then a string of letters in the string
5117 specifies the exact set of options required. The form of this string
5118 is exactly as described for the @option{-gnatVx} compiler switch (see the
5119 GNAT users guide for details). For example the following two methods
5120 can be used to enable validity checking for mode @code{in} and
5121 @code{in out} subprogram parameters:
5125 @smallexample @c ada
5126 pragma Validity_Checks ("im");
5131 gcc -c -gnatVim @dots{}
5136 The form ALL_CHECKS activates all standard checks (its use is equivalent
5137 to the use of the @code{gnatva} switch.
5139 The forms with @code{Off} and @code{On}
5140 can be used to temporarily disable validity checks
5141 as shown in the following example:
5143 @smallexample @c ada
5147 pragma Validity_Checks ("c"); -- validity checks for copies
5148 pragma Validity_Checks (Off); -- turn off validity checks
5149 A := B; -- B will not be validity checked
5150 pragma Validity_Checks (On); -- turn validity checks back on
5151 A := C; -- C will be validity checked
5154 @node Pragma Volatile
5155 @unnumberedsec Pragma Volatile
5160 @smallexample @c ada
5161 pragma Volatile (LOCAL_NAME);
5165 This pragma is defined by the Ada Reference Manual, and the GNAT
5166 implementation is fully conformant with this definition. The reason it
5167 is mentioned in this section is that a pragma of the same name was supplied
5168 in some Ada 83 compilers, including DEC Ada 83. The Ada 95 / Ada 2005
5169 implementation of pragma Volatile is upwards compatible with the
5170 implementation in DEC Ada 83.
5172 @node Pragma Warnings
5173 @unnumberedsec Pragma Warnings
5178 @smallexample @c ada
5179 pragma Warnings (On | Off);
5180 pragma Warnings (On | Off, LOCAL_NAME);
5181 pragma Warnings (static_string_EXPRESSION);
5182 pragma Warnings (On | Off, static_string_EXPRESSION);
5186 Normally warnings are enabled, with the output being controlled by
5187 the command line switch. Warnings (@code{Off}) turns off generation of
5188 warnings until a Warnings (@code{On}) is encountered or the end of the
5189 current unit. If generation of warnings is turned off using this
5190 pragma, then no warning messages are output, regardless of the
5191 setting of the command line switches.
5193 The form with a single argument may be used as a configuration pragma.
5195 If the @var{LOCAL_NAME} parameter is present, warnings are suppressed for
5196 the specified entity. This suppression is effective from the point where
5197 it occurs till the end of the extended scope of the variable (similar to
5198 the scope of @code{Suppress}).
5200 The form with a single static_string_EXPRESSION argument provides more precise
5201 control over which warnings are active. The string is a list of letters
5202 specifying which warnings are to be activated and which deactivated. The
5203 code for these letters is the same as the string used in the command
5204 line switch controlling warnings. For a brief summary, use the gnatmake
5205 command with no arguments, which will generate usage information containing
5206 the list of warnings switches supported. For
5207 full details see @ref{Warning Message Control,,, gnat_ugn, @value{EDITION}
5211 The specified warnings will be in effect until the end of the program
5212 or another pragma Warnings is encountered. The effect of the pragma is
5213 cumulative. Initially the set of warnings is the standard default set
5214 as possibly modified by compiler switches. Then each pragma Warning
5215 modifies this set of warnings as specified. This form of the pragma may
5216 also be used as a configuration pragma.
5218 The fourth form, with an On|Off parameter and a string, is used to
5219 control individual messages, based on their text. The string argument
5220 is a pattern that is used to match against the text of individual
5221 warning messages (not including the initial "warning: " tag).
5223 The pattern may contain asterisks, which match zero or more characters in
5224 the message. For example, you can use
5225 @code{pragma Warnings (Off, "*bits of*unused")} to suppress the warning
5226 message @code{warning: 960 bits of "a" unused}. No other regular
5227 expression notations are permitted. All characters other than asterisk in
5228 these three specific cases are treated as literal characters in the match.
5230 There are two ways to use this pragma. The OFF form can be used as a
5231 configuration pragma. The effect is to suppress all warnings (if any)
5232 that match the pattern string throughout the compilation.
5234 The second usage is to suppress a warning locally, and in this case, two
5235 pragmas must appear in sequence:
5237 @smallexample @c ada
5238 pragma Warnings (Off, Pattern);
5239 @dots{} code where given warning is to be suppressed
5240 pragma Warnings (On, Pattern);
5244 In this usage, the pattern string must match in the Off and On pragmas,
5245 and at least one matching warning must be suppressed.
5247 Note: the debug flag -gnatd.i (@code{/NOWARNINGS_PRAGMAS} in VMS) can be
5248 used to cause the compiler to entirely ignore all WARNINGS pragmas. This can
5249 be useful in checking whether obsolete pragmas in existing programs are hiding
5252 @node Pragma Weak_External
5253 @unnumberedsec Pragma Weak_External
5254 @findex Weak_External
5258 @smallexample @c ada
5259 pragma Weak_External ([Entity =>] LOCAL_NAME);
5263 @var{LOCAL_NAME} must refer to an object that is declared at the library
5264 level. This pragma specifies that the given entity should be marked as a
5265 weak symbol for the linker. It is equivalent to @code{__attribute__((weak))}
5266 in GNU C and causes @var{LOCAL_NAME} to be emitted as a weak symbol instead
5267 of a regular symbol, that is to say a symbol that does not have to be
5268 resolved by the linker if used in conjunction with a pragma Import.
5270 When a weak symbol is not resolved by the linker, its address is set to
5271 zero. This is useful in writing interfaces to external modules that may
5272 or may not be linked in the final executable, for example depending on
5273 configuration settings.
5275 If a program references at run time an entity to which this pragma has been
5276 applied, and the corresponding symbol was not resolved at link time, then
5277 the execution of the program is erroneous. It is not erroneous to take the
5278 Address of such an entity, for example to guard potential references,
5279 as shown in the example below.
5281 Some file formats do not support weak symbols so not all target machines
5282 support this pragma.
5284 @smallexample @c ada
5285 -- Example of the use of pragma Weak_External
5287 package External_Module is
5289 pragma Import (C, key);
5290 pragma Weak_External (key);
5291 function Present return boolean;
5292 end External_Module;
5294 with System; use System;
5295 package body External_Module is
5296 function Present return boolean is
5298 return key'Address /= System.Null_Address;
5300 end External_Module;
5303 @node Pragma Wide_Character_Encoding
5304 @unnumberedsec Pragma Wide_Character_Encoding
5305 @findex Wide_Character_Encoding
5309 @smallexample @c ada
5310 pragma Wide_Character_Encoding (IDENTIFIER | CHARACTER_LITERAL);
5314 This pragma specifies the wide character encoding to be used in program
5315 source text appearing subsequently. It is a configuration pragma, but may
5316 also be used at any point that a pragma is allowed, and it is permissible
5317 to have more than one such pragma in a file, allowing multiple encodings
5318 to appear within the same file.
5320 The argument can be an identifier or a character literal. In the identifier
5321 case, it is one of @code{HEX}, @code{UPPER}, @code{SHIFT_JIS},
5322 @code{EUC}, @code{UTF8}, or @code{BRACKETS}. In the character literal
5323 case it is correspondingly one of the characters @samp{h}, @samp{u},
5324 @samp{s}, @samp{e}, @samp{8}, or @samp{b}.
5326 Note that when the pragma is used within a file, it affects only the
5327 encoding within that file, and does not affect withed units, specs,
5330 @node Implementation Defined Attributes
5331 @chapter Implementation Defined Attributes
5332 Ada defines (throughout the Ada reference manual,
5333 summarized in Annex K),
5334 a set of attributes that provide useful additional functionality in all
5335 areas of the language. These language defined attributes are implemented
5336 in GNAT and work as described in the Ada Reference Manual.
5338 In addition, Ada allows implementations to define additional
5339 attributes whose meaning is defined by the implementation. GNAT provides
5340 a number of these implementation-dependent attributes which can be used
5341 to extend and enhance the functionality of the compiler. This section of
5342 the GNAT reference manual describes these additional attributes.
5344 Note that any program using these attributes may not be portable to
5345 other compilers (although GNAT implements this set of attributes on all
5346 platforms). Therefore if portability to other compilers is an important
5347 consideration, you should minimize the use of these attributes.
5357 * Compiler_Version::
5359 * Default_Bit_Order::
5369 * Has_Access_Values::
5370 * Has_Discriminants::
5377 * Max_Interrupt_Priority::
5379 * Maximum_Alignment::
5384 * Passed_By_Reference::
5398 * Unconstrained_Array::
5399 * Universal_Literal_String::
5400 * Unrestricted_Access::
5408 @unnumberedsec Abort_Signal
5409 @findex Abort_Signal
5411 @code{Standard'Abort_Signal} (@code{Standard} is the only allowed
5412 prefix) provides the entity for the special exception used to signal
5413 task abort or asynchronous transfer of control. Normally this attribute
5414 should only be used in the tasking runtime (it is highly peculiar, and
5415 completely outside the normal semantics of Ada, for a user program to
5416 intercept the abort exception).
5419 @unnumberedsec Address_Size
5420 @cindex Size of @code{Address}
5421 @findex Address_Size
5423 @code{Standard'Address_Size} (@code{Standard} is the only allowed
5424 prefix) is a static constant giving the number of bits in an
5425 @code{Address}. It is the same value as System.Address'Size,
5426 but has the advantage of being static, while a direct
5427 reference to System.Address'Size is non-static because Address
5431 @unnumberedsec Asm_Input
5434 The @code{Asm_Input} attribute denotes a function that takes two
5435 parameters. The first is a string, the second is an expression of the
5436 type designated by the prefix. The first (string) argument is required
5437 to be a static expression, and is the constraint for the parameter,
5438 (e.g.@: what kind of register is required). The second argument is the
5439 value to be used as the input argument. The possible values for the
5440 constant are the same as those used in the RTL, and are dependent on
5441 the configuration file used to built the GCC back end.
5442 @ref{Machine Code Insertions}
5445 @unnumberedsec Asm_Output
5448 The @code{Asm_Output} attribute denotes a function that takes two
5449 parameters. The first is a string, the second is the name of a variable
5450 of the type designated by the attribute prefix. The first (string)
5451 argument is required to be a static expression and designates the
5452 constraint for the parameter (e.g.@: what kind of register is
5453 required). The second argument is the variable to be updated with the
5454 result. The possible values for constraint are the same as those used in
5455 the RTL, and are dependent on the configuration file used to build the
5456 GCC back end. If there are no output operands, then this argument may
5457 either be omitted, or explicitly given as @code{No_Output_Operands}.
5458 @ref{Machine Code Insertions}
5461 @unnumberedsec AST_Entry
5465 This attribute is implemented only in OpenVMS versions of GNAT@. Applied to
5466 the name of an entry, it yields a value of the predefined type AST_Handler
5467 (declared in the predefined package System, as extended by the use of
5468 pragma @code{Extend_System (Aux_DEC)}). This value enables the given entry to
5469 be called when an AST occurs. For further details, refer to the @cite{DEC Ada
5470 Language Reference Manual}, section 9.12a.
5475 @code{@var{obj}'Bit}, where @var{obj} is any object, yields the bit
5476 offset within the storage unit (byte) that contains the first bit of
5477 storage allocated for the object. The value of this attribute is of the
5478 type @code{Universal_Integer}, and is always a non-negative number not
5479 exceeding the value of @code{System.Storage_Unit}.
5481 For an object that is a variable or a constant allocated in a register,
5482 the value is zero. (The use of this attribute does not force the
5483 allocation of a variable to memory).
5485 For an object that is a formal parameter, this attribute applies
5486 to either the matching actual parameter or to a copy of the
5487 matching actual parameter.
5489 For an access object the value is zero. Note that
5490 @code{@var{obj}.all'Bit} is subject to an @code{Access_Check} for the
5491 designated object. Similarly for a record component
5492 @code{@var{X}.@var{C}'Bit} is subject to a discriminant check and
5493 @code{@var{X}(@var{I}).Bit} and @code{@var{X}(@var{I1}..@var{I2})'Bit}
5494 are subject to index checks.
5496 This attribute is designed to be compatible with the DEC Ada 83 definition
5497 and implementation of the @code{Bit} attribute.
5500 @unnumberedsec Bit_Position
5501 @findex Bit_Position
5503 @code{@var{R.C}'Bit}, where @var{R} is a record object and C is one
5504 of the fields of the record type, yields the bit
5505 offset within the record contains the first bit of
5506 storage allocated for the object. The value of this attribute is of the
5507 type @code{Universal_Integer}. The value depends only on the field
5508 @var{C} and is independent of the alignment of
5509 the containing record @var{R}.
5511 @node Compiler_Version
5512 @unnumberedsec Compiler_Version
5513 @findex Compiler_Version
5515 @code{Standard'Compiler_Version} (@code{Standard} is the only allowed
5516 prefix) yields a static string identifying the version of the compiler
5517 being used to compile the unit containing the attribute reference. A
5518 typical result would be something like "GNAT Pro 6.3.0w (20090221)".
5521 @unnumberedsec Code_Address
5522 @findex Code_Address
5523 @cindex Subprogram address
5524 @cindex Address of subprogram code
5527 attribute may be applied to subprograms in Ada 95 and Ada 2005, but the
5528 intended effect seems to be to provide
5529 an address value which can be used to call the subprogram by means of
5530 an address clause as in the following example:
5532 @smallexample @c ada
5533 procedure K is @dots{}
5536 for L'Address use K'Address;
5537 pragma Import (Ada, L);
5541 A call to @code{L} is then expected to result in a call to @code{K}@.
5542 In Ada 83, where there were no access-to-subprogram values, this was
5543 a common work-around for getting the effect of an indirect call.
5544 GNAT implements the above use of @code{Address} and the technique
5545 illustrated by the example code works correctly.
5547 However, for some purposes, it is useful to have the address of the start
5548 of the generated code for the subprogram. On some architectures, this is
5549 not necessarily the same as the @code{Address} value described above.
5550 For example, the @code{Address} value may reference a subprogram
5551 descriptor rather than the subprogram itself.
5553 The @code{'Code_Address} attribute, which can only be applied to
5554 subprogram entities, always returns the address of the start of the
5555 generated code of the specified subprogram, which may or may not be
5556 the same value as is returned by the corresponding @code{'Address}
5559 @node Default_Bit_Order
5560 @unnumberedsec Default_Bit_Order
5562 @cindex Little endian
5563 @findex Default_Bit_Order
5565 @code{Standard'Default_Bit_Order} (@code{Standard} is the only
5566 permissible prefix), provides the value @code{System.Default_Bit_Order}
5567 as a @code{Pos} value (0 for @code{High_Order_First}, 1 for
5568 @code{Low_Order_First}). This is used to construct the definition of
5569 @code{Default_Bit_Order} in package @code{System}.
5572 @unnumberedsec Elaborated
5575 The prefix of the @code{'Elaborated} attribute must be a unit name. The
5576 value is a Boolean which indicates whether or not the given unit has been
5577 elaborated. This attribute is primarily intended for internal use by the
5578 generated code for dynamic elaboration checking, but it can also be used
5579 in user programs. The value will always be True once elaboration of all
5580 units has been completed. An exception is for units which need no
5581 elaboration, the value is always False for such units.
5584 @unnumberedsec Elab_Body
5587 This attribute can only be applied to a program unit name. It returns
5588 the entity for the corresponding elaboration procedure for elaborating
5589 the body of the referenced unit. This is used in the main generated
5590 elaboration procedure by the binder and is not normally used in any
5591 other context. However, there may be specialized situations in which it
5592 is useful to be able to call this elaboration procedure from Ada code,
5593 e.g.@: if it is necessary to do selective re-elaboration to fix some
5597 @unnumberedsec Elab_Spec
5600 This attribute can only be applied to a program unit name. It returns
5601 the entity for the corresponding elaboration procedure for elaborating
5602 the spec of the referenced unit. This is used in the main
5603 generated elaboration procedure by the binder and is not normally used
5604 in any other context. However, there may be specialized situations in
5605 which it is useful to be able to call this elaboration procedure from
5606 Ada code, e.g.@: if it is necessary to do selective re-elaboration to fix
5611 @cindex Ada 83 attributes
5614 The @code{Emax} attribute is provided for compatibility with Ada 83. See
5615 the Ada 83 reference manual for an exact description of the semantics of
5619 @unnumberedsec Enabled
5622 The @code{Enabled} attribute allows an application program to check at compile
5623 time to see if the designated check is currently enabled. The prefix is a
5624 simple identifier, referencing any predefined check name (other than
5625 @code{All_Checks}) or a check name introduced by pragma Check_Name. If
5626 no argument is given for the attribute, the check is for the general state
5627 of the check, if an argument is given, then it is an entity name, and the
5628 check indicates whether an @code{Suppress} or @code{Unsuppress} has been
5629 given naming the entity (if not, then the argument is ignored).
5631 Note that instantiations inherit the check status at the point of the
5632 instantiation, so a useful idiom is to have a library package that
5633 introduces a check name with @code{pragma Check_Name}, and then contains
5634 generic packages or subprograms which use the @code{Enabled} attribute
5635 to see if the check is enabled. A user of this package can then issue
5636 a @code{pragma Suppress} or @code{pragma Unsuppress} before instantiating
5637 the package or subprogram, controlling whether the check will be present.
5640 @unnumberedsec Enum_Rep
5641 @cindex Representation of enums
5644 For every enumeration subtype @var{S}, @code{@var{S}'Enum_Rep} denotes a
5645 function with the following spec:
5647 @smallexample @c ada
5648 function @var{S}'Enum_Rep (Arg : @var{S}'Base)
5649 return @i{Universal_Integer};
5653 It is also allowable to apply @code{Enum_Rep} directly to an object of an
5654 enumeration type or to a non-overloaded enumeration
5655 literal. In this case @code{@var{S}'Enum_Rep} is equivalent to
5656 @code{@var{typ}'Enum_Rep(@var{S})} where @var{typ} is the type of the
5657 enumeration literal or object.
5659 The function returns the representation value for the given enumeration
5660 value. This will be equal to value of the @code{Pos} attribute in the
5661 absence of an enumeration representation clause. This is a static
5662 attribute (i.e.@: the result is static if the argument is static).
5664 @code{@var{S}'Enum_Rep} can also be used with integer types and objects,
5665 in which case it simply returns the integer value. The reason for this
5666 is to allow it to be used for @code{(<>)} discrete formal arguments in
5667 a generic unit that can be instantiated with either enumeration types
5668 or integer types. Note that if @code{Enum_Rep} is used on a modular
5669 type whose upper bound exceeds the upper bound of the largest signed
5670 integer type, and the argument is a variable, so that the universal
5671 integer calculation is done at run time, then the call to @code{Enum_Rep}
5672 may raise @code{Constraint_Error}.
5675 @unnumberedsec Enum_Val
5676 @cindex Representation of enums
5679 For every enumeration subtype @var{S}, @code{@var{S}'Enum_Rep} denotes a
5680 function with the following spec:
5682 @smallexample @c ada
5683 function @var{S}'Enum_Rep (Arg : @i{Universal_Integer)
5684 return @var{S}'Base};
5688 The function returns the enumeration value whose representation matches the
5689 argument, or raises Constraint_Error if no enumeration literal of the type
5690 has the matching value.
5691 This will be equal to value of the @code{Val} attribute in the
5692 absence of an enumeration representation clause. This is a static
5693 attribute (i.e.@: the result is static if the argument is static).
5696 @unnumberedsec Epsilon
5697 @cindex Ada 83 attributes
5700 The @code{Epsilon} attribute is provided for compatibility with Ada 83. See
5701 the Ada 83 reference manual for an exact description of the semantics of
5705 @unnumberedsec Fixed_Value
5708 For every fixed-point type @var{S}, @code{@var{S}'Fixed_Value} denotes a
5709 function with the following specification:
5711 @smallexample @c ada
5712 function @var{S}'Fixed_Value (Arg : @i{Universal_Integer})
5717 The value returned is the fixed-point value @var{V} such that
5719 @smallexample @c ada
5720 @var{V} = Arg * @var{S}'Small
5724 The effect is thus similar to first converting the argument to the
5725 integer type used to represent @var{S}, and then doing an unchecked
5726 conversion to the fixed-point type. The difference is
5727 that there are full range checks, to ensure that the result is in range.
5728 This attribute is primarily intended for use in implementation of the
5729 input-output functions for fixed-point values.
5731 @node Has_Access_Values
5732 @unnumberedsec Has_Access_Values
5733 @cindex Access values, testing for
5734 @findex Has_Access_Values
5736 The prefix of the @code{Has_Access_Values} attribute is a type. The result
5737 is a Boolean value which is True if the is an access type, or is a composite
5738 type with a component (at any nesting depth) that is an access type, and is
5740 The intended use of this attribute is in conjunction with generic
5741 definitions. If the attribute is applied to a generic private type, it
5742 indicates whether or not the corresponding actual type has access values.
5744 @node Has_Discriminants
5745 @unnumberedsec Has_Discriminants
5746 @cindex Discriminants, testing for
5747 @findex Has_Discriminants
5749 The prefix of the @code{Has_Discriminants} attribute is a type. The result
5750 is a Boolean value which is True if the type has discriminants, and False
5751 otherwise. The intended use of this attribute is in conjunction with generic
5752 definitions. If the attribute is applied to a generic private type, it
5753 indicates whether or not the corresponding actual type has discriminants.
5759 The @code{Img} attribute differs from @code{Image} in that it may be
5760 applied to objects as well as types, in which case it gives the
5761 @code{Image} for the subtype of the object. This is convenient for
5764 @smallexample @c ada
5765 Put_Line ("X = " & X'Img);
5769 has the same meaning as the more verbose:
5771 @smallexample @c ada
5772 Put_Line ("X = " & @var{T}'Image (X));
5776 where @var{T} is the (sub)type of the object @code{X}.
5779 @unnumberedsec Integer_Value
5780 @findex Integer_Value
5782 For every integer type @var{S}, @code{@var{S}'Integer_Value} denotes a
5783 function with the following spec:
5785 @smallexample @c ada
5786 function @var{S}'Integer_Value (Arg : @i{Universal_Fixed})
5791 The value returned is the integer value @var{V}, such that
5793 @smallexample @c ada
5794 Arg = @var{V} * @var{T}'Small
5798 where @var{T} is the type of @code{Arg}.
5799 The effect is thus similar to first doing an unchecked conversion from
5800 the fixed-point type to its corresponding implementation type, and then
5801 converting the result to the target integer type. The difference is
5802 that there are full range checks, to ensure that the result is in range.
5803 This attribute is primarily intended for use in implementation of the
5804 standard input-output functions for fixed-point values.
5807 @unnumberedsec Invalid_Value
5808 @findex Invalid_Value
5810 For every scalar type S, S'Invalid_Value returns an undefined value of the
5811 type. If possible this value is an invalid representation for the type. The
5812 value returned is identical to the value used to initialize an otherwise
5813 uninitialized value of the type if pragma Initialize_Scalars is used,
5814 including the ability to modify the value with the binder -Sxx flag and
5815 relevant environment variables at run time.
5818 @unnumberedsec Large
5819 @cindex Ada 83 attributes
5822 The @code{Large} attribute is provided for compatibility with Ada 83. See
5823 the Ada 83 reference manual for an exact description of the semantics of
5827 @unnumberedsec Machine_Size
5828 @findex Machine_Size
5830 This attribute is identical to the @code{Object_Size} attribute. It is
5831 provided for compatibility with the DEC Ada 83 attribute of this name.
5834 @unnumberedsec Mantissa
5835 @cindex Ada 83 attributes
5838 The @code{Mantissa} attribute is provided for compatibility with Ada 83. See
5839 the Ada 83 reference manual for an exact description of the semantics of
5842 @node Max_Interrupt_Priority
5843 @unnumberedsec Max_Interrupt_Priority
5844 @cindex Interrupt priority, maximum
5845 @findex Max_Interrupt_Priority
5847 @code{Standard'Max_Interrupt_Priority} (@code{Standard} is the only
5848 permissible prefix), provides the same value as
5849 @code{System.Max_Interrupt_Priority}.
5852 @unnumberedsec Max_Priority
5853 @cindex Priority, maximum
5854 @findex Max_Priority
5856 @code{Standard'Max_Priority} (@code{Standard} is the only permissible
5857 prefix) provides the same value as @code{System.Max_Priority}.
5859 @node Maximum_Alignment
5860 @unnumberedsec Maximum_Alignment
5861 @cindex Alignment, maximum
5862 @findex Maximum_Alignment
5864 @code{Standard'Maximum_Alignment} (@code{Standard} is the only
5865 permissible prefix) provides the maximum useful alignment value for the
5866 target. This is a static value that can be used to specify the alignment
5867 for an object, guaranteeing that it is properly aligned in all
5870 @node Mechanism_Code
5871 @unnumberedsec Mechanism_Code
5872 @cindex Return values, passing mechanism
5873 @cindex Parameters, passing mechanism
5874 @findex Mechanism_Code
5876 @code{@var{function}'Mechanism_Code} yields an integer code for the
5877 mechanism used for the result of function, and
5878 @code{@var{subprogram}'Mechanism_Code (@var{n})} yields the mechanism
5879 used for formal parameter number @var{n} (a static integer value with 1
5880 meaning the first parameter) of @var{subprogram}. The code returned is:
5888 by descriptor (default descriptor class)
5890 by descriptor (UBS: unaligned bit string)
5892 by descriptor (UBSB: aligned bit string with arbitrary bounds)
5894 by descriptor (UBA: unaligned bit array)
5896 by descriptor (S: string, also scalar access type parameter)
5898 by descriptor (SB: string with arbitrary bounds)
5900 by descriptor (A: contiguous array)
5902 by descriptor (NCA: non-contiguous array)
5906 Values from 3 through 10 are only relevant to Digital OpenVMS implementations.
5909 @node Null_Parameter
5910 @unnumberedsec Null_Parameter
5911 @cindex Zero address, passing
5912 @findex Null_Parameter
5914 A reference @code{@var{T}'Null_Parameter} denotes an imaginary object of
5915 type or subtype @var{T} allocated at machine address zero. The attribute
5916 is allowed only as the default expression of a formal parameter, or as
5917 an actual expression of a subprogram call. In either case, the
5918 subprogram must be imported.
5920 The identity of the object is represented by the address zero in the
5921 argument list, independent of the passing mechanism (explicit or
5924 This capability is needed to specify that a zero address should be
5925 passed for a record or other composite object passed by reference.
5926 There is no way of indicating this without the @code{Null_Parameter}
5930 @unnumberedsec Object_Size
5931 @cindex Size, used for objects
5934 The size of an object is not necessarily the same as the size of the type
5935 of an object. This is because by default object sizes are increased to be
5936 a multiple of the alignment of the object. For example,
5937 @code{Natural'Size} is
5938 31, but by default objects of type @code{Natural} will have a size of 32 bits.
5939 Similarly, a record containing an integer and a character:
5941 @smallexample @c ada
5949 will have a size of 40 (that is @code{Rec'Size} will be 40. The
5950 alignment will be 4, because of the
5951 integer field, and so the default size of record objects for this type
5952 will be 64 (8 bytes).
5956 @cindex Capturing Old values
5957 @cindex Postconditions
5959 The attribute Prefix'Old can be used within a
5960 subprogram to refer to the value of the prefix on entry. So for
5961 example if you have an argument of a record type X called Arg1,
5962 you can refer to Arg1.Field'Old which yields the value of
5963 Arg1.Field on entry. The implementation simply involves generating
5964 an object declaration which captures the value on entry. Any
5965 prefix is allowed except one of a limited type (since limited
5966 types cannot be copied to capture their values) or a local variable
5967 (since it does not exist at subprogram entry time).
5969 The following example shows the use of 'Old to implement
5970 a test of a postcondition:
5972 @smallexample @c ada
5983 package body Old_Pkg is
5984 Count : Natural := 0;
5988 ... code manipulating the value of Count
5990 pragma Assert (Count = Count'Old + 1);
5996 Note that it is allowed to apply 'Old to a constant entity, but this will
5997 result in a warning, since the old and new values will always be the same.
5999 @node Passed_By_Reference
6000 @unnumberedsec Passed_By_Reference
6001 @cindex Parameters, when passed by reference
6002 @findex Passed_By_Reference
6004 @code{@var{type}'Passed_By_Reference} for any subtype @var{type} returns
6005 a value of type @code{Boolean} value that is @code{True} if the type is
6006 normally passed by reference and @code{False} if the type is normally
6007 passed by copy in calls. For scalar types, the result is always @code{False}
6008 and is static. For non-scalar types, the result is non-static.
6011 @unnumberedsec Pool_Address
6012 @cindex Parameters, when passed by reference
6013 @findex Pool_Address
6015 @code{@var{X}'Pool_Address} for any object @var{X} returns the address
6016 of X within its storage pool. This is the same as
6017 @code{@var{X}'Address}, except that for an unconstrained array whose
6018 bounds are allocated just before the first component,
6019 @code{@var{X}'Pool_Address} returns the address of those bounds,
6020 whereas @code{@var{X}'Address} returns the address of the first
6023 Here, we are interpreting ``storage pool'' broadly to mean ``wherever
6024 the object is allocated'', which could be a user-defined storage pool,
6025 the global heap, on the stack, or in a static memory area. For an
6026 object created by @code{new}, @code{@var{Ptr.all}'Pool_Address} is
6027 what is passed to @code{Allocate} and returned from @code{Deallocate}.
6030 @unnumberedsec Range_Length
6031 @findex Range_Length
6033 @code{@var{type}'Range_Length} for any discrete type @var{type} yields
6034 the number of values represented by the subtype (zero for a null
6035 range). The result is static for static subtypes. @code{Range_Length}
6036 applied to the index subtype of a one dimensional array always gives the
6037 same result as @code{Range} applied to the array itself.
6040 @unnumberedsec Result
6043 @code{@var{function}'Result} can only be used with in a Postcondition pragma
6044 for a function. The prefix must be the name of the corresponding function. This
6045 is used to refer to the result of the function in the postcondition expression.
6046 For a further discussion of the use of this attribute and examples of its use,
6047 see the description of pragma Postcondition.
6050 @unnumberedsec Safe_Emax
6051 @cindex Ada 83 attributes
6054 The @code{Safe_Emax} attribute is provided for compatibility with Ada 83. See
6055 the Ada 83 reference manual for an exact description of the semantics of
6059 @unnumberedsec Safe_Large
6060 @cindex Ada 83 attributes
6063 The @code{Safe_Large} attribute is provided for compatibility with Ada 83. See
6064 the Ada 83 reference manual for an exact description of the semantics of
6068 @unnumberedsec Small
6069 @cindex Ada 83 attributes
6072 The @code{Small} attribute is defined in Ada 95 (and Ada 2005) only for
6074 GNAT also allows this attribute to be applied to floating-point types
6075 for compatibility with Ada 83. See
6076 the Ada 83 reference manual for an exact description of the semantics of
6077 this attribute when applied to floating-point types.
6080 @unnumberedsec Storage_Unit
6081 @findex Storage_Unit
6083 @code{Standard'Storage_Unit} (@code{Standard} is the only permissible
6084 prefix) provides the same value as @code{System.Storage_Unit}.
6087 @unnumberedsec Stub_Type
6090 The GNAT implementation of remote access-to-classwide types is
6091 organized as described in AARM section E.4 (20.t): a value of an RACW type
6092 (designating a remote object) is represented as a normal access
6093 value, pointing to a "stub" object which in turn contains the
6094 necessary information to contact the designated remote object. A
6095 call on any dispatching operation of such a stub object does the
6096 remote call, if necessary, using the information in the stub object
6097 to locate the target partition, etc.
6099 For a prefix @code{T} that denotes a remote access-to-classwide type,
6100 @code{T'Stub_Type} denotes the type of the corresponding stub objects.
6102 By construction, the layout of @code{T'Stub_Type} is identical to that of
6103 type @code{RACW_Stub_Type} declared in the internal implementation-defined
6104 unit @code{System.Partition_Interface}. Use of this attribute will create
6105 an implicit dependency on this unit.
6108 @unnumberedsec Target_Name
6111 @code{Standard'Target_Name} (@code{Standard} is the only permissible
6112 prefix) provides a static string value that identifies the target
6113 for the current compilation. For GCC implementations, this is the
6114 standard gcc target name without the terminating slash (for
6115 example, GNAT 5.0 on windows yields "i586-pc-mingw32msv").
6121 @code{Standard'Tick} (@code{Standard} is the only permissible prefix)
6122 provides the same value as @code{System.Tick},
6125 @unnumberedsec To_Address
6128 The @code{System'To_Address}
6129 (@code{System} is the only permissible prefix)
6130 denotes a function identical to
6131 @code{System.Storage_Elements.To_Address} except that
6132 it is a static attribute. This means that if its argument is
6133 a static expression, then the result of the attribute is a
6134 static expression. The result is that such an expression can be
6135 used in contexts (e.g.@: preelaborable packages) which require a
6136 static expression and where the function call could not be used
6137 (since the function call is always non-static, even if its
6138 argument is static).
6141 @unnumberedsec Type_Class
6144 @code{@var{type}'Type_Class} for any type or subtype @var{type} yields
6145 the value of the type class for the full type of @var{type}. If
6146 @var{type} is a generic formal type, the value is the value for the
6147 corresponding actual subtype. The value of this attribute is of type
6148 @code{System.Aux_DEC.Type_Class}, which has the following definition:
6150 @smallexample @c ada
6152 (Type_Class_Enumeration,
6154 Type_Class_Fixed_Point,
6155 Type_Class_Floating_Point,
6160 Type_Class_Address);
6164 Protected types yield the value @code{Type_Class_Task}, which thus
6165 applies to all concurrent types. This attribute is designed to
6166 be compatible with the DEC Ada 83 attribute of the same name.
6169 @unnumberedsec UET_Address
6172 The @code{UET_Address} attribute can only be used for a prefix which
6173 denotes a library package. It yields the address of the unit exception
6174 table when zero cost exception handling is used. This attribute is
6175 intended only for use within the GNAT implementation. See the unit
6176 @code{Ada.Exceptions} in files @file{a-except.ads} and @file{a-except.adb}
6177 for details on how this attribute is used in the implementation.
6179 @node Unconstrained_Array
6180 @unnumberedsec Unconstrained_Array
6181 @findex Unconstrained_Array
6183 The @code{Unconstrained_Array} attribute can be used with a prefix that
6184 denotes any type or subtype. It is a static attribute that yields
6185 @code{True} if the prefix designates an unconstrained array,
6186 and @code{False} otherwise. In a generic instance, the result is
6187 still static, and yields the result of applying this test to the
6190 @node Universal_Literal_String
6191 @unnumberedsec Universal_Literal_String
6192 @cindex Named numbers, representation of
6193 @findex Universal_Literal_String
6195 The prefix of @code{Universal_Literal_String} must be a named
6196 number. The static result is the string consisting of the characters of
6197 the number as defined in the original source. This allows the user
6198 program to access the actual text of named numbers without intermediate
6199 conversions and without the need to enclose the strings in quotes (which
6200 would preclude their use as numbers). This is used internally for the
6201 construction of values of the floating-point attributes from the file
6202 @file{ttypef.ads}, but may also be used by user programs.
6204 For example, the following program prints the first 50 digits of pi:
6206 @smallexample @c ada
6207 with Text_IO; use Text_IO;
6211 Put (Ada.Numerics.Pi'Universal_Literal_String);
6215 @node Unrestricted_Access
6216 @unnumberedsec Unrestricted_Access
6217 @cindex @code{Access}, unrestricted
6218 @findex Unrestricted_Access
6220 The @code{Unrestricted_Access} attribute is similar to @code{Access}
6221 except that all accessibility and aliased view checks are omitted. This
6222 is a user-beware attribute. It is similar to
6223 @code{Address}, for which it is a desirable replacement where the value
6224 desired is an access type. In other words, its effect is identical to
6225 first applying the @code{Address} attribute and then doing an unchecked
6226 conversion to a desired access type. In GNAT, but not necessarily in
6227 other implementations, the use of static chains for inner level
6228 subprograms means that @code{Unrestricted_Access} applied to a
6229 subprogram yields a value that can be called as long as the subprogram
6230 is in scope (normal Ada accessibility rules restrict this usage).
6232 It is possible to use @code{Unrestricted_Access} for any type, but care
6233 must be exercised if it is used to create pointers to unconstrained
6234 objects. In this case, the resulting pointer has the same scope as the
6235 context of the attribute, and may not be returned to some enclosing
6236 scope. For instance, a function cannot use @code{Unrestricted_Access}
6237 to create a unconstrained pointer and then return that value to the
6241 @unnumberedsec VADS_Size
6242 @cindex @code{Size}, VADS compatibility
6245 The @code{'VADS_Size} attribute is intended to make it easier to port
6246 legacy code which relies on the semantics of @code{'Size} as implemented
6247 by the VADS Ada 83 compiler. GNAT makes a best effort at duplicating the
6248 same semantic interpretation. In particular, @code{'VADS_Size} applied
6249 to a predefined or other primitive type with no Size clause yields the
6250 Object_Size (for example, @code{Natural'Size} is 32 rather than 31 on
6251 typical machines). In addition @code{'VADS_Size} applied to an object
6252 gives the result that would be obtained by applying the attribute to
6253 the corresponding type.
6256 @unnumberedsec Value_Size
6257 @cindex @code{Size}, setting for not-first subtype
6259 @code{@var{type}'Value_Size} is the number of bits required to represent
6260 a value of the given subtype. It is the same as @code{@var{type}'Size},
6261 but, unlike @code{Size}, may be set for non-first subtypes.
6264 @unnumberedsec Wchar_T_Size
6265 @findex Wchar_T_Size
6266 @code{Standard'Wchar_T_Size} (@code{Standard} is the only permissible
6267 prefix) provides the size in bits of the C @code{wchar_t} type
6268 primarily for constructing the definition of this type in
6269 package @code{Interfaces.C}.
6272 @unnumberedsec Word_Size
6274 @code{Standard'Word_Size} (@code{Standard} is the only permissible
6275 prefix) provides the value @code{System.Word_Size}.
6277 @c ------------------------
6278 @node Implementation Advice
6279 @chapter Implementation Advice
6281 The main text of the Ada Reference Manual describes the required
6282 behavior of all Ada compilers, and the GNAT compiler conforms to
6285 In addition, there are sections throughout the Ada Reference Manual headed
6286 by the phrase ``Implementation advice''. These sections are not normative,
6287 i.e., they do not specify requirements that all compilers must
6288 follow. Rather they provide advice on generally desirable behavior. You
6289 may wonder why they are not requirements. The most typical answer is
6290 that they describe behavior that seems generally desirable, but cannot
6291 be provided on all systems, or which may be undesirable on some systems.
6293 As far as practical, GNAT follows the implementation advice sections in
6294 the Ada Reference Manual. This chapter contains a table giving the
6295 reference manual section number, paragraph number and several keywords
6296 for each advice. Each entry consists of the text of the advice followed
6297 by the GNAT interpretation of this advice. Most often, this simply says
6298 ``followed'', which means that GNAT follows the advice. However, in a
6299 number of cases, GNAT deliberately deviates from this advice, in which
6300 case the text describes what GNAT does and why.
6302 @cindex Error detection
6303 @unnumberedsec 1.1.3(20): Error Detection
6306 If an implementation detects the use of an unsupported Specialized Needs
6307 Annex feature at run time, it should raise @code{Program_Error} if
6310 Not relevant. All specialized needs annex features are either supported,
6311 or diagnosed at compile time.
6314 @unnumberedsec 1.1.3(31): Child Units
6317 If an implementation wishes to provide implementation-defined
6318 extensions to the functionality of a language-defined library unit, it
6319 should normally do so by adding children to the library unit.
6323 @cindex Bounded errors
6324 @unnumberedsec 1.1.5(12): Bounded Errors
6327 If an implementation detects a bounded error or erroneous
6328 execution, it should raise @code{Program_Error}.
6330 Followed in all cases in which the implementation detects a bounded
6331 error or erroneous execution. Not all such situations are detected at
6335 @unnumberedsec 2.8(16): Pragmas
6338 Normally, implementation-defined pragmas should have no semantic effect
6339 for error-free programs; that is, if the implementation-defined pragmas
6340 are removed from a working program, the program should still be legal,
6341 and should still have the same semantics.
6343 The following implementation defined pragmas are exceptions to this
6355 @item CPP_Constructor
6359 @item Interface_Name
6361 @item Machine_Attribute
6363 @item Unimplemented_Unit
6365 @item Unchecked_Union
6370 In each of the above cases, it is essential to the purpose of the pragma
6371 that this advice not be followed. For details see the separate section
6372 on implementation defined pragmas.
6374 @unnumberedsec 2.8(17-19): Pragmas
6377 Normally, an implementation should not define pragmas that can
6378 make an illegal program legal, except as follows:
6382 A pragma used to complete a declaration, such as a pragma @code{Import};
6386 A pragma used to configure the environment by adding, removing, or
6387 replacing @code{library_items}.
6389 See response to paragraph 16 of this same section.
6391 @cindex Character Sets
6392 @cindex Alternative Character Sets
6393 @unnumberedsec 3.5.2(5): Alternative Character Sets
6396 If an implementation supports a mode with alternative interpretations
6397 for @code{Character} and @code{Wide_Character}, the set of graphic
6398 characters of @code{Character} should nevertheless remain a proper
6399 subset of the set of graphic characters of @code{Wide_Character}. Any
6400 character set ``localizations'' should be reflected in the results of
6401 the subprograms defined in the language-defined package
6402 @code{Characters.Handling} (see A.3) available in such a mode. In a mode with
6403 an alternative interpretation of @code{Character}, the implementation should
6404 also support a corresponding change in what is a legal
6405 @code{identifier_letter}.
6407 Not all wide character modes follow this advice, in particular the JIS
6408 and IEC modes reflect standard usage in Japan, and in these encoding,
6409 the upper half of the Latin-1 set is not part of the wide-character
6410 subset, since the most significant bit is used for wide character
6411 encoding. However, this only applies to the external forms. Internally
6412 there is no such restriction.
6414 @cindex Integer types
6415 @unnumberedsec 3.5.4(28): Integer Types
6419 An implementation should support @code{Long_Integer} in addition to
6420 @code{Integer} if the target machine supports 32-bit (or longer)
6421 arithmetic. No other named integer subtypes are recommended for package
6422 @code{Standard}. Instead, appropriate named integer subtypes should be
6423 provided in the library package @code{Interfaces} (see B.2).
6425 @code{Long_Integer} is supported. Other standard integer types are supported
6426 so this advice is not fully followed. These types
6427 are supported for convenient interface to C, and so that all hardware
6428 types of the machine are easily available.
6429 @unnumberedsec 3.5.4(29): Integer Types
6433 An implementation for a two's complement machine should support
6434 modular types with a binary modulus up to @code{System.Max_Int*2+2}. An
6435 implementation should support a non-binary modules up to @code{Integer'Last}.
6439 @cindex Enumeration values
6440 @unnumberedsec 3.5.5(8): Enumeration Values
6443 For the evaluation of a call on @code{@var{S}'Pos} for an enumeration
6444 subtype, if the value of the operand does not correspond to the internal
6445 code for any enumeration literal of its type (perhaps due to an
6446 un-initialized variable), then the implementation should raise
6447 @code{Program_Error}. This is particularly important for enumeration
6448 types with noncontiguous internal codes specified by an
6449 enumeration_representation_clause.
6454 @unnumberedsec 3.5.7(17): Float Types
6457 An implementation should support @code{Long_Float} in addition to
6458 @code{Float} if the target machine supports 11 or more digits of
6459 precision. No other named floating point subtypes are recommended for
6460 package @code{Standard}. Instead, appropriate named floating point subtypes
6461 should be provided in the library package @code{Interfaces} (see B.2).
6463 @code{Short_Float} and @code{Long_Long_Float} are also provided. The
6464 former provides improved compatibility with other implementations
6465 supporting this type. The latter corresponds to the highest precision
6466 floating-point type supported by the hardware. On most machines, this
6467 will be the same as @code{Long_Float}, but on some machines, it will
6468 correspond to the IEEE extended form. The notable case is all ia32
6469 (x86) implementations, where @code{Long_Long_Float} corresponds to
6470 the 80-bit extended precision format supported in hardware on this
6471 processor. Note that the 128-bit format on SPARC is not supported,
6472 since this is a software rather than a hardware format.
6474 @cindex Multidimensional arrays
6475 @cindex Arrays, multidimensional
6476 @unnumberedsec 3.6.2(11): Multidimensional Arrays
6479 An implementation should normally represent multidimensional arrays in
6480 row-major order, consistent with the notation used for multidimensional
6481 array aggregates (see 4.3.3). However, if a pragma @code{Convention}
6482 (@code{Fortran}, @dots{}) applies to a multidimensional array type, then
6483 column-major order should be used instead (see B.5, ``Interfacing with
6488 @findex Duration'Small
6489 @unnumberedsec 9.6(30-31): Duration'Small
6492 Whenever possible in an implementation, the value of @code{Duration'Small}
6493 should be no greater than 100 microseconds.
6495 Followed. (@code{Duration'Small} = 10**(@minus{}9)).
6499 The time base for @code{delay_relative_statements} should be monotonic;
6500 it need not be the same time base as used for @code{Calendar.Clock}.
6504 @unnumberedsec 10.2.1(12): Consistent Representation
6507 In an implementation, a type declared in a pre-elaborated package should
6508 have the same representation in every elaboration of a given version of
6509 the package, whether the elaborations occur in distinct executions of
6510 the same program, or in executions of distinct programs or partitions
6511 that include the given version.
6513 Followed, except in the case of tagged types. Tagged types involve
6514 implicit pointers to a local copy of a dispatch table, and these pointers
6515 have representations which thus depend on a particular elaboration of the
6516 package. It is not easy to see how it would be possible to follow this
6517 advice without severely impacting efficiency of execution.
6519 @cindex Exception information
6520 @unnumberedsec 11.4.1(19): Exception Information
6523 @code{Exception_Message} by default and @code{Exception_Information}
6524 should produce information useful for
6525 debugging. @code{Exception_Message} should be short, about one
6526 line. @code{Exception_Information} can be long. @code{Exception_Message}
6527 should not include the
6528 @code{Exception_Name}. @code{Exception_Information} should include both
6529 the @code{Exception_Name} and the @code{Exception_Message}.
6531 Followed. For each exception that doesn't have a specified
6532 @code{Exception_Message}, the compiler generates one containing the location
6533 of the raise statement. This location has the form ``file:line'', where
6534 file is the short file name (without path information) and line is the line
6535 number in the file. Note that in the case of the Zero Cost Exception
6536 mechanism, these messages become redundant with the Exception_Information that
6537 contains a full backtrace of the calling sequence, so they are disabled.
6538 To disable explicitly the generation of the source location message, use the
6539 Pragma @code{Discard_Names}.
6541 @cindex Suppression of checks
6542 @cindex Checks, suppression of
6543 @unnumberedsec 11.5(28): Suppression of Checks
6546 The implementation should minimize the code executed for checks that
6547 have been suppressed.
6551 @cindex Representation clauses
6552 @unnumberedsec 13.1 (21-24): Representation Clauses
6555 The recommended level of support for all representation items is
6556 qualified as follows:
6560 An implementation need not support representation items containing
6561 non-static expressions, except that an implementation should support a
6562 representation item for a given entity if each non-static expression in
6563 the representation item is a name that statically denotes a constant
6564 declared before the entity.
6566 Followed. In fact, GNAT goes beyond the recommended level of support
6567 by allowing nonstatic expressions in some representation clauses even
6568 without the need to declare constants initialized with the values of
6572 @smallexample @c ada
6575 for Y'Address use X'Address;>>
6581 An implementation need not support a specification for the @code{Size}
6582 for a given composite subtype, nor the size or storage place for an
6583 object (including a component) of a given composite subtype, unless the
6584 constraints on the subtype and its composite subcomponents (if any) are
6585 all static constraints.
6587 Followed. Size Clauses are not permitted on non-static components, as
6592 An aliased component, or a component whose type is by-reference, should
6593 always be allocated at an addressable location.
6597 @cindex Packed types
6598 @unnumberedsec 13.2(6-8): Packed Types
6601 If a type is packed, then the implementation should try to minimize
6602 storage allocated to objects of the type, possibly at the expense of
6603 speed of accessing components, subject to reasonable complexity in
6604 addressing calculations.
6608 The recommended level of support pragma @code{Pack} is:
6610 For a packed record type, the components should be packed as tightly as
6611 possible subject to the Sizes of the component subtypes, and subject to
6612 any @code{record_representation_clause} that applies to the type; the
6613 implementation may, but need not, reorder components or cross aligned
6614 word boundaries to improve the packing. A component whose @code{Size} is
6615 greater than the word size may be allocated an integral number of words.
6617 Followed. Tight packing of arrays is supported for all component sizes
6618 up to 64-bits. If the array component size is 1 (that is to say, if
6619 the component is a boolean type or an enumeration type with two values)
6620 then values of the type are implicitly initialized to zero. This
6621 happens both for objects of the packed type, and for objects that have a
6622 subcomponent of the packed type.
6626 An implementation should support Address clauses for imported
6630 @cindex @code{Address} clauses
6631 @unnumberedsec 13.3(14-19): Address Clauses
6635 For an array @var{X}, @code{@var{X}'Address} should point at the first
6636 component of the array, and not at the array bounds.
6642 The recommended level of support for the @code{Address} attribute is:
6644 @code{@var{X}'Address} should produce a useful result if @var{X} is an
6645 object that is aliased or of a by-reference type, or is an entity whose
6646 @code{Address} has been specified.
6648 Followed. A valid address will be produced even if none of those
6649 conditions have been met. If necessary, the object is forced into
6650 memory to ensure the address is valid.
6654 An implementation should support @code{Address} clauses for imported
6661 Objects (including subcomponents) that are aliased or of a by-reference
6662 type should be allocated on storage element boundaries.
6668 If the @code{Address} of an object is specified, or it is imported or exported,
6669 then the implementation should not perform optimizations based on
6670 assumptions of no aliases.
6674 @cindex @code{Alignment} clauses
6675 @unnumberedsec 13.3(29-35): Alignment Clauses
6678 The recommended level of support for the @code{Alignment} attribute for
6681 An implementation should support specified Alignments that are factors
6682 and multiples of the number of storage elements per word, subject to the
6689 An implementation need not support specified @code{Alignment}s for
6690 combinations of @code{Size}s and @code{Alignment}s that cannot be easily
6691 loaded and stored by available machine instructions.
6697 An implementation need not support specified @code{Alignment}s that are
6698 greater than the maximum @code{Alignment} the implementation ever returns by
6705 The recommended level of support for the @code{Alignment} attribute for
6708 Same as above, for subtypes, but in addition:
6714 For stand-alone library-level objects of statically constrained
6715 subtypes, the implementation should support all @code{Alignment}s
6716 supported by the target linker. For example, page alignment is likely to
6717 be supported for such objects, but not for subtypes.
6721 @cindex @code{Size} clauses
6722 @unnumberedsec 13.3(42-43): Size Clauses
6725 The recommended level of support for the @code{Size} attribute of
6728 A @code{Size} clause should be supported for an object if the specified
6729 @code{Size} is at least as large as its subtype's @code{Size}, and
6730 corresponds to a size in storage elements that is a multiple of the
6731 object's @code{Alignment} (if the @code{Alignment} is nonzero).
6735 @unnumberedsec 13.3(50-56): Size Clauses
6738 If the @code{Size} of a subtype is specified, and allows for efficient
6739 independent addressability (see 9.10) on the target architecture, then
6740 the @code{Size} of the following objects of the subtype should equal the
6741 @code{Size} of the subtype:
6743 Aliased objects (including components).
6749 @code{Size} clause on a composite subtype should not affect the
6750 internal layout of components.
6752 Followed. But note that this can be overridden by use of the implementation
6753 pragma Implicit_Packing in the case of packed arrays.
6757 The recommended level of support for the @code{Size} attribute of subtypes is:
6761 The @code{Size} (if not specified) of a static discrete or fixed point
6762 subtype should be the number of bits needed to represent each value
6763 belonging to the subtype using an unbiased representation, leaving space
6764 for a sign bit only if the subtype contains negative values. If such a
6765 subtype is a first subtype, then an implementation should support a
6766 specified @code{Size} for it that reflects this representation.
6772 For a subtype implemented with levels of indirection, the @code{Size}
6773 should include the size of the pointers, but not the size of what they
6778 @cindex @code{Component_Size} clauses
6779 @unnumberedsec 13.3(71-73): Component Size Clauses
6782 The recommended level of support for the @code{Component_Size}
6787 An implementation need not support specified @code{Component_Sizes} that are
6788 less than the @code{Size} of the component subtype.
6794 An implementation should support specified @code{Component_Size}s that
6795 are factors and multiples of the word size. For such
6796 @code{Component_Size}s, the array should contain no gaps between
6797 components. For other @code{Component_Size}s (if supported), the array
6798 should contain no gaps between components when packing is also
6799 specified; the implementation should forbid this combination in cases
6800 where it cannot support a no-gaps representation.
6804 @cindex Enumeration representation clauses
6805 @cindex Representation clauses, enumeration
6806 @unnumberedsec 13.4(9-10): Enumeration Representation Clauses
6809 The recommended level of support for enumeration representation clauses
6812 An implementation need not support enumeration representation clauses
6813 for boolean types, but should at minimum support the internal codes in
6814 the range @code{System.Min_Int.System.Max_Int}.
6818 @cindex Record representation clauses
6819 @cindex Representation clauses, records
6820 @unnumberedsec 13.5.1(17-22): Record Representation Clauses
6823 The recommended level of support for
6824 @*@code{record_representation_clauses} is:
6826 An implementation should support storage places that can be extracted
6827 with a load, mask, shift sequence of machine code, and set with a load,
6828 shift, mask, store sequence, given the available machine instructions
6835 A storage place should be supported if its size is equal to the
6836 @code{Size} of the component subtype, and it starts and ends on a
6837 boundary that obeys the @code{Alignment} of the component subtype.
6843 If the default bit ordering applies to the declaration of a given type,
6844 then for a component whose subtype's @code{Size} is less than the word
6845 size, any storage place that does not cross an aligned word boundary
6846 should be supported.
6852 An implementation may reserve a storage place for the tag field of a
6853 tagged type, and disallow other components from overlapping that place.
6855 Followed. The storage place for the tag field is the beginning of the tagged
6856 record, and its size is Address'Size. GNAT will reject an explicit component
6857 clause for the tag field.
6861 An implementation need not support a @code{component_clause} for a
6862 component of an extension part if the storage place is not after the
6863 storage places of all components of the parent type, whether or not
6864 those storage places had been specified.
6866 Followed. The above advice on record representation clauses is followed,
6867 and all mentioned features are implemented.
6869 @cindex Storage place attributes
6870 @unnumberedsec 13.5.2(5): Storage Place Attributes
6873 If a component is represented using some form of pointer (such as an
6874 offset) to the actual data of the component, and this data is contiguous
6875 with the rest of the object, then the storage place attributes should
6876 reflect the place of the actual data, not the pointer. If a component is
6877 allocated discontinuously from the rest of the object, then a warning
6878 should be generated upon reference to one of its storage place
6881 Followed. There are no such components in GNAT@.
6883 @cindex Bit ordering
6884 @unnumberedsec 13.5.3(7-8): Bit Ordering
6887 The recommended level of support for the non-default bit ordering is:
6891 If @code{Word_Size} = @code{Storage_Unit}, then the implementation
6892 should support the non-default bit ordering in addition to the default
6895 Followed. Word size does not equal storage size in this implementation.
6896 Thus non-default bit ordering is not supported.
6898 @cindex @code{Address}, as private type
6899 @unnumberedsec 13.7(37): Address as Private
6902 @code{Address} should be of a private type.
6906 @cindex Operations, on @code{Address}
6907 @cindex @code{Address}, operations of
6908 @unnumberedsec 13.7.1(16): Address Operations
6911 Operations in @code{System} and its children should reflect the target
6912 environment semantics as closely as is reasonable. For example, on most
6913 machines, it makes sense for address arithmetic to ``wrap around''.
6914 Operations that do not make sense should raise @code{Program_Error}.
6916 Followed. Address arithmetic is modular arithmetic that wraps around. No
6917 operation raises @code{Program_Error}, since all operations make sense.
6919 @cindex Unchecked conversion
6920 @unnumberedsec 13.9(14-17): Unchecked Conversion
6923 The @code{Size} of an array object should not include its bounds; hence,
6924 the bounds should not be part of the converted data.
6930 The implementation should not generate unnecessary run-time checks to
6931 ensure that the representation of @var{S} is a representation of the
6932 target type. It should take advantage of the permission to return by
6933 reference when possible. Restrictions on unchecked conversions should be
6934 avoided unless required by the target environment.
6936 Followed. There are no restrictions on unchecked conversion. A warning is
6937 generated if the source and target types do not have the same size since
6938 the semantics in this case may be target dependent.
6942 The recommended level of support for unchecked conversions is:
6946 Unchecked conversions should be supported and should be reversible in
6947 the cases where this clause defines the result. To enable meaningful use
6948 of unchecked conversion, a contiguous representation should be used for
6949 elementary subtypes, for statically constrained array subtypes whose
6950 component subtype is one of the subtypes described in this paragraph,
6951 and for record subtypes without discriminants whose component subtypes
6952 are described in this paragraph.
6956 @cindex Heap usage, implicit
6957 @unnumberedsec 13.11(23-25): Implicit Heap Usage
6960 An implementation should document any cases in which it dynamically
6961 allocates heap storage for a purpose other than the evaluation of an
6964 Followed, the only other points at which heap storage is dynamically
6965 allocated are as follows:
6969 At initial elaboration time, to allocate dynamically sized global
6973 To allocate space for a task when a task is created.
6976 To extend the secondary stack dynamically when needed. The secondary
6977 stack is used for returning variable length results.
6982 A default (implementation-provided) storage pool for an
6983 access-to-constant type should not have overhead to support deallocation of
6990 A storage pool for an anonymous access type should be created at the
6991 point of an allocator for the type, and be reclaimed when the designated
6992 object becomes inaccessible.
6996 @cindex Unchecked deallocation
6997 @unnumberedsec 13.11.2(17): Unchecked De-allocation
7000 For a standard storage pool, @code{Free} should actually reclaim the
7005 @cindex Stream oriented attributes
7006 @unnumberedsec 13.13.2(17): Stream Oriented Attributes
7009 If a stream element is the same size as a storage element, then the
7010 normal in-memory representation should be used by @code{Read} and
7011 @code{Write} for scalar objects. Otherwise, @code{Read} and @code{Write}
7012 should use the smallest number of stream elements needed to represent
7013 all values in the base range of the scalar type.
7016 Followed. By default, GNAT uses the interpretation suggested by AI-195,
7017 which specifies using the size of the first subtype.
7018 However, such an implementation is based on direct binary
7019 representations and is therefore target- and endianness-dependent.
7020 To address this issue, GNAT also supplies an alternate implementation
7021 of the stream attributes @code{Read} and @code{Write},
7022 which uses the target-independent XDR standard representation
7024 @cindex XDR representation
7025 @cindex @code{Read} attribute
7026 @cindex @code{Write} attribute
7027 @cindex Stream oriented attributes
7028 The XDR implementation is provided as an alternative body of the
7029 @code{System.Stream_Attributes} package, in the file
7030 @file{s-strxdr.adb} in the GNAT library.
7031 There is no @file{s-strxdr.ads} file.
7032 In order to install the XDR implementation, do the following:
7034 @item Replace the default implementation of the
7035 @code{System.Stream_Attributes} package with the XDR implementation.
7036 For example on a Unix platform issue the commands:
7038 $ mv s-stratt.adb s-strold.adb
7039 $ mv s-strxdr.adb s-stratt.adb
7043 Rebuild the GNAT run-time library as documented in
7044 @ref{GNAT and Libraries,,, gnat_ugn, @value{EDITION} User's Guide}.
7047 @unnumberedsec A.1(52): Names of Predefined Numeric Types
7050 If an implementation provides additional named predefined integer types,
7051 then the names should end with @samp{Integer} as in
7052 @samp{Long_Integer}. If an implementation provides additional named
7053 predefined floating point types, then the names should end with
7054 @samp{Float} as in @samp{Long_Float}.
7058 @findex Ada.Characters.Handling
7059 @unnumberedsec A.3.2(49): @code{Ada.Characters.Handling}
7062 If an implementation provides a localized definition of @code{Character}
7063 or @code{Wide_Character}, then the effects of the subprograms in
7064 @code{Characters.Handling} should reflect the localizations. See also
7067 Followed. GNAT provides no such localized definitions.
7069 @cindex Bounded-length strings
7070 @unnumberedsec A.4.4(106): Bounded-Length String Handling
7073 Bounded string objects should not be implemented by implicit pointers
7074 and dynamic allocation.
7076 Followed. No implicit pointers or dynamic allocation are used.
7078 @cindex Random number generation
7079 @unnumberedsec A.5.2(46-47): Random Number Generation
7082 Any storage associated with an object of type @code{Generator} should be
7083 reclaimed on exit from the scope of the object.
7089 If the generator period is sufficiently long in relation to the number
7090 of distinct initiator values, then each possible value of
7091 @code{Initiator} passed to @code{Reset} should initiate a sequence of
7092 random numbers that does not, in a practical sense, overlap the sequence
7093 initiated by any other value. If this is not possible, then the mapping
7094 between initiator values and generator states should be a rapidly
7095 varying function of the initiator value.
7097 Followed. The generator period is sufficiently long for the first
7098 condition here to hold true.
7100 @findex Get_Immediate
7101 @unnumberedsec A.10.7(23): @code{Get_Immediate}
7104 The @code{Get_Immediate} procedures should be implemented with
7105 unbuffered input. For a device such as a keyboard, input should be
7106 @dfn{available} if a key has already been typed, whereas for a disk
7107 file, input should always be available except at end of file. For a file
7108 associated with a keyboard-like device, any line-editing features of the
7109 underlying operating system should be disabled during the execution of
7110 @code{Get_Immediate}.
7112 Followed on all targets except VxWorks. For VxWorks, there is no way to
7113 provide this functionality that does not result in the input buffer being
7114 flushed before the @code{Get_Immediate} call. A special unit
7115 @code{Interfaces.Vxworks.IO} is provided that contains routines to enable
7119 @unnumberedsec B.1(39-41): Pragma @code{Export}
7122 If an implementation supports pragma @code{Export} to a given language,
7123 then it should also allow the main subprogram to be written in that
7124 language. It should support some mechanism for invoking the elaboration
7125 of the Ada library units included in the system, and for invoking the
7126 finalization of the environment task. On typical systems, the
7127 recommended mechanism is to provide two subprograms whose link names are
7128 @code{adainit} and @code{adafinal}. @code{adainit} should contain the
7129 elaboration code for library units. @code{adafinal} should contain the
7130 finalization code. These subprograms should have no effect the second
7131 and subsequent time they are called.
7137 Automatic elaboration of pre-elaborated packages should be
7138 provided when pragma @code{Export} is supported.
7140 Followed when the main program is in Ada. If the main program is in a
7141 foreign language, then
7142 @code{adainit} must be called to elaborate pre-elaborated
7147 For each supported convention @var{L} other than @code{Intrinsic}, an
7148 implementation should support @code{Import} and @code{Export} pragmas
7149 for objects of @var{L}-compatible types and for subprograms, and pragma
7150 @code{Convention} for @var{L}-eligible types and for subprograms,
7151 presuming the other language has corresponding features. Pragma
7152 @code{Convention} need not be supported for scalar types.
7156 @cindex Package @code{Interfaces}
7158 @unnumberedsec B.2(12-13): Package @code{Interfaces}
7161 For each implementation-defined convention identifier, there should be a
7162 child package of package Interfaces with the corresponding name. This
7163 package should contain any declarations that would be useful for
7164 interfacing to the language (implementation) represented by the
7165 convention. Any declarations useful for interfacing to any language on
7166 the given hardware architecture should be provided directly in
7169 Followed. An additional package not defined
7170 in the Ada Reference Manual is @code{Interfaces.CPP}, used
7171 for interfacing to C++.
7175 An implementation supporting an interface to C, COBOL, or Fortran should
7176 provide the corresponding package or packages described in the following
7179 Followed. GNAT provides all the packages described in this section.
7181 @cindex C, interfacing with
7182 @unnumberedsec B.3(63-71): Interfacing with C
7185 An implementation should support the following interface correspondences
7192 An Ada procedure corresponds to a void-returning C function.
7198 An Ada function corresponds to a non-void C function.
7204 An Ada @code{in} scalar parameter is passed as a scalar argument to a C
7211 An Ada @code{in} parameter of an access-to-object type with designated
7212 type @var{T} is passed as a @code{@var{t}*} argument to a C function,
7213 where @var{t} is the C type corresponding to the Ada type @var{T}.
7219 An Ada access @var{T} parameter, or an Ada @code{out} or @code{in out}
7220 parameter of an elementary type @var{T}, is passed as a @code{@var{t}*}
7221 argument to a C function, where @var{t} is the C type corresponding to
7222 the Ada type @var{T}. In the case of an elementary @code{out} or
7223 @code{in out} parameter, a pointer to a temporary copy is used to
7224 preserve by-copy semantics.
7230 An Ada parameter of a record type @var{T}, of any mode, is passed as a
7231 @code{@var{t}*} argument to a C function, where @var{t} is the C
7232 structure corresponding to the Ada type @var{T}.
7234 Followed. This convention may be overridden by the use of the C_Pass_By_Copy
7235 pragma, or Convention, or by explicitly specifying the mechanism for a given
7236 call using an extended import or export pragma.
7240 An Ada parameter of an array type with component type @var{T}, of any
7241 mode, is passed as a @code{@var{t}*} argument to a C function, where
7242 @var{t} is the C type corresponding to the Ada type @var{T}.
7248 An Ada parameter of an access-to-subprogram type is passed as a pointer
7249 to a C function whose prototype corresponds to the designated
7250 subprogram's specification.
7254 @cindex COBOL, interfacing with
7255 @unnumberedsec B.4(95-98): Interfacing with COBOL
7258 An Ada implementation should support the following interface
7259 correspondences between Ada and COBOL@.
7265 An Ada access @var{T} parameter is passed as a @samp{BY REFERENCE} data item of
7266 the COBOL type corresponding to @var{T}.
7272 An Ada in scalar parameter is passed as a @samp{BY CONTENT} data item of
7273 the corresponding COBOL type.
7279 Any other Ada parameter is passed as a @samp{BY REFERENCE} data item of the
7280 COBOL type corresponding to the Ada parameter type; for scalars, a local
7281 copy is used if necessary to ensure by-copy semantics.
7285 @cindex Fortran, interfacing with
7286 @unnumberedsec B.5(22-26): Interfacing with Fortran
7289 An Ada implementation should support the following interface
7290 correspondences between Ada and Fortran:
7296 An Ada procedure corresponds to a Fortran subroutine.
7302 An Ada function corresponds to a Fortran function.
7308 An Ada parameter of an elementary, array, or record type @var{T} is
7309 passed as a @var{T} argument to a Fortran procedure, where @var{T} is
7310 the Fortran type corresponding to the Ada type @var{T}, and where the
7311 INTENT attribute of the corresponding dummy argument matches the Ada
7312 formal parameter mode; the Fortran implementation's parameter passing
7313 conventions are used. For elementary types, a local copy is used if
7314 necessary to ensure by-copy semantics.
7320 An Ada parameter of an access-to-subprogram type is passed as a
7321 reference to a Fortran procedure whose interface corresponds to the
7322 designated subprogram's specification.
7326 @cindex Machine operations
7327 @unnumberedsec C.1(3-5): Access to Machine Operations
7330 The machine code or intrinsic support should allow access to all
7331 operations normally available to assembly language programmers for the
7332 target environment, including privileged instructions, if any.
7338 The interfacing pragmas (see Annex B) should support interface to
7339 assembler; the default assembler should be associated with the
7340 convention identifier @code{Assembler}.
7346 If an entity is exported to assembly language, then the implementation
7347 should allocate it at an addressable location, and should ensure that it
7348 is retained by the linking process, even if not otherwise referenced
7349 from the Ada code. The implementation should assume that any call to a
7350 machine code or assembler subprogram is allowed to read or update every
7351 object that is specified as exported.
7355 @unnumberedsec C.1(10-16): Access to Machine Operations
7358 The implementation should ensure that little or no overhead is
7359 associated with calling intrinsic and machine-code subprograms.
7361 Followed for both intrinsics and machine-code subprograms.
7365 It is recommended that intrinsic subprograms be provided for convenient
7366 access to any machine operations that provide special capabilities or
7367 efficiency and that are not otherwise available through the language
7370 Followed. A full set of machine operation intrinsic subprograms is provided.
7374 Atomic read-modify-write operations---e.g.@:, test and set, compare and
7375 swap, decrement and test, enqueue/dequeue.
7377 Followed on any target supporting such operations.
7381 Standard numeric functions---e.g.@:, sin, log.
7383 Followed on any target supporting such operations.
7387 String manipulation operations---e.g.@:, translate and test.
7389 Followed on any target supporting such operations.
7393 Vector operations---e.g.@:, compare vector against thresholds.
7395 Followed on any target supporting such operations.
7399 Direct operations on I/O ports.
7401 Followed on any target supporting such operations.
7403 @cindex Interrupt support
7404 @unnumberedsec C.3(28): Interrupt Support
7407 If the @code{Ceiling_Locking} policy is not in effect, the
7408 implementation should provide means for the application to specify which
7409 interrupts are to be blocked during protected actions, if the underlying
7410 system allows for a finer-grain control of interrupt blocking.
7412 Followed. The underlying system does not allow for finer-grain control
7413 of interrupt blocking.
7415 @cindex Protected procedure handlers
7416 @unnumberedsec C.3.1(20-21): Protected Procedure Handlers
7419 Whenever possible, the implementation should allow interrupt handlers to
7420 be called directly by the hardware.
7424 This is never possible under IRIX, so this is followed by default.
7426 Followed on any target where the underlying operating system permits
7431 Whenever practical, violations of any
7432 implementation-defined restrictions should be detected before run time.
7434 Followed. Compile time warnings are given when possible.
7436 @cindex Package @code{Interrupts}
7438 @unnumberedsec C.3.2(25): Package @code{Interrupts}
7442 If implementation-defined forms of interrupt handler procedures are
7443 supported, such as protected procedures with parameters, then for each
7444 such form of a handler, a type analogous to @code{Parameterless_Handler}
7445 should be specified in a child package of @code{Interrupts}, with the
7446 same operations as in the predefined package Interrupts.
7450 @cindex Pre-elaboration requirements
7451 @unnumberedsec C.4(14): Pre-elaboration Requirements
7454 It is recommended that pre-elaborated packages be implemented in such a
7455 way that there should be little or no code executed at run time for the
7456 elaboration of entities not already covered by the Implementation
7459 Followed. Executable code is generated in some cases, e.g.@: loops
7460 to initialize large arrays.
7462 @unnumberedsec C.5(8): Pragma @code{Discard_Names}
7466 If the pragma applies to an entity, then the implementation should
7467 reduce the amount of storage used for storing names associated with that
7472 @cindex Package @code{Task_Attributes}
7473 @findex Task_Attributes
7474 @unnumberedsec C.7.2(30): The Package Task_Attributes
7477 Some implementations are targeted to domains in which memory use at run
7478 time must be completely deterministic. For such implementations, it is
7479 recommended that the storage for task attributes will be pre-allocated
7480 statically and not from the heap. This can be accomplished by either
7481 placing restrictions on the number and the size of the task's
7482 attributes, or by using the pre-allocated storage for the first @var{N}
7483 attribute objects, and the heap for the others. In the latter case,
7484 @var{N} should be documented.
7486 Not followed. This implementation is not targeted to such a domain.
7488 @cindex Locking Policies
7489 @unnumberedsec D.3(17): Locking Policies
7493 The implementation should use names that end with @samp{_Locking} for
7494 locking policies defined by the implementation.
7496 Followed. A single implementation-defined locking policy is defined,
7497 whose name (@code{Inheritance_Locking}) follows this suggestion.
7499 @cindex Entry queuing policies
7500 @unnumberedsec D.4(16): Entry Queuing Policies
7503 Names that end with @samp{_Queuing} should be used
7504 for all implementation-defined queuing policies.
7506 Followed. No such implementation-defined queuing policies exist.
7508 @cindex Preemptive abort
7509 @unnumberedsec D.6(9-10): Preemptive Abort
7512 Even though the @code{abort_statement} is included in the list of
7513 potentially blocking operations (see 9.5.1), it is recommended that this
7514 statement be implemented in a way that never requires the task executing
7515 the @code{abort_statement} to block.
7521 On a multi-processor, the delay associated with aborting a task on
7522 another processor should be bounded; the implementation should use
7523 periodic polling, if necessary, to achieve this.
7527 @cindex Tasking restrictions
7528 @unnumberedsec D.7(21): Tasking Restrictions
7531 When feasible, the implementation should take advantage of the specified
7532 restrictions to produce a more efficient implementation.
7534 GNAT currently takes advantage of these restrictions by providing an optimized
7535 run time when the Ravenscar profile and the GNAT restricted run time set
7536 of restrictions are specified. See pragma @code{Profile (Ravenscar)} and
7537 pragma @code{Profile (Restricted)} for more details.
7539 @cindex Time, monotonic
7540 @unnumberedsec D.8(47-49): Monotonic Time
7543 When appropriate, implementations should provide configuration
7544 mechanisms to change the value of @code{Tick}.
7546 Such configuration mechanisms are not appropriate to this implementation
7547 and are thus not supported.
7551 It is recommended that @code{Calendar.Clock} and @code{Real_Time.Clock}
7552 be implemented as transformations of the same time base.
7558 It is recommended that the @dfn{best} time base which exists in
7559 the underlying system be available to the application through
7560 @code{Clock}. @dfn{Best} may mean highest accuracy or largest range.
7564 @cindex Partition communication subsystem
7566 @unnumberedsec E.5(28-29): Partition Communication Subsystem
7569 Whenever possible, the PCS on the called partition should allow for
7570 multiple tasks to call the RPC-receiver with different messages and
7571 should allow them to block until the corresponding subprogram body
7574 Followed by GLADE, a separately supplied PCS that can be used with
7579 The @code{Write} operation on a stream of type @code{Params_Stream_Type}
7580 should raise @code{Storage_Error} if it runs out of space trying to
7581 write the @code{Item} into the stream.
7583 Followed by GLADE, a separately supplied PCS that can be used with
7586 @cindex COBOL support
7587 @unnumberedsec F(7): COBOL Support
7590 If COBOL (respectively, C) is widely supported in the target
7591 environment, implementations supporting the Information Systems Annex
7592 should provide the child package @code{Interfaces.COBOL} (respectively,
7593 @code{Interfaces.C}) specified in Annex B and should support a
7594 @code{convention_identifier} of COBOL (respectively, C) in the interfacing
7595 pragmas (see Annex B), thus allowing Ada programs to interface with
7596 programs written in that language.
7600 @cindex Decimal radix support
7601 @unnumberedsec F.1(2): Decimal Radix Support
7604 Packed decimal should be used as the internal representation for objects
7605 of subtype @var{S} when @var{S}'Machine_Radix = 10.
7607 Not followed. GNAT ignores @var{S}'Machine_Radix and always uses binary
7611 @unnumberedsec G: Numerics
7614 If Fortran (respectively, C) is widely supported in the target
7615 environment, implementations supporting the Numerics Annex
7616 should provide the child package @code{Interfaces.Fortran} (respectively,
7617 @code{Interfaces.C}) specified in Annex B and should support a
7618 @code{convention_identifier} of Fortran (respectively, C) in the interfacing
7619 pragmas (see Annex B), thus allowing Ada programs to interface with
7620 programs written in that language.
7624 @cindex Complex types
7625 @unnumberedsec G.1.1(56-58): Complex Types
7628 Because the usual mathematical meaning of multiplication of a complex
7629 operand and a real operand is that of the scaling of both components of
7630 the former by the latter, an implementation should not perform this
7631 operation by first promoting the real operand to complex type and then
7632 performing a full complex multiplication. In systems that, in the
7633 future, support an Ada binding to IEC 559:1989, the latter technique
7634 will not generate the required result when one of the components of the
7635 complex operand is infinite. (Explicit multiplication of the infinite
7636 component by the zero component obtained during promotion yields a NaN
7637 that propagates into the final result.) Analogous advice applies in the
7638 case of multiplication of a complex operand and a pure-imaginary
7639 operand, and in the case of division of a complex operand by a real or
7640 pure-imaginary operand.
7646 Similarly, because the usual mathematical meaning of addition of a
7647 complex operand and a real operand is that the imaginary operand remains
7648 unchanged, an implementation should not perform this operation by first
7649 promoting the real operand to complex type and then performing a full
7650 complex addition. In implementations in which the @code{Signed_Zeros}
7651 attribute of the component type is @code{True} (and which therefore
7652 conform to IEC 559:1989 in regard to the handling of the sign of zero in
7653 predefined arithmetic operations), the latter technique will not
7654 generate the required result when the imaginary component of the complex
7655 operand is a negatively signed zero. (Explicit addition of the negative
7656 zero to the zero obtained during promotion yields a positive zero.)
7657 Analogous advice applies in the case of addition of a complex operand
7658 and a pure-imaginary operand, and in the case of subtraction of a
7659 complex operand and a real or pure-imaginary operand.
7665 Implementations in which @code{Real'Signed_Zeros} is @code{True} should
7666 attempt to provide a rational treatment of the signs of zero results and
7667 result components. As one example, the result of the @code{Argument}
7668 function should have the sign of the imaginary component of the
7669 parameter @code{X} when the point represented by that parameter lies on
7670 the positive real axis; as another, the sign of the imaginary component
7671 of the @code{Compose_From_Polar} function should be the same as
7672 (respectively, the opposite of) that of the @code{Argument} parameter when that
7673 parameter has a value of zero and the @code{Modulus} parameter has a
7674 nonnegative (respectively, negative) value.
7678 @cindex Complex elementary functions
7679 @unnumberedsec G.1.2(49): Complex Elementary Functions
7682 Implementations in which @code{Complex_Types.Real'Signed_Zeros} is
7683 @code{True} should attempt to provide a rational treatment of the signs
7684 of zero results and result components. For example, many of the complex
7685 elementary functions have components that are odd functions of one of
7686 the parameter components; in these cases, the result component should
7687 have the sign of the parameter component at the origin. Other complex
7688 elementary functions have zero components whose sign is opposite that of
7689 a parameter component at the origin, or is always positive or always
7694 @cindex Accuracy requirements
7695 @unnumberedsec G.2.4(19): Accuracy Requirements
7698 The versions of the forward trigonometric functions without a
7699 @code{Cycle} parameter should not be implemented by calling the
7700 corresponding version with a @code{Cycle} parameter of
7701 @code{2.0*Numerics.Pi}, since this will not provide the required
7702 accuracy in some portions of the domain. For the same reason, the
7703 version of @code{Log} without a @code{Base} parameter should not be
7704 implemented by calling the corresponding version with a @code{Base}
7705 parameter of @code{Numerics.e}.
7709 @cindex Complex arithmetic accuracy
7710 @cindex Accuracy, complex arithmetic
7711 @unnumberedsec G.2.6(15): Complex Arithmetic Accuracy
7715 The version of the @code{Compose_From_Polar} function without a
7716 @code{Cycle} parameter should not be implemented by calling the
7717 corresponding version with a @code{Cycle} parameter of
7718 @code{2.0*Numerics.Pi}, since this will not provide the required
7719 accuracy in some portions of the domain.
7723 @c -----------------------------------------
7724 @node Implementation Defined Characteristics
7725 @chapter Implementation Defined Characteristics
7728 In addition to the implementation dependent pragmas and attributes, and
7729 the implementation advice, there are a number of other Ada features
7730 that are potentially implementation dependent. These are mentioned
7731 throughout the Ada Reference Manual, and are summarized in Annex M@.
7733 A requirement for conforming Ada compilers is that they provide
7734 documentation describing how the implementation deals with each of these
7735 issues. In this chapter, you will find each point in Annex M listed
7736 followed by a description in italic font of how GNAT
7740 implementation on IRIX 5.3 operating system or greater
7742 handles the implementation dependence.
7744 You can use this chapter as a guide to minimizing implementation
7745 dependent features in your programs if portability to other compilers
7746 and other operating systems is an important consideration. The numbers
7747 in each section below correspond to the paragraph number in the Ada
7753 @strong{2}. Whether or not each recommendation given in Implementation
7754 Advice is followed. See 1.1.2(37).
7757 @xref{Implementation Advice}.
7762 @strong{3}. Capacity limitations of the implementation. See 1.1.3(3).
7765 The complexity of programs that can be processed is limited only by the
7766 total amount of available virtual memory, and disk space for the
7767 generated object files.
7772 @strong{4}. Variations from the standard that are impractical to avoid
7773 given the implementation's execution environment. See 1.1.3(6).
7776 There are no variations from the standard.
7781 @strong{5}. Which @code{code_statement}s cause external
7782 interactions. See 1.1.3(10).
7785 Any @code{code_statement} can potentially cause external interactions.
7790 @strong{6}. The coded representation for the text of an Ada
7791 program. See 2.1(4).
7794 See separate section on source representation.
7799 @strong{7}. The control functions allowed in comments. See 2.1(14).
7802 See separate section on source representation.
7807 @strong{8}. The representation for an end of line. See 2.2(2).
7810 See separate section on source representation.
7815 @strong{9}. Maximum supported line length and lexical element
7816 length. See 2.2(15).
7819 The maximum line length is 255 characters and the maximum length of a
7820 lexical element is also 255 characters.
7825 @strong{10}. Implementation defined pragmas. See 2.8(14).
7829 @xref{Implementation Defined Pragmas}.
7834 @strong{11}. Effect of pragma @code{Optimize}. See 2.8(27).
7837 Pragma @code{Optimize}, if given with a @code{Time} or @code{Space}
7838 parameter, checks that the optimization flag is set, and aborts if it is
7844 @strong{12}. The sequence of characters of the value returned by
7845 @code{@var{S}'Image} when some of the graphic characters of
7846 @code{@var{S}'Wide_Image} are not defined in @code{Character}. See
7850 The sequence of characters is as defined by the wide character encoding
7851 method used for the source. See section on source representation for
7857 @strong{13}. The predefined integer types declared in
7858 @code{Standard}. See 3.5.4(25).
7862 @item Short_Short_Integer
7865 (Short) 16 bit signed
7869 64 bit signed (Alpha OpenVMS only)
7870 32 bit signed (all other targets)
7871 @item Long_Long_Integer
7878 @strong{14}. Any nonstandard integer types and the operators defined
7879 for them. See 3.5.4(26).
7882 There are no nonstandard integer types.
7887 @strong{15}. Any nonstandard real types and the operators defined for
7891 There are no nonstandard real types.
7896 @strong{16}. What combinations of requested decimal precision and range
7897 are supported for floating point types. See 3.5.7(7).
7900 The precision and range is as defined by the IEEE standard.
7905 @strong{17}. The predefined floating point types declared in
7906 @code{Standard}. See 3.5.7(16).
7913 (Short) 32 bit IEEE short
7916 @item Long_Long_Float
7917 64 bit IEEE long (80 bit IEEE long on x86 processors)
7923 @strong{18}. The small of an ordinary fixed point type. See 3.5.9(8).
7926 @code{Fine_Delta} is 2**(@minus{}63)
7931 @strong{19}. What combinations of small, range, and digits are
7932 supported for fixed point types. See 3.5.9(10).
7935 Any combinations are permitted that do not result in a small less than
7936 @code{Fine_Delta} and do not result in a mantissa larger than 63 bits.
7937 If the mantissa is larger than 53 bits on machines where Long_Long_Float
7938 is 64 bits (true of all architectures except ia32), then the output from
7939 Text_IO is accurate to only 53 bits, rather than the full mantissa. This
7940 is because floating-point conversions are used to convert fixed point.
7945 @strong{20}. The result of @code{Tags.Expanded_Name} for types declared
7946 within an unnamed @code{block_statement}. See 3.9(10).
7949 Block numbers of the form @code{B@var{nnn}}, where @var{nnn} is a
7950 decimal integer are allocated.
7955 @strong{21}. Implementation-defined attributes. See 4.1.4(12).
7958 @xref{Implementation Defined Attributes}.
7963 @strong{22}. Any implementation-defined time types. See 9.6(6).
7966 There are no implementation-defined time types.
7971 @strong{23}. The time base associated with relative delays.
7974 See 9.6(20). The time base used is that provided by the C library
7975 function @code{gettimeofday}.
7980 @strong{24}. The time base of the type @code{Calendar.Time}. See
7984 The time base used is that provided by the C library function
7985 @code{gettimeofday}.
7990 @strong{25}. The time zone used for package @code{Calendar}
7991 operations. See 9.6(24).
7994 The time zone used by package @code{Calendar} is the current system time zone
7995 setting for local time, as accessed by the C library function
8001 @strong{26}. Any limit on @code{delay_until_statements} of
8002 @code{select_statements}. See 9.6(29).
8005 There are no such limits.
8010 @strong{27}. Whether or not two non-overlapping parts of a composite
8011 object are independently addressable, in the case where packing, record
8012 layout, or @code{Component_Size} is specified for the object. See
8016 Separate components are independently addressable if they do not share
8017 overlapping storage units.
8022 @strong{28}. The representation for a compilation. See 10.1(2).
8025 A compilation is represented by a sequence of files presented to the
8026 compiler in a single invocation of the @command{gcc} command.
8031 @strong{29}. Any restrictions on compilations that contain multiple
8032 compilation_units. See 10.1(4).
8035 No single file can contain more than one compilation unit, but any
8036 sequence of files can be presented to the compiler as a single
8042 @strong{30}. The mechanisms for creating an environment and for adding
8043 and replacing compilation units. See 10.1.4(3).
8046 See separate section on compilation model.
8051 @strong{31}. The manner of explicitly assigning library units to a
8052 partition. See 10.2(2).
8055 If a unit contains an Ada main program, then the Ada units for the partition
8056 are determined by recursive application of the rules in the Ada Reference
8057 Manual section 10.2(2-6). In other words, the Ada units will be those that
8058 are needed by the main program, and then this definition of need is applied
8059 recursively to those units, and the partition contains the transitive
8060 closure determined by this relationship. In short, all the necessary units
8061 are included, with no need to explicitly specify the list. If additional
8062 units are required, e.g.@: by foreign language units, then all units must be
8063 mentioned in the context clause of one of the needed Ada units.
8065 If the partition contains no main program, or if the main program is in
8066 a language other than Ada, then GNAT
8067 provides the binder options @option{-z} and @option{-n} respectively, and in
8068 this case a list of units can be explicitly supplied to the binder for
8069 inclusion in the partition (all units needed by these units will also
8070 be included automatically). For full details on the use of these
8071 options, refer to @ref{The GNAT Make Program gnatmake,,, gnat_ugn,
8072 @value{EDITION} User's Guide}.
8077 @strong{32}. The implementation-defined means, if any, of specifying
8078 which compilation units are needed by a given compilation unit. See
8082 The units needed by a given compilation unit are as defined in
8083 the Ada Reference Manual section 10.2(2-6). There are no
8084 implementation-defined pragmas or other implementation-defined
8085 means for specifying needed units.
8090 @strong{33}. The manner of designating the main subprogram of a
8091 partition. See 10.2(7).
8094 The main program is designated by providing the name of the
8095 corresponding @file{ALI} file as the input parameter to the binder.
8100 @strong{34}. The order of elaboration of @code{library_items}. See
8104 The first constraint on ordering is that it meets the requirements of
8105 Chapter 10 of the Ada Reference Manual. This still leaves some
8106 implementation dependent choices, which are resolved by first
8107 elaborating bodies as early as possible (i.e., in preference to specs
8108 where there is a choice), and second by evaluating the immediate with
8109 clauses of a unit to determine the probably best choice, and
8110 third by elaborating in alphabetical order of unit names
8111 where a choice still remains.
8116 @strong{35}. Parameter passing and function return for the main
8117 subprogram. See 10.2(21).
8120 The main program has no parameters. It may be a procedure, or a function
8121 returning an integer type. In the latter case, the returned integer
8122 value is the return code of the program (overriding any value that
8123 may have been set by a call to @code{Ada.Command_Line.Set_Exit_Status}).
8128 @strong{36}. The mechanisms for building and running partitions. See
8132 GNAT itself supports programs with only a single partition. The GNATDIST
8133 tool provided with the GLADE package (which also includes an implementation
8134 of the PCS) provides a completely flexible method for building and running
8135 programs consisting of multiple partitions. See the separate GLADE manual
8141 @strong{37}. The details of program execution, including program
8142 termination. See 10.2(25).
8145 See separate section on compilation model.
8150 @strong{38}. The semantics of any non-active partitions supported by the
8151 implementation. See 10.2(28).
8154 Passive partitions are supported on targets where shared memory is
8155 provided by the operating system. See the GLADE reference manual for
8161 @strong{39}. The information returned by @code{Exception_Message}. See
8165 Exception message returns the null string unless a specific message has
8166 been passed by the program.
8171 @strong{40}. The result of @code{Exceptions.Exception_Name} for types
8172 declared within an unnamed @code{block_statement}. See 11.4.1(12).
8175 Blocks have implementation defined names of the form @code{B@var{nnn}}
8176 where @var{nnn} is an integer.
8181 @strong{41}. The information returned by
8182 @code{Exception_Information}. See 11.4.1(13).
8185 @code{Exception_Information} returns a string in the following format:
8188 @emph{Exception_Name:} nnnnn
8189 @emph{Message:} mmmmm
8191 @emph{Call stack traceback locations:}
8192 0xhhhh 0xhhhh 0xhhhh ... 0xhhh
8200 @code{nnnn} is the fully qualified name of the exception in all upper
8201 case letters. This line is always present.
8204 @code{mmmm} is the message (this line present only if message is non-null)
8207 @code{ppp} is the Process Id value as a decimal integer (this line is
8208 present only if the Process Id is nonzero). Currently we are
8209 not making use of this field.
8212 The Call stack traceback locations line and the following values
8213 are present only if at least one traceback location was recorded.
8214 The values are given in C style format, with lower case letters
8215 for a-f, and only as many digits present as are necessary.
8219 The line terminator sequence at the end of each line, including
8220 the last line is a single @code{LF} character (@code{16#0A#}).
8225 @strong{42}. Implementation-defined check names. See 11.5(27).
8228 The implementation defined check name Alignment_Check controls checking of
8229 address clause values for proper alignment (that is, the address supplied
8230 must be consistent with the alignment of the type).
8232 In addition, a user program can add implementation-defined check names
8233 by means of the pragma Check_Name.
8238 @strong{43}. The interpretation of each aspect of representation. See
8242 See separate section on data representations.
8247 @strong{44}. Any restrictions placed upon representation items. See
8251 See separate section on data representations.
8256 @strong{45}. The meaning of @code{Size} for indefinite subtypes. See
8260 Size for an indefinite subtype is the maximum possible size, except that
8261 for the case of a subprogram parameter, the size of the parameter object
8267 @strong{46}. The default external representation for a type tag. See
8271 The default external representation for a type tag is the fully expanded
8272 name of the type in upper case letters.
8277 @strong{47}. What determines whether a compilation unit is the same in
8278 two different partitions. See 13.3(76).
8281 A compilation unit is the same in two different partitions if and only
8282 if it derives from the same source file.
8287 @strong{48}. Implementation-defined components. See 13.5.1(15).
8290 The only implementation defined component is the tag for a tagged type,
8291 which contains a pointer to the dispatching table.
8296 @strong{49}. If @code{Word_Size} = @code{Storage_Unit}, the default bit
8297 ordering. See 13.5.3(5).
8300 @code{Word_Size} (32) is not the same as @code{Storage_Unit} (8) for this
8301 implementation, so no non-default bit ordering is supported. The default
8302 bit ordering corresponds to the natural endianness of the target architecture.
8307 @strong{50}. The contents of the visible part of package @code{System}
8308 and its language-defined children. See 13.7(2).
8311 See the definition of these packages in files @file{system.ads} and
8312 @file{s-stoele.ads}.
8317 @strong{51}. The contents of the visible part of package
8318 @code{System.Machine_Code}, and the meaning of
8319 @code{code_statements}. See 13.8(7).
8322 See the definition and documentation in file @file{s-maccod.ads}.
8327 @strong{52}. The effect of unchecked conversion. See 13.9(11).
8330 Unchecked conversion between types of the same size
8331 results in an uninterpreted transmission of the bits from one type
8332 to the other. If the types are of unequal sizes, then in the case of
8333 discrete types, a shorter source is first zero or sign extended as
8334 necessary, and a shorter target is simply truncated on the left.
8335 For all non-discrete types, the source is first copied if necessary
8336 to ensure that the alignment requirements of the target are met, then
8337 a pointer is constructed to the source value, and the result is obtained
8338 by dereferencing this pointer after converting it to be a pointer to the
8339 target type. Unchecked conversions where the target subtype is an
8340 unconstrained array are not permitted. If the target alignment is
8341 greater than the source alignment, then a copy of the result is
8342 made with appropriate alignment
8347 @strong{53}. The manner of choosing a storage pool for an access type
8348 when @code{Storage_Pool} is not specified for the type. See 13.11(17).
8351 There are 3 different standard pools used by the compiler when
8352 @code{Storage_Pool} is not specified depending whether the type is local
8353 to a subprogram or defined at the library level and whether
8354 @code{Storage_Size}is specified or not. See documentation in the runtime
8355 library units @code{System.Pool_Global}, @code{System.Pool_Size} and
8356 @code{System.Pool_Local} in files @file{s-poosiz.ads},
8357 @file{s-pooglo.ads} and @file{s-pooloc.ads} for full details on the
8363 @strong{54}. Whether or not the implementation provides user-accessible
8364 names for the standard pool type(s). See 13.11(17).
8368 See documentation in the sources of the run time mentioned in paragraph
8369 @strong{53} . All these pools are accessible by means of @code{with}'ing
8375 @strong{55}. The meaning of @code{Storage_Size}. See 13.11(18).
8378 @code{Storage_Size} is measured in storage units, and refers to the
8379 total space available for an access type collection, or to the primary
8380 stack space for a task.
8385 @strong{56}. Implementation-defined aspects of storage pools. See
8389 See documentation in the sources of the run time mentioned in paragraph
8390 @strong{53} for details on GNAT-defined aspects of storage pools.
8395 @strong{57}. The set of restrictions allowed in a pragma
8396 @code{Restrictions}. See 13.12(7).
8399 All RM defined Restriction identifiers are implemented. The following
8400 additional restriction identifiers are provided. There are two separate
8401 lists of implementation dependent restriction identifiers. The first
8402 set requires consistency throughout a partition (in other words, if the
8403 restriction identifier is used for any compilation unit in the partition,
8404 then all compilation units in the partition must obey the restriction.
8408 @item Simple_Barriers
8409 @findex Simple_Barriers
8410 This restriction ensures at compile time that barriers in entry declarations
8411 for protected types are restricted to either static boolean expressions or
8412 references to simple boolean variables defined in the private part of the
8413 protected type. No other form of entry barriers is permitted. This is one
8414 of the restrictions of the Ravenscar profile for limited tasking (see also
8415 pragma @code{Profile (Ravenscar)}).
8417 @item Max_Entry_Queue_Length => Expr
8418 @findex Max_Entry_Queue_Length
8419 This restriction is a declaration that any protected entry compiled in
8420 the scope of the restriction has at most the specified number of
8421 tasks waiting on the entry
8422 at any one time, and so no queue is required. This restriction is not
8423 checked at compile time. A program execution is erroneous if an attempt
8424 is made to queue more than the specified number of tasks on such an entry.
8428 This restriction ensures at compile time that there is no implicit or
8429 explicit dependence on the package @code{Ada.Calendar}.
8431 @item No_Default_Initialization
8432 @findex No_Default_Initialization
8434 This restriction prohibits any instance of default initialization of variables.
8435 The binder implements a consistency rule which prevents any unit compiled
8436 without the restriction from with'ing a unit with the restriction (this allows
8437 the generation of initialization procedures to be skipped, since you can be
8438 sure that no call is ever generated to an initialization procedure in a unit
8439 with the restriction active). If used in conjunction with Initialize_Scalars or
8440 Normalize_Scalars, the effect is to prohibit all cases of variables declared
8441 without a specific initializer (including the case of OUT scalar parameters).
8443 @item No_Direct_Boolean_Operators
8444 @findex No_Direct_Boolean_Operators
8445 This restriction ensures that no logical (and/or/xor) are used on
8446 operands of type Boolean (or any type derived
8447 from Boolean). This is intended for use in safety critical programs
8448 where the certification protocol requires the use of short-circuit
8449 (and then, or else) forms for all composite boolean operations.
8451 @item No_Dispatching_Calls
8452 @findex No_Dispatching_Calls
8453 This restriction ensures at compile time that the code generated by the
8454 compiler involves no dispatching calls. The use of this restriction allows the
8455 safe use of record extensions, classwide membership tests and other classwide
8456 features not involving implicit dispatching. This restriction ensures that
8457 the code contains no indirect calls through a dispatching mechanism. Note that
8458 this includes internally-generated calls created by the compiler, for example
8459 in the implementation of class-wide objects assignments. The
8460 membership test is allowed in the presence of this restriction, because its
8461 implementation requires no dispatching.
8462 This restriction is comparable to the official Ada restriction
8463 @code{No_Dispatch} except that it is a bit less restrictive in that it allows
8464 all classwide constructs that do not imply dispatching.
8465 The following example indicates constructs that violate this restriction.
8469 type T is tagged record
8472 procedure P (X : T);
8474 type DT is new T with record
8475 More_Data : Natural;
8477 procedure Q (X : DT);
8481 procedure Example is
8482 procedure Test (O : T'Class) is
8483 N : Natural := O'Size;-- Error: Dispatching call
8484 C : T'Class := O; -- Error: implicit Dispatching Call
8486 if O in DT'Class then -- OK : Membership test
8487 Q (DT (O)); -- OK : Type conversion plus direct call
8489 P (O); -- Error: Dispatching call
8495 P (Obj); -- OK : Direct call
8496 P (T (Obj)); -- OK : Type conversion plus direct call
8497 P (T'Class (Obj)); -- Error: Dispatching call
8499 Test (Obj); -- OK : Type conversion
8501 if Obj in T'Class then -- OK : Membership test
8507 @item No_Dynamic_Attachment
8508 @findex No_Dynamic_Attachment
8509 This restriction ensures that there is no call to any of the operations
8510 defined in package Ada.Interrupts.
8512 @item No_Enumeration_Maps
8513 @findex No_Enumeration_Maps
8514 This restriction ensures at compile time that no operations requiring
8515 enumeration maps are used (that is Image and Value attributes applied
8516 to enumeration types).
8518 @item No_Entry_Calls_In_Elaboration_Code
8519 @findex No_Entry_Calls_In_Elaboration_Code
8520 This restriction ensures at compile time that no task or protected entry
8521 calls are made during elaboration code. As a result of the use of this
8522 restriction, the compiler can assume that no code past an accept statement
8523 in a task can be executed at elaboration time.
8525 @item No_Exception_Handlers
8526 @findex No_Exception_Handlers
8527 This restriction ensures at compile time that there are no explicit
8528 exception handlers. It also indicates that no exception propagation will
8529 be provided. In this mode, exceptions may be raised but will result in
8530 an immediate call to the last chance handler, a routine that the user
8531 must define with the following profile:
8533 @smallexample @c ada
8534 procedure Last_Chance_Handler
8535 (Source_Location : System.Address; Line : Integer);
8536 pragma Export (C, Last_Chance_Handler,
8537 "__gnat_last_chance_handler");
8540 The parameter is a C null-terminated string representing a message to be
8541 associated with the exception (typically the source location of the raise
8542 statement generated by the compiler). The Line parameter when nonzero
8543 represents the line number in the source program where the raise occurs.
8545 @item No_Exception_Propagation
8546 @findex No_Exception_Propagation
8547 This restriction guarantees that exceptions are never propagated to an outer
8548 subprogram scope). The only case in which an exception may be raised is when
8549 the handler is statically in the same subprogram, so that the effect of a raise
8550 is essentially like a goto statement. Any other raise statement (implicit or
8551 explicit) will be considered unhandled. Exception handlers are allowed, but may
8552 not contain an exception occurrence identifier (exception choice). In addition
8553 use of the package GNAT.Current_Exception is not permitted, and reraise
8554 statements (raise with no operand) are not permitted.
8556 @item No_Exception_Registration
8557 @findex No_Exception_Registration
8558 This restriction ensures at compile time that no stream operations for
8559 types Exception_Id or Exception_Occurrence are used. This also makes it
8560 impossible to pass exceptions to or from a partition with this restriction
8561 in a distributed environment. If this exception is active, then the generated
8562 code is simplified by omitting the otherwise-required global registration
8563 of exceptions when they are declared.
8565 @item No_Implicit_Conditionals
8566 @findex No_Implicit_Conditionals
8567 This restriction ensures that the generated code does not contain any
8568 implicit conditionals, either by modifying the generated code where possible,
8569 or by rejecting any construct that would otherwise generate an implicit
8570 conditional. Note that this check does not include run time constraint
8571 checks, which on some targets may generate implicit conditionals as
8572 well. To control the latter, constraint checks can be suppressed in the
8573 normal manner. Constructs generating implicit conditionals include comparisons
8574 of composite objects and the Max/Min attributes.
8576 @item No_Implicit_Dynamic_Code
8577 @findex No_Implicit_Dynamic_Code
8579 This restriction prevents the compiler from building ``trampolines''.
8580 This is a structure that is built on the stack and contains dynamic
8581 code to be executed at run time. On some targets, a trampoline is
8582 built for the following features: @code{Access},
8583 @code{Unrestricted_Access}, or @code{Address} of a nested subprogram;
8584 nested task bodies; primitive operations of nested tagged types.
8585 Trampolines do not work on machines that prevent execution of stack
8586 data. For example, on windows systems, enabling DEP (data execution
8587 protection) will cause trampolines to raise an exception.
8588 Trampolines are also quite slow at run time.
8590 On many targets, trampolines have been largely eliminated. Look at the
8591 version of system.ads for your target --- if it has
8592 Always_Compatible_Rep equal to False, then trampolines are largely
8593 eliminated. In particular, a trampoline is built for the following
8594 features: @code{Address} of a nested subprogram;
8595 @code{Access} or @code{Unrestricted_Access} of a nested subprogram,
8596 but only if pragma Favor_Top_Level applies, or the access type has a
8597 foreign-language convention; primitive operations of nested tagged
8600 @item No_Implicit_Loops
8601 @findex No_Implicit_Loops
8602 This restriction ensures that the generated code does not contain any
8603 implicit @code{for} loops, either by modifying
8604 the generated code where possible,
8605 or by rejecting any construct that would otherwise generate an implicit
8606 @code{for} loop. If this restriction is active, it is possible to build
8607 large array aggregates with all static components without generating an
8608 intermediate temporary, and without generating a loop to initialize individual
8609 components. Otherwise, a loop is created for arrays larger than about 5000
8612 @item No_Initialize_Scalars
8613 @findex No_Initialize_Scalars
8614 This restriction ensures that no unit in the partition is compiled with
8615 pragma Initialize_Scalars. This allows the generation of more efficient
8616 code, and in particular eliminates dummy null initialization routines that
8617 are otherwise generated for some record and array types.
8619 @item No_Local_Protected_Objects
8620 @findex No_Local_Protected_Objects
8621 This restriction ensures at compile time that protected objects are
8622 only declared at the library level.
8624 @item No_Protected_Type_Allocators
8625 @findex No_Protected_Type_Allocators
8626 This restriction ensures at compile time that there are no allocator
8627 expressions that attempt to allocate protected objects.
8629 @item No_Secondary_Stack
8630 @findex No_Secondary_Stack
8631 This restriction ensures at compile time that the generated code does not
8632 contain any reference to the secondary stack. The secondary stack is used
8633 to implement functions returning unconstrained objects (arrays or records)
8636 @item No_Select_Statements
8637 @findex No_Select_Statements
8638 This restriction ensures at compile time no select statements of any kind
8639 are permitted, that is the keyword @code{select} may not appear.
8640 This is one of the restrictions of the Ravenscar
8641 profile for limited tasking (see also pragma @code{Profile (Ravenscar)}).
8643 @item No_Standard_Storage_Pools
8644 @findex No_Standard_Storage_Pools
8645 This restriction ensures at compile time that no access types
8646 use the standard default storage pool. Any access type declared must
8647 have an explicit Storage_Pool attribute defined specifying a
8648 user-defined storage pool.
8652 This restriction ensures at compile/bind time that there are no
8653 stream objects created and no use of stream attributes.
8654 This restriction does not forbid dependences on the package
8655 @code{Ada.Streams}. So it is permissible to with
8656 @code{Ada.Streams} (or another package that does so itself)
8657 as long as no actual stream objects are created and no
8658 stream attributes are used.
8660 Note that the use of restriction allows optimization of tagged types,
8661 since they do not need to worry about dispatching stream operations.
8662 To take maximum advantage of this space-saving optimization, any
8663 unit declaring a tagged type should be compiled with the restriction,
8664 though this is not required.
8666 @item No_Task_Attributes_Package
8667 @findex No_Task_Attributes_Package
8668 This restriction ensures at compile time that there are no implicit or
8669 explicit dependencies on the package @code{Ada.Task_Attributes}.
8671 @item No_Task_Termination
8672 @findex No_Task_Termination
8673 This restriction ensures at compile time that no terminate alternatives
8674 appear in any task body.
8678 This restriction prevents the declaration of tasks or task types throughout
8679 the partition. It is similar in effect to the use of @code{Max_Tasks => 0}
8680 except that violations are caught at compile time and cause an error message
8681 to be output either by the compiler or binder.
8683 @item Static_Priorities
8684 @findex Static_Priorities
8685 This restriction ensures at compile time that all priority expressions
8686 are static, and that there are no dependencies on the package
8687 @code{Ada.Dynamic_Priorities}.
8689 @item Static_Storage_Size
8690 @findex Static_Storage_Size
8691 This restriction ensures at compile time that any expression appearing
8692 in a Storage_Size pragma or attribute definition clause is static.
8697 The second set of implementation dependent restriction identifiers
8698 does not require partition-wide consistency.
8699 The restriction may be enforced for a single
8700 compilation unit without any effect on any of the
8701 other compilation units in the partition.
8705 @item No_Elaboration_Code
8706 @findex No_Elaboration_Code
8707 This restriction ensures at compile time that no elaboration code is
8708 generated. Note that this is not the same condition as is enforced
8709 by pragma @code{Preelaborate}. There are cases in which pragma
8710 @code{Preelaborate} still permits code to be generated (e.g.@: code
8711 to initialize a large array to all zeroes), and there are cases of units
8712 which do not meet the requirements for pragma @code{Preelaborate},
8713 but for which no elaboration code is generated. Generally, it is
8714 the case that preelaborable units will meet the restrictions, with
8715 the exception of large aggregates initialized with an others_clause,
8716 and exception declarations (which generate calls to a run-time
8717 registry procedure). This restriction is enforced on
8718 a unit by unit basis, it need not be obeyed consistently
8719 throughout a partition.
8721 In the case of aggregates with others, if the aggregate has a dynamic
8722 size, there is no way to eliminate the elaboration code (such dynamic
8723 bounds would be incompatible with @code{Preelaborate} in any case). If
8724 the bounds are static, then use of this restriction actually modifies
8725 the code choice of the compiler to avoid generating a loop, and instead
8726 generate the aggregate statically if possible, no matter how many times
8727 the data for the others clause must be repeatedly generated.
8729 It is not possible to precisely document
8730 the constructs which are compatible with this restriction, since,
8731 unlike most other restrictions, this is not a restriction on the
8732 source code, but a restriction on the generated object code. For
8733 example, if the source contains a declaration:
8736 Val : constant Integer := X;
8740 where X is not a static constant, it may be possible, depending
8741 on complex optimization circuitry, for the compiler to figure
8742 out the value of X at compile time, in which case this initialization
8743 can be done by the loader, and requires no initialization code. It
8744 is not possible to document the precise conditions under which the
8745 optimizer can figure this out.
8747 Note that this the implementation of this restriction requires full
8748 code generation. If it is used in conjunction with "semantics only"
8749 checking, then some cases of violations may be missed.
8751 @item No_Entry_Queue
8752 @findex No_Entry_Queue
8753 This restriction is a declaration that any protected entry compiled in
8754 the scope of the restriction has at most one task waiting on the entry
8755 at any one time, and so no queue is required. This restriction is not
8756 checked at compile time. A program execution is erroneous if an attempt
8757 is made to queue a second task on such an entry.
8759 @item No_Implementation_Attributes
8760 @findex No_Implementation_Attributes
8761 This restriction checks at compile time that no GNAT-defined attributes
8762 are present. With this restriction, the only attributes that can be used
8763 are those defined in the Ada Reference Manual.
8765 @item No_Implementation_Pragmas
8766 @findex No_Implementation_Pragmas
8767 This restriction checks at compile time that no GNAT-defined pragmas
8768 are present. With this restriction, the only pragmas that can be used
8769 are those defined in the Ada Reference Manual.
8771 @item No_Implementation_Restrictions
8772 @findex No_Implementation_Restrictions
8773 This restriction checks at compile time that no GNAT-defined restriction
8774 identifiers (other than @code{No_Implementation_Restrictions} itself)
8775 are present. With this restriction, the only other restriction identifiers
8776 that can be used are those defined in the Ada Reference Manual.
8778 @item No_Wide_Characters
8779 @findex No_Wide_Characters
8780 This restriction ensures at compile time that no uses of the types
8781 @code{Wide_Character} or @code{Wide_String} or corresponding wide
8783 appear, and that no wide or wide wide string or character literals
8784 appear in the program (that is literals representing characters not in
8785 type @code{Character}.
8792 @strong{58}. The consequences of violating limitations on
8793 @code{Restrictions} pragmas. See 13.12(9).
8796 Restrictions that can be checked at compile time result in illegalities
8797 if violated. Currently there are no other consequences of violating
8803 @strong{59}. The representation used by the @code{Read} and
8804 @code{Write} attributes of elementary types in terms of stream
8805 elements. See 13.13.2(9).
8808 The representation is the in-memory representation of the base type of
8809 the type, using the number of bits corresponding to the
8810 @code{@var{type}'Size} value, and the natural ordering of the machine.
8815 @strong{60}. The names and characteristics of the numeric subtypes
8816 declared in the visible part of package @code{Standard}. See A.1(3).
8819 See items describing the integer and floating-point types supported.
8824 @strong{61}. The accuracy actually achieved by the elementary
8825 functions. See A.5.1(1).
8828 The elementary functions correspond to the functions available in the C
8829 library. Only fast math mode is implemented.
8834 @strong{62}. The sign of a zero result from some of the operators or
8835 functions in @code{Numerics.Generic_Elementary_Functions}, when
8836 @code{Float_Type'Signed_Zeros} is @code{True}. See A.5.1(46).
8839 The sign of zeroes follows the requirements of the IEEE 754 standard on
8845 @strong{63}. The value of
8846 @code{Numerics.Float_Random.Max_Image_Width}. See A.5.2(27).
8849 Maximum image width is 649, see library file @file{a-numran.ads}.
8854 @strong{64}. The value of
8855 @code{Numerics.Discrete_Random.Max_Image_Width}. See A.5.2(27).
8858 Maximum image width is 80, see library file @file{a-nudira.ads}.
8863 @strong{65}. The algorithms for random number generation. See
8867 The algorithm is documented in the source files @file{a-numran.ads} and
8868 @file{a-numran.adb}.
8873 @strong{66}. The string representation of a random number generator's
8874 state. See A.5.2(38).
8877 See the documentation contained in the file @file{a-numran.adb}.
8882 @strong{67}. The minimum time interval between calls to the
8883 time-dependent Reset procedure that are guaranteed to initiate different
8884 random number sequences. See A.5.2(45).
8887 The minimum period between reset calls to guarantee distinct series of
8888 random numbers is one microsecond.
8893 @strong{68}. The values of the @code{Model_Mantissa},
8894 @code{Model_Emin}, @code{Model_Epsilon}, @code{Model},
8895 @code{Safe_First}, and @code{Safe_Last} attributes, if the Numerics
8896 Annex is not supported. See A.5.3(72).
8899 See the source file @file{ttypef.ads} for the values of all numeric
8905 @strong{69}. Any implementation-defined characteristics of the
8906 input-output packages. See A.7(14).
8909 There are no special implementation defined characteristics for these
8915 @strong{70}. The value of @code{Buffer_Size} in @code{Storage_IO}. See
8919 All type representations are contiguous, and the @code{Buffer_Size} is
8920 the value of @code{@var{type}'Size} rounded up to the next storage unit
8926 @strong{71}. External files for standard input, standard output, and
8927 standard error See A.10(5).
8930 These files are mapped onto the files provided by the C streams
8931 libraries. See source file @file{i-cstrea.ads} for further details.
8936 @strong{72}. The accuracy of the value produced by @code{Put}. See
8940 If more digits are requested in the output than are represented by the
8941 precision of the value, zeroes are output in the corresponding least
8942 significant digit positions.
8947 @strong{73}. The meaning of @code{Argument_Count}, @code{Argument}, and
8948 @code{Command_Name}. See A.15(1).
8951 These are mapped onto the @code{argv} and @code{argc} parameters of the
8952 main program in the natural manner.
8957 @strong{74}. Implementation-defined convention names. See B.1(11).
8960 The following convention names are supported
8968 Synonym for Assembler
8970 Synonym for Assembler
8973 @item C_Pass_By_Copy
8974 Allowed only for record types, like C, but also notes that record
8975 is to be passed by copy rather than reference.
8978 @item C_Plus_Plus (or CPP)
8981 Treated the same as C
8983 Treated the same as C
8987 For support of pragma @code{Import} with convention Intrinsic, see
8988 separate section on Intrinsic Subprograms.
8990 Stdcall (used for Windows implementations only). This convention correspond
8991 to the WINAPI (previously called Pascal convention) C/C++ convention under
8992 Windows. A function with this convention cleans the stack before exit.
8998 Stubbed is a special convention used to indicate that the body of the
8999 subprogram will be entirely ignored. Any call to the subprogram
9000 is converted into a raise of the @code{Program_Error} exception. If a
9001 pragma @code{Import} specifies convention @code{stubbed} then no body need
9002 be present at all. This convention is useful during development for the
9003 inclusion of subprograms whose body has not yet been written.
9007 In addition, all otherwise unrecognized convention names are also
9008 treated as being synonymous with convention C@. In all implementations
9009 except for VMS, use of such other names results in a warning. In VMS
9010 implementations, these names are accepted silently.
9015 @strong{75}. The meaning of link names. See B.1(36).
9018 Link names are the actual names used by the linker.
9023 @strong{76}. The manner of choosing link names when neither the link
9024 name nor the address of an imported or exported entity is specified. See
9028 The default linker name is that which would be assigned by the relevant
9029 external language, interpreting the Ada name as being in all lower case
9035 @strong{77}. The effect of pragma @code{Linker_Options}. See B.1(37).
9038 The string passed to @code{Linker_Options} is presented uninterpreted as
9039 an argument to the link command, unless it contains ASCII.NUL characters.
9040 NUL characters if they appear act as argument separators, so for example
9042 @smallexample @c ada
9043 pragma Linker_Options ("-labc" & ASCII.NUL & "-ldef");
9047 causes two separate arguments @code{-labc} and @code{-ldef} to be passed to the
9048 linker. The order of linker options is preserved for a given unit. The final
9049 list of options passed to the linker is in reverse order of the elaboration
9050 order. For example, linker options for a body always appear before the options
9051 from the corresponding package spec.
9056 @strong{78}. The contents of the visible part of package
9057 @code{Interfaces} and its language-defined descendants. See B.2(1).
9060 See files with prefix @file{i-} in the distributed library.
9065 @strong{79}. Implementation-defined children of package
9066 @code{Interfaces}. The contents of the visible part of package
9067 @code{Interfaces}. See B.2(11).
9070 See files with prefix @file{i-} in the distributed library.
9075 @strong{80}. The types @code{Floating}, @code{Long_Floating},
9076 @code{Binary}, @code{Long_Binary}, @code{Decimal_ Element}, and
9077 @code{COBOL_Character}; and the initialization of the variables
9078 @code{Ada_To_COBOL} and @code{COBOL_To_Ada}, in
9079 @code{Interfaces.COBOL}. See B.4(50).
9086 (Floating) Long_Float
9091 @item Decimal_Element
9093 @item COBOL_Character
9098 For initialization, see the file @file{i-cobol.ads} in the distributed library.
9103 @strong{81}. Support for access to machine instructions. See C.1(1).
9106 See documentation in file @file{s-maccod.ads} in the distributed library.
9111 @strong{82}. Implementation-defined aspects of access to machine
9112 operations. See C.1(9).
9115 See documentation in file @file{s-maccod.ads} in the distributed library.
9120 @strong{83}. Implementation-defined aspects of interrupts. See C.3(2).
9123 Interrupts are mapped to signals or conditions as appropriate. See
9125 @code{Ada.Interrupt_Names} in source file @file{a-intnam.ads} for details
9126 on the interrupts supported on a particular target.
9131 @strong{84}. Implementation-defined aspects of pre-elaboration. See
9135 GNAT does not permit a partition to be restarted without reloading,
9136 except under control of the debugger.
9141 @strong{85}. The semantics of pragma @code{Discard_Names}. See C.5(7).
9144 Pragma @code{Discard_Names} causes names of enumeration literals to
9145 be suppressed. In the presence of this pragma, the Image attribute
9146 provides the image of the Pos of the literal, and Value accepts
9152 @strong{86}. The result of the @code{Task_Identification.Image}
9153 attribute. See C.7.1(7).
9156 The result of this attribute is a string that identifies
9157 the object or component that denotes a given task. If a variable @code{Var}
9158 has a task type, the image for this task will have the form @code{Var_@var{XXXXXXXX}},
9160 is the hexadecimal representation of the virtual address of the corresponding
9161 task control block. If the variable is an array of tasks, the image of each
9162 task will have the form of an indexed component indicating the position of a
9163 given task in the array, e.g.@: @code{Group(5)_@var{XXXXXXX}}. If the task is a
9164 component of a record, the image of the task will have the form of a selected
9165 component. These rules are fully recursive, so that the image of a task that
9166 is a subcomponent of a composite object corresponds to the expression that
9167 designates this task.
9169 If a task is created by an allocator, its image depends on the context. If the
9170 allocator is part of an object declaration, the rules described above are used
9171 to construct its image, and this image is not affected by subsequent
9172 assignments. If the allocator appears within an expression, the image
9173 includes only the name of the task type.
9175 If the configuration pragma Discard_Names is present, or if the restriction
9176 No_Implicit_Heap_Allocation is in effect, the image reduces to
9177 the numeric suffix, that is to say the hexadecimal representation of the
9178 virtual address of the control block of the task.
9182 @strong{87}. The value of @code{Current_Task} when in a protected entry
9183 or interrupt handler. See C.7.1(17).
9186 Protected entries or interrupt handlers can be executed by any
9187 convenient thread, so the value of @code{Current_Task} is undefined.
9192 @strong{88}. The effect of calling @code{Current_Task} from an entry
9193 body or interrupt handler. See C.7.1(19).
9196 The effect of calling @code{Current_Task} from an entry body or
9197 interrupt handler is to return the identification of the task currently
9203 @strong{89}. Implementation-defined aspects of
9204 @code{Task_Attributes}. See C.7.2(19).
9207 There are no implementation-defined aspects of @code{Task_Attributes}.
9212 @strong{90}. Values of all @code{Metrics}. See D(2).
9215 The metrics information for GNAT depends on the performance of the
9216 underlying operating system. The sources of the run-time for tasking
9217 implementation, together with the output from @option{-gnatG} can be
9218 used to determine the exact sequence of operating systems calls made
9219 to implement various tasking constructs. Together with appropriate
9220 information on the performance of the underlying operating system,
9221 on the exact target in use, this information can be used to determine
9222 the required metrics.
9227 @strong{91}. The declarations of @code{Any_Priority} and
9228 @code{Priority}. See D.1(11).
9231 See declarations in file @file{system.ads}.
9236 @strong{92}. Implementation-defined execution resources. See D.1(15).
9239 There are no implementation-defined execution resources.
9244 @strong{93}. Whether, on a multiprocessor, a task that is waiting for
9245 access to a protected object keeps its processor busy. See D.2.1(3).
9248 On a multi-processor, a task that is waiting for access to a protected
9249 object does not keep its processor busy.
9254 @strong{94}. The affect of implementation defined execution resources
9255 on task dispatching. See D.2.1(9).
9260 Tasks map to IRIX threads, and the dispatching policy is as defined by
9261 the IRIX implementation of threads.
9263 Tasks map to threads in the threads package used by GNAT@. Where possible
9264 and appropriate, these threads correspond to native threads of the
9265 underlying operating system.
9270 @strong{95}. Implementation-defined @code{policy_identifiers} allowed
9271 in a pragma @code{Task_Dispatching_Policy}. See D.2.2(3).
9274 There are no implementation-defined policy-identifiers allowed in this
9280 @strong{96}. Implementation-defined aspects of priority inversion. See
9284 Execution of a task cannot be preempted by the implementation processing
9285 of delay expirations for lower priority tasks.
9290 @strong{97}. Implementation defined task dispatching. See D.2.2(18).
9295 Tasks map to IRIX threads, and the dispatching policy is as defined by
9296 the IRIX implementation of threads.
9298 The policy is the same as that of the underlying threads implementation.
9303 @strong{98}. Implementation-defined @code{policy_identifiers} allowed
9304 in a pragma @code{Locking_Policy}. See D.3(4).
9307 The only implementation defined policy permitted in GNAT is
9308 @code{Inheritance_Locking}. On targets that support this policy, locking
9309 is implemented by inheritance, i.e.@: the task owning the lock operates
9310 at a priority equal to the highest priority of any task currently
9311 requesting the lock.
9316 @strong{99}. Default ceiling priorities. See D.3(10).
9319 The ceiling priority of protected objects of the type
9320 @code{System.Interrupt_Priority'Last} as described in the Ada
9321 Reference Manual D.3(10),
9326 @strong{100}. The ceiling of any protected object used internally by
9327 the implementation. See D.3(16).
9330 The ceiling priority of internal protected objects is
9331 @code{System.Priority'Last}.
9336 @strong{101}. Implementation-defined queuing policies. See D.4(1).
9339 There are no implementation-defined queuing policies.
9344 @strong{102}. On a multiprocessor, any conditions that cause the
9345 completion of an aborted construct to be delayed later than what is
9346 specified for a single processor. See D.6(3).
9349 The semantics for abort on a multi-processor is the same as on a single
9350 processor, there are no further delays.
9355 @strong{103}. Any operations that implicitly require heap storage
9356 allocation. See D.7(8).
9359 The only operation that implicitly requires heap storage allocation is
9365 @strong{104}. Implementation-defined aspects of pragma
9366 @code{Restrictions}. See D.7(20).
9369 There are no such implementation-defined aspects.
9374 @strong{105}. Implementation-defined aspects of package
9375 @code{Real_Time}. See D.8(17).
9378 There are no implementation defined aspects of package @code{Real_Time}.
9383 @strong{106}. Implementation-defined aspects of
9384 @code{delay_statements}. See D.9(8).
9387 Any difference greater than one microsecond will cause the task to be
9388 delayed (see D.9(7)).
9393 @strong{107}. The upper bound on the duration of interrupt blocking
9394 caused by the implementation. See D.12(5).
9397 The upper bound is determined by the underlying operating system. In
9398 no cases is it more than 10 milliseconds.
9403 @strong{108}. The means for creating and executing distributed
9407 The GLADE package provides a utility GNATDIST for creating and executing
9408 distributed programs. See the GLADE reference manual for further details.
9413 @strong{109}. Any events that can result in a partition becoming
9414 inaccessible. See E.1(7).
9417 See the GLADE reference manual for full details on such events.
9422 @strong{110}. The scheduling policies, treatment of priorities, and
9423 management of shared resources between partitions in certain cases. See
9427 See the GLADE reference manual for full details on these aspects of
9428 multi-partition execution.
9433 @strong{111}. Events that cause the version of a compilation unit to
9437 Editing the source file of a compilation unit, or the source files of
9438 any units on which it is dependent in a significant way cause the version
9439 to change. No other actions cause the version number to change. All changes
9440 are significant except those which affect only layout, capitalization or
9446 @strong{112}. Whether the execution of the remote subprogram is
9447 immediately aborted as a result of cancellation. See E.4(13).
9450 See the GLADE reference manual for details on the effect of abort in
9451 a distributed application.
9456 @strong{113}. Implementation-defined aspects of the PCS@. See E.5(25).
9459 See the GLADE reference manual for a full description of all implementation
9460 defined aspects of the PCS@.
9465 @strong{114}. Implementation-defined interfaces in the PCS@. See
9469 See the GLADE reference manual for a full description of all
9470 implementation defined interfaces.
9475 @strong{115}. The values of named numbers in the package
9476 @code{Decimal}. See F.2(7).
9488 @item Max_Decimal_Digits
9495 @strong{116}. The value of @code{Max_Picture_Length} in the package
9496 @code{Text_IO.Editing}. See F.3.3(16).
9504 @strong{117}. The value of @code{Max_Picture_Length} in the package
9505 @code{Wide_Text_IO.Editing}. See F.3.4(5).
9513 @strong{118}. The accuracy actually achieved by the complex elementary
9514 functions and by other complex arithmetic operations. See G.1(1).
9517 Standard library functions are used for the complex arithmetic
9518 operations. Only fast math mode is currently supported.
9523 @strong{119}. The sign of a zero result (or a component thereof) from
9524 any operator or function in @code{Numerics.Generic_Complex_Types}, when
9525 @code{Real'Signed_Zeros} is True. See G.1.1(53).
9528 The signs of zero values are as recommended by the relevant
9529 implementation advice.
9534 @strong{120}. The sign of a zero result (or a component thereof) from
9535 any operator or function in
9536 @code{Numerics.Generic_Complex_Elementary_Functions}, when
9537 @code{Real'Signed_Zeros} is @code{True}. See G.1.2(45).
9540 The signs of zero values are as recommended by the relevant
9541 implementation advice.
9546 @strong{121}. Whether the strict mode or the relaxed mode is the
9547 default. See G.2(2).
9550 The strict mode is the default. There is no separate relaxed mode. GNAT
9551 provides a highly efficient implementation of strict mode.
9556 @strong{122}. The result interval in certain cases of fixed-to-float
9557 conversion. See G.2.1(10).
9560 For cases where the result interval is implementation dependent, the
9561 accuracy is that provided by performing all operations in 64-bit IEEE
9562 floating-point format.
9567 @strong{123}. The result of a floating point arithmetic operation in
9568 overflow situations, when the @code{Machine_Overflows} attribute of the
9569 result type is @code{False}. See G.2.1(13).
9572 Infinite and NaN values are produced as dictated by the IEEE
9573 floating-point standard.
9575 Note that on machines that are not fully compliant with the IEEE
9576 floating-point standard, such as Alpha, the @option{-mieee} compiler flag
9577 must be used for achieving IEEE confirming behavior (although at the cost
9578 of a significant performance penalty), so infinite and NaN values are
9584 @strong{124}. The result interval for division (or exponentiation by a
9585 negative exponent), when the floating point hardware implements division
9586 as multiplication by a reciprocal. See G.2.1(16).
9589 Not relevant, division is IEEE exact.
9594 @strong{125}. The definition of close result set, which determines the
9595 accuracy of certain fixed point multiplications and divisions. See
9599 Operations in the close result set are performed using IEEE long format
9600 floating-point arithmetic. The input operands are converted to
9601 floating-point, the operation is done in floating-point, and the result
9602 is converted to the target type.
9607 @strong{126}. Conditions on a @code{universal_real} operand of a fixed
9608 point multiplication or division for which the result shall be in the
9609 perfect result set. See G.2.3(22).
9612 The result is only defined to be in the perfect result set if the result
9613 can be computed by a single scaling operation involving a scale factor
9614 representable in 64-bits.
9619 @strong{127}. The result of a fixed point arithmetic operation in
9620 overflow situations, when the @code{Machine_Overflows} attribute of the
9621 result type is @code{False}. See G.2.3(27).
9624 Not relevant, @code{Machine_Overflows} is @code{True} for fixed-point
9630 @strong{128}. The result of an elementary function reference in
9631 overflow situations, when the @code{Machine_Overflows} attribute of the
9632 result type is @code{False}. See G.2.4(4).
9635 IEEE infinite and Nan values are produced as appropriate.
9640 @strong{129}. The value of the angle threshold, within which certain
9641 elementary functions, complex arithmetic operations, and complex
9642 elementary functions yield results conforming to a maximum relative
9643 error bound. See G.2.4(10).
9646 Information on this subject is not yet available.
9651 @strong{130}. The accuracy of certain elementary functions for
9652 parameters beyond the angle threshold. See G.2.4(10).
9655 Information on this subject is not yet available.
9660 @strong{131}. The result of a complex arithmetic operation or complex
9661 elementary function reference in overflow situations, when the
9662 @code{Machine_Overflows} attribute of the corresponding real type is
9663 @code{False}. See G.2.6(5).
9666 IEEE infinite and Nan values are produced as appropriate.
9671 @strong{132}. The accuracy of certain complex arithmetic operations and
9672 certain complex elementary functions for parameters (or components
9673 thereof) beyond the angle threshold. See G.2.6(8).
9676 Information on those subjects is not yet available.
9681 @strong{133}. Information regarding bounded errors and erroneous
9682 execution. See H.2(1).
9685 Information on this subject is not yet available.
9690 @strong{134}. Implementation-defined aspects of pragma
9691 @code{Inspection_Point}. See H.3.2(8).
9694 Pragma @code{Inspection_Point} ensures that the variable is live and can
9695 be examined by the debugger at the inspection point.
9700 @strong{135}. Implementation-defined aspects of pragma
9701 @code{Restrictions}. See H.4(25).
9704 There are no implementation-defined aspects of pragma @code{Restrictions}. The
9705 use of pragma @code{Restrictions [No_Exceptions]} has no effect on the
9706 generated code. Checks must suppressed by use of pragma @code{Suppress}.
9711 @strong{136}. Any restrictions on pragma @code{Restrictions}. See
9715 There are no restrictions on pragma @code{Restrictions}.
9717 @node Intrinsic Subprograms
9718 @chapter Intrinsic Subprograms
9719 @cindex Intrinsic Subprograms
9722 * Intrinsic Operators::
9723 * Enclosing_Entity::
9724 * Exception_Information::
9725 * Exception_Message::
9733 * Shift_Right_Arithmetic::
9738 GNAT allows a user application program to write the declaration:
9740 @smallexample @c ada
9741 pragma Import (Intrinsic, name);
9745 providing that the name corresponds to one of the implemented intrinsic
9746 subprograms in GNAT, and that the parameter profile of the referenced
9747 subprogram meets the requirements. This chapter describes the set of
9748 implemented intrinsic subprograms, and the requirements on parameter profiles.
9749 Note that no body is supplied; as with other uses of pragma Import, the
9750 body is supplied elsewhere (in this case by the compiler itself). Note
9751 that any use of this feature is potentially non-portable, since the
9752 Ada standard does not require Ada compilers to implement this feature.
9754 @node Intrinsic Operators
9755 @section Intrinsic Operators
9756 @cindex Intrinsic operator
9759 All the predefined numeric operators in package Standard
9760 in @code{pragma Import (Intrinsic,..)}
9761 declarations. In the binary operator case, the operands must have the same
9762 size. The operand or operands must also be appropriate for
9763 the operator. For example, for addition, the operands must
9764 both be floating-point or both be fixed-point, and the
9765 right operand for @code{"**"} must have a root type of
9766 @code{Standard.Integer'Base}.
9767 You can use an intrinsic operator declaration as in the following example:
9769 @smallexample @c ada
9770 type Int1 is new Integer;
9771 type Int2 is new Integer;
9773 function "+" (X1 : Int1; X2 : Int2) return Int1;
9774 function "+" (X1 : Int1; X2 : Int2) return Int2;
9775 pragma Import (Intrinsic, "+");
9779 This declaration would permit ``mixed mode'' arithmetic on items
9780 of the differing types @code{Int1} and @code{Int2}.
9781 It is also possible to specify such operators for private types, if the
9782 full views are appropriate arithmetic types.
9784 @node Enclosing_Entity
9785 @section Enclosing_Entity
9786 @cindex Enclosing_Entity
9788 This intrinsic subprogram is used in the implementation of the
9789 library routine @code{GNAT.Source_Info}. The only useful use of the
9790 intrinsic import in this case is the one in this unit, so an
9791 application program should simply call the function
9792 @code{GNAT.Source_Info.Enclosing_Entity} to obtain the name of
9793 the current subprogram, package, task, entry, or protected subprogram.
9795 @node Exception_Information
9796 @section Exception_Information
9797 @cindex Exception_Information'
9799 This intrinsic subprogram is used in the implementation of the
9800 library routine @code{GNAT.Current_Exception}. The only useful
9801 use of the intrinsic import in this case is the one in this unit,
9802 so an application program should simply call the function
9803 @code{GNAT.Current_Exception.Exception_Information} to obtain
9804 the exception information associated with the current exception.
9806 @node Exception_Message
9807 @section Exception_Message
9808 @cindex Exception_Message
9810 This intrinsic subprogram is used in the implementation of the
9811 library routine @code{GNAT.Current_Exception}. The only useful
9812 use of the intrinsic import in this case is the one in this unit,
9813 so an application program should simply call the function
9814 @code{GNAT.Current_Exception.Exception_Message} to obtain
9815 the message associated with the current exception.
9817 @node Exception_Name
9818 @section Exception_Name
9819 @cindex Exception_Name
9821 This intrinsic subprogram is used in the implementation of the
9822 library routine @code{GNAT.Current_Exception}. The only useful
9823 use of the intrinsic import in this case is the one in this unit,
9824 so an application program should simply call the function
9825 @code{GNAT.Current_Exception.Exception_Name} to obtain
9826 the name of the current exception.
9832 This intrinsic subprogram is used in the implementation of the
9833 library routine @code{GNAT.Source_Info}. The only useful use of the
9834 intrinsic import in this case is the one in this unit, so an
9835 application program should simply call the function
9836 @code{GNAT.Source_Info.File} to obtain the name of the current
9843 This intrinsic subprogram is used in the implementation of the
9844 library routine @code{GNAT.Source_Info}. The only useful use of the
9845 intrinsic import in this case is the one in this unit, so an
9846 application program should simply call the function
9847 @code{GNAT.Source_Info.Line} to obtain the number of the current
9851 @section Rotate_Left
9854 In standard Ada, the @code{Rotate_Left} function is available only
9855 for the predefined modular types in package @code{Interfaces}. However, in
9856 GNAT it is possible to define a Rotate_Left function for a user
9857 defined modular type or any signed integer type as in this example:
9859 @smallexample @c ada
9861 (Value : My_Modular_Type;
9863 return My_Modular_Type;
9867 The requirements are that the profile be exactly as in the example
9868 above. The only modifications allowed are in the formal parameter
9869 names, and in the type of @code{Value} and the return type, which
9870 must be the same, and must be either a signed integer type, or
9871 a modular integer type with a binary modulus, and the size must
9872 be 8. 16, 32 or 64 bits.
9875 @section Rotate_Right
9876 @cindex Rotate_Right
9878 A @code{Rotate_Right} function can be defined for any user defined
9879 binary modular integer type, or signed integer type, as described
9880 above for @code{Rotate_Left}.
9886 A @code{Shift_Left} function can be defined for any user defined
9887 binary modular integer type, or signed integer type, as described
9888 above for @code{Rotate_Left}.
9891 @section Shift_Right
9894 A @code{Shift_Right} function can be defined for any user defined
9895 binary modular integer type, or signed integer type, as described
9896 above for @code{Rotate_Left}.
9898 @node Shift_Right_Arithmetic
9899 @section Shift_Right_Arithmetic
9900 @cindex Shift_Right_Arithmetic
9902 A @code{Shift_Right_Arithmetic} function can be defined for any user
9903 defined binary modular integer type, or signed integer type, as described
9904 above for @code{Rotate_Left}.
9906 @node Source_Location
9907 @section Source_Location
9908 @cindex Source_Location
9910 This intrinsic subprogram is used in the implementation of the
9911 library routine @code{GNAT.Source_Info}. The only useful use of the
9912 intrinsic import in this case is the one in this unit, so an
9913 application program should simply call the function
9914 @code{GNAT.Source_Info.Source_Location} to obtain the current
9915 source file location.
9917 @node Representation Clauses and Pragmas
9918 @chapter Representation Clauses and Pragmas
9919 @cindex Representation Clauses
9922 * Alignment Clauses::
9924 * Storage_Size Clauses::
9925 * Size of Variant Record Objects::
9926 * Biased Representation ::
9927 * Value_Size and Object_Size Clauses::
9928 * Component_Size Clauses::
9929 * Bit_Order Clauses::
9930 * Effect of Bit_Order on Byte Ordering::
9931 * Pragma Pack for Arrays::
9932 * Pragma Pack for Records::
9933 * Record Representation Clauses::
9934 * Enumeration Clauses::
9936 * Effect of Convention on Representation::
9937 * Determining the Representations chosen by GNAT::
9941 @cindex Representation Clause
9942 @cindex Representation Pragma
9943 @cindex Pragma, representation
9944 This section describes the representation clauses accepted by GNAT, and
9945 their effect on the representation of corresponding data objects.
9947 GNAT fully implements Annex C (Systems Programming). This means that all
9948 the implementation advice sections in chapter 13 are fully implemented.
9949 However, these sections only require a minimal level of support for
9950 representation clauses. GNAT provides much more extensive capabilities,
9951 and this section describes the additional capabilities provided.
9953 @node Alignment Clauses
9954 @section Alignment Clauses
9955 @cindex Alignment Clause
9958 GNAT requires that all alignment clauses specify a power of 2, and all
9959 default alignments are always a power of 2. The default alignment
9960 values are as follows:
9963 @item @emph{Primitive Types}.
9964 For primitive types, the alignment is the minimum of the actual size of
9965 objects of the type divided by @code{Storage_Unit},
9966 and the maximum alignment supported by the target.
9967 (This maximum alignment is given by the GNAT-specific attribute
9968 @code{Standard'Maximum_Alignment}; see @ref{Maximum_Alignment}.)
9969 @cindex @code{Maximum_Alignment} attribute
9970 For example, for type @code{Long_Float}, the object size is 8 bytes, and the
9971 default alignment will be 8 on any target that supports alignments
9972 this large, but on some targets, the maximum alignment may be smaller
9973 than 8, in which case objects of type @code{Long_Float} will be maximally
9976 @item @emph{Arrays}.
9977 For arrays, the alignment is equal to the alignment of the component type
9978 for the normal case where no packing or component size is given. If the
9979 array is packed, and the packing is effective (see separate section on
9980 packed arrays), then the alignment will be one for long packed arrays,
9981 or arrays whose length is not known at compile time. For short packed
9982 arrays, which are handled internally as modular types, the alignment
9983 will be as described for primitive types, e.g.@: a packed array of length
9984 31 bits will have an object size of four bytes, and an alignment of 4.
9986 @item @emph{Records}.
9987 For the normal non-packed case, the alignment of a record is equal to
9988 the maximum alignment of any of its components. For tagged records, this
9989 includes the implicit access type used for the tag. If a pragma @code{Pack}
9990 is used and all components are packable (see separate section on pragma
9991 @code{Pack}), then the resulting alignment is 1, unless the layout of the
9992 record makes it profitable to increase it.
9994 A special case is when:
9997 the size of the record is given explicitly, or a
9998 full record representation clause is given, and
10000 the size of the record is 2, 4, or 8 bytes.
10003 In this case, an alignment is chosen to match the
10004 size of the record. For example, if we have:
10006 @smallexample @c ada
10007 type Small is record
10010 for Small'Size use 16;
10014 then the default alignment of the record type @code{Small} is 2, not 1. This
10015 leads to more efficient code when the record is treated as a unit, and also
10016 allows the type to specified as @code{Atomic} on architectures requiring
10022 An alignment clause may specify a larger alignment than the default value
10023 up to some maximum value dependent on the target (obtainable by using the
10024 attribute reference @code{Standard'Maximum_Alignment}). It may also specify
10025 a smaller alignment than the default value for enumeration, integer and
10026 fixed point types, as well as for record types, for example
10028 @smallexample @c ada
10033 for V'alignment use 1;
10037 @cindex Alignment, default
10038 The default alignment for the type @code{V} is 4, as a result of the
10039 Integer field in the record, but it is permissible, as shown, to
10040 override the default alignment of the record with a smaller value.
10043 @section Size Clauses
10044 @cindex Size Clause
10047 The default size for a type @code{T} is obtainable through the
10048 language-defined attribute @code{T'Size} and also through the
10049 equivalent GNAT-defined attribute @code{T'Value_Size}.
10050 For objects of type @code{T}, GNAT will generally increase the type size
10051 so that the object size (obtainable through the GNAT-defined attribute
10052 @code{T'Object_Size})
10053 is a multiple of @code{T'Alignment * Storage_Unit}.
10056 @smallexample @c ada
10057 type Smallint is range 1 .. 6;
10066 In this example, @code{Smallint'Size} = @code{Smallint'Value_Size} = 3,
10067 as specified by the RM rules,
10068 but objects of this type will have a size of 8
10069 (@code{Smallint'Object_Size} = 8),
10070 since objects by default occupy an integral number
10071 of storage units. On some targets, notably older
10072 versions of the Digital Alpha, the size of stand
10073 alone objects of this type may be 32, reflecting
10074 the inability of the hardware to do byte load/stores.
10076 Similarly, the size of type @code{Rec} is 40 bits
10077 (@code{Rec'Size} = @code{Rec'Value_Size} = 40), but
10078 the alignment is 4, so objects of this type will have
10079 their size increased to 64 bits so that it is a multiple
10080 of the alignment (in bits). This decision is
10081 in accordance with the specific Implementation Advice in RM 13.3(43):
10084 A @code{Size} clause should be supported for an object if the specified
10085 @code{Size} is at least as large as its subtype's @code{Size}, and corresponds
10086 to a size in storage elements that is a multiple of the object's
10087 @code{Alignment} (if the @code{Alignment} is nonzero).
10091 An explicit size clause may be used to override the default size by
10092 increasing it. For example, if we have:
10094 @smallexample @c ada
10095 type My_Boolean is new Boolean;
10096 for My_Boolean'Size use 32;
10100 then values of this type will always be 32 bits long. In the case of
10101 discrete types, the size can be increased up to 64 bits, with the effect
10102 that the entire specified field is used to hold the value, sign- or
10103 zero-extended as appropriate. If more than 64 bits is specified, then
10104 padding space is allocated after the value, and a warning is issued that
10105 there are unused bits.
10107 Similarly the size of records and arrays may be increased, and the effect
10108 is to add padding bits after the value. This also causes a warning message
10111 The largest Size value permitted in GNAT is 2**31@minus{}1. Since this is a
10112 Size in bits, this corresponds to an object of size 256 megabytes (minus
10113 one). This limitation is true on all targets. The reason for this
10114 limitation is that it improves the quality of the code in many cases
10115 if it is known that a Size value can be accommodated in an object of
10118 @node Storage_Size Clauses
10119 @section Storage_Size Clauses
10120 @cindex Storage_Size Clause
10123 For tasks, the @code{Storage_Size} clause specifies the amount of space
10124 to be allocated for the task stack. This cannot be extended, and if the
10125 stack is exhausted, then @code{Storage_Error} will be raised (if stack
10126 checking is enabled). Use a @code{Storage_Size} attribute definition clause,
10127 or a @code{Storage_Size} pragma in the task definition to set the
10128 appropriate required size. A useful technique is to include in every
10129 task definition a pragma of the form:
10131 @smallexample @c ada
10132 pragma Storage_Size (Default_Stack_Size);
10136 Then @code{Default_Stack_Size} can be defined in a global package, and
10137 modified as required. Any tasks requiring stack sizes different from the
10138 default can have an appropriate alternative reference in the pragma.
10140 You can also use the @option{-d} binder switch to modify the default stack
10143 For access types, the @code{Storage_Size} clause specifies the maximum
10144 space available for allocation of objects of the type. If this space is
10145 exceeded then @code{Storage_Error} will be raised by an allocation attempt.
10146 In the case where the access type is declared local to a subprogram, the
10147 use of a @code{Storage_Size} clause triggers automatic use of a special
10148 predefined storage pool (@code{System.Pool_Size}) that ensures that all
10149 space for the pool is automatically reclaimed on exit from the scope in
10150 which the type is declared.
10152 A special case recognized by the compiler is the specification of a
10153 @code{Storage_Size} of zero for an access type. This means that no
10154 items can be allocated from the pool, and this is recognized at compile
10155 time, and all the overhead normally associated with maintaining a fixed
10156 size storage pool is eliminated. Consider the following example:
10158 @smallexample @c ada
10160 type R is array (Natural) of Character;
10161 type P is access all R;
10162 for P'Storage_Size use 0;
10163 -- Above access type intended only for interfacing purposes
10167 procedure g (m : P);
10168 pragma Import (C, g);
10179 As indicated in this example, these dummy storage pools are often useful in
10180 connection with interfacing where no object will ever be allocated. If you
10181 compile the above example, you get the warning:
10184 p.adb:16:09: warning: allocation from empty storage pool
10185 p.adb:16:09: warning: Storage_Error will be raised at run time
10189 Of course in practice, there will not be any explicit allocators in the
10190 case of such an access declaration.
10192 @node Size of Variant Record Objects
10193 @section Size of Variant Record Objects
10194 @cindex Size, variant record objects
10195 @cindex Variant record objects, size
10198 In the case of variant record objects, there is a question whether Size gives
10199 information about a particular variant, or the maximum size required
10200 for any variant. Consider the following program
10202 @smallexample @c ada
10203 with Text_IO; use Text_IO;
10205 type R1 (A : Boolean := False) is record
10207 when True => X : Character;
10208 when False => null;
10216 Put_Line (Integer'Image (V1'Size));
10217 Put_Line (Integer'Image (V2'Size));
10222 Here we are dealing with a variant record, where the True variant
10223 requires 16 bits, and the False variant requires 8 bits.
10224 In the above example, both V1 and V2 contain the False variant,
10225 which is only 8 bits long. However, the result of running the
10234 The reason for the difference here is that the discriminant value of
10235 V1 is fixed, and will always be False. It is not possible to assign
10236 a True variant value to V1, therefore 8 bits is sufficient. On the
10237 other hand, in the case of V2, the initial discriminant value is
10238 False (from the default), but it is possible to assign a True
10239 variant value to V2, therefore 16 bits must be allocated for V2
10240 in the general case, even fewer bits may be needed at any particular
10241 point during the program execution.
10243 As can be seen from the output of this program, the @code{'Size}
10244 attribute applied to such an object in GNAT gives the actual allocated
10245 size of the variable, which is the largest size of any of the variants.
10246 The Ada Reference Manual is not completely clear on what choice should
10247 be made here, but the GNAT behavior seems most consistent with the
10248 language in the RM@.
10250 In some cases, it may be desirable to obtain the size of the current
10251 variant, rather than the size of the largest variant. This can be
10252 achieved in GNAT by making use of the fact that in the case of a
10253 subprogram parameter, GNAT does indeed return the size of the current
10254 variant (because a subprogram has no way of knowing how much space
10255 is actually allocated for the actual).
10257 Consider the following modified version of the above program:
10259 @smallexample @c ada
10260 with Text_IO; use Text_IO;
10262 type R1 (A : Boolean := False) is record
10264 when True => X : Character;
10265 when False => null;
10271 function Size (V : R1) return Integer is
10277 Put_Line (Integer'Image (V2'Size));
10278 Put_Line (Integer'IMage (Size (V2)));
10280 Put_Line (Integer'Image (V2'Size));
10281 Put_Line (Integer'IMage (Size (V2)));
10286 The output from this program is
10296 Here we see that while the @code{'Size} attribute always returns
10297 the maximum size, regardless of the current variant value, the
10298 @code{Size} function does indeed return the size of the current
10301 @node Biased Representation
10302 @section Biased Representation
10303 @cindex Size for biased representation
10304 @cindex Biased representation
10307 In the case of scalars with a range starting at other than zero, it is
10308 possible in some cases to specify a size smaller than the default minimum
10309 value, and in such cases, GNAT uses an unsigned biased representation,
10310 in which zero is used to represent the lower bound, and successive values
10311 represent successive values of the type.
10313 For example, suppose we have the declaration:
10315 @smallexample @c ada
10316 type Small is range -7 .. -4;
10317 for Small'Size use 2;
10321 Although the default size of type @code{Small} is 4, the @code{Size}
10322 clause is accepted by GNAT and results in the following representation
10326 -7 is represented as 2#00#
10327 -6 is represented as 2#01#
10328 -5 is represented as 2#10#
10329 -4 is represented as 2#11#
10333 Biased representation is only used if the specified @code{Size} clause
10334 cannot be accepted in any other manner. These reduced sizes that force
10335 biased representation can be used for all discrete types except for
10336 enumeration types for which a representation clause is given.
10338 @node Value_Size and Object_Size Clauses
10339 @section Value_Size and Object_Size Clauses
10341 @findex Object_Size
10342 @cindex Size, of objects
10345 In Ada 95 and Ada 2005, @code{T'Size} for a type @code{T} is the minimum
10346 number of bits required to hold values of type @code{T}.
10347 Although this interpretation was allowed in Ada 83, it was not required,
10348 and this requirement in practice can cause some significant difficulties.
10349 For example, in most Ada 83 compilers, @code{Natural'Size} was 32.
10350 However, in Ada 95 and Ada 2005,
10351 @code{Natural'Size} is
10352 typically 31. This means that code may change in behavior when moving
10353 from Ada 83 to Ada 95 or Ada 2005. For example, consider:
10355 @smallexample @c ada
10356 type Rec is record;
10362 at 0 range 0 .. Natural'Size - 1;
10363 at 0 range Natural'Size .. 2 * Natural'Size - 1;
10368 In the above code, since the typical size of @code{Natural} objects
10369 is 32 bits and @code{Natural'Size} is 31, the above code can cause
10370 unexpected inefficient packing in Ada 95 and Ada 2005, and in general
10371 there are cases where the fact that the object size can exceed the
10372 size of the type causes surprises.
10374 To help get around this problem GNAT provides two implementation
10375 defined attributes, @code{Value_Size} and @code{Object_Size}. When
10376 applied to a type, these attributes yield the size of the type
10377 (corresponding to the RM defined size attribute), and the size of
10378 objects of the type respectively.
10380 The @code{Object_Size} is used for determining the default size of
10381 objects and components. This size value can be referred to using the
10382 @code{Object_Size} attribute. The phrase ``is used'' here means that it is
10383 the basis of the determination of the size. The backend is free to
10384 pad this up if necessary for efficiency, e.g.@: an 8-bit stand-alone
10385 character might be stored in 32 bits on a machine with no efficient
10386 byte access instructions such as the Alpha.
10388 The default rules for the value of @code{Object_Size} for
10389 discrete types are as follows:
10393 The @code{Object_Size} for base subtypes reflect the natural hardware
10394 size in bits (run the compiler with @option{-gnatS} to find those values
10395 for numeric types). Enumeration types and fixed-point base subtypes have
10396 8, 16, 32 or 64 bits for this size, depending on the range of values
10400 The @code{Object_Size} of a subtype is the same as the
10401 @code{Object_Size} of
10402 the type from which it is obtained.
10405 The @code{Object_Size} of a derived base type is copied from the parent
10406 base type, and the @code{Object_Size} of a derived first subtype is copied
10407 from the parent first subtype.
10411 The @code{Value_Size} attribute
10412 is the (minimum) number of bits required to store a value
10414 This value is used to determine how tightly to pack
10415 records or arrays with components of this type, and also affects
10416 the semantics of unchecked conversion (unchecked conversions where
10417 the @code{Value_Size} values differ generate a warning, and are potentially
10420 The default rules for the value of @code{Value_Size} are as follows:
10424 The @code{Value_Size} for a base subtype is the minimum number of bits
10425 required to store all values of the type (including the sign bit
10426 only if negative values are possible).
10429 If a subtype statically matches the first subtype of a given type, then it has
10430 by default the same @code{Value_Size} as the first subtype. This is a
10431 consequence of RM 13.1(14) (``if two subtypes statically match,
10432 then their subtype-specific aspects are the same''.)
10435 All other subtypes have a @code{Value_Size} corresponding to the minimum
10436 number of bits required to store all values of the subtype. For
10437 dynamic bounds, it is assumed that the value can range down or up
10438 to the corresponding bound of the ancestor
10442 The RM defined attribute @code{Size} corresponds to the
10443 @code{Value_Size} attribute.
10445 The @code{Size} attribute may be defined for a first-named subtype. This sets
10446 the @code{Value_Size} of
10447 the first-named subtype to the given value, and the
10448 @code{Object_Size} of this first-named subtype to the given value padded up
10449 to an appropriate boundary. It is a consequence of the default rules
10450 above that this @code{Object_Size} will apply to all further subtypes. On the
10451 other hand, @code{Value_Size} is affected only for the first subtype, any
10452 dynamic subtypes obtained from it directly, and any statically matching
10453 subtypes. The @code{Value_Size} of any other static subtypes is not affected.
10455 @code{Value_Size} and
10456 @code{Object_Size} may be explicitly set for any subtype using
10457 an attribute definition clause. Note that the use of these attributes
10458 can cause the RM 13.1(14) rule to be violated. If two access types
10459 reference aliased objects whose subtypes have differing @code{Object_Size}
10460 values as a result of explicit attribute definition clauses, then it
10461 is erroneous to convert from one access subtype to the other.
10463 At the implementation level, Esize stores the Object_Size and the
10464 RM_Size field stores the @code{Value_Size} (and hence the value of the
10465 @code{Size} attribute,
10466 which, as noted above, is equivalent to @code{Value_Size}).
10468 To get a feel for the difference, consider the following examples (note
10469 that in each case the base is @code{Short_Short_Integer} with a size of 8):
10472 Object_Size Value_Size
10474 type x1 is range 0 .. 5; 8 3
10476 type x2 is range 0 .. 5;
10477 for x2'size use 12; 16 12
10479 subtype x3 is x2 range 0 .. 3; 16 2
10481 subtype x4 is x2'base range 0 .. 10; 8 4
10483 subtype x5 is x2 range 0 .. dynamic; 16 3*
10485 subtype x6 is x2'base range 0 .. dynamic; 8 3*
10490 Note: the entries marked ``3*'' are not actually specified by the Ada
10491 Reference Manual, but it seems in the spirit of the RM rules to allocate
10492 the minimum number of bits (here 3, given the range for @code{x2})
10493 known to be large enough to hold the given range of values.
10495 So far, so good, but GNAT has to obey the RM rules, so the question is
10496 under what conditions must the RM @code{Size} be used.
10497 The following is a list
10498 of the occasions on which the RM @code{Size} must be used:
10502 Component size for packed arrays or records
10505 Value of the attribute @code{Size} for a type
10508 Warning about sizes not matching for unchecked conversion
10512 For record types, the @code{Object_Size} is always a multiple of the
10513 alignment of the type (this is true for all types). In some cases the
10514 @code{Value_Size} can be smaller. Consider:
10524 On a typical 32-bit architecture, the X component will be four bytes, and
10525 require four-byte alignment, and the Y component will be one byte. In this
10526 case @code{R'Value_Size} will be 40 (bits) since this is the minimum size
10527 required to store a value of this type, and for example, it is permissible
10528 to have a component of type R in an outer array whose component size is
10529 specified to be 48 bits. However, @code{R'Object_Size} will be 64 (bits),
10530 since it must be rounded up so that this value is a multiple of the
10531 alignment (4 bytes = 32 bits).
10534 For all other types, the @code{Object_Size}
10535 and Value_Size are the same (and equivalent to the RM attribute @code{Size}).
10536 Only @code{Size} may be specified for such types.
10538 @node Component_Size Clauses
10539 @section Component_Size Clauses
10540 @cindex Component_Size Clause
10543 Normally, the value specified in a component size clause must be consistent
10544 with the subtype of the array component with regard to size and alignment.
10545 In other words, the value specified must be at least equal to the size
10546 of this subtype, and must be a multiple of the alignment value.
10548 In addition, component size clauses are allowed which cause the array
10549 to be packed, by specifying a smaller value. A first case is for
10550 component size values in the range 1 through 63. The value specified
10551 must not be smaller than the Size of the subtype. GNAT will accurately
10552 honor all packing requests in this range. For example, if we have:
10554 @smallexample @c ada
10555 type r is array (1 .. 8) of Natural;
10556 for r'Component_Size use 31;
10560 then the resulting array has a length of 31 bytes (248 bits = 8 * 31).
10561 Of course access to the components of such an array is considerably
10562 less efficient than if the natural component size of 32 is used.
10563 A second case is when the subtype of the component is a record type
10564 padded because of its default alignment. For example, if we have:
10566 @smallexample @c ada
10573 type a is array (1 .. 8) of r;
10574 for a'Component_Size use 72;
10578 then the resulting array has a length of 72 bytes, instead of 96 bytes
10579 if the alignment of the record (4) was obeyed.
10581 Note that there is no point in giving both a component size clause
10582 and a pragma Pack for the same array type. if such duplicate
10583 clauses are given, the pragma Pack will be ignored.
10585 @node Bit_Order Clauses
10586 @section Bit_Order Clauses
10587 @cindex Bit_Order Clause
10588 @cindex bit ordering
10589 @cindex ordering, of bits
10592 For record subtypes, GNAT permits the specification of the @code{Bit_Order}
10593 attribute. The specification may either correspond to the default bit
10594 order for the target, in which case the specification has no effect and
10595 places no additional restrictions, or it may be for the non-standard
10596 setting (that is the opposite of the default).
10598 In the case where the non-standard value is specified, the effect is
10599 to renumber bits within each byte, but the ordering of bytes is not
10600 affected. There are certain
10601 restrictions placed on component clauses as follows:
10605 @item Components fitting within a single storage unit.
10607 These are unrestricted, and the effect is merely to renumber bits. For
10608 example if we are on a little-endian machine with @code{Low_Order_First}
10609 being the default, then the following two declarations have exactly
10612 @smallexample @c ada
10615 B : Integer range 1 .. 120;
10619 A at 0 range 0 .. 0;
10620 B at 0 range 1 .. 7;
10625 B : Integer range 1 .. 120;
10628 for R2'Bit_Order use High_Order_First;
10631 A at 0 range 7 .. 7;
10632 B at 0 range 0 .. 6;
10637 The useful application here is to write the second declaration with the
10638 @code{Bit_Order} attribute definition clause, and know that it will be treated
10639 the same, regardless of whether the target is little-endian or big-endian.
10641 @item Components occupying an integral number of bytes.
10643 These are components that exactly fit in two or more bytes. Such component
10644 declarations are allowed, but have no effect, since it is important to realize
10645 that the @code{Bit_Order} specification does not affect the ordering of bytes.
10646 In particular, the following attempt at getting an endian-independent integer
10649 @smallexample @c ada
10654 for R2'Bit_Order use High_Order_First;
10657 A at 0 range 0 .. 31;
10662 This declaration will result in a little-endian integer on a
10663 little-endian machine, and a big-endian integer on a big-endian machine.
10664 If byte flipping is required for interoperability between big- and
10665 little-endian machines, this must be explicitly programmed. This capability
10666 is not provided by @code{Bit_Order}.
10668 @item Components that are positioned across byte boundaries
10670 but do not occupy an integral number of bytes. Given that bytes are not
10671 reordered, such fields would occupy a non-contiguous sequence of bits
10672 in memory, requiring non-trivial code to reassemble. They are for this
10673 reason not permitted, and any component clause specifying such a layout
10674 will be flagged as illegal by GNAT@.
10679 Since the misconception that Bit_Order automatically deals with all
10680 endian-related incompatibilities is a common one, the specification of
10681 a component field that is an integral number of bytes will always
10682 generate a warning. This warning may be suppressed using @code{pragma
10683 Warnings (Off)} if desired. The following section contains additional
10684 details regarding the issue of byte ordering.
10686 @node Effect of Bit_Order on Byte Ordering
10687 @section Effect of Bit_Order on Byte Ordering
10688 @cindex byte ordering
10689 @cindex ordering, of bytes
10692 In this section we will review the effect of the @code{Bit_Order} attribute
10693 definition clause on byte ordering. Briefly, it has no effect at all, but
10694 a detailed example will be helpful. Before giving this
10695 example, let us review the precise
10696 definition of the effect of defining @code{Bit_Order}. The effect of a
10697 non-standard bit order is described in section 15.5.3 of the Ada
10701 2 A bit ordering is a method of interpreting the meaning of
10702 the storage place attributes.
10706 To understand the precise definition of storage place attributes in
10707 this context, we visit section 13.5.1 of the manual:
10710 13 A record_representation_clause (without the mod_clause)
10711 specifies the layout. The storage place attributes (see 13.5.2)
10712 are taken from the values of the position, first_bit, and last_bit
10713 expressions after normalizing those values so that first_bit is
10714 less than Storage_Unit.
10718 The critical point here is that storage places are taken from
10719 the values after normalization, not before. So the @code{Bit_Order}
10720 interpretation applies to normalized values. The interpretation
10721 is described in the later part of the 15.5.3 paragraph:
10724 2 A bit ordering is a method of interpreting the meaning of
10725 the storage place attributes. High_Order_First (known in the
10726 vernacular as ``big endian'') means that the first bit of a
10727 storage element (bit 0) is the most significant bit (interpreting
10728 the sequence of bits that represent a component as an unsigned
10729 integer value). Low_Order_First (known in the vernacular as
10730 ``little endian'') means the opposite: the first bit is the
10735 Note that the numbering is with respect to the bits of a storage
10736 unit. In other words, the specification affects only the numbering
10737 of bits within a single storage unit.
10739 We can make the effect clearer by giving an example.
10741 Suppose that we have an external device which presents two bytes, the first
10742 byte presented, which is the first (low addressed byte) of the two byte
10743 record is called Master, and the second byte is called Slave.
10745 The left most (most significant bit is called Control for each byte, and
10746 the remaining 7 bits are called V1, V2, @dots{} V7, where V7 is the rightmost
10747 (least significant) bit.
10749 On a big-endian machine, we can write the following representation clause
10751 @smallexample @c ada
10752 type Data is record
10753 Master_Control : Bit;
10761 Slave_Control : Bit;
10771 for Data use record
10772 Master_Control at 0 range 0 .. 0;
10773 Master_V1 at 0 range 1 .. 1;
10774 Master_V2 at 0 range 2 .. 2;
10775 Master_V3 at 0 range 3 .. 3;
10776 Master_V4 at 0 range 4 .. 4;
10777 Master_V5 at 0 range 5 .. 5;
10778 Master_V6 at 0 range 6 .. 6;
10779 Master_V7 at 0 range 7 .. 7;
10780 Slave_Control at 1 range 0 .. 0;
10781 Slave_V1 at 1 range 1 .. 1;
10782 Slave_V2 at 1 range 2 .. 2;
10783 Slave_V3 at 1 range 3 .. 3;
10784 Slave_V4 at 1 range 4 .. 4;
10785 Slave_V5 at 1 range 5 .. 5;
10786 Slave_V6 at 1 range 6 .. 6;
10787 Slave_V7 at 1 range 7 .. 7;
10792 Now if we move this to a little endian machine, then the bit ordering within
10793 the byte is backwards, so we have to rewrite the record rep clause as:
10795 @smallexample @c ada
10796 for Data use record
10797 Master_Control at 0 range 7 .. 7;
10798 Master_V1 at 0 range 6 .. 6;
10799 Master_V2 at 0 range 5 .. 5;
10800 Master_V3 at 0 range 4 .. 4;
10801 Master_V4 at 0 range 3 .. 3;
10802 Master_V5 at 0 range 2 .. 2;
10803 Master_V6 at 0 range 1 .. 1;
10804 Master_V7 at 0 range 0 .. 0;
10805 Slave_Control at 1 range 7 .. 7;
10806 Slave_V1 at 1 range 6 .. 6;
10807 Slave_V2 at 1 range 5 .. 5;
10808 Slave_V3 at 1 range 4 .. 4;
10809 Slave_V4 at 1 range 3 .. 3;
10810 Slave_V5 at 1 range 2 .. 2;
10811 Slave_V6 at 1 range 1 .. 1;
10812 Slave_V7 at 1 range 0 .. 0;
10817 It is a nuisance to have to rewrite the clause, especially if
10818 the code has to be maintained on both machines. However,
10819 this is a case that we can handle with the
10820 @code{Bit_Order} attribute if it is implemented.
10821 Note that the implementation is not required on byte addressed
10822 machines, but it is indeed implemented in GNAT.
10823 This means that we can simply use the
10824 first record clause, together with the declaration
10826 @smallexample @c ada
10827 for Data'Bit_Order use High_Order_First;
10831 and the effect is what is desired, namely the layout is exactly the same,
10832 independent of whether the code is compiled on a big-endian or little-endian
10835 The important point to understand is that byte ordering is not affected.
10836 A @code{Bit_Order} attribute definition never affects which byte a field
10837 ends up in, only where it ends up in that byte.
10838 To make this clear, let us rewrite the record rep clause of the previous
10841 @smallexample @c ada
10842 for Data'Bit_Order use High_Order_First;
10843 for Data use record
10844 Master_Control at 0 range 0 .. 0;
10845 Master_V1 at 0 range 1 .. 1;
10846 Master_V2 at 0 range 2 .. 2;
10847 Master_V3 at 0 range 3 .. 3;
10848 Master_V4 at 0 range 4 .. 4;
10849 Master_V5 at 0 range 5 .. 5;
10850 Master_V6 at 0 range 6 .. 6;
10851 Master_V7 at 0 range 7 .. 7;
10852 Slave_Control at 0 range 8 .. 8;
10853 Slave_V1 at 0 range 9 .. 9;
10854 Slave_V2 at 0 range 10 .. 10;
10855 Slave_V3 at 0 range 11 .. 11;
10856 Slave_V4 at 0 range 12 .. 12;
10857 Slave_V5 at 0 range 13 .. 13;
10858 Slave_V6 at 0 range 14 .. 14;
10859 Slave_V7 at 0 range 15 .. 15;
10864 This is exactly equivalent to saying (a repeat of the first example):
10866 @smallexample @c ada
10867 for Data'Bit_Order use High_Order_First;
10868 for Data use record
10869 Master_Control at 0 range 0 .. 0;
10870 Master_V1 at 0 range 1 .. 1;
10871 Master_V2 at 0 range 2 .. 2;
10872 Master_V3 at 0 range 3 .. 3;
10873 Master_V4 at 0 range 4 .. 4;
10874 Master_V5 at 0 range 5 .. 5;
10875 Master_V6 at 0 range 6 .. 6;
10876 Master_V7 at 0 range 7 .. 7;
10877 Slave_Control at 1 range 0 .. 0;
10878 Slave_V1 at 1 range 1 .. 1;
10879 Slave_V2 at 1 range 2 .. 2;
10880 Slave_V3 at 1 range 3 .. 3;
10881 Slave_V4 at 1 range 4 .. 4;
10882 Slave_V5 at 1 range 5 .. 5;
10883 Slave_V6 at 1 range 6 .. 6;
10884 Slave_V7 at 1 range 7 .. 7;
10889 Why are they equivalent? Well take a specific field, the @code{Slave_V2}
10890 field. The storage place attributes are obtained by normalizing the
10891 values given so that the @code{First_Bit} value is less than 8. After
10892 normalizing the values (0,10,10) we get (1,2,2) which is exactly what
10893 we specified in the other case.
10895 Now one might expect that the @code{Bit_Order} attribute might affect
10896 bit numbering within the entire record component (two bytes in this
10897 case, thus affecting which byte fields end up in), but that is not
10898 the way this feature is defined, it only affects numbering of bits,
10899 not which byte they end up in.
10901 Consequently it never makes sense to specify a starting bit number
10902 greater than 7 (for a byte addressable field) if an attribute
10903 definition for @code{Bit_Order} has been given, and indeed it
10904 may be actively confusing to specify such a value, so the compiler
10905 generates a warning for such usage.
10907 If you do need to control byte ordering then appropriate conditional
10908 values must be used. If in our example, the slave byte came first on
10909 some machines we might write:
10911 @smallexample @c ada
10912 Master_Byte_First constant Boolean := @dots{};
10914 Master_Byte : constant Natural :=
10915 1 - Boolean'Pos (Master_Byte_First);
10916 Slave_Byte : constant Natural :=
10917 Boolean'Pos (Master_Byte_First);
10919 for Data'Bit_Order use High_Order_First;
10920 for Data use record
10921 Master_Control at Master_Byte range 0 .. 0;
10922 Master_V1 at Master_Byte range 1 .. 1;
10923 Master_V2 at Master_Byte range 2 .. 2;
10924 Master_V3 at Master_Byte range 3 .. 3;
10925 Master_V4 at Master_Byte range 4 .. 4;
10926 Master_V5 at Master_Byte range 5 .. 5;
10927 Master_V6 at Master_Byte range 6 .. 6;
10928 Master_V7 at Master_Byte range 7 .. 7;
10929 Slave_Control at Slave_Byte range 0 .. 0;
10930 Slave_V1 at Slave_Byte range 1 .. 1;
10931 Slave_V2 at Slave_Byte range 2 .. 2;
10932 Slave_V3 at Slave_Byte range 3 .. 3;
10933 Slave_V4 at Slave_Byte range 4 .. 4;
10934 Slave_V5 at Slave_Byte range 5 .. 5;
10935 Slave_V6 at Slave_Byte range 6 .. 6;
10936 Slave_V7 at Slave_Byte range 7 .. 7;
10941 Now to switch between machines, all that is necessary is
10942 to set the boolean constant @code{Master_Byte_First} in
10943 an appropriate manner.
10945 @node Pragma Pack for Arrays
10946 @section Pragma Pack for Arrays
10947 @cindex Pragma Pack (for arrays)
10950 Pragma @code{Pack} applied to an array has no effect unless the component type
10951 is packable. For a component type to be packable, it must be one of the
10958 Any type whose size is specified with a size clause
10960 Any packed array type with a static size
10962 Any record type padded because of its default alignment
10966 For all these cases, if the component subtype size is in the range
10967 1 through 63, then the effect of the pragma @code{Pack} is exactly as though a
10968 component size were specified giving the component subtype size.
10969 For example if we have:
10971 @smallexample @c ada
10972 type r is range 0 .. 17;
10974 type ar is array (1 .. 8) of r;
10979 Then the component size of @code{ar} will be set to 5 (i.e.@: to @code{r'size},
10980 and the size of the array @code{ar} will be exactly 40 bits.
10982 Note that in some cases this rather fierce approach to packing can produce
10983 unexpected effects. For example, in Ada 95 and Ada 2005,
10984 subtype @code{Natural} typically has a size of 31, meaning that if you
10985 pack an array of @code{Natural}, you get 31-bit
10986 close packing, which saves a few bits, but results in far less efficient
10987 access. Since many other Ada compilers will ignore such a packing request,
10988 GNAT will generate a warning on some uses of pragma @code{Pack} that it guesses
10989 might not be what is intended. You can easily remove this warning by
10990 using an explicit @code{Component_Size} setting instead, which never generates
10991 a warning, since the intention of the programmer is clear in this case.
10993 GNAT treats packed arrays in one of two ways. If the size of the array is
10994 known at compile time and is less than 64 bits, then internally the array
10995 is represented as a single modular type, of exactly the appropriate number
10996 of bits. If the length is greater than 63 bits, or is not known at compile
10997 time, then the packed array is represented as an array of bytes, and the
10998 length is always a multiple of 8 bits.
11000 Note that to represent a packed array as a modular type, the alignment must
11001 be suitable for the modular type involved. For example, on typical machines
11002 a 32-bit packed array will be represented by a 32-bit modular integer with
11003 an alignment of four bytes. If you explicitly override the default alignment
11004 with an alignment clause that is too small, the modular representation
11005 cannot be used. For example, consider the following set of declarations:
11007 @smallexample @c ada
11008 type R is range 1 .. 3;
11009 type S is array (1 .. 31) of R;
11010 for S'Component_Size use 2;
11012 for S'Alignment use 1;
11016 If the alignment clause were not present, then a 62-bit modular
11017 representation would be chosen (typically with an alignment of 4 or 8
11018 bytes depending on the target). But the default alignment is overridden
11019 with the explicit alignment clause. This means that the modular
11020 representation cannot be used, and instead the array of bytes
11021 representation must be used, meaning that the length must be a multiple
11022 of 8. Thus the above set of declarations will result in a diagnostic
11023 rejecting the size clause and noting that the minimum size allowed is 64.
11025 @cindex Pragma Pack (for type Natural)
11026 @cindex Pragma Pack warning
11028 One special case that is worth noting occurs when the base type of the
11029 component size is 8/16/32 and the subtype is one bit less. Notably this
11030 occurs with subtype @code{Natural}. Consider:
11032 @smallexample @c ada
11033 type Arr is array (1 .. 32) of Natural;
11038 In all commonly used Ada 83 compilers, this pragma Pack would be ignored,
11039 since typically @code{Natural'Size} is 32 in Ada 83, and in any case most
11040 Ada 83 compilers did not attempt 31 bit packing.
11042 In Ada 95 and Ada 2005, @code{Natural'Size} is required to be 31. Furthermore,
11043 GNAT really does pack 31-bit subtype to 31 bits. This may result in a
11044 substantial unintended performance penalty when porting legacy Ada 83 code.
11045 To help prevent this, GNAT generates a warning in such cases. If you really
11046 want 31 bit packing in a case like this, you can set the component size
11049 @smallexample @c ada
11050 type Arr is array (1 .. 32) of Natural;
11051 for Arr'Component_Size use 31;
11055 Here 31-bit packing is achieved as required, and no warning is generated,
11056 since in this case the programmer intention is clear.
11058 @node Pragma Pack for Records
11059 @section Pragma Pack for Records
11060 @cindex Pragma Pack (for records)
11063 Pragma @code{Pack} applied to a record will pack the components to reduce
11064 wasted space from alignment gaps and by reducing the amount of space
11065 taken by components. We distinguish between @emph{packable} components and
11066 @emph{non-packable} components.
11067 Components of the following types are considered packable:
11070 All primitive types are packable.
11073 Small packed arrays, whose size does not exceed 64 bits, and where the
11074 size is statically known at compile time, are represented internally
11075 as modular integers, and so they are also packable.
11080 All packable components occupy the exact number of bits corresponding to
11081 their @code{Size} value, and are packed with no padding bits, i.e.@: they
11082 can start on an arbitrary bit boundary.
11084 All other types are non-packable, they occupy an integral number of
11086 are placed at a boundary corresponding to their alignment requirements.
11088 For example, consider the record
11090 @smallexample @c ada
11091 type Rb1 is array (1 .. 13) of Boolean;
11094 type Rb2 is array (1 .. 65) of Boolean;
11109 The representation for the record x2 is as follows:
11111 @smallexample @c ada
11112 for x2'Size use 224;
11114 l1 at 0 range 0 .. 0;
11115 l2 at 0 range 1 .. 64;
11116 l3 at 12 range 0 .. 31;
11117 l4 at 16 range 0 .. 0;
11118 l5 at 16 range 1 .. 13;
11119 l6 at 18 range 0 .. 71;
11124 Studying this example, we see that the packable fields @code{l1}
11126 of length equal to their sizes, and placed at specific bit boundaries (and
11127 not byte boundaries) to
11128 eliminate padding. But @code{l3} is of a non-packable float type, so
11129 it is on the next appropriate alignment boundary.
11131 The next two fields are fully packable, so @code{l4} and @code{l5} are
11132 minimally packed with no gaps. However, type @code{Rb2} is a packed
11133 array that is longer than 64 bits, so it is itself non-packable. Thus
11134 the @code{l6} field is aligned to the next byte boundary, and takes an
11135 integral number of bytes, i.e.@: 72 bits.
11137 @node Record Representation Clauses
11138 @section Record Representation Clauses
11139 @cindex Record Representation Clause
11142 Record representation clauses may be given for all record types, including
11143 types obtained by record extension. Component clauses are allowed for any
11144 static component. The restrictions on component clauses depend on the type
11147 @cindex Component Clause
11148 For all components of an elementary type, the only restriction on component
11149 clauses is that the size must be at least the 'Size value of the type
11150 (actually the Value_Size). There are no restrictions due to alignment,
11151 and such components may freely cross storage boundaries.
11153 Packed arrays with a size up to and including 64 bits are represented
11154 internally using a modular type with the appropriate number of bits, and
11155 thus the same lack of restriction applies. For example, if you declare:
11157 @smallexample @c ada
11158 type R is array (1 .. 49) of Boolean;
11164 then a component clause for a component of type R may start on any
11165 specified bit boundary, and may specify a value of 49 bits or greater.
11167 For packed bit arrays that are longer than 64 bits, there are two
11168 cases. If the component size is a power of 2 (1,2,4,8,16,32 bits),
11169 including the important case of single bits or boolean values, then
11170 there are no limitations on placement of such components, and they
11171 may start and end at arbitrary bit boundaries.
11173 If the component size is not a power of 2 (e.g.@: 3 or 5), then
11174 an array of this type longer than 64 bits must always be placed on
11175 on a storage unit (byte) boundary and occupy an integral number
11176 of storage units (bytes). Any component clause that does not
11177 meet this requirement will be rejected.
11179 Any aliased component, or component of an aliased type, must
11180 have its normal alignment and size. A component clause that
11181 does not meet this requirement will be rejected.
11183 The tag field of a tagged type always occupies an address sized field at
11184 the start of the record. No component clause may attempt to overlay this
11185 tag. When a tagged type appears as a component, the tag field must have
11188 In the case of a record extension T1, of a type T, no component clause applied
11189 to the type T1 can specify a storage location that would overlap the first
11190 T'Size bytes of the record.
11192 For all other component types, including non-bit-packed arrays,
11193 the component can be placed at an arbitrary bit boundary,
11194 so for example, the following is permitted:
11196 @smallexample @c ada
11197 type R is array (1 .. 10) of Boolean;
11206 G at 0 range 0 .. 0;
11207 H at 0 range 1 .. 1;
11208 L at 0 range 2 .. 81;
11209 R at 0 range 82 .. 161;
11214 Note: the above rules apply to recent releases of GNAT 5.
11215 In GNAT 3, there are more severe restrictions on larger components.
11216 For non-primitive types, including packed arrays with a size greater than
11217 64 bits, component clauses must respect the alignment requirement of the
11218 type, in particular, always starting on a byte boundary, and the length
11219 must be a multiple of the storage unit.
11221 @node Enumeration Clauses
11222 @section Enumeration Clauses
11224 The only restriction on enumeration clauses is that the range of values
11225 must be representable. For the signed case, if one or more of the
11226 representation values are negative, all values must be in the range:
11228 @smallexample @c ada
11229 System.Min_Int .. System.Max_Int
11233 For the unsigned case, where all values are nonnegative, the values must
11236 @smallexample @c ada
11237 0 .. System.Max_Binary_Modulus;
11241 A @emph{confirming} representation clause is one in which the values range
11242 from 0 in sequence, i.e.@: a clause that confirms the default representation
11243 for an enumeration type.
11244 Such a confirming representation
11245 is permitted by these rules, and is specially recognized by the compiler so
11246 that no extra overhead results from the use of such a clause.
11248 If an array has an index type which is an enumeration type to which an
11249 enumeration clause has been applied, then the array is stored in a compact
11250 manner. Consider the declarations:
11252 @smallexample @c ada
11253 type r is (A, B, C);
11254 for r use (A => 1, B => 5, C => 10);
11255 type t is array (r) of Character;
11259 The array type t corresponds to a vector with exactly three elements and
11260 has a default size equal to @code{3*Character'Size}. This ensures efficient
11261 use of space, but means that accesses to elements of the array will incur
11262 the overhead of converting representation values to the corresponding
11263 positional values, (i.e.@: the value delivered by the @code{Pos} attribute).
11265 @node Address Clauses
11266 @section Address Clauses
11267 @cindex Address Clause
11269 The reference manual allows a general restriction on representation clauses,
11270 as found in RM 13.1(22):
11273 An implementation need not support representation
11274 items containing nonstatic expressions, except that
11275 an implementation should support a representation item
11276 for a given entity if each nonstatic expression in the
11277 representation item is a name that statically denotes
11278 a constant declared before the entity.
11282 In practice this is applicable only to address clauses, since this is the
11283 only case in which a non-static expression is permitted by the syntax. As
11284 the AARM notes in sections 13.1 (22.a-22.h):
11287 22.a Reason: This is to avoid the following sort of thing:
11289 22.b X : Integer := F(@dots{});
11290 Y : Address := G(@dots{});
11291 for X'Address use Y;
11293 22.c In the above, we have to evaluate the
11294 initialization expression for X before we
11295 know where to put the result. This seems
11296 like an unreasonable implementation burden.
11298 22.d The above code should instead be written
11301 22.e Y : constant Address := G(@dots{});
11302 X : Integer := F(@dots{});
11303 for X'Address use Y;
11305 22.f This allows the expression ``Y'' to be safely
11306 evaluated before X is created.
11308 22.g The constant could be a formal parameter of mode in.
11310 22.h An implementation can support other nonstatic
11311 expressions if it wants to. Expressions of type
11312 Address are hardly ever static, but their value
11313 might be known at compile time anyway in many
11318 GNAT does indeed permit many additional cases of non-static expressions. In
11319 particular, if the type involved is elementary there are no restrictions
11320 (since in this case, holding a temporary copy of the initialization value,
11321 if one is present, is inexpensive). In addition, if there is no implicit or
11322 explicit initialization, then there are no restrictions. GNAT will reject
11323 only the case where all three of these conditions hold:
11328 The type of the item is non-elementary (e.g.@: a record or array).
11331 There is explicit or implicit initialization required for the object.
11332 Note that access values are always implicitly initialized, and also
11333 in GNAT, certain bit-packed arrays (those having a dynamic length or
11334 a length greater than 64) will also be implicitly initialized to zero.
11337 The address value is non-static. Here GNAT is more permissive than the
11338 RM, and allows the address value to be the address of a previously declared
11339 stand-alone variable, as long as it does not itself have an address clause.
11341 @smallexample @c ada
11342 Anchor : Some_Initialized_Type;
11343 Overlay : Some_Initialized_Type;
11344 for Overlay'Address use Anchor'Address;
11348 However, the prefix of the address clause cannot be an array component, or
11349 a component of a discriminated record.
11354 As noted above in section 22.h, address values are typically non-static. In
11355 particular the To_Address function, even if applied to a literal value, is
11356 a non-static function call. To avoid this minor annoyance, GNAT provides
11357 the implementation defined attribute 'To_Address. The following two
11358 expressions have identical values:
11362 @smallexample @c ada
11363 To_Address (16#1234_0000#)
11364 System'To_Address (16#1234_0000#);
11368 except that the second form is considered to be a static expression, and
11369 thus when used as an address clause value is always permitted.
11372 Additionally, GNAT treats as static an address clause that is an
11373 unchecked_conversion of a static integer value. This simplifies the porting
11374 of legacy code, and provides a portable equivalent to the GNAT attribute
11377 Another issue with address clauses is the interaction with alignment
11378 requirements. When an address clause is given for an object, the address
11379 value must be consistent with the alignment of the object (which is usually
11380 the same as the alignment of the type of the object). If an address clause
11381 is given that specifies an inappropriately aligned address value, then the
11382 program execution is erroneous.
11384 Since this source of erroneous behavior can have unfortunate effects, GNAT
11385 checks (at compile time if possible, generating a warning, or at execution
11386 time with a run-time check) that the alignment is appropriate. If the
11387 run-time check fails, then @code{Program_Error} is raised. This run-time
11388 check is suppressed if range checks are suppressed, or if the special GNAT
11389 check Alignment_Check is suppressed, or if
11390 @code{pragma Restrictions (No_Elaboration_Code)} is in effect.
11392 Finally, GNAT does not permit overlaying of objects of controlled types or
11393 composite types containing a controlled component. In most cases, the compiler
11394 can detect an attempt at such overlays and will generate a warning at compile
11395 time and a Program_Error exception at run time.
11398 An address clause cannot be given for an exported object. More
11399 understandably the real restriction is that objects with an address
11400 clause cannot be exported. This is because such variables are not
11401 defined by the Ada program, so there is no external object to export.
11404 It is permissible to give an address clause and a pragma Import for the
11405 same object. In this case, the variable is not really defined by the
11406 Ada program, so there is no external symbol to be linked. The link name
11407 and the external name are ignored in this case. The reason that we allow this
11408 combination is that it provides a useful idiom to avoid unwanted
11409 initializations on objects with address clauses.
11411 When an address clause is given for an object that has implicit or
11412 explicit initialization, then by default initialization takes place. This
11413 means that the effect of the object declaration is to overwrite the
11414 memory at the specified address. This is almost always not what the
11415 programmer wants, so GNAT will output a warning:
11425 for Ext'Address use System'To_Address (16#1234_1234#);
11427 >>> warning: implicit initialization of "Ext" may
11428 modify overlaid storage
11429 >>> warning: use pragma Import for "Ext" to suppress
11430 initialization (RM B(24))
11436 As indicated by the warning message, the solution is to use a (dummy) pragma
11437 Import to suppress this initialization. The pragma tell the compiler that the
11438 object is declared and initialized elsewhere. The following package compiles
11439 without warnings (and the initialization is suppressed):
11441 @smallexample @c ada
11449 for Ext'Address use System'To_Address (16#1234_1234#);
11450 pragma Import (Ada, Ext);
11455 A final issue with address clauses involves their use for overlaying
11456 variables, as in the following example:
11457 @cindex Overlaying of objects
11459 @smallexample @c ada
11462 for B'Address use A'Address;
11466 or alternatively, using the form recommended by the RM:
11468 @smallexample @c ada
11470 Addr : constant Address := A'Address;
11472 for B'Address use Addr;
11476 In both of these cases, @code{A}
11477 and @code{B} become aliased to one another via the
11478 address clause. This use of address clauses to overlay
11479 variables, achieving an effect similar to unchecked
11480 conversion was erroneous in Ada 83, but in Ada 95 and Ada 2005
11481 the effect is implementation defined. Furthermore, the
11482 Ada RM specifically recommends that in a situation
11483 like this, @code{B} should be subject to the following
11484 implementation advice (RM 13.3(19)):
11487 19 If the Address of an object is specified, or it is imported
11488 or exported, then the implementation should not perform
11489 optimizations based on assumptions of no aliases.
11493 GNAT follows this recommendation, and goes further by also applying
11494 this recommendation to the overlaid variable (@code{A}
11495 in the above example) in this case. This means that the overlay
11496 works "as expected", in that a modification to one of the variables
11497 will affect the value of the other.
11499 @node Effect of Convention on Representation
11500 @section Effect of Convention on Representation
11501 @cindex Convention, effect on representation
11504 Normally the specification of a foreign language convention for a type or
11505 an object has no effect on the chosen representation. In particular, the
11506 representation chosen for data in GNAT generally meets the standard system
11507 conventions, and for example records are laid out in a manner that is
11508 consistent with C@. This means that specifying convention C (for example)
11511 There are four exceptions to this general rule:
11515 @item Convention Fortran and array subtypes
11516 If pragma Convention Fortran is specified for an array subtype, then in
11517 accordance with the implementation advice in section 3.6.2(11) of the
11518 Ada Reference Manual, the array will be stored in a Fortran-compatible
11519 column-major manner, instead of the normal default row-major order.
11521 @item Convention C and enumeration types
11522 GNAT normally stores enumeration types in 8, 16, or 32 bits as required
11523 to accommodate all values of the type. For example, for the enumeration
11526 @smallexample @c ada
11527 type Color is (Red, Green, Blue);
11531 8 bits is sufficient to store all values of the type, so by default, objects
11532 of type @code{Color} will be represented using 8 bits. However, normal C
11533 convention is to use 32 bits for all enum values in C, since enum values
11534 are essentially of type int. If pragma @code{Convention C} is specified for an
11535 Ada enumeration type, then the size is modified as necessary (usually to
11536 32 bits) to be consistent with the C convention for enum values.
11538 Note that this treatment applies only to types. If Convention C is given for
11539 an enumeration object, where the enumeration type is not Convention C, then
11540 Object_Size bits are allocated. For example, for a normal enumeration type,
11541 with less than 256 elements, only 8 bits will be allocated for the object.
11542 Since this may be a surprise in terms of what C expects, GNAT will issue a
11543 warning in this situation. The warning can be suppressed by giving an explicit
11544 size clause specifying the desired size.
11546 @item Convention C/Fortran and Boolean types
11547 In C, the usual convention for boolean values, that is values used for
11548 conditions, is that zero represents false, and nonzero values represent
11549 true. In Ada, the normal convention is that two specific values, typically
11550 0/1, are used to represent false/true respectively.
11552 Fortran has a similar convention for @code{LOGICAL} values (any nonzero
11553 value represents true).
11555 To accommodate the Fortran and C conventions, if a pragma Convention specifies
11556 C or Fortran convention for a derived Boolean, as in the following example:
11558 @smallexample @c ada
11559 type C_Switch is new Boolean;
11560 pragma Convention (C, C_Switch);
11564 then the GNAT generated code will treat any nonzero value as true. For truth
11565 values generated by GNAT, the conventional value 1 will be used for True, but
11566 when one of these values is read, any nonzero value is treated as True.
11568 @item Access types on OpenVMS
11569 For 64-bit OpenVMS systems, access types (other than those for unconstrained
11570 arrays) are 64-bits long. An exception to this rule is for the case of
11571 C-convention access types where there is no explicit size clause present (or
11572 inherited for derived types). In this case, GNAT chooses to make these
11573 pointers 32-bits, which provides an easier path for migration of 32-bit legacy
11574 code. size clause specifying 64-bits must be used to obtain a 64-bit pointer.
11578 @node Determining the Representations chosen by GNAT
11579 @section Determining the Representations chosen by GNAT
11580 @cindex Representation, determination of
11581 @cindex @option{-gnatR} switch
11584 Although the descriptions in this section are intended to be complete, it is
11585 often easier to simply experiment to see what GNAT accepts and what the
11586 effect is on the layout of types and objects.
11588 As required by the Ada RM, if a representation clause is not accepted, then
11589 it must be rejected as illegal by the compiler. However, when a
11590 representation clause or pragma is accepted, there can still be questions
11591 of what the compiler actually does. For example, if a partial record
11592 representation clause specifies the location of some components and not
11593 others, then where are the non-specified components placed? Or if pragma
11594 @code{Pack} is used on a record, then exactly where are the resulting
11595 fields placed? The section on pragma @code{Pack} in this chapter can be
11596 used to answer the second question, but it is often easier to just see
11597 what the compiler does.
11599 For this purpose, GNAT provides the option @option{-gnatR}. If you compile
11600 with this option, then the compiler will output information on the actual
11601 representations chosen, in a format similar to source representation
11602 clauses. For example, if we compile the package:
11604 @smallexample @c ada
11606 type r (x : boolean) is tagged record
11608 when True => S : String (1 .. 100);
11609 when False => null;
11613 type r2 is new r (false) with record
11618 y2 at 16 range 0 .. 31;
11625 type x1 is array (1 .. 10) of x;
11626 for x1'component_size use 11;
11628 type ia is access integer;
11630 type Rb1 is array (1 .. 13) of Boolean;
11633 type Rb2 is array (1 .. 65) of Boolean;
11649 using the switch @option{-gnatR} we obtain the following output:
11652 Representation information for unit q
11653 -------------------------------------
11656 for r'Alignment use 4;
11658 x at 4 range 0 .. 7;
11659 _tag at 0 range 0 .. 31;
11660 s at 5 range 0 .. 799;
11663 for r2'Size use 160;
11664 for r2'Alignment use 4;
11666 x at 4 range 0 .. 7;
11667 _tag at 0 range 0 .. 31;
11668 _parent at 0 range 0 .. 63;
11669 y2 at 16 range 0 .. 31;
11673 for x'Alignment use 1;
11675 y at 0 range 0 .. 7;
11678 for x1'Size use 112;
11679 for x1'Alignment use 1;
11680 for x1'Component_Size use 11;
11682 for rb1'Size use 13;
11683 for rb1'Alignment use 2;
11684 for rb1'Component_Size use 1;
11686 for rb2'Size use 72;
11687 for rb2'Alignment use 1;
11688 for rb2'Component_Size use 1;
11690 for x2'Size use 224;
11691 for x2'Alignment use 4;
11693 l1 at 0 range 0 .. 0;
11694 l2 at 0 range 1 .. 64;
11695 l3 at 12 range 0 .. 31;
11696 l4 at 16 range 0 .. 0;
11697 l5 at 16 range 1 .. 13;
11698 l6 at 18 range 0 .. 71;
11703 The Size values are actually the Object_Size, i.e.@: the default size that
11704 will be allocated for objects of the type.
11705 The ?? size for type r indicates that we have a variant record, and the
11706 actual size of objects will depend on the discriminant value.
11708 The Alignment values show the actual alignment chosen by the compiler
11709 for each record or array type.
11711 The record representation clause for type r shows where all fields
11712 are placed, including the compiler generated tag field (whose location
11713 cannot be controlled by the programmer).
11715 The record representation clause for the type extension r2 shows all the
11716 fields present, including the parent field, which is a copy of the fields
11717 of the parent type of r2, i.e.@: r1.
11719 The component size and size clauses for types rb1 and rb2 show
11720 the exact effect of pragma @code{Pack} on these arrays, and the record
11721 representation clause for type x2 shows how pragma @code{Pack} affects
11724 In some cases, it may be useful to cut and paste the representation clauses
11725 generated by the compiler into the original source to fix and guarantee
11726 the actual representation to be used.
11728 @node Standard Library Routines
11729 @chapter Standard Library Routines
11732 The Ada Reference Manual contains in Annex A a full description of an
11733 extensive set of standard library routines that can be used in any Ada
11734 program, and which must be provided by all Ada compilers. They are
11735 analogous to the standard C library used by C programs.
11737 GNAT implements all of the facilities described in annex A, and for most
11738 purposes the description in the Ada Reference Manual, or appropriate Ada
11739 text book, will be sufficient for making use of these facilities.
11741 In the case of the input-output facilities,
11742 @xref{The Implementation of Standard I/O},
11743 gives details on exactly how GNAT interfaces to the
11744 file system. For the remaining packages, the Ada Reference Manual
11745 should be sufficient. The following is a list of the packages included,
11746 together with a brief description of the functionality that is provided.
11748 For completeness, references are included to other predefined library
11749 routines defined in other sections of the Ada Reference Manual (these are
11750 cross-indexed from Annex A).
11754 This is a parent package for all the standard library packages. It is
11755 usually included implicitly in your program, and itself contains no
11756 useful data or routines.
11758 @item Ada.Calendar (9.6)
11759 @code{Calendar} provides time of day access, and routines for
11760 manipulating times and durations.
11762 @item Ada.Characters (A.3.1)
11763 This is a dummy parent package that contains no useful entities
11765 @item Ada.Characters.Handling (A.3.2)
11766 This package provides some basic character handling capabilities,
11767 including classification functions for classes of characters (e.g.@: test
11768 for letters, or digits).
11770 @item Ada.Characters.Latin_1 (A.3.3)
11771 This package includes a complete set of definitions of the characters
11772 that appear in type CHARACTER@. It is useful for writing programs that
11773 will run in international environments. For example, if you want an
11774 upper case E with an acute accent in a string, it is often better to use
11775 the definition of @code{UC_E_Acute} in this package. Then your program
11776 will print in an understandable manner even if your environment does not
11777 support these extended characters.
11779 @item Ada.Command_Line (A.15)
11780 This package provides access to the command line parameters and the name
11781 of the current program (analogous to the use of @code{argc} and @code{argv}
11782 in C), and also allows the exit status for the program to be set in a
11783 system-independent manner.
11785 @item Ada.Decimal (F.2)
11786 This package provides constants describing the range of decimal numbers
11787 implemented, and also a decimal divide routine (analogous to the COBOL
11788 verb DIVIDE @dots{} GIVING @dots{} REMAINDER @dots{})
11790 @item Ada.Direct_IO (A.8.4)
11791 This package provides input-output using a model of a set of records of
11792 fixed-length, containing an arbitrary definite Ada type, indexed by an
11793 integer record number.
11795 @item Ada.Dynamic_Priorities (D.5)
11796 This package allows the priorities of a task to be adjusted dynamically
11797 as the task is running.
11799 @item Ada.Exceptions (11.4.1)
11800 This package provides additional information on exceptions, and also
11801 contains facilities for treating exceptions as data objects, and raising
11802 exceptions with associated messages.
11804 @item Ada.Finalization (7.6)
11805 This package contains the declarations and subprograms to support the
11806 use of controlled types, providing for automatic initialization and
11807 finalization (analogous to the constructors and destructors of C++)
11809 @item Ada.Interrupts (C.3.2)
11810 This package provides facilities for interfacing to interrupts, which
11811 includes the set of signals or conditions that can be raised and
11812 recognized as interrupts.
11814 @item Ada.Interrupts.Names (C.3.2)
11815 This package provides the set of interrupt names (actually signal
11816 or condition names) that can be handled by GNAT@.
11818 @item Ada.IO_Exceptions (A.13)
11819 This package defines the set of exceptions that can be raised by use of
11820 the standard IO packages.
11823 This package contains some standard constants and exceptions used
11824 throughout the numerics packages. Note that the constants pi and e are
11825 defined here, and it is better to use these definitions than rolling
11828 @item Ada.Numerics.Complex_Elementary_Functions
11829 Provides the implementation of standard elementary functions (such as
11830 log and trigonometric functions) operating on complex numbers using the
11831 standard @code{Float} and the @code{Complex} and @code{Imaginary} types
11832 created by the package @code{Numerics.Complex_Types}.
11834 @item Ada.Numerics.Complex_Types
11835 This is a predefined instantiation of
11836 @code{Numerics.Generic_Complex_Types} using @code{Standard.Float} to
11837 build the type @code{Complex} and @code{Imaginary}.
11839 @item Ada.Numerics.Discrete_Random
11840 This package provides a random number generator suitable for generating
11841 random integer values from a specified range.
11843 @item Ada.Numerics.Float_Random
11844 This package provides a random number generator suitable for generating
11845 uniformly distributed floating point values.
11847 @item Ada.Numerics.Generic_Complex_Elementary_Functions
11848 This is a generic version of the package that provides the
11849 implementation of standard elementary functions (such as log and
11850 trigonometric functions) for an arbitrary complex type.
11852 The following predefined instantiations of this package are provided:
11856 @code{Ada.Numerics.Short_Complex_Elementary_Functions}
11858 @code{Ada.Numerics.Complex_Elementary_Functions}
11860 @code{Ada.Numerics.Long_Complex_Elementary_Functions}
11863 @item Ada.Numerics.Generic_Complex_Types
11864 This is a generic package that allows the creation of complex types,
11865 with associated complex arithmetic operations.
11867 The following predefined instantiations of this package exist
11870 @code{Ada.Numerics.Short_Complex_Complex_Types}
11872 @code{Ada.Numerics.Complex_Complex_Types}
11874 @code{Ada.Numerics.Long_Complex_Complex_Types}
11877 @item Ada.Numerics.Generic_Elementary_Functions
11878 This is a generic package that provides the implementation of standard
11879 elementary functions (such as log an trigonometric functions) for an
11880 arbitrary float type.
11882 The following predefined instantiations of this package exist
11886 @code{Ada.Numerics.Short_Elementary_Functions}
11888 @code{Ada.Numerics.Elementary_Functions}
11890 @code{Ada.Numerics.Long_Elementary_Functions}
11893 @item Ada.Real_Time (D.8)
11894 This package provides facilities similar to those of @code{Calendar}, but
11895 operating with a finer clock suitable for real time control. Note that
11896 annex D requires that there be no backward clock jumps, and GNAT generally
11897 guarantees this behavior, but of course if the external clock on which
11898 the GNAT runtime depends is deliberately reset by some external event,
11899 then such a backward jump may occur.
11901 @item Ada.Sequential_IO (A.8.1)
11902 This package provides input-output facilities for sequential files,
11903 which can contain a sequence of values of a single type, which can be
11904 any Ada type, including indefinite (unconstrained) types.
11906 @item Ada.Storage_IO (A.9)
11907 This package provides a facility for mapping arbitrary Ada types to and
11908 from a storage buffer. It is primarily intended for the creation of new
11911 @item Ada.Streams (13.13.1)
11912 This is a generic package that provides the basic support for the
11913 concept of streams as used by the stream attributes (@code{Input},
11914 @code{Output}, @code{Read} and @code{Write}).
11916 @item Ada.Streams.Stream_IO (A.12.1)
11917 This package is a specialization of the type @code{Streams} defined in
11918 package @code{Streams} together with a set of operations providing
11919 Stream_IO capability. The Stream_IO model permits both random and
11920 sequential access to a file which can contain an arbitrary set of values
11921 of one or more Ada types.
11923 @item Ada.Strings (A.4.1)
11924 This package provides some basic constants used by the string handling
11927 @item Ada.Strings.Bounded (A.4.4)
11928 This package provides facilities for handling variable length
11929 strings. The bounded model requires a maximum length. It is thus
11930 somewhat more limited than the unbounded model, but avoids the use of
11931 dynamic allocation or finalization.
11933 @item Ada.Strings.Fixed (A.4.3)
11934 This package provides facilities for handling fixed length strings.
11936 @item Ada.Strings.Maps (A.4.2)
11937 This package provides facilities for handling character mappings and
11938 arbitrarily defined subsets of characters. For instance it is useful in
11939 defining specialized translation tables.
11941 @item Ada.Strings.Maps.Constants (A.4.6)
11942 This package provides a standard set of predefined mappings and
11943 predefined character sets. For example, the standard upper to lower case
11944 conversion table is found in this package. Note that upper to lower case
11945 conversion is non-trivial if you want to take the entire set of
11946 characters, including extended characters like E with an acute accent,
11947 into account. You should use the mappings in this package (rather than
11948 adding 32 yourself) to do case mappings.
11950 @item Ada.Strings.Unbounded (A.4.5)
11951 This package provides facilities for handling variable length
11952 strings. The unbounded model allows arbitrary length strings, but
11953 requires the use of dynamic allocation and finalization.
11955 @item Ada.Strings.Wide_Bounded (A.4.7)
11956 @itemx Ada.Strings.Wide_Fixed (A.4.7)
11957 @itemx Ada.Strings.Wide_Maps (A.4.7)
11958 @itemx Ada.Strings.Wide_Maps.Constants (A.4.7)
11959 @itemx Ada.Strings.Wide_Unbounded (A.4.7)
11960 These packages provide analogous capabilities to the corresponding
11961 packages without @samp{Wide_} in the name, but operate with the types
11962 @code{Wide_String} and @code{Wide_Character} instead of @code{String}
11963 and @code{Character}.
11965 @item Ada.Strings.Wide_Wide_Bounded (A.4.7)
11966 @itemx Ada.Strings.Wide_Wide_Fixed (A.4.7)
11967 @itemx Ada.Strings.Wide_Wide_Maps (A.4.7)
11968 @itemx Ada.Strings.Wide_Wide_Maps.Constants (A.4.7)
11969 @itemx Ada.Strings.Wide_Wide_Unbounded (A.4.7)
11970 These packages provide analogous capabilities to the corresponding
11971 packages without @samp{Wide_} in the name, but operate with the types
11972 @code{Wide_Wide_String} and @code{Wide_Wide_Character} instead
11973 of @code{String} and @code{Character}.
11975 @item Ada.Synchronous_Task_Control (D.10)
11976 This package provides some standard facilities for controlling task
11977 communication in a synchronous manner.
11980 This package contains definitions for manipulation of the tags of tagged
11983 @item Ada.Task_Attributes
11984 This package provides the capability of associating arbitrary
11985 task-specific data with separate tasks.
11988 This package provides basic text input-output capabilities for
11989 character, string and numeric data. The subpackages of this
11990 package are listed next.
11992 @item Ada.Text_IO.Decimal_IO
11993 Provides input-output facilities for decimal fixed-point types
11995 @item Ada.Text_IO.Enumeration_IO
11996 Provides input-output facilities for enumeration types.
11998 @item Ada.Text_IO.Fixed_IO
11999 Provides input-output facilities for ordinary fixed-point types.
12001 @item Ada.Text_IO.Float_IO
12002 Provides input-output facilities for float types. The following
12003 predefined instantiations of this generic package are available:
12007 @code{Short_Float_Text_IO}
12009 @code{Float_Text_IO}
12011 @code{Long_Float_Text_IO}
12014 @item Ada.Text_IO.Integer_IO
12015 Provides input-output facilities for integer types. The following
12016 predefined instantiations of this generic package are available:
12019 @item Short_Short_Integer
12020 @code{Ada.Short_Short_Integer_Text_IO}
12021 @item Short_Integer
12022 @code{Ada.Short_Integer_Text_IO}
12024 @code{Ada.Integer_Text_IO}
12026 @code{Ada.Long_Integer_Text_IO}
12027 @item Long_Long_Integer
12028 @code{Ada.Long_Long_Integer_Text_IO}
12031 @item Ada.Text_IO.Modular_IO
12032 Provides input-output facilities for modular (unsigned) types
12034 @item Ada.Text_IO.Complex_IO (G.1.3)
12035 This package provides basic text input-output capabilities for complex
12038 @item Ada.Text_IO.Editing (F.3.3)
12039 This package contains routines for edited output, analogous to the use
12040 of pictures in COBOL@. The picture formats used by this package are a
12041 close copy of the facility in COBOL@.
12043 @item Ada.Text_IO.Text_Streams (A.12.2)
12044 This package provides a facility that allows Text_IO files to be treated
12045 as streams, so that the stream attributes can be used for writing
12046 arbitrary data, including binary data, to Text_IO files.
12048 @item Ada.Unchecked_Conversion (13.9)
12049 This generic package allows arbitrary conversion from one type to
12050 another of the same size, providing for breaking the type safety in
12051 special circumstances.
12053 If the types have the same Size (more accurately the same Value_Size),
12054 then the effect is simply to transfer the bits from the source to the
12055 target type without any modification. This usage is well defined, and
12056 for simple types whose representation is typically the same across
12057 all implementations, gives a portable method of performing such
12060 If the types do not have the same size, then the result is implementation
12061 defined, and thus may be non-portable. The following describes how GNAT
12062 handles such unchecked conversion cases.
12064 If the types are of different sizes, and are both discrete types, then
12065 the effect is of a normal type conversion without any constraint checking.
12066 In particular if the result type has a larger size, the result will be
12067 zero or sign extended. If the result type has a smaller size, the result
12068 will be truncated by ignoring high order bits.
12070 If the types are of different sizes, and are not both discrete types,
12071 then the conversion works as though pointers were created to the source
12072 and target, and the pointer value is converted. The effect is that bits
12073 are copied from successive low order storage units and bits of the source
12074 up to the length of the target type.
12076 A warning is issued if the lengths differ, since the effect in this
12077 case is implementation dependent, and the above behavior may not match
12078 that of some other compiler.
12080 A pointer to one type may be converted to a pointer to another type using
12081 unchecked conversion. The only case in which the effect is undefined is
12082 when one or both pointers are pointers to unconstrained array types. In
12083 this case, the bounds information may get incorrectly transferred, and in
12084 particular, GNAT uses double size pointers for such types, and it is
12085 meaningless to convert between such pointer types. GNAT will issue a
12086 warning if the alignment of the target designated type is more strict
12087 than the alignment of the source designated type (since the result may
12088 be unaligned in this case).
12090 A pointer other than a pointer to an unconstrained array type may be
12091 converted to and from System.Address. Such usage is common in Ada 83
12092 programs, but note that Ada.Address_To_Access_Conversions is the
12093 preferred method of performing such conversions in Ada 95 and Ada 2005.
12095 unchecked conversion nor Ada.Address_To_Access_Conversions should be
12096 used in conjunction with pointers to unconstrained objects, since
12097 the bounds information cannot be handled correctly in this case.
12099 @item Ada.Unchecked_Deallocation (13.11.2)
12100 This generic package allows explicit freeing of storage previously
12101 allocated by use of an allocator.
12103 @item Ada.Wide_Text_IO (A.11)
12104 This package is similar to @code{Ada.Text_IO}, except that the external
12105 file supports wide character representations, and the internal types are
12106 @code{Wide_Character} and @code{Wide_String} instead of @code{Character}
12107 and @code{String}. It contains generic subpackages listed next.
12109 @item Ada.Wide_Text_IO.Decimal_IO
12110 Provides input-output facilities for decimal fixed-point types
12112 @item Ada.Wide_Text_IO.Enumeration_IO
12113 Provides input-output facilities for enumeration types.
12115 @item Ada.Wide_Text_IO.Fixed_IO
12116 Provides input-output facilities for ordinary fixed-point types.
12118 @item Ada.Wide_Text_IO.Float_IO
12119 Provides input-output facilities for float types. The following
12120 predefined instantiations of this generic package are available:
12124 @code{Short_Float_Wide_Text_IO}
12126 @code{Float_Wide_Text_IO}
12128 @code{Long_Float_Wide_Text_IO}
12131 @item Ada.Wide_Text_IO.Integer_IO
12132 Provides input-output facilities for integer types. The following
12133 predefined instantiations of this generic package are available:
12136 @item Short_Short_Integer
12137 @code{Ada.Short_Short_Integer_Wide_Text_IO}
12138 @item Short_Integer
12139 @code{Ada.Short_Integer_Wide_Text_IO}
12141 @code{Ada.Integer_Wide_Text_IO}
12143 @code{Ada.Long_Integer_Wide_Text_IO}
12144 @item Long_Long_Integer
12145 @code{Ada.Long_Long_Integer_Wide_Text_IO}
12148 @item Ada.Wide_Text_IO.Modular_IO
12149 Provides input-output facilities for modular (unsigned) types
12151 @item Ada.Wide_Text_IO.Complex_IO (G.1.3)
12152 This package is similar to @code{Ada.Text_IO.Complex_IO}, except that the
12153 external file supports wide character representations.
12155 @item Ada.Wide_Text_IO.Editing (F.3.4)
12156 This package is similar to @code{Ada.Text_IO.Editing}, except that the
12157 types are @code{Wide_Character} and @code{Wide_String} instead of
12158 @code{Character} and @code{String}.
12160 @item Ada.Wide_Text_IO.Streams (A.12.3)
12161 This package is similar to @code{Ada.Text_IO.Streams}, except that the
12162 types are @code{Wide_Character} and @code{Wide_String} instead of
12163 @code{Character} and @code{String}.
12165 @item Ada.Wide_Wide_Text_IO (A.11)
12166 This package is similar to @code{Ada.Text_IO}, except that the external
12167 file supports wide character representations, and the internal types are
12168 @code{Wide_Character} and @code{Wide_String} instead of @code{Character}
12169 and @code{String}. It contains generic subpackages listed next.
12171 @item Ada.Wide_Wide_Text_IO.Decimal_IO
12172 Provides input-output facilities for decimal fixed-point types
12174 @item Ada.Wide_Wide_Text_IO.Enumeration_IO
12175 Provides input-output facilities for enumeration types.
12177 @item Ada.Wide_Wide_Text_IO.Fixed_IO
12178 Provides input-output facilities for ordinary fixed-point types.
12180 @item Ada.Wide_Wide_Text_IO.Float_IO
12181 Provides input-output facilities for float types. The following
12182 predefined instantiations of this generic package are available:
12186 @code{Short_Float_Wide_Wide_Text_IO}
12188 @code{Float_Wide_Wide_Text_IO}
12190 @code{Long_Float_Wide_Wide_Text_IO}
12193 @item Ada.Wide_Wide_Text_IO.Integer_IO
12194 Provides input-output facilities for integer types. The following
12195 predefined instantiations of this generic package are available:
12198 @item Short_Short_Integer
12199 @code{Ada.Short_Short_Integer_Wide_Wide_Text_IO}
12200 @item Short_Integer
12201 @code{Ada.Short_Integer_Wide_Wide_Text_IO}
12203 @code{Ada.Integer_Wide_Wide_Text_IO}
12205 @code{Ada.Long_Integer_Wide_Wide_Text_IO}
12206 @item Long_Long_Integer
12207 @code{Ada.Long_Long_Integer_Wide_Wide_Text_IO}
12210 @item Ada.Wide_Wide_Text_IO.Modular_IO
12211 Provides input-output facilities for modular (unsigned) types
12213 @item Ada.Wide_Wide_Text_IO.Complex_IO (G.1.3)
12214 This package is similar to @code{Ada.Text_IO.Complex_IO}, except that the
12215 external file supports wide character representations.
12217 @item Ada.Wide_Wide_Text_IO.Editing (F.3.4)
12218 This package is similar to @code{Ada.Text_IO.Editing}, except that the
12219 types are @code{Wide_Character} and @code{Wide_String} instead of
12220 @code{Character} and @code{String}.
12222 @item Ada.Wide_Wide_Text_IO.Streams (A.12.3)
12223 This package is similar to @code{Ada.Text_IO.Streams}, except that the
12224 types are @code{Wide_Character} and @code{Wide_String} instead of
12225 @code{Character} and @code{String}.
12230 @node The Implementation of Standard I/O
12231 @chapter The Implementation of Standard I/O
12234 GNAT implements all the required input-output facilities described in
12235 A.6 through A.14. These sections of the Ada Reference Manual describe the
12236 required behavior of these packages from the Ada point of view, and if
12237 you are writing a portable Ada program that does not need to know the
12238 exact manner in which Ada maps to the outside world when it comes to
12239 reading or writing external files, then you do not need to read this
12240 chapter. As long as your files are all regular files (not pipes or
12241 devices), and as long as you write and read the files only from Ada, the
12242 description in the Ada Reference Manual is sufficient.
12244 However, if you want to do input-output to pipes or other devices, such
12245 as the keyboard or screen, or if the files you are dealing with are
12246 either generated by some other language, or to be read by some other
12247 language, then you need to know more about the details of how the GNAT
12248 implementation of these input-output facilities behaves.
12250 In this chapter we give a detailed description of exactly how GNAT
12251 interfaces to the file system. As always, the sources of the system are
12252 available to you for answering questions at an even more detailed level,
12253 but for most purposes the information in this chapter will suffice.
12255 Another reason that you may need to know more about how input-output is
12256 implemented arises when you have a program written in mixed languages
12257 where, for example, files are shared between the C and Ada sections of
12258 the same program. GNAT provides some additional facilities, in the form
12259 of additional child library packages, that facilitate this sharing, and
12260 these additional facilities are also described in this chapter.
12263 * Standard I/O Packages::
12269 * Wide_Wide_Text_IO::
12271 * Text Translation::
12273 * Filenames encoding::
12275 * Operations on C Streams::
12276 * Interfacing to C Streams::
12279 @node Standard I/O Packages
12280 @section Standard I/O Packages
12283 The Standard I/O packages described in Annex A for
12289 Ada.Text_IO.Complex_IO
12291 Ada.Text_IO.Text_Streams
12295 Ada.Wide_Text_IO.Complex_IO
12297 Ada.Wide_Text_IO.Text_Streams
12299 Ada.Wide_Wide_Text_IO
12301 Ada.Wide_Wide_Text_IO.Complex_IO
12303 Ada.Wide_Wide_Text_IO.Text_Streams
12313 are implemented using the C
12314 library streams facility; where
12318 All files are opened using @code{fopen}.
12320 All input/output operations use @code{fread}/@code{fwrite}.
12324 There is no internal buffering of any kind at the Ada library level. The only
12325 buffering is that provided at the system level in the implementation of the
12326 library routines that support streams. This facilitates shared use of these
12327 streams by mixed language programs. Note though that system level buffering is
12328 explicitly enabled at elaboration of the standard I/O packages and that can
12329 have an impact on mixed language programs, in particular those using I/O before
12330 calling the Ada elaboration routine (e.g.@: adainit). It is recommended to call
12331 the Ada elaboration routine before performing any I/O or when impractical,
12332 flush the common I/O streams and in particular Standard_Output before
12333 elaborating the Ada code.
12336 @section FORM Strings
12339 The format of a FORM string in GNAT is:
12342 "keyword=value,keyword=value,@dots{},keyword=value"
12346 where letters may be in upper or lower case, and there are no spaces
12347 between values. The order of the entries is not important. Currently
12348 the following keywords defined.
12351 TEXT_TRANSLATION=[YES|NO]
12353 WCEM=[n|h|u|s|e|8|b]
12354 ENCODING=[UTF8|8BITS]
12358 The use of these parameters is described later in this section.
12364 Direct_IO can only be instantiated for definite types. This is a
12365 restriction of the Ada language, which means that the records are fixed
12366 length (the length being determined by @code{@var{type}'Size}, rounded
12367 up to the next storage unit boundary if necessary).
12369 The records of a Direct_IO file are simply written to the file in index
12370 sequence, with the first record starting at offset zero, and subsequent
12371 records following. There is no control information of any kind. For
12372 example, if 32-bit integers are being written, each record takes
12373 4-bytes, so the record at index @var{K} starts at offset
12374 (@var{K}@minus{}1)*4.
12376 There is no limit on the size of Direct_IO files, they are expanded as
12377 necessary to accommodate whatever records are written to the file.
12379 @node Sequential_IO
12380 @section Sequential_IO
12383 Sequential_IO may be instantiated with either a definite (constrained)
12384 or indefinite (unconstrained) type.
12386 For the definite type case, the elements written to the file are simply
12387 the memory images of the data values with no control information of any
12388 kind. The resulting file should be read using the same type, no validity
12389 checking is performed on input.
12391 For the indefinite type case, the elements written consist of two
12392 parts. First is the size of the data item, written as the memory image
12393 of a @code{Interfaces.C.size_t} value, followed by the memory image of
12394 the data value. The resulting file can only be read using the same
12395 (unconstrained) type. Normal assignment checks are performed on these
12396 read operations, and if these checks fail, @code{Data_Error} is
12397 raised. In particular, in the array case, the lengths must match, and in
12398 the variant record case, if the variable for a particular read operation
12399 is constrained, the discriminants must match.
12401 Note that it is not possible to use Sequential_IO to write variable
12402 length array items, and then read the data back into different length
12403 arrays. For example, the following will raise @code{Data_Error}:
12405 @smallexample @c ada
12406 package IO is new Sequential_IO (String);
12411 IO.Write (F, "hello!")
12412 IO.Reset (F, Mode=>In_File);
12419 On some Ada implementations, this will print @code{hell}, but the program is
12420 clearly incorrect, since there is only one element in the file, and that
12421 element is the string @code{hello!}.
12423 In Ada 95 and Ada 2005, this kind of behavior can be legitimately achieved
12424 using Stream_IO, and this is the preferred mechanism. In particular, the
12425 above program fragment rewritten to use Stream_IO will work correctly.
12431 Text_IO files consist of a stream of characters containing the following
12432 special control characters:
12435 LF (line feed, 16#0A#) Line Mark
12436 FF (form feed, 16#0C#) Page Mark
12440 A canonical Text_IO file is defined as one in which the following
12441 conditions are met:
12445 The character @code{LF} is used only as a line mark, i.e.@: to mark the end
12449 The character @code{FF} is used only as a page mark, i.e.@: to mark the
12450 end of a page and consequently can appear only immediately following a
12451 @code{LF} (line mark) character.
12454 The file ends with either @code{LF} (line mark) or @code{LF}-@code{FF}
12455 (line mark, page mark). In the former case, the page mark is implicitly
12456 assumed to be present.
12460 A file written using Text_IO will be in canonical form provided that no
12461 explicit @code{LF} or @code{FF} characters are written using @code{Put}
12462 or @code{Put_Line}. There will be no @code{FF} character at the end of
12463 the file unless an explicit @code{New_Page} operation was performed
12464 before closing the file.
12466 A canonical Text_IO file that is a regular file (i.e., not a device or a
12467 pipe) can be read using any of the routines in Text_IO@. The
12468 semantics in this case will be exactly as defined in the Ada Reference
12469 Manual, and all the routines in Text_IO are fully implemented.
12471 A text file that does not meet the requirements for a canonical Text_IO
12472 file has one of the following:
12476 The file contains @code{FF} characters not immediately following a
12477 @code{LF} character.
12480 The file contains @code{LF} or @code{FF} characters written by
12481 @code{Put} or @code{Put_Line}, which are not logically considered to be
12482 line marks or page marks.
12485 The file ends in a character other than @code{LF} or @code{FF},
12486 i.e.@: there is no explicit line mark or page mark at the end of the file.
12490 Text_IO can be used to read such non-standard text files but subprograms
12491 to do with line or page numbers do not have defined meanings. In
12492 particular, a @code{FF} character that does not follow a @code{LF}
12493 character may or may not be treated as a page mark from the point of
12494 view of page and line numbering. Every @code{LF} character is considered
12495 to end a line, and there is an implied @code{LF} character at the end of
12499 * Text_IO Stream Pointer Positioning::
12500 * Text_IO Reading and Writing Non-Regular Files::
12502 * Treating Text_IO Files as Streams::
12503 * Text_IO Extensions::
12504 * Text_IO Facilities for Unbounded Strings::
12507 @node Text_IO Stream Pointer Positioning
12508 @subsection Stream Pointer Positioning
12511 @code{Ada.Text_IO} has a definition of current position for a file that
12512 is being read. No internal buffering occurs in Text_IO, and usually the
12513 physical position in the stream used to implement the file corresponds
12514 to this logical position defined by Text_IO@. There are two exceptions:
12518 After a call to @code{End_Of_Page} that returns @code{True}, the stream
12519 is positioned past the @code{LF} (line mark) that precedes the page
12520 mark. Text_IO maintains an internal flag so that subsequent read
12521 operations properly handle the logical position which is unchanged by
12522 the @code{End_Of_Page} call.
12525 After a call to @code{End_Of_File} that returns @code{True}, if the
12526 Text_IO file was positioned before the line mark at the end of file
12527 before the call, then the logical position is unchanged, but the stream
12528 is physically positioned right at the end of file (past the line mark,
12529 and past a possible page mark following the line mark. Again Text_IO
12530 maintains internal flags so that subsequent read operations properly
12531 handle the logical position.
12535 These discrepancies have no effect on the observable behavior of
12536 Text_IO, but if a single Ada stream is shared between a C program and
12537 Ada program, or shared (using @samp{shared=yes} in the form string)
12538 between two Ada files, then the difference may be observable in some
12541 @node Text_IO Reading and Writing Non-Regular Files
12542 @subsection Reading and Writing Non-Regular Files
12545 A non-regular file is a device (such as a keyboard), or a pipe. Text_IO
12546 can be used for reading and writing. Writing is not affected and the
12547 sequence of characters output is identical to the normal file case, but
12548 for reading, the behavior of Text_IO is modified to avoid undesirable
12549 look-ahead as follows:
12551 An input file that is not a regular file is considered to have no page
12552 marks. Any @code{Ascii.FF} characters (the character normally used for a
12553 page mark) appearing in the file are considered to be data
12554 characters. In particular:
12558 @code{Get_Line} and @code{Skip_Line} do not test for a page mark
12559 following a line mark. If a page mark appears, it will be treated as a
12563 This avoids the need to wait for an extra character to be typed or
12564 entered from the pipe to complete one of these operations.
12567 @code{End_Of_Page} always returns @code{False}
12570 @code{End_Of_File} will return @code{False} if there is a page mark at
12571 the end of the file.
12575 Output to non-regular files is the same as for regular files. Page marks
12576 may be written to non-regular files using @code{New_Page}, but as noted
12577 above they will not be treated as page marks on input if the output is
12578 piped to another Ada program.
12580 Another important discrepancy when reading non-regular files is that the end
12581 of file indication is not ``sticky''. If an end of file is entered, e.g.@: by
12582 pressing the @key{EOT} key,
12584 is signaled once (i.e.@: the test @code{End_Of_File}
12585 will yield @code{True}, or a read will
12586 raise @code{End_Error}), but then reading can resume
12587 to read data past that end of
12588 file indication, until another end of file indication is entered.
12590 @node Get_Immediate
12591 @subsection Get_Immediate
12592 @cindex Get_Immediate
12595 Get_Immediate returns the next character (including control characters)
12596 from the input file. In particular, Get_Immediate will return LF or FF
12597 characters used as line marks or page marks. Such operations leave the
12598 file positioned past the control character, and it is thus not treated
12599 as having its normal function. This means that page, line and column
12600 counts after this kind of Get_Immediate call are set as though the mark
12601 did not occur. In the case where a Get_Immediate leaves the file
12602 positioned between the line mark and page mark (which is not normally
12603 possible), it is undefined whether the FF character will be treated as a
12606 @node Treating Text_IO Files as Streams
12607 @subsection Treating Text_IO Files as Streams
12608 @cindex Stream files
12611 The package @code{Text_IO.Streams} allows a Text_IO file to be treated
12612 as a stream. Data written to a Text_IO file in this stream mode is
12613 binary data. If this binary data contains bytes 16#0A# (@code{LF}) or
12614 16#0C# (@code{FF}), the resulting file may have non-standard
12615 format. Similarly if read operations are used to read from a Text_IO
12616 file treated as a stream, then @code{LF} and @code{FF} characters may be
12617 skipped and the effect is similar to that described above for
12618 @code{Get_Immediate}.
12620 @node Text_IO Extensions
12621 @subsection Text_IO Extensions
12622 @cindex Text_IO extensions
12625 A package GNAT.IO_Aux in the GNAT library provides some useful extensions
12626 to the standard @code{Text_IO} package:
12629 @item function File_Exists (Name : String) return Boolean;
12630 Determines if a file of the given name exists.
12632 @item function Get_Line return String;
12633 Reads a string from the standard input file. The value returned is exactly
12634 the length of the line that was read.
12636 @item function Get_Line (File : Ada.Text_IO.File_Type) return String;
12637 Similar, except that the parameter File specifies the file from which
12638 the string is to be read.
12642 @node Text_IO Facilities for Unbounded Strings
12643 @subsection Text_IO Facilities for Unbounded Strings
12644 @cindex Text_IO for unbounded strings
12645 @cindex Unbounded_String, Text_IO operations
12648 The package @code{Ada.Strings.Unbounded.Text_IO}
12649 in library files @code{a-suteio.ads/adb} contains some GNAT-specific
12650 subprograms useful for Text_IO operations on unbounded strings:
12654 @item function Get_Line (File : File_Type) return Unbounded_String;
12655 Reads a line from the specified file
12656 and returns the result as an unbounded string.
12658 @item procedure Put (File : File_Type; U : Unbounded_String);
12659 Writes the value of the given unbounded string to the specified file
12660 Similar to the effect of
12661 @code{Put (To_String (U))} except that an extra copy is avoided.
12663 @item procedure Put_Line (File : File_Type; U : Unbounded_String);
12664 Writes the value of the given unbounded string to the specified file,
12665 followed by a @code{New_Line}.
12666 Similar to the effect of @code{Put_Line (To_String (U))} except
12667 that an extra copy is avoided.
12671 In the above procedures, @code{File} is of type @code{Ada.Text_IO.File_Type}
12672 and is optional. If the parameter is omitted, then the standard input or
12673 output file is referenced as appropriate.
12675 The package @code{Ada.Strings.Wide_Unbounded.Wide_Text_IO} in library
12676 files @file{a-swuwti.ads} and @file{a-swuwti.adb} provides similar extended
12677 @code{Wide_Text_IO} functionality for unbounded wide strings.
12679 The package @code{Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO} in library
12680 files @file{a-szuzti.ads} and @file{a-szuzti.adb} provides similar extended
12681 @code{Wide_Wide_Text_IO} functionality for unbounded wide wide strings.
12684 @section Wide_Text_IO
12687 @code{Wide_Text_IO} is similar in most respects to Text_IO, except that
12688 both input and output files may contain special sequences that represent
12689 wide character values. The encoding scheme for a given file may be
12690 specified using a FORM parameter:
12697 as part of the FORM string (WCEM = wide character encoding method),
12698 where @var{x} is one of the following characters
12704 Upper half encoding
12716 The encoding methods match those that
12717 can be used in a source
12718 program, but there is no requirement that the encoding method used for
12719 the source program be the same as the encoding method used for files,
12720 and different files may use different encoding methods.
12722 The default encoding method for the standard files, and for opened files
12723 for which no WCEM parameter is given in the FORM string matches the
12724 wide character encoding specified for the main program (the default
12725 being brackets encoding if no coding method was specified with -gnatW).
12729 In this encoding, a wide character is represented by a five character
12737 where @var{a}, @var{b}, @var{c}, @var{d} are the four hexadecimal
12738 characters (using upper case letters) of the wide character code. For
12739 example, ESC A345 is used to represent the wide character with code
12740 16#A345#. This scheme is compatible with use of the full
12741 @code{Wide_Character} set.
12743 @item Upper Half Coding
12744 The wide character with encoding 16#abcd#, where the upper bit is on
12745 (i.e.@: a is in the range 8-F) is represented as two bytes 16#ab# and
12746 16#cd#. The second byte may never be a format control character, but is
12747 not required to be in the upper half. This method can be also used for
12748 shift-JIS or EUC where the internal coding matches the external coding.
12750 @item Shift JIS Coding
12751 A wide character is represented by a two character sequence 16#ab# and
12752 16#cd#, with the restrictions described for upper half encoding as
12753 described above. The internal character code is the corresponding JIS
12754 character according to the standard algorithm for Shift-JIS
12755 conversion. Only characters defined in the JIS code set table can be
12756 used with this encoding method.
12759 A wide character is represented by a two character sequence 16#ab# and
12760 16#cd#, with both characters being in the upper half. The internal
12761 character code is the corresponding JIS character according to the EUC
12762 encoding algorithm. Only characters defined in the JIS code set table
12763 can be used with this encoding method.
12766 A wide character is represented using
12767 UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO
12768 10646-1/Am.2. Depending on the character value, the representation
12769 is a one, two, or three byte sequence:
12772 16#0000#-16#007f#: 2#0xxxxxxx#
12773 16#0080#-16#07ff#: 2#110xxxxx# 2#10xxxxxx#
12774 16#0800#-16#ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#
12778 where the @var{xxx} bits correspond to the left-padded bits of the
12779 16-bit character value. Note that all lower half ASCII characters
12780 are represented as ASCII bytes and all upper half characters and
12781 other wide characters are represented as sequences of upper-half
12782 (The full UTF-8 scheme allows for encoding 31-bit characters as
12783 6-byte sequences, but in this implementation, all UTF-8 sequences
12784 of four or more bytes length will raise a Constraint_Error, as
12785 will all invalid UTF-8 sequences.)
12787 @item Brackets Coding
12788 In this encoding, a wide character is represented by the following eight
12789 character sequence:
12796 where @code{a}, @code{b}, @code{c}, @code{d} are the four hexadecimal
12797 characters (using uppercase letters) of the wide character code. For
12798 example, @code{["A345"]} is used to represent the wide character with code
12800 This scheme is compatible with use of the full Wide_Character set.
12801 On input, brackets coding can also be used for upper half characters,
12802 e.g.@: @code{["C1"]} for lower case a. However, on output, brackets notation
12803 is only used for wide characters with a code greater than @code{16#FF#}.
12805 Note that brackets coding is not normally used in the context of
12806 Wide_Text_IO or Wide_Wide_Text_IO, since it is really just designed as
12807 a portable way of encoding source files. In the context of Wide_Text_IO
12808 or Wide_Wide_Text_IO, it can only be used if the file does not contain
12809 any instance of the left bracket character other than to encode wide
12810 character values using the brackets encoding method. In practice it is
12811 expected that some standard wide character encoding method such
12812 as UTF-8 will be used for text input output.
12814 If brackets notation is used, then any occurrence of a left bracket
12815 in the input file which is not the start of a valid wide character
12816 sequence will cause Constraint_Error to be raised. It is possible to
12817 encode a left bracket as ["5B"] and Wide_Text_IO and Wide_Wide_Text_IO
12818 input will interpret this as a left bracket.
12820 However, when a left bracket is output, it will be output as a left bracket
12821 and not as ["5B"]. We make this decision because for normal use of
12822 Wide_Text_IO for outputting messages, it is unpleasant to clobber left
12823 brackets. For example, if we write:
12826 Put_Line ("Start of output [first run]");
12830 we really do not want to have the left bracket in this message clobbered so
12831 that the output reads:
12834 Start of output ["5B"]first run]
12838 In practice brackets encoding is reasonably useful for normal Put_Line use
12839 since we won't get confused between left brackets and wide character
12840 sequences in the output. But for input, or when files are written out
12841 and read back in, it really makes better sense to use one of the standard
12842 encoding methods such as UTF-8.
12847 For the coding schemes other than UTF-8, Hex, or Brackets encoding,
12848 not all wide character
12849 values can be represented. An attempt to output a character that cannot
12850 be represented using the encoding scheme for the file causes
12851 Constraint_Error to be raised. An invalid wide character sequence on
12852 input also causes Constraint_Error to be raised.
12855 * Wide_Text_IO Stream Pointer Positioning::
12856 * Wide_Text_IO Reading and Writing Non-Regular Files::
12859 @node Wide_Text_IO Stream Pointer Positioning
12860 @subsection Stream Pointer Positioning
12863 @code{Ada.Wide_Text_IO} is similar to @code{Ada.Text_IO} in its handling
12864 of stream pointer positioning (@pxref{Text_IO}). There is one additional
12867 If @code{Ada.Wide_Text_IO.Look_Ahead} reads a character outside the
12868 normal lower ASCII set (i.e.@: a character in the range:
12870 @smallexample @c ada
12871 Wide_Character'Val (16#0080#) .. Wide_Character'Val (16#FFFF#)
12875 then although the logical position of the file pointer is unchanged by
12876 the @code{Look_Ahead} call, the stream is physically positioned past the
12877 wide character sequence. Again this is to avoid the need for buffering
12878 or backup, and all @code{Wide_Text_IO} routines check the internal
12879 indication that this situation has occurred so that this is not visible
12880 to a normal program using @code{Wide_Text_IO}. However, this discrepancy
12881 can be observed if the wide text file shares a stream with another file.
12883 @node Wide_Text_IO Reading and Writing Non-Regular Files
12884 @subsection Reading and Writing Non-Regular Files
12887 As in the case of Text_IO, when a non-regular file is read, it is
12888 assumed that the file contains no page marks (any form characters are
12889 treated as data characters), and @code{End_Of_Page} always returns
12890 @code{False}. Similarly, the end of file indication is not sticky, so
12891 it is possible to read beyond an end of file.
12893 @node Wide_Wide_Text_IO
12894 @section Wide_Wide_Text_IO
12897 @code{Wide_Wide_Text_IO} is similar in most respects to Text_IO, except that
12898 both input and output files may contain special sequences that represent
12899 wide wide character values. The encoding scheme for a given file may be
12900 specified using a FORM parameter:
12907 as part of the FORM string (WCEM = wide character encoding method),
12908 where @var{x} is one of the following characters
12914 Upper half encoding
12926 The encoding methods match those that
12927 can be used in a source
12928 program, but there is no requirement that the encoding method used for
12929 the source program be the same as the encoding method used for files,
12930 and different files may use different encoding methods.
12932 The default encoding method for the standard files, and for opened files
12933 for which no WCEM parameter is given in the FORM string matches the
12934 wide character encoding specified for the main program (the default
12935 being brackets encoding if no coding method was specified with -gnatW).
12940 A wide character is represented using
12941 UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO
12942 10646-1/Am.2. Depending on the character value, the representation
12943 is a one, two, three, or four byte sequence:
12946 16#000000#-16#00007f#: 2#0xxxxxxx#
12947 16#000080#-16#0007ff#: 2#110xxxxx# 2#10xxxxxx#
12948 16#000800#-16#00ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#
12949 16#010000#-16#10ffff#: 2#11110xxx# 2#10xxxxxx# 2#10xxxxxx# 2#10xxxxxx#
12953 where the @var{xxx} bits correspond to the left-padded bits of the
12954 21-bit character value. Note that all lower half ASCII characters
12955 are represented as ASCII bytes and all upper half characters and
12956 other wide characters are represented as sequences of upper-half
12959 @item Brackets Coding
12960 In this encoding, a wide wide character is represented by the following eight
12961 character sequence if is in wide character range
12967 and by the following ten character sequence if not
12970 [ " a b c d e f " ]
12974 where @code{a}, @code{b}, @code{c}, @code{d}, @code{e}, and @code{f}
12975 are the four or six hexadecimal
12976 characters (using uppercase letters) of the wide wide character code. For
12977 example, @code{["01A345"]} is used to represent the wide wide character
12978 with code @code{16#01A345#}.
12980 This scheme is compatible with use of the full Wide_Wide_Character set.
12981 On input, brackets coding can also be used for upper half characters,
12982 e.g.@: @code{["C1"]} for lower case a. However, on output, brackets notation
12983 is only used for wide characters with a code greater than @code{16#FF#}.
12988 If is also possible to use the other Wide_Character encoding methods,
12989 such as Shift-JIS, but the other schemes cannot support the full range
12990 of wide wide characters.
12991 An attempt to output a character that cannot
12992 be represented using the encoding scheme for the file causes
12993 Constraint_Error to be raised. An invalid wide character sequence on
12994 input also causes Constraint_Error to be raised.
12997 * Wide_Wide_Text_IO Stream Pointer Positioning::
12998 * Wide_Wide_Text_IO Reading and Writing Non-Regular Files::
13001 @node Wide_Wide_Text_IO Stream Pointer Positioning
13002 @subsection Stream Pointer Positioning
13005 @code{Ada.Wide_Wide_Text_IO} is similar to @code{Ada.Text_IO} in its handling
13006 of stream pointer positioning (@pxref{Text_IO}). There is one additional
13009 If @code{Ada.Wide_Wide_Text_IO.Look_Ahead} reads a character outside the
13010 normal lower ASCII set (i.e.@: a character in the range:
13012 @smallexample @c ada
13013 Wide_Wide_Character'Val (16#0080#) .. Wide_Wide_Character'Val (16#10FFFF#)
13017 then although the logical position of the file pointer is unchanged by
13018 the @code{Look_Ahead} call, the stream is physically positioned past the
13019 wide character sequence. Again this is to avoid the need for buffering
13020 or backup, and all @code{Wide_Wide_Text_IO} routines check the internal
13021 indication that this situation has occurred so that this is not visible
13022 to a normal program using @code{Wide_Wide_Text_IO}. However, this discrepancy
13023 can be observed if the wide text file shares a stream with another file.
13025 @node Wide_Wide_Text_IO Reading and Writing Non-Regular Files
13026 @subsection Reading and Writing Non-Regular Files
13029 As in the case of Text_IO, when a non-regular file is read, it is
13030 assumed that the file contains no page marks (any form characters are
13031 treated as data characters), and @code{End_Of_Page} always returns
13032 @code{False}. Similarly, the end of file indication is not sticky, so
13033 it is possible to read beyond an end of file.
13039 A stream file is a sequence of bytes, where individual elements are
13040 written to the file as described in the Ada Reference Manual. The type
13041 @code{Stream_Element} is simply a byte. There are two ways to read or
13042 write a stream file.
13046 The operations @code{Read} and @code{Write} directly read or write a
13047 sequence of stream elements with no control information.
13050 The stream attributes applied to a stream file transfer data in the
13051 manner described for stream attributes.
13054 @node Text Translation
13055 @section Text Translation
13058 @samp{Text_Translation=@var{xxx}} may be used as the Form parameter
13059 passed to Text_IO.Create and Text_IO.Open:
13060 @samp{Text_Translation=@var{Yes}} is the default, which means to
13061 translate LF to/from CR/LF on Windows systems.
13062 @samp{Text_Translation=@var{No}} disables this translation; i.e. it
13063 uses binary mode. For output files, @samp{Text_Translation=@var{No}}
13064 may be used to create Unix-style files on
13065 Windows. @samp{Text_Translation=@var{xxx}} has no effect on Unix
13069 @section Shared Files
13072 Section A.14 of the Ada Reference Manual allows implementations to
13073 provide a wide variety of behavior if an attempt is made to access the
13074 same external file with two or more internal files.
13076 To provide a full range of functionality, while at the same time
13077 minimizing the problems of portability caused by this implementation
13078 dependence, GNAT handles file sharing as follows:
13082 In the absence of a @samp{shared=@var{xxx}} form parameter, an attempt
13083 to open two or more files with the same full name is considered an error
13084 and is not supported. The exception @code{Use_Error} will be
13085 raised. Note that a file that is not explicitly closed by the program
13086 remains open until the program terminates.
13089 If the form parameter @samp{shared=no} appears in the form string, the
13090 file can be opened or created with its own separate stream identifier,
13091 regardless of whether other files sharing the same external file are
13092 opened. The exact effect depends on how the C stream routines handle
13093 multiple accesses to the same external files using separate streams.
13096 If the form parameter @samp{shared=yes} appears in the form string for
13097 each of two or more files opened using the same full name, the same
13098 stream is shared between these files, and the semantics are as described
13099 in Ada Reference Manual, Section A.14.
13103 When a program that opens multiple files with the same name is ported
13104 from another Ada compiler to GNAT, the effect will be that
13105 @code{Use_Error} is raised.
13107 The documentation of the original compiler and the documentation of the
13108 program should then be examined to determine if file sharing was
13109 expected, and @samp{shared=@var{xxx}} parameters added to @code{Open}
13110 and @code{Create} calls as required.
13112 When a program is ported from GNAT to some other Ada compiler, no
13113 special attention is required unless the @samp{shared=@var{xxx}} form
13114 parameter is used in the program. In this case, you must examine the
13115 documentation of the new compiler to see if it supports the required
13116 file sharing semantics, and form strings modified appropriately. Of
13117 course it may be the case that the program cannot be ported if the
13118 target compiler does not support the required functionality. The best
13119 approach in writing portable code is to avoid file sharing (and hence
13120 the use of the @samp{shared=@var{xxx}} parameter in the form string)
13123 One common use of file sharing in Ada 83 is the use of instantiations of
13124 Sequential_IO on the same file with different types, to achieve
13125 heterogeneous input-output. Although this approach will work in GNAT if
13126 @samp{shared=yes} is specified, it is preferable in Ada to use Stream_IO
13127 for this purpose (using the stream attributes)
13129 @node Filenames encoding
13130 @section Filenames encoding
13133 An encoding form parameter can be used to specify the filename
13134 encoding @samp{encoding=@var{xxx}}.
13138 If the form parameter @samp{encoding=utf8} appears in the form string, the
13139 filename must be encoded in UTF-8.
13142 If the form parameter @samp{encoding=8bits} appears in the form
13143 string, the filename must be a standard 8bits string.
13146 In the absence of a @samp{encoding=@var{xxx}} form parameter, the
13147 encoding is controlled by the @samp{GNAT_CODE_PAGE} environment
13148 variable. And if not set @samp{utf8} is assumed.
13152 The current system Windows ANSI code page.
13157 This encoding form parameter is only supported on the Windows
13158 platform. On the other Operating Systems the run-time is supporting
13162 @section Open Modes
13165 @code{Open} and @code{Create} calls result in a call to @code{fopen}
13166 using the mode shown in the following table:
13169 @center @code{Open} and @code{Create} Call Modes
13171 @b{OPEN } @b{CREATE}
13172 Append_File "r+" "w+"
13174 Out_File (Direct_IO) "r+" "w"
13175 Out_File (all other cases) "w" "w"
13176 Inout_File "r+" "w+"
13180 If text file translation is required, then either @samp{b} or @samp{t}
13181 is added to the mode, depending on the setting of Text. Text file
13182 translation refers to the mapping of CR/LF sequences in an external file
13183 to LF characters internally. This mapping only occurs in DOS and
13184 DOS-like systems, and is not relevant to other systems.
13186 A special case occurs with Stream_IO@. As shown in the above table, the
13187 file is initially opened in @samp{r} or @samp{w} mode for the
13188 @code{In_File} and @code{Out_File} cases. If a @code{Set_Mode} operation
13189 subsequently requires switching from reading to writing or vice-versa,
13190 then the file is reopened in @samp{r+} mode to permit the required operation.
13192 @node Operations on C Streams
13193 @section Operations on C Streams
13194 The package @code{Interfaces.C_Streams} provides an Ada program with direct
13195 access to the C library functions for operations on C streams:
13197 @smallexample @c adanocomment
13198 package Interfaces.C_Streams is
13199 -- Note: the reason we do not use the types that are in
13200 -- Interfaces.C is that we want to avoid dragging in the
13201 -- code in this unit if possible.
13202 subtype chars is System.Address;
13203 -- Pointer to null-terminated array of characters
13204 subtype FILEs is System.Address;
13205 -- Corresponds to the C type FILE*
13206 subtype voids is System.Address;
13207 -- Corresponds to the C type void*
13208 subtype int is Integer;
13209 subtype long is Long_Integer;
13210 -- Note: the above types are subtypes deliberately, and it
13211 -- is part of this spec that the above correspondences are
13212 -- guaranteed. This means that it is legitimate to, for
13213 -- example, use Integer instead of int. We provide these
13214 -- synonyms for clarity, but in some cases it may be
13215 -- convenient to use the underlying types (for example to
13216 -- avoid an unnecessary dependency of a spec on the spec
13218 type size_t is mod 2 ** Standard'Address_Size;
13219 NULL_Stream : constant FILEs;
13220 -- Value returned (NULL in C) to indicate an
13221 -- fdopen/fopen/tmpfile error
13222 ----------------------------------
13223 -- Constants Defined in stdio.h --
13224 ----------------------------------
13225 EOF : constant int;
13226 -- Used by a number of routines to indicate error or
13228 IOFBF : constant int;
13229 IOLBF : constant int;
13230 IONBF : constant int;
13231 -- Used to indicate buffering mode for setvbuf call
13232 SEEK_CUR : constant int;
13233 SEEK_END : constant int;
13234 SEEK_SET : constant int;
13235 -- Used to indicate origin for fseek call
13236 function stdin return FILEs;
13237 function stdout return FILEs;
13238 function stderr return FILEs;
13239 -- Streams associated with standard files
13240 --------------------------
13241 -- Standard C functions --
13242 --------------------------
13243 -- The functions selected below are ones that are
13244 -- available in DOS, OS/2, UNIX and Xenix (but not
13245 -- necessarily in ANSI C). These are very thin interfaces
13246 -- which copy exactly the C headers. For more
13247 -- documentation on these functions, see the Microsoft C
13248 -- "Run-Time Library Reference" (Microsoft Press, 1990,
13249 -- ISBN 1-55615-225-6), which includes useful information
13250 -- on system compatibility.
13251 procedure clearerr (stream : FILEs);
13252 function fclose (stream : FILEs) return int;
13253 function fdopen (handle : int; mode : chars) return FILEs;
13254 function feof (stream : FILEs) return int;
13255 function ferror (stream : FILEs) return int;
13256 function fflush (stream : FILEs) return int;
13257 function fgetc (stream : FILEs) return int;
13258 function fgets (strng : chars; n : int; stream : FILEs)
13260 function fileno (stream : FILEs) return int;
13261 function fopen (filename : chars; Mode : chars)
13263 -- Note: to maintain target independence, use
13264 -- text_translation_required, a boolean variable defined in
13265 -- a-sysdep.c to deal with the target dependent text
13266 -- translation requirement. If this variable is set,
13267 -- then b/t should be appended to the standard mode
13268 -- argument to set the text translation mode off or on
13270 function fputc (C : int; stream : FILEs) return int;
13271 function fputs (Strng : chars; Stream : FILEs) return int;
13288 function ftell (stream : FILEs) return long;
13295 function isatty (handle : int) return int;
13296 procedure mktemp (template : chars);
13297 -- The return value (which is just a pointer to template)
13299 procedure rewind (stream : FILEs);
13300 function rmtmp return int;
13308 function tmpfile return FILEs;
13309 function ungetc (c : int; stream : FILEs) return int;
13310 function unlink (filename : chars) return int;
13311 ---------------------
13312 -- Extra functions --
13313 ---------------------
13314 -- These functions supply slightly thicker bindings than
13315 -- those above. They are derived from functions in the
13316 -- C Run-Time Library, but may do a bit more work than
13317 -- just directly calling one of the Library functions.
13318 function is_regular_file (handle : int) return int;
13319 -- Tests if given handle is for a regular file (result 1)
13320 -- or for a non-regular file (pipe or device, result 0).
13321 ---------------------------------
13322 -- Control of Text/Binary Mode --
13323 ---------------------------------
13324 -- If text_translation_required is true, then the following
13325 -- functions may be used to dynamically switch a file from
13326 -- binary to text mode or vice versa. These functions have
13327 -- no effect if text_translation_required is false (i.e.@: in
13328 -- normal UNIX mode). Use fileno to get a stream handle.
13329 procedure set_binary_mode (handle : int);
13330 procedure set_text_mode (handle : int);
13331 ----------------------------
13332 -- Full Path Name support --
13333 ----------------------------
13334 procedure full_name (nam : chars; buffer : chars);
13335 -- Given a NUL terminated string representing a file
13336 -- name, returns in buffer a NUL terminated string
13337 -- representing the full path name for the file name.
13338 -- On systems where it is relevant the drive is also
13339 -- part of the full path name. It is the responsibility
13340 -- of the caller to pass an actual parameter for buffer
13341 -- that is big enough for any full path name. Use
13342 -- max_path_len given below as the size of buffer.
13343 max_path_len : integer;
13344 -- Maximum length of an allowable full path name on the
13345 -- system, including a terminating NUL character.
13346 end Interfaces.C_Streams;
13349 @node Interfacing to C Streams
13350 @section Interfacing to C Streams
13353 The packages in this section permit interfacing Ada files to C Stream
13356 @smallexample @c ada
13357 with Interfaces.C_Streams;
13358 package Ada.Sequential_IO.C_Streams is
13359 function C_Stream (F : File_Type)
13360 return Interfaces.C_Streams.FILEs;
13362 (File : in out File_Type;
13363 Mode : in File_Mode;
13364 C_Stream : in Interfaces.C_Streams.FILEs;
13365 Form : in String := "");
13366 end Ada.Sequential_IO.C_Streams;
13368 with Interfaces.C_Streams;
13369 package Ada.Direct_IO.C_Streams is
13370 function C_Stream (F : File_Type)
13371 return Interfaces.C_Streams.FILEs;
13373 (File : in out File_Type;
13374 Mode : in File_Mode;
13375 C_Stream : in Interfaces.C_Streams.FILEs;
13376 Form : in String := "");
13377 end Ada.Direct_IO.C_Streams;
13379 with Interfaces.C_Streams;
13380 package Ada.Text_IO.C_Streams is
13381 function C_Stream (F : File_Type)
13382 return Interfaces.C_Streams.FILEs;
13384 (File : in out File_Type;
13385 Mode : in File_Mode;
13386 C_Stream : in Interfaces.C_Streams.FILEs;
13387 Form : in String := "");
13388 end Ada.Text_IO.C_Streams;
13390 with Interfaces.C_Streams;
13391 package Ada.Wide_Text_IO.C_Streams is
13392 function C_Stream (F : File_Type)
13393 return Interfaces.C_Streams.FILEs;
13395 (File : in out File_Type;
13396 Mode : in File_Mode;
13397 C_Stream : in Interfaces.C_Streams.FILEs;
13398 Form : in String := "");
13399 end Ada.Wide_Text_IO.C_Streams;
13401 with Interfaces.C_Streams;
13402 package Ada.Wide_Wide_Text_IO.C_Streams is
13403 function C_Stream (F : File_Type)
13404 return Interfaces.C_Streams.FILEs;
13406 (File : in out File_Type;
13407 Mode : in File_Mode;
13408 C_Stream : in Interfaces.C_Streams.FILEs;
13409 Form : in String := "");
13410 end Ada.Wide_Wide_Text_IO.C_Streams;
13412 with Interfaces.C_Streams;
13413 package Ada.Stream_IO.C_Streams is
13414 function C_Stream (F : File_Type)
13415 return Interfaces.C_Streams.FILEs;
13417 (File : in out File_Type;
13418 Mode : in File_Mode;
13419 C_Stream : in Interfaces.C_Streams.FILEs;
13420 Form : in String := "");
13421 end Ada.Stream_IO.C_Streams;
13425 In each of these six packages, the @code{C_Stream} function obtains the
13426 @code{FILE} pointer from a currently opened Ada file. It is then
13427 possible to use the @code{Interfaces.C_Streams} package to operate on
13428 this stream, or the stream can be passed to a C program which can
13429 operate on it directly. Of course the program is responsible for
13430 ensuring that only appropriate sequences of operations are executed.
13432 One particular use of relevance to an Ada program is that the
13433 @code{setvbuf} function can be used to control the buffering of the
13434 stream used by an Ada file. In the absence of such a call the standard
13435 default buffering is used.
13437 The @code{Open} procedures in these packages open a file giving an
13438 existing C Stream instead of a file name. Typically this stream is
13439 imported from a C program, allowing an Ada file to operate on an
13442 @node The GNAT Library
13443 @chapter The GNAT Library
13446 The GNAT library contains a number of general and special purpose packages.
13447 It represents functionality that the GNAT developers have found useful, and
13448 which is made available to GNAT users. The packages described here are fully
13449 supported, and upwards compatibility will be maintained in future releases,
13450 so you can use these facilities with the confidence that the same functionality
13451 will be available in future releases.
13453 The chapter here simply gives a brief summary of the facilities available.
13454 The full documentation is found in the spec file for the package. The full
13455 sources of these library packages, including both spec and body, are provided
13456 with all GNAT releases. For example, to find out the full specifications of
13457 the SPITBOL pattern matching capability, including a full tutorial and
13458 extensive examples, look in the @file{g-spipat.ads} file in the library.
13460 For each entry here, the package name (as it would appear in a @code{with}
13461 clause) is given, followed by the name of the corresponding spec file in
13462 parentheses. The packages are children in four hierarchies, @code{Ada},
13463 @code{Interfaces}, @code{System}, and @code{GNAT}, the latter being a
13464 GNAT-specific hierarchy.
13466 Note that an application program should only use packages in one of these
13467 four hierarchies if the package is defined in the Ada Reference Manual,
13468 or is listed in this section of the GNAT Programmers Reference Manual.
13469 All other units should be considered internal implementation units and
13470 should not be directly @code{with}'ed by application code. The use of
13471 a @code{with} statement that references one of these internal implementation
13472 units makes an application potentially dependent on changes in versions
13473 of GNAT, and will generate a warning message.
13476 * Ada.Characters.Latin_9 (a-chlat9.ads)::
13477 * Ada.Characters.Wide_Latin_1 (a-cwila1.ads)::
13478 * Ada.Characters.Wide_Latin_9 (a-cwila9.ads)::
13479 * Ada.Characters.Wide_Wide_Latin_1 (a-chzla1.ads)::
13480 * Ada.Characters.Wide_Wide_Latin_9 (a-chzla9.ads)::
13481 * Ada.Command_Line.Environment (a-colien.ads)::
13482 * Ada.Command_Line.Remove (a-colire.ads)::
13483 * Ada.Command_Line.Response_File (a-clrefi.ads)::
13484 * Ada.Direct_IO.C_Streams (a-diocst.ads)::
13485 * Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads)::
13486 * Ada.Exceptions.Last_Chance_Handler (a-elchha.ads)::
13487 * Ada.Exceptions.Traceback (a-exctra.ads)::
13488 * Ada.Sequential_IO.C_Streams (a-siocst.ads)::
13489 * Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads)::
13490 * Ada.Strings.Unbounded.Text_IO (a-suteio.ads)::
13491 * Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads)::
13492 * Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO (a-szuzti.ads)::
13493 * Ada.Text_IO.C_Streams (a-tiocst.ads)::
13494 * Ada.Text_IO.Reset_Standard_Files (a-tirsfi.ads)::
13495 * Ada.Wide_Characters.Unicode (a-wichun.ads)::
13496 * Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads)::
13497 * Ada.Wide_Text_IO.Reset_Standard_Files (a-wrstfi.ads)::
13498 * Ada.Wide_Wide_Characters.Unicode (a-zchuni.ads)::
13499 * Ada.Wide_Wide_Text_IO.C_Streams (a-ztcstr.ads)::
13500 * Ada.Wide_Wide_Text_IO.Reset_Standard_Files (a-zrstfi.ads)::
13501 * GNAT.Altivec (g-altive.ads)::
13502 * GNAT.Altivec.Conversions (g-altcon.ads)::
13503 * GNAT.Altivec.Vector_Operations (g-alveop.ads)::
13504 * GNAT.Altivec.Vector_Types (g-alvety.ads)::
13505 * GNAT.Altivec.Vector_Views (g-alvevi.ads)::
13506 * GNAT.Array_Split (g-arrspl.ads)::
13507 * GNAT.AWK (g-awk.ads)::
13508 * GNAT.Bounded_Buffers (g-boubuf.ads)::
13509 * GNAT.Bounded_Mailboxes (g-boumai.ads)::
13510 * GNAT.Bubble_Sort (g-bubsor.ads)::
13511 * GNAT.Bubble_Sort_A (g-busora.ads)::
13512 * GNAT.Bubble_Sort_G (g-busorg.ads)::
13513 * GNAT.Byte_Order_Mark (g-byorma.ads)::
13514 * GNAT.Byte_Swapping (g-bytswa.ads)::
13515 * GNAT.Calendar (g-calend.ads)::
13516 * GNAT.Calendar.Time_IO (g-catiio.ads)::
13517 * GNAT.Case_Util (g-casuti.ads)::
13518 * GNAT.CGI (g-cgi.ads)::
13519 * GNAT.CGI.Cookie (g-cgicoo.ads)::
13520 * GNAT.CGI.Debug (g-cgideb.ads)::
13521 * GNAT.Command_Line (g-comlin.ads)::
13522 * GNAT.Compiler_Version (g-comver.ads)::
13523 * GNAT.Ctrl_C (g-ctrl_c.ads)::
13524 * GNAT.CRC32 (g-crc32.ads)::
13525 * GNAT.Current_Exception (g-curexc.ads)::
13526 * GNAT.Debug_Pools (g-debpoo.ads)::
13527 * GNAT.Debug_Utilities (g-debuti.ads)::
13528 * GNAT.Decode_String (g-decstr.ads)::
13529 * GNAT.Decode_UTF8_String (g-deutst.ads)::
13530 * GNAT.Directory_Operations (g-dirope.ads)::
13531 * GNAT.Directory_Operations.Iteration (g-diopit.ads)::
13532 * GNAT.Dynamic_HTables (g-dynhta.ads)::
13533 * GNAT.Dynamic_Tables (g-dyntab.ads)::
13534 * GNAT.Encode_String (g-encstr.ads)::
13535 * GNAT.Encode_UTF8_String (g-enutst.ads)::
13536 * GNAT.Exception_Actions (g-excact.ads)::
13537 * GNAT.Exception_Traces (g-exctra.ads)::
13538 * GNAT.Exceptions (g-except.ads)::
13539 * GNAT.Expect (g-expect.ads)::
13540 * GNAT.Float_Control (g-flocon.ads)::
13541 * GNAT.Heap_Sort (g-heasor.ads)::
13542 * GNAT.Heap_Sort_A (g-hesora.ads)::
13543 * GNAT.Heap_Sort_G (g-hesorg.ads)::
13544 * GNAT.HTable (g-htable.ads)::
13545 * GNAT.IO (g-io.ads)::
13546 * GNAT.IO_Aux (g-io_aux.ads)::
13547 * GNAT.Lock_Files (g-locfil.ads)::
13548 * GNAT.MD5 (g-md5.ads)::
13549 * GNAT.Memory_Dump (g-memdum.ads)::
13550 * GNAT.Most_Recent_Exception (g-moreex.ads)::
13551 * GNAT.OS_Lib (g-os_lib.ads)::
13552 * GNAT.Perfect_Hash_Generators (g-pehage.ads)::
13553 * GNAT.Random_Numbers (g-rannum.ads)::
13554 * GNAT.Regexp (g-regexp.ads)::
13555 * GNAT.Registry (g-regist.ads)::
13556 * GNAT.Regpat (g-regpat.ads)::
13557 * GNAT.Secondary_Stack_Info (g-sestin.ads)::
13558 * GNAT.Semaphores (g-semaph.ads)::
13559 * GNAT.Serial_Communications (g-sercom.ads)::
13560 * GNAT.SHA1 (g-sha1.ads)::
13561 * GNAT.SHA224 (g-sha224.ads)::
13562 * GNAT.SHA256 (g-sha256.ads)::
13563 * GNAT.SHA384 (g-sha384.ads)::
13564 * GNAT.SHA512 (g-sha512.ads)::
13565 * GNAT.Signals (g-signal.ads)::
13566 * GNAT.Sockets (g-socket.ads)::
13567 * GNAT.Source_Info (g-souinf.ads)::
13568 * GNAT.Spelling_Checker (g-speche.ads)::
13569 * GNAT.Spelling_Checker_Generic (g-spchge.ads)::
13570 * GNAT.Spitbol.Patterns (g-spipat.ads)::
13571 * GNAT.Spitbol (g-spitbo.ads)::
13572 * GNAT.Spitbol.Table_Boolean (g-sptabo.ads)::
13573 * GNAT.Spitbol.Table_Integer (g-sptain.ads)::
13574 * GNAT.Spitbol.Table_VString (g-sptavs.ads)::
13575 * GNAT.SSE (g-sse.ads)::
13576 * GNAT.SSE.Vector_Types (g-ssvety.ads)::
13577 * GNAT.Strings (g-string.ads)::
13578 * GNAT.String_Split (g-strspl.ads)::
13579 * GNAT.Table (g-table.ads)::
13580 * GNAT.Task_Lock (g-tasloc.ads)::
13581 * GNAT.Threads (g-thread.ads)::
13582 * GNAT.Time_Stamp (g-timsta.ads)::
13583 * GNAT.Traceback (g-traceb.ads)::
13584 * GNAT.Traceback.Symbolic (g-trasym.ads)::
13585 * GNAT.UTF_32 (g-utf_32.ads)::
13586 * GNAT.UTF_32_Spelling_Checker (g-u3spch.ads)::
13587 * GNAT.Wide_Spelling_Checker (g-wispch.ads)::
13588 * GNAT.Wide_String_Split (g-wistsp.ads)::
13589 * GNAT.Wide_Wide_Spelling_Checker (g-zspche.ads)::
13590 * GNAT.Wide_Wide_String_Split (g-zistsp.ads)::
13591 * Interfaces.C.Extensions (i-cexten.ads)::
13592 * Interfaces.C.Streams (i-cstrea.ads)::
13593 * Interfaces.CPP (i-cpp.ads)::
13594 * Interfaces.Packed_Decimal (i-pacdec.ads)::
13595 * Interfaces.VxWorks (i-vxwork.ads)::
13596 * Interfaces.VxWorks.IO (i-vxwoio.ads)::
13597 * System.Address_Image (s-addima.ads)::
13598 * System.Assertions (s-assert.ads)::
13599 * System.Memory (s-memory.ads)::
13600 * System.Partition_Interface (s-parint.ads)::
13601 * System.Pool_Global (s-pooglo.ads)::
13602 * System.Pool_Local (s-pooloc.ads)::
13603 * System.Restrictions (s-restri.ads)::
13604 * System.Rident (s-rident.ads)::
13605 * System.Strings.Stream_Ops (s-ststop.ads)::
13606 * System.Task_Info (s-tasinf.ads)::
13607 * System.Wch_Cnv (s-wchcnv.ads)::
13608 * System.Wch_Con (s-wchcon.ads)::
13611 @node Ada.Characters.Latin_9 (a-chlat9.ads)
13612 @section @code{Ada.Characters.Latin_9} (@file{a-chlat9.ads})
13613 @cindex @code{Ada.Characters.Latin_9} (@file{a-chlat9.ads})
13614 @cindex Latin_9 constants for Character
13617 This child of @code{Ada.Characters}
13618 provides a set of definitions corresponding to those in the
13619 RM-defined package @code{Ada.Characters.Latin_1} but with the
13620 few modifications required for @code{Latin-9}
13621 The provision of such a package
13622 is specifically authorized by the Ada Reference Manual
13625 @node Ada.Characters.Wide_Latin_1 (a-cwila1.ads)
13626 @section @code{Ada.Characters.Wide_Latin_1} (@file{a-cwila1.ads})
13627 @cindex @code{Ada.Characters.Wide_Latin_1} (@file{a-cwila1.ads})
13628 @cindex Latin_1 constants for Wide_Character
13631 This child of @code{Ada.Characters}
13632 provides a set of definitions corresponding to those in the
13633 RM-defined package @code{Ada.Characters.Latin_1} but with the
13634 types of the constants being @code{Wide_Character}
13635 instead of @code{Character}. The provision of such a package
13636 is specifically authorized by the Ada Reference Manual
13639 @node Ada.Characters.Wide_Latin_9 (a-cwila9.ads)
13640 @section @code{Ada.Characters.Wide_Latin_9} (@file{a-cwila1.ads})
13641 @cindex @code{Ada.Characters.Wide_Latin_9} (@file{a-cwila1.ads})
13642 @cindex Latin_9 constants for Wide_Character
13645 This child of @code{Ada.Characters}
13646 provides a set of definitions corresponding to those in the
13647 GNAT defined package @code{Ada.Characters.Latin_9} but with the
13648 types of the constants being @code{Wide_Character}
13649 instead of @code{Character}. The provision of such a package
13650 is specifically authorized by the Ada Reference Manual
13653 @node Ada.Characters.Wide_Wide_Latin_1 (a-chzla1.ads)
13654 @section @code{Ada.Characters.Wide_Wide_Latin_1} (@file{a-chzla1.ads})
13655 @cindex @code{Ada.Characters.Wide_Wide_Latin_1} (@file{a-chzla1.ads})
13656 @cindex Latin_1 constants for Wide_Wide_Character
13659 This child of @code{Ada.Characters}
13660 provides a set of definitions corresponding to those in the
13661 RM-defined package @code{Ada.Characters.Latin_1} but with the
13662 types of the constants being @code{Wide_Wide_Character}
13663 instead of @code{Character}. The provision of such a package
13664 is specifically authorized by the Ada Reference Manual
13667 @node Ada.Characters.Wide_Wide_Latin_9 (a-chzla9.ads)
13668 @section @code{Ada.Characters.Wide_Wide_Latin_9} (@file{a-chzla9.ads})
13669 @cindex @code{Ada.Characters.Wide_Wide_Latin_9} (@file{a-chzla9.ads})
13670 @cindex Latin_9 constants for Wide_Wide_Character
13673 This child of @code{Ada.Characters}
13674 provides a set of definitions corresponding to those in the
13675 GNAT defined package @code{Ada.Characters.Latin_9} but with the
13676 types of the constants being @code{Wide_Wide_Character}
13677 instead of @code{Character}. The provision of such a package
13678 is specifically authorized by the Ada Reference Manual
13681 @node Ada.Command_Line.Environment (a-colien.ads)
13682 @section @code{Ada.Command_Line.Environment} (@file{a-colien.ads})
13683 @cindex @code{Ada.Command_Line.Environment} (@file{a-colien.ads})
13684 @cindex Environment entries
13687 This child of @code{Ada.Command_Line}
13688 provides a mechanism for obtaining environment values on systems
13689 where this concept makes sense.
13691 @node Ada.Command_Line.Remove (a-colire.ads)
13692 @section @code{Ada.Command_Line.Remove} (@file{a-colire.ads})
13693 @cindex @code{Ada.Command_Line.Remove} (@file{a-colire.ads})
13694 @cindex Removing command line arguments
13695 @cindex Command line, argument removal
13698 This child of @code{Ada.Command_Line}
13699 provides a mechanism for logically removing
13700 arguments from the argument list. Once removed, an argument is not visible
13701 to further calls on the subprograms in @code{Ada.Command_Line} will not
13702 see the removed argument.
13704 @node Ada.Command_Line.Response_File (a-clrefi.ads)
13705 @section @code{Ada.Command_Line.Response_File} (@file{a-clrefi.ads})
13706 @cindex @code{Ada.Command_Line.Response_File} (@file{a-clrefi.ads})
13707 @cindex Response file for command line
13708 @cindex Command line, response file
13709 @cindex Command line, handling long command lines
13712 This child of @code{Ada.Command_Line} provides a mechanism facilities for
13713 getting command line arguments from a text file, called a "response file".
13714 Using a response file allow passing a set of arguments to an executable longer
13715 than the maximum allowed by the system on the command line.
13717 @node Ada.Direct_IO.C_Streams (a-diocst.ads)
13718 @section @code{Ada.Direct_IO.C_Streams} (@file{a-diocst.ads})
13719 @cindex @code{Ada.Direct_IO.C_Streams} (@file{a-diocst.ads})
13720 @cindex C Streams, Interfacing with Direct_IO
13723 This package provides subprograms that allow interfacing between
13724 C streams and @code{Direct_IO}. The stream identifier can be
13725 extracted from a file opened on the Ada side, and an Ada file
13726 can be constructed from a stream opened on the C side.
13728 @node Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads)
13729 @section @code{Ada.Exceptions.Is_Null_Occurrence} (@file{a-einuoc.ads})
13730 @cindex @code{Ada.Exceptions.Is_Null_Occurrence} (@file{a-einuoc.ads})
13731 @cindex Null_Occurrence, testing for
13734 This child subprogram provides a way of testing for the null
13735 exception occurrence (@code{Null_Occurrence}) without raising
13738 @node Ada.Exceptions.Last_Chance_Handler (a-elchha.ads)
13739 @section @code{Ada.Exceptions.Last_Chance_Handler} (@file{a-elchha.ads})
13740 @cindex @code{Ada.Exceptions.Last_Chance_Handler} (@file{a-elchha.ads})
13741 @cindex Null_Occurrence, testing for
13744 This child subprogram is used for handling otherwise unhandled
13745 exceptions (hence the name last chance), and perform clean ups before
13746 terminating the program. Note that this subprogram never returns.
13748 @node Ada.Exceptions.Traceback (a-exctra.ads)
13749 @section @code{Ada.Exceptions.Traceback} (@file{a-exctra.ads})
13750 @cindex @code{Ada.Exceptions.Traceback} (@file{a-exctra.ads})
13751 @cindex Traceback for Exception Occurrence
13754 This child package provides the subprogram (@code{Tracebacks}) to
13755 give a traceback array of addresses based on an exception
13758 @node Ada.Sequential_IO.C_Streams (a-siocst.ads)
13759 @section @code{Ada.Sequential_IO.C_Streams} (@file{a-siocst.ads})
13760 @cindex @code{Ada.Sequential_IO.C_Streams} (@file{a-siocst.ads})
13761 @cindex C Streams, Interfacing with Sequential_IO
13764 This package provides subprograms that allow interfacing between
13765 C streams and @code{Sequential_IO}. The stream identifier can be
13766 extracted from a file opened on the Ada side, and an Ada file
13767 can be constructed from a stream opened on the C side.
13769 @node Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads)
13770 @section @code{Ada.Streams.Stream_IO.C_Streams} (@file{a-ssicst.ads})
13771 @cindex @code{Ada.Streams.Stream_IO.C_Streams} (@file{a-ssicst.ads})
13772 @cindex C Streams, Interfacing with Stream_IO
13775 This package provides subprograms that allow interfacing between
13776 C streams and @code{Stream_IO}. The stream identifier can be
13777 extracted from a file opened on the Ada side, and an Ada file
13778 can be constructed from a stream opened on the C side.
13780 @node Ada.Strings.Unbounded.Text_IO (a-suteio.ads)
13781 @section @code{Ada.Strings.Unbounded.Text_IO} (@file{a-suteio.ads})
13782 @cindex @code{Ada.Strings.Unbounded.Text_IO} (@file{a-suteio.ads})
13783 @cindex @code{Unbounded_String}, IO support
13784 @cindex @code{Text_IO}, extensions for unbounded strings
13787 This package provides subprograms for Text_IO for unbounded
13788 strings, avoiding the necessity for an intermediate operation
13789 with ordinary strings.
13791 @node Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads)
13792 @section @code{Ada.Strings.Wide_Unbounded.Wide_Text_IO} (@file{a-swuwti.ads})
13793 @cindex @code{Ada.Strings.Wide_Unbounded.Wide_Text_IO} (@file{a-swuwti.ads})
13794 @cindex @code{Unbounded_Wide_String}, IO support
13795 @cindex @code{Text_IO}, extensions for unbounded wide strings
13798 This package provides subprograms for Text_IO for unbounded
13799 wide strings, avoiding the necessity for an intermediate operation
13800 with ordinary wide strings.
13802 @node Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO (a-szuzti.ads)
13803 @section @code{Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO} (@file{a-szuzti.ads})
13804 @cindex @code{Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO} (@file{a-szuzti.ads})
13805 @cindex @code{Unbounded_Wide_Wide_String}, IO support
13806 @cindex @code{Text_IO}, extensions for unbounded wide wide strings
13809 This package provides subprograms for Text_IO for unbounded
13810 wide wide strings, avoiding the necessity for an intermediate operation
13811 with ordinary wide wide strings.
13813 @node Ada.Text_IO.C_Streams (a-tiocst.ads)
13814 @section @code{Ada.Text_IO.C_Streams} (@file{a-tiocst.ads})
13815 @cindex @code{Ada.Text_IO.C_Streams} (@file{a-tiocst.ads})
13816 @cindex C Streams, Interfacing with @code{Text_IO}
13819 This package provides subprograms that allow interfacing between
13820 C streams and @code{Text_IO}. The stream identifier can be
13821 extracted from a file opened on the Ada side, and an Ada file
13822 can be constructed from a stream opened on the C side.
13824 @node Ada.Text_IO.Reset_Standard_Files (a-tirsfi.ads)
13825 @section @code{Ada.Text_IO.Reset_Standard_Files} (@file{a-tirsfi.ads})
13826 @cindex @code{Ada.Text_IO.Reset_Standard_Files} (@file{a-tirsfi.ads})
13827 @cindex @code{Text_IO} resetting standard files
13830 This procedure is used to reset the status of the standard files used
13831 by Ada.Text_IO. This is useful in a situation (such as a restart in an
13832 embedded application) where the status of the files may change during
13833 execution (for example a standard input file may be redefined to be
13836 @node Ada.Wide_Characters.Unicode (a-wichun.ads)
13837 @section @code{Ada.Wide_Characters.Unicode} (@file{a-wichun.ads})
13838 @cindex @code{Ada.Wide_Characters.Unicode} (@file{a-wichun.ads})
13839 @cindex Unicode categorization, Wide_Character
13842 This package provides subprograms that allow categorization of
13843 Wide_Character values according to Unicode categories.
13845 @node Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads)
13846 @section @code{Ada.Wide_Text_IO.C_Streams} (@file{a-wtcstr.ads})
13847 @cindex @code{Ada.Wide_Text_IO.C_Streams} (@file{a-wtcstr.ads})
13848 @cindex C Streams, Interfacing with @code{Wide_Text_IO}
13851 This package provides subprograms that allow interfacing between
13852 C streams and @code{Wide_Text_IO}. The stream identifier can be
13853 extracted from a file opened on the Ada side, and an Ada file
13854 can be constructed from a stream opened on the C side.
13856 @node Ada.Wide_Text_IO.Reset_Standard_Files (a-wrstfi.ads)
13857 @section @code{Ada.Wide_Text_IO.Reset_Standard_Files} (@file{a-wrstfi.ads})
13858 @cindex @code{Ada.Wide_Text_IO.Reset_Standard_Files} (@file{a-wrstfi.ads})
13859 @cindex @code{Wide_Text_IO} resetting standard files
13862 This procedure is used to reset the status of the standard files used
13863 by Ada.Wide_Text_IO. This is useful in a situation (such as a restart in an
13864 embedded application) where the status of the files may change during
13865 execution (for example a standard input file may be redefined to be
13868 @node Ada.Wide_Wide_Characters.Unicode (a-zchuni.ads)
13869 @section @code{Ada.Wide_Wide_Characters.Unicode} (@file{a-zchuni.ads})
13870 @cindex @code{Ada.Wide_Wide_Characters.Unicode} (@file{a-zchuni.ads})
13871 @cindex Unicode categorization, Wide_Wide_Character
13874 This package provides subprograms that allow categorization of
13875 Wide_Wide_Character values according to Unicode categories.
13877 @node Ada.Wide_Wide_Text_IO.C_Streams (a-ztcstr.ads)
13878 @section @code{Ada.Wide_Wide_Text_IO.C_Streams} (@file{a-ztcstr.ads})
13879 @cindex @code{Ada.Wide_Wide_Text_IO.C_Streams} (@file{a-ztcstr.ads})
13880 @cindex C Streams, Interfacing with @code{Wide_Wide_Text_IO}
13883 This package provides subprograms that allow interfacing between
13884 C streams and @code{Wide_Wide_Text_IO}. The stream identifier can be
13885 extracted from a file opened on the Ada side, and an Ada file
13886 can be constructed from a stream opened on the C side.
13888 @node Ada.Wide_Wide_Text_IO.Reset_Standard_Files (a-zrstfi.ads)
13889 @section @code{Ada.Wide_Wide_Text_IO.Reset_Standard_Files} (@file{a-zrstfi.ads})
13890 @cindex @code{Ada.Wide_Wide_Text_IO.Reset_Standard_Files} (@file{a-zrstfi.ads})
13891 @cindex @code{Wide_Wide_Text_IO} resetting standard files
13894 This procedure is used to reset the status of the standard files used
13895 by Ada.Wide_Wide_Text_IO. This is useful in a situation (such as a
13896 restart in an embedded application) where the status of the files may
13897 change during execution (for example a standard input file may be
13898 redefined to be interactive).
13900 @node GNAT.Altivec (g-altive.ads)
13901 @section @code{GNAT.Altivec} (@file{g-altive.ads})
13902 @cindex @code{GNAT.Altivec} (@file{g-altive.ads})
13906 This is the root package of the GNAT AltiVec binding. It provides
13907 definitions of constants and types common to all the versions of the
13910 @node GNAT.Altivec.Conversions (g-altcon.ads)
13911 @section @code{GNAT.Altivec.Conversions} (@file{g-altcon.ads})
13912 @cindex @code{GNAT.Altivec.Conversions} (@file{g-altcon.ads})
13916 This package provides the Vector/View conversion routines.
13918 @node GNAT.Altivec.Vector_Operations (g-alveop.ads)
13919 @section @code{GNAT.Altivec.Vector_Operations} (@file{g-alveop.ads})
13920 @cindex @code{GNAT.Altivec.Vector_Operations} (@file{g-alveop.ads})
13924 This package exposes the Ada interface to the AltiVec operations on
13925 vector objects. A soft emulation is included by default in the GNAT
13926 library. The hard binding is provided as a separate package. This unit
13927 is common to both bindings.
13929 @node GNAT.Altivec.Vector_Types (g-alvety.ads)
13930 @section @code{GNAT.Altivec.Vector_Types} (@file{g-alvety.ads})
13931 @cindex @code{GNAT.Altivec.Vector_Types} (@file{g-alvety.ads})
13935 This package exposes the various vector types part of the Ada binding
13936 to AltiVec facilities.
13938 @node GNAT.Altivec.Vector_Views (g-alvevi.ads)
13939 @section @code{GNAT.Altivec.Vector_Views} (@file{g-alvevi.ads})
13940 @cindex @code{GNAT.Altivec.Vector_Views} (@file{g-alvevi.ads})
13944 This package provides public 'View' data types from/to which private
13945 vector representations can be converted via
13946 GNAT.Altivec.Conversions. This allows convenient access to individual
13947 vector elements and provides a simple way to initialize vector
13950 @node GNAT.Array_Split (g-arrspl.ads)
13951 @section @code{GNAT.Array_Split} (@file{g-arrspl.ads})
13952 @cindex @code{GNAT.Array_Split} (@file{g-arrspl.ads})
13953 @cindex Array splitter
13956 Useful array-manipulation routines: given a set of separators, split
13957 an array wherever the separators appear, and provide direct access
13958 to the resulting slices.
13960 @node GNAT.AWK (g-awk.ads)
13961 @section @code{GNAT.AWK} (@file{g-awk.ads})
13962 @cindex @code{GNAT.AWK} (@file{g-awk.ads})
13967 Provides AWK-like parsing functions, with an easy interface for parsing one
13968 or more files containing formatted data. The file is viewed as a database
13969 where each record is a line and a field is a data element in this line.
13971 @node GNAT.Bounded_Buffers (g-boubuf.ads)
13972 @section @code{GNAT.Bounded_Buffers} (@file{g-boubuf.ads})
13973 @cindex @code{GNAT.Bounded_Buffers} (@file{g-boubuf.ads})
13975 @cindex Bounded Buffers
13978 Provides a concurrent generic bounded buffer abstraction. Instances are
13979 useful directly or as parts of the implementations of other abstractions,
13982 @node GNAT.Bounded_Mailboxes (g-boumai.ads)
13983 @section @code{GNAT.Bounded_Mailboxes} (@file{g-boumai.ads})
13984 @cindex @code{GNAT.Bounded_Mailboxes} (@file{g-boumai.ads})
13989 Provides a thread-safe asynchronous intertask mailbox communication facility.
13991 @node GNAT.Bubble_Sort (g-bubsor.ads)
13992 @section @code{GNAT.Bubble_Sort} (@file{g-bubsor.ads})
13993 @cindex @code{GNAT.Bubble_Sort} (@file{g-bubsor.ads})
13995 @cindex Bubble sort
13998 Provides a general implementation of bubble sort usable for sorting arbitrary
13999 data items. Exchange and comparison procedures are provided by passing
14000 access-to-procedure values.
14002 @node GNAT.Bubble_Sort_A (g-busora.ads)
14003 @section @code{GNAT.Bubble_Sort_A} (@file{g-busora.ads})
14004 @cindex @code{GNAT.Bubble_Sort_A} (@file{g-busora.ads})
14006 @cindex Bubble sort
14009 Provides a general implementation of bubble sort usable for sorting arbitrary
14010 data items. Move and comparison procedures are provided by passing
14011 access-to-procedure values. This is an older version, retained for
14012 compatibility. Usually @code{GNAT.Bubble_Sort} will be preferable.
14014 @node GNAT.Bubble_Sort_G (g-busorg.ads)
14015 @section @code{GNAT.Bubble_Sort_G} (@file{g-busorg.ads})
14016 @cindex @code{GNAT.Bubble_Sort_G} (@file{g-busorg.ads})
14018 @cindex Bubble sort
14021 Similar to @code{Bubble_Sort_A} except that the move and sorting procedures
14022 are provided as generic parameters, this improves efficiency, especially
14023 if the procedures can be inlined, at the expense of duplicating code for
14024 multiple instantiations.
14026 @node GNAT.Byte_Order_Mark (g-byorma.ads)
14027 @section @code{GNAT.Byte_Order_Mark} (@file{g-byorma.ads})
14028 @cindex @code{GNAT.Byte_Order_Mark} (@file{g-byorma.ads})
14029 @cindex UTF-8 representation
14030 @cindex Wide characte representations
14033 Provides a routine which given a string, reads the start of the string to
14034 see whether it is one of the standard byte order marks (BOM's) which signal
14035 the encoding of the string. The routine includes detection of special XML
14036 sequences for various UCS input formats.
14038 @node GNAT.Byte_Swapping (g-bytswa.ads)
14039 @section @code{GNAT.Byte_Swapping} (@file{g-bytswa.ads})
14040 @cindex @code{GNAT.Byte_Swapping} (@file{g-bytswa.ads})
14041 @cindex Byte swapping
14045 General routines for swapping the bytes in 2-, 4-, and 8-byte quantities.
14046 Machine-specific implementations are available in some cases.
14048 @node GNAT.Calendar (g-calend.ads)
14049 @section @code{GNAT.Calendar} (@file{g-calend.ads})
14050 @cindex @code{GNAT.Calendar} (@file{g-calend.ads})
14051 @cindex @code{Calendar}
14054 Extends the facilities provided by @code{Ada.Calendar} to include handling
14055 of days of the week, an extended @code{Split} and @code{Time_Of} capability.
14056 Also provides conversion of @code{Ada.Calendar.Time} values to and from the
14057 C @code{timeval} format.
14059 @node GNAT.Calendar.Time_IO (g-catiio.ads)
14060 @section @code{GNAT.Calendar.Time_IO} (@file{g-catiio.ads})
14061 @cindex @code{Calendar}
14063 @cindex @code{GNAT.Calendar.Time_IO} (@file{g-catiio.ads})
14065 @node GNAT.CRC32 (g-crc32.ads)
14066 @section @code{GNAT.CRC32} (@file{g-crc32.ads})
14067 @cindex @code{GNAT.CRC32} (@file{g-crc32.ads})
14069 @cindex Cyclic Redundancy Check
14072 This package implements the CRC-32 algorithm. For a full description
14073 of this algorithm see
14074 ``Computation of Cyclic Redundancy Checks via Table Look-Up'',
14075 @cite{Communications of the ACM}, Vol.@: 31 No.@: 8, pp.@: 1008-1013,
14076 Aug.@: 1988. Sarwate, D.V@.
14078 @node GNAT.Case_Util (g-casuti.ads)
14079 @section @code{GNAT.Case_Util} (@file{g-casuti.ads})
14080 @cindex @code{GNAT.Case_Util} (@file{g-casuti.ads})
14081 @cindex Casing utilities
14082 @cindex Character handling (@code{GNAT.Case_Util})
14085 A set of simple routines for handling upper and lower casing of strings
14086 without the overhead of the full casing tables
14087 in @code{Ada.Characters.Handling}.
14089 @node GNAT.CGI (g-cgi.ads)
14090 @section @code{GNAT.CGI} (@file{g-cgi.ads})
14091 @cindex @code{GNAT.CGI} (@file{g-cgi.ads})
14092 @cindex CGI (Common Gateway Interface)
14095 This is a package for interfacing a GNAT program with a Web server via the
14096 Common Gateway Interface (CGI)@. Basically this package parses the CGI
14097 parameters, which are a set of key/value pairs sent by the Web server. It
14098 builds a table whose index is the key and provides some services to deal
14101 @node GNAT.CGI.Cookie (g-cgicoo.ads)
14102 @section @code{GNAT.CGI.Cookie} (@file{g-cgicoo.ads})
14103 @cindex @code{GNAT.CGI.Cookie} (@file{g-cgicoo.ads})
14104 @cindex CGI (Common Gateway Interface) cookie support
14105 @cindex Cookie support in CGI
14108 This is a package to interface a GNAT program with a Web server via the
14109 Common Gateway Interface (CGI). It exports services to deal with Web
14110 cookies (piece of information kept in the Web client software).
14112 @node GNAT.CGI.Debug (g-cgideb.ads)
14113 @section @code{GNAT.CGI.Debug} (@file{g-cgideb.ads})
14114 @cindex @code{GNAT.CGI.Debug} (@file{g-cgideb.ads})
14115 @cindex CGI (Common Gateway Interface) debugging
14118 This is a package to help debugging CGI (Common Gateway Interface)
14119 programs written in Ada.
14121 @node GNAT.Command_Line (g-comlin.ads)
14122 @section @code{GNAT.Command_Line} (@file{g-comlin.ads})
14123 @cindex @code{GNAT.Command_Line} (@file{g-comlin.ads})
14124 @cindex Command line
14127 Provides a high level interface to @code{Ada.Command_Line} facilities,
14128 including the ability to scan for named switches with optional parameters
14129 and expand file names using wild card notations.
14131 @node GNAT.Compiler_Version (g-comver.ads)
14132 @section @code{GNAT.Compiler_Version} (@file{g-comver.ads})
14133 @cindex @code{GNAT.Compiler_Version} (@file{g-comver.ads})
14134 @cindex Compiler Version
14135 @cindex Version, of compiler
14138 Provides a routine for obtaining the version of the compiler used to
14139 compile the program. More accurately this is the version of the binder
14140 used to bind the program (this will normally be the same as the version
14141 of the compiler if a consistent tool set is used to compile all units
14144 @node GNAT.Ctrl_C (g-ctrl_c.ads)
14145 @section @code{GNAT.Ctrl_C} (@file{g-ctrl_c.ads})
14146 @cindex @code{GNAT.Ctrl_C} (@file{g-ctrl_c.ads})
14150 Provides a simple interface to handle Ctrl-C keyboard events.
14152 @node GNAT.Current_Exception (g-curexc.ads)
14153 @section @code{GNAT.Current_Exception} (@file{g-curexc.ads})
14154 @cindex @code{GNAT.Current_Exception} (@file{g-curexc.ads})
14155 @cindex Current exception
14156 @cindex Exception retrieval
14159 Provides access to information on the current exception that has been raised
14160 without the need for using the Ada 95 / Ada 2005 exception choice parameter
14161 specification syntax.
14162 This is particularly useful in simulating typical facilities for
14163 obtaining information about exceptions provided by Ada 83 compilers.
14165 @node GNAT.Debug_Pools (g-debpoo.ads)
14166 @section @code{GNAT.Debug_Pools} (@file{g-debpoo.ads})
14167 @cindex @code{GNAT.Debug_Pools} (@file{g-debpoo.ads})
14169 @cindex Debug pools
14170 @cindex Memory corruption debugging
14173 Provide a debugging storage pools that helps tracking memory corruption
14174 problems. @xref{The GNAT Debug Pool Facility,,, gnat_ugn,
14175 @value{EDITION} User's Guide}.
14177 @node GNAT.Debug_Utilities (g-debuti.ads)
14178 @section @code{GNAT.Debug_Utilities} (@file{g-debuti.ads})
14179 @cindex @code{GNAT.Debug_Utilities} (@file{g-debuti.ads})
14183 Provides a few useful utilities for debugging purposes, including conversion
14184 to and from string images of address values. Supports both C and Ada formats
14185 for hexadecimal literals.
14187 @node GNAT.Decode_String (g-decstr.ads)
14188 @section @code{GNAT.Decode_String} (@file{g-decstr.ads})
14189 @cindex @code{GNAT.Decode_String} (@file{g-decstr.ads})
14190 @cindex Decoding strings
14191 @cindex String decoding
14192 @cindex Wide character encoding
14197 A generic package providing routines for decoding wide character and wide wide
14198 character strings encoded as sequences of 8-bit characters using a specified
14199 encoding method. Includes validation routines, and also routines for stepping
14200 to next or previous encoded character in an encoded string.
14201 Useful in conjunction with Unicode character coding. Note there is a
14202 preinstantiation for UTF-8. See next entry.
14204 @node GNAT.Decode_UTF8_String (g-deutst.ads)
14205 @section @code{GNAT.Decode_UTF8_String} (@file{g-deutst.ads})
14206 @cindex @code{GNAT.Decode_UTF8_String} (@file{g-deutst.ads})
14207 @cindex Decoding strings
14208 @cindex Decoding UTF-8 strings
14209 @cindex UTF-8 string decoding
14210 @cindex Wide character decoding
14215 A preinstantiation of GNAT.Decode_Strings for UTF-8 encoding.
14217 @node GNAT.Directory_Operations (g-dirope.ads)
14218 @section @code{GNAT.Directory_Operations} (@file{g-dirope.ads})
14219 @cindex @code{GNAT.Directory_Operations} (@file{g-dirope.ads})
14220 @cindex Directory operations
14223 Provides a set of routines for manipulating directories, including changing
14224 the current directory, making new directories, and scanning the files in a
14227 @node GNAT.Directory_Operations.Iteration (g-diopit.ads)
14228 @section @code{GNAT.Directory_Operations.Iteration} (@file{g-diopit.ads})
14229 @cindex @code{GNAT.Directory_Operations.Iteration} (@file{g-diopit.ads})
14230 @cindex Directory operations iteration
14233 A child unit of GNAT.Directory_Operations providing additional operations
14234 for iterating through directories.
14236 @node GNAT.Dynamic_HTables (g-dynhta.ads)
14237 @section @code{GNAT.Dynamic_HTables} (@file{g-dynhta.ads})
14238 @cindex @code{GNAT.Dynamic_HTables} (@file{g-dynhta.ads})
14239 @cindex Hash tables
14242 A generic implementation of hash tables that can be used to hash arbitrary
14243 data. Provided in two forms, a simple form with built in hash functions,
14244 and a more complex form in which the hash function is supplied.
14247 This package provides a facility similar to that of @code{GNAT.HTable},
14248 except that this package declares a type that can be used to define
14249 dynamic instances of the hash table, while an instantiation of
14250 @code{GNAT.HTable} creates a single instance of the hash table.
14252 @node GNAT.Dynamic_Tables (g-dyntab.ads)
14253 @section @code{GNAT.Dynamic_Tables} (@file{g-dyntab.ads})
14254 @cindex @code{GNAT.Dynamic_Tables} (@file{g-dyntab.ads})
14255 @cindex Table implementation
14256 @cindex Arrays, extendable
14259 A generic package providing a single dimension array abstraction where the
14260 length of the array can be dynamically modified.
14263 This package provides a facility similar to that of @code{GNAT.Table},
14264 except that this package declares a type that can be used to define
14265 dynamic instances of the table, while an instantiation of
14266 @code{GNAT.Table} creates a single instance of the table type.
14268 @node GNAT.Encode_String (g-encstr.ads)
14269 @section @code{GNAT.Encode_String} (@file{g-encstr.ads})
14270 @cindex @code{GNAT.Encode_String} (@file{g-encstr.ads})
14271 @cindex Encoding strings
14272 @cindex String encoding
14273 @cindex Wide character encoding
14278 A generic package providing routines for encoding wide character and wide
14279 wide character strings as sequences of 8-bit characters using a specified
14280 encoding method. Useful in conjunction with Unicode character coding.
14281 Note there is a preinstantiation for UTF-8. See next entry.
14283 @node GNAT.Encode_UTF8_String (g-enutst.ads)
14284 @section @code{GNAT.Encode_UTF8_String} (@file{g-enutst.ads})
14285 @cindex @code{GNAT.Encode_UTF8_String} (@file{g-enutst.ads})
14286 @cindex Encoding strings
14287 @cindex Encoding UTF-8 strings
14288 @cindex UTF-8 string encoding
14289 @cindex Wide character encoding
14294 A preinstantiation of GNAT.Encode_Strings for UTF-8 encoding.
14296 @node GNAT.Exception_Actions (g-excact.ads)
14297 @section @code{GNAT.Exception_Actions} (@file{g-excact.ads})
14298 @cindex @code{GNAT.Exception_Actions} (@file{g-excact.ads})
14299 @cindex Exception actions
14302 Provides callbacks when an exception is raised. Callbacks can be registered
14303 for specific exceptions, or when any exception is raised. This
14304 can be used for instance to force a core dump to ease debugging.
14306 @node GNAT.Exception_Traces (g-exctra.ads)
14307 @section @code{GNAT.Exception_Traces} (@file{g-exctra.ads})
14308 @cindex @code{GNAT.Exception_Traces} (@file{g-exctra.ads})
14309 @cindex Exception traces
14313 Provides an interface allowing to control automatic output upon exception
14316 @node GNAT.Exceptions (g-except.ads)
14317 @section @code{GNAT.Exceptions} (@file{g-expect.ads})
14318 @cindex @code{GNAT.Exceptions} (@file{g-expect.ads})
14319 @cindex Exceptions, Pure
14320 @cindex Pure packages, exceptions
14323 Normally it is not possible to raise an exception with
14324 a message from a subprogram in a pure package, since the
14325 necessary types and subprograms are in @code{Ada.Exceptions}
14326 which is not a pure unit. @code{GNAT.Exceptions} provides a
14327 facility for getting around this limitation for a few
14328 predefined exceptions, and for example allow raising
14329 @code{Constraint_Error} with a message from a pure subprogram.
14331 @node GNAT.Expect (g-expect.ads)
14332 @section @code{GNAT.Expect} (@file{g-expect.ads})
14333 @cindex @code{GNAT.Expect} (@file{g-expect.ads})
14336 Provides a set of subprograms similar to what is available
14337 with the standard Tcl Expect tool.
14338 It allows you to easily spawn and communicate with an external process.
14339 You can send commands or inputs to the process, and compare the output
14340 with some expected regular expression. Currently @code{GNAT.Expect}
14341 is implemented on all native GNAT ports except for OpenVMS@.
14342 It is not implemented for cross ports, and in particular is not
14343 implemented for VxWorks or LynxOS@.
14345 @node GNAT.Float_Control (g-flocon.ads)
14346 @section @code{GNAT.Float_Control} (@file{g-flocon.ads})
14347 @cindex @code{GNAT.Float_Control} (@file{g-flocon.ads})
14348 @cindex Floating-Point Processor
14351 Provides an interface for resetting the floating-point processor into the
14352 mode required for correct semantic operation in Ada. Some third party
14353 library calls may cause this mode to be modified, and the Reset procedure
14354 in this package can be used to reestablish the required mode.
14356 @node GNAT.Heap_Sort (g-heasor.ads)
14357 @section @code{GNAT.Heap_Sort} (@file{g-heasor.ads})
14358 @cindex @code{GNAT.Heap_Sort} (@file{g-heasor.ads})
14362 Provides a general implementation of heap sort usable for sorting arbitrary
14363 data items. Exchange and comparison procedures are provided by passing
14364 access-to-procedure values. The algorithm used is a modified heap sort
14365 that performs approximately N*log(N) comparisons in the worst case.
14367 @node GNAT.Heap_Sort_A (g-hesora.ads)
14368 @section @code{GNAT.Heap_Sort_A} (@file{g-hesora.ads})
14369 @cindex @code{GNAT.Heap_Sort_A} (@file{g-hesora.ads})
14373 Provides a general implementation of heap sort usable for sorting arbitrary
14374 data items. Move and comparison procedures are provided by passing
14375 access-to-procedure values. The algorithm used is a modified heap sort
14376 that performs approximately N*log(N) comparisons in the worst case.
14377 This differs from @code{GNAT.Heap_Sort} in having a less convenient
14378 interface, but may be slightly more efficient.
14380 @node GNAT.Heap_Sort_G (g-hesorg.ads)
14381 @section @code{GNAT.Heap_Sort_G} (@file{g-hesorg.ads})
14382 @cindex @code{GNAT.Heap_Sort_G} (@file{g-hesorg.ads})
14386 Similar to @code{Heap_Sort_A} except that the move and sorting procedures
14387 are provided as generic parameters, this improves efficiency, especially
14388 if the procedures can be inlined, at the expense of duplicating code for
14389 multiple instantiations.
14391 @node GNAT.HTable (g-htable.ads)
14392 @section @code{GNAT.HTable} (@file{g-htable.ads})
14393 @cindex @code{GNAT.HTable} (@file{g-htable.ads})
14394 @cindex Hash tables
14397 A generic implementation of hash tables that can be used to hash arbitrary
14398 data. Provides two approaches, one a simple static approach, and the other
14399 allowing arbitrary dynamic hash tables.
14401 @node GNAT.IO (g-io.ads)
14402 @section @code{GNAT.IO} (@file{g-io.ads})
14403 @cindex @code{GNAT.IO} (@file{g-io.ads})
14405 @cindex Input/Output facilities
14408 A simple preelaborable input-output package that provides a subset of
14409 simple Text_IO functions for reading characters and strings from
14410 Standard_Input, and writing characters, strings and integers to either
14411 Standard_Output or Standard_Error.
14413 @node GNAT.IO_Aux (g-io_aux.ads)
14414 @section @code{GNAT.IO_Aux} (@file{g-io_aux.ads})
14415 @cindex @code{GNAT.IO_Aux} (@file{g-io_aux.ads})
14417 @cindex Input/Output facilities
14419 Provides some auxiliary functions for use with Text_IO, including a test
14420 for whether a file exists, and functions for reading a line of text.
14422 @node GNAT.Lock_Files (g-locfil.ads)
14423 @section @code{GNAT.Lock_Files} (@file{g-locfil.ads})
14424 @cindex @code{GNAT.Lock_Files} (@file{g-locfil.ads})
14425 @cindex File locking
14426 @cindex Locking using files
14429 Provides a general interface for using files as locks. Can be used for
14430 providing program level synchronization.
14432 @node GNAT.MD5 (g-md5.ads)
14433 @section @code{GNAT.MD5} (@file{g-md5.ads})
14434 @cindex @code{GNAT.MD5} (@file{g-md5.ads})
14435 @cindex Message Digest MD5
14438 Implements the MD5 Message-Digest Algorithm as described in RFC 1321.
14440 @node GNAT.Memory_Dump (g-memdum.ads)
14441 @section @code{GNAT.Memory_Dump} (@file{g-memdum.ads})
14442 @cindex @code{GNAT.Memory_Dump} (@file{g-memdum.ads})
14443 @cindex Dump Memory
14446 Provides a convenient routine for dumping raw memory to either the
14447 standard output or standard error files. Uses GNAT.IO for actual
14450 @node GNAT.Most_Recent_Exception (g-moreex.ads)
14451 @section @code{GNAT.Most_Recent_Exception} (@file{g-moreex.ads})
14452 @cindex @code{GNAT.Most_Recent_Exception} (@file{g-moreex.ads})
14453 @cindex Exception, obtaining most recent
14456 Provides access to the most recently raised exception. Can be used for
14457 various logging purposes, including duplicating functionality of some
14458 Ada 83 implementation dependent extensions.
14460 @node GNAT.OS_Lib (g-os_lib.ads)
14461 @section @code{GNAT.OS_Lib} (@file{g-os_lib.ads})
14462 @cindex @code{GNAT.OS_Lib} (@file{g-os_lib.ads})
14463 @cindex Operating System interface
14464 @cindex Spawn capability
14467 Provides a range of target independent operating system interface functions,
14468 including time/date management, file operations, subprocess management,
14469 including a portable spawn procedure, and access to environment variables
14470 and error return codes.
14472 @node GNAT.Perfect_Hash_Generators (g-pehage.ads)
14473 @section @code{GNAT.Perfect_Hash_Generators} (@file{g-pehage.ads})
14474 @cindex @code{GNAT.Perfect_Hash_Generators} (@file{g-pehage.ads})
14475 @cindex Hash functions
14478 Provides a generator of static minimal perfect hash functions. No
14479 collisions occur and each item can be retrieved from the table in one
14480 probe (perfect property). The hash table size corresponds to the exact
14481 size of the key set and no larger (minimal property). The key set has to
14482 be know in advance (static property). The hash functions are also order
14483 preserving. If w2 is inserted after w1 in the generator, their
14484 hashcode are in the same order. These hashing functions are very
14485 convenient for use with realtime applications.
14487 @node GNAT.Random_Numbers (g-rannum.ads)
14488 @section @code{GNAT.Random_Numbers} (@file{g-rannum.ads})
14489 @cindex @code{GNAT.Random_Numbers} (@file{g-rannum.ads})
14490 @cindex Random number generation
14493 Provides random number capabilities which extend those available in the
14494 standard Ada library and are more convenient to use.
14496 @node GNAT.Regexp (g-regexp.ads)
14497 @section @code{GNAT.Regexp} (@file{g-regexp.ads})
14498 @cindex @code{GNAT.Regexp} (@file{g-regexp.ads})
14499 @cindex Regular expressions
14500 @cindex Pattern matching
14503 A simple implementation of regular expressions, using a subset of regular
14504 expression syntax copied from familiar Unix style utilities. This is the
14505 simples of the three pattern matching packages provided, and is particularly
14506 suitable for ``file globbing'' applications.
14508 @node GNAT.Registry (g-regist.ads)
14509 @section @code{GNAT.Registry} (@file{g-regist.ads})
14510 @cindex @code{GNAT.Registry} (@file{g-regist.ads})
14511 @cindex Windows Registry
14514 This is a high level binding to the Windows registry. It is possible to
14515 do simple things like reading a key value, creating a new key. For full
14516 registry API, but at a lower level of abstraction, refer to the Win32.Winreg
14517 package provided with the Win32Ada binding
14519 @node GNAT.Regpat (g-regpat.ads)
14520 @section @code{GNAT.Regpat} (@file{g-regpat.ads})
14521 @cindex @code{GNAT.Regpat} (@file{g-regpat.ads})
14522 @cindex Regular expressions
14523 @cindex Pattern matching
14526 A complete implementation of Unix-style regular expression matching, copied
14527 from the original V7 style regular expression library written in C by
14528 Henry Spencer (and binary compatible with this C library).
14530 @node GNAT.Secondary_Stack_Info (g-sestin.ads)
14531 @section @code{GNAT.Secondary_Stack_Info} (@file{g-sestin.ads})
14532 @cindex @code{GNAT.Secondary_Stack_Info} (@file{g-sestin.ads})
14533 @cindex Secondary Stack Info
14536 Provide the capability to query the high water mark of the current task's
14539 @node GNAT.Semaphores (g-semaph.ads)
14540 @section @code{GNAT.Semaphores} (@file{g-semaph.ads})
14541 @cindex @code{GNAT.Semaphores} (@file{g-semaph.ads})
14545 Provides classic counting and binary semaphores using protected types.
14547 @node GNAT.Serial_Communications (g-sercom.ads)
14548 @section @code{GNAT.Serial_Communications} (@file{g-sercom.ads})
14549 @cindex @code{GNAT.Serial_Communications} (@file{g-sercom.ads})
14550 @cindex Serial_Communications
14553 Provides a simple interface to send and receive data over a serial
14554 port. This is only supported on GNU/Linux and Windows.
14556 @node GNAT.SHA1 (g-sha1.ads)
14557 @section @code{GNAT.SHA1} (@file{g-sha1.ads})
14558 @cindex @code{GNAT.SHA1} (@file{g-sha1.ads})
14559 @cindex Secure Hash Algorithm SHA-1
14562 Implements the SHA-1 Secure Hash Algorithm as described in FIPS PUB 180-3
14565 @node GNAT.SHA224 (g-sha224.ads)
14566 @section @code{GNAT.SHA224} (@file{g-sha224.ads})
14567 @cindex @code{GNAT.SHA224} (@file{g-sha224.ads})
14568 @cindex Secure Hash Algorithm SHA-224
14571 Implements the SHA-224 Secure Hash Algorithm as described in FIPS PUB 180-3.
14573 @node GNAT.SHA256 (g-sha256.ads)
14574 @section @code{GNAT.SHA256} (@file{g-sha256.ads})
14575 @cindex @code{GNAT.SHA256} (@file{g-sha256.ads})
14576 @cindex Secure Hash Algorithm SHA-256
14579 Implements the SHA-256 Secure Hash Algorithm as described in FIPS PUB 180-3.
14581 @node GNAT.SHA384 (g-sha384.ads)
14582 @section @code{GNAT.SHA384} (@file{g-sha384.ads})
14583 @cindex @code{GNAT.SHA384} (@file{g-sha384.ads})
14584 @cindex Secure Hash Algorithm SHA-384
14587 Implements the SHA-384 Secure Hash Algorithm as described in FIPS PUB 180-3.
14589 @node GNAT.SHA512 (g-sha512.ads)
14590 @section @code{GNAT.SHA512} (@file{g-sha512.ads})
14591 @cindex @code{GNAT.SHA512} (@file{g-sha512.ads})
14592 @cindex Secure Hash Algorithm SHA-512
14595 Implements the SHA-512 Secure Hash Algorithm as described in FIPS PUB 180-3.
14597 @node GNAT.Signals (g-signal.ads)
14598 @section @code{GNAT.Signals} (@file{g-signal.ads})
14599 @cindex @code{GNAT.Signals} (@file{g-signal.ads})
14603 Provides the ability to manipulate the blocked status of signals on supported
14606 @node GNAT.Sockets (g-socket.ads)
14607 @section @code{GNAT.Sockets} (@file{g-socket.ads})
14608 @cindex @code{GNAT.Sockets} (@file{g-socket.ads})
14612 A high level and portable interface to develop sockets based applications.
14613 This package is based on the sockets thin binding found in
14614 @code{GNAT.Sockets.Thin}. Currently @code{GNAT.Sockets} is implemented
14615 on all native GNAT ports except for OpenVMS@. It is not implemented
14616 for the LynxOS@ cross port.
14618 @node GNAT.Source_Info (g-souinf.ads)
14619 @section @code{GNAT.Source_Info} (@file{g-souinf.ads})
14620 @cindex @code{GNAT.Source_Info} (@file{g-souinf.ads})
14621 @cindex Source Information
14624 Provides subprograms that give access to source code information known at
14625 compile time, such as the current file name and line number.
14627 @node GNAT.Spelling_Checker (g-speche.ads)
14628 @section @code{GNAT.Spelling_Checker} (@file{g-speche.ads})
14629 @cindex @code{GNAT.Spelling_Checker} (@file{g-speche.ads})
14630 @cindex Spell checking
14633 Provides a function for determining whether one string is a plausible
14634 near misspelling of another string.
14636 @node GNAT.Spelling_Checker_Generic (g-spchge.ads)
14637 @section @code{GNAT.Spelling_Checker_Generic} (@file{g-spchge.ads})
14638 @cindex @code{GNAT.Spelling_Checker_Generic} (@file{g-spchge.ads})
14639 @cindex Spell checking
14642 Provides a generic function that can be instantiated with a string type for
14643 determining whether one string is a plausible near misspelling of another
14646 @node GNAT.Spitbol.Patterns (g-spipat.ads)
14647 @section @code{GNAT.Spitbol.Patterns} (@file{g-spipat.ads})
14648 @cindex @code{GNAT.Spitbol.Patterns} (@file{g-spipat.ads})
14649 @cindex SPITBOL pattern matching
14650 @cindex Pattern matching
14653 A complete implementation of SNOBOL4 style pattern matching. This is the
14654 most elaborate of the pattern matching packages provided. It fully duplicates
14655 the SNOBOL4 dynamic pattern construction and matching capabilities, using the
14656 efficient algorithm developed by Robert Dewar for the SPITBOL system.
14658 @node GNAT.Spitbol (g-spitbo.ads)
14659 @section @code{GNAT.Spitbol} (@file{g-spitbo.ads})
14660 @cindex @code{GNAT.Spitbol} (@file{g-spitbo.ads})
14661 @cindex SPITBOL interface
14664 The top level package of the collection of SPITBOL-style functionality, this
14665 package provides basic SNOBOL4 string manipulation functions, such as
14666 Pad, Reverse, Trim, Substr capability, as well as a generic table function
14667 useful for constructing arbitrary mappings from strings in the style of
14668 the SNOBOL4 TABLE function.
14670 @node GNAT.Spitbol.Table_Boolean (g-sptabo.ads)
14671 @section @code{GNAT.Spitbol.Table_Boolean} (@file{g-sptabo.ads})
14672 @cindex @code{GNAT.Spitbol.Table_Boolean} (@file{g-sptabo.ads})
14673 @cindex Sets of strings
14674 @cindex SPITBOL Tables
14677 A library level of instantiation of @code{GNAT.Spitbol.Patterns.Table}
14678 for type @code{Standard.Boolean}, giving an implementation of sets of
14681 @node GNAT.Spitbol.Table_Integer (g-sptain.ads)
14682 @section @code{GNAT.Spitbol.Table_Integer} (@file{g-sptain.ads})
14683 @cindex @code{GNAT.Spitbol.Table_Integer} (@file{g-sptain.ads})
14684 @cindex Integer maps
14686 @cindex SPITBOL Tables
14689 A library level of instantiation of @code{GNAT.Spitbol.Patterns.Table}
14690 for type @code{Standard.Integer}, giving an implementation of maps
14691 from string to integer values.
14693 @node GNAT.Spitbol.Table_VString (g-sptavs.ads)
14694 @section @code{GNAT.Spitbol.Table_VString} (@file{g-sptavs.ads})
14695 @cindex @code{GNAT.Spitbol.Table_VString} (@file{g-sptavs.ads})
14696 @cindex String maps
14698 @cindex SPITBOL Tables
14701 A library level of instantiation of @code{GNAT.Spitbol.Patterns.Table} for
14702 a variable length string type, giving an implementation of general
14703 maps from strings to strings.
14705 @node GNAT.SSE (g-sse.ads)
14706 @section @code{GNAT.SSE} (@file{g-sse.ads})
14707 @cindex @code{GNAT.SSE} (@file{g-sse.ads})
14710 Root of a set of units aimed at offering Ada bindings to a subset of
14711 the Intel(r) Streaming SIMD Extensions with GNAT on the x86 family of
14712 targets. It exposes vector component types together with a general
14713 introduction to the binding contents and use.
14715 @node GNAT.SSE.Vector_Types (g-ssvety.ads)
14716 @section @code{GNAT.SSE.Vector_Types} (@file{g-ssvety.ads})
14717 @cindex @code{GNAT.SSE.Vector_Types} (@file{g-ssvety.ads})
14720 SSE vector types for use with SSE related intrinsics.
14722 @node GNAT.Strings (g-string.ads)
14723 @section @code{GNAT.Strings} (@file{g-string.ads})
14724 @cindex @code{GNAT.Strings} (@file{g-string.ads})
14727 Common String access types and related subprograms. Basically it
14728 defines a string access and an array of string access types.
14730 @node GNAT.String_Split (g-strspl.ads)
14731 @section @code{GNAT.String_Split} (@file{g-strspl.ads})
14732 @cindex @code{GNAT.String_Split} (@file{g-strspl.ads})
14733 @cindex String splitter
14736 Useful string manipulation routines: given a set of separators, split
14737 a string wherever the separators appear, and provide direct access
14738 to the resulting slices. This package is instantiated from
14739 @code{GNAT.Array_Split}.
14741 @node GNAT.Table (g-table.ads)
14742 @section @code{GNAT.Table} (@file{g-table.ads})
14743 @cindex @code{GNAT.Table} (@file{g-table.ads})
14744 @cindex Table implementation
14745 @cindex Arrays, extendable
14748 A generic package providing a single dimension array abstraction where the
14749 length of the array can be dynamically modified.
14752 This package provides a facility similar to that of @code{GNAT.Dynamic_Tables},
14753 except that this package declares a single instance of the table type,
14754 while an instantiation of @code{GNAT.Dynamic_Tables} creates a type that can be
14755 used to define dynamic instances of the table.
14757 @node GNAT.Task_Lock (g-tasloc.ads)
14758 @section @code{GNAT.Task_Lock} (@file{g-tasloc.ads})
14759 @cindex @code{GNAT.Task_Lock} (@file{g-tasloc.ads})
14760 @cindex Task synchronization
14761 @cindex Task locking
14765 A very simple facility for locking and unlocking sections of code using a
14766 single global task lock. Appropriate for use in situations where contention
14767 between tasks is very rarely expected.
14769 @node GNAT.Time_Stamp (g-timsta.ads)
14770 @section @code{GNAT.Time_Stamp} (@file{g-timsta.ads})
14771 @cindex @code{GNAT.Time_Stamp} (@file{g-timsta.ads})
14773 @cindex Current time
14776 Provides a simple function that returns a string YYYY-MM-DD HH:MM:SS.SS that
14777 represents the current date and time in ISO 8601 format. This is a very simple
14778 routine with minimal code and there are no dependencies on any other unit.
14780 @node GNAT.Threads (g-thread.ads)
14781 @section @code{GNAT.Threads} (@file{g-thread.ads})
14782 @cindex @code{GNAT.Threads} (@file{g-thread.ads})
14783 @cindex Foreign threads
14784 @cindex Threads, foreign
14787 Provides facilities for dealing with foreign threads which need to be known
14788 by the GNAT run-time system. Consult the documentation of this package for
14789 further details if your program has threads that are created by a non-Ada
14790 environment which then accesses Ada code.
14792 @node GNAT.Traceback (g-traceb.ads)
14793 @section @code{GNAT.Traceback} (@file{g-traceb.ads})
14794 @cindex @code{GNAT.Traceback} (@file{g-traceb.ads})
14795 @cindex Trace back facilities
14798 Provides a facility for obtaining non-symbolic traceback information, useful
14799 in various debugging situations.
14801 @node GNAT.Traceback.Symbolic (g-trasym.ads)
14802 @section @code{GNAT.Traceback.Symbolic} (@file{g-trasym.ads})
14803 @cindex @code{GNAT.Traceback.Symbolic} (@file{g-trasym.ads})
14804 @cindex Trace back facilities
14806 @node GNAT.UTF_32 (g-utf_32.ads)
14807 @section @code{GNAT.UTF_32} (@file{g-table.ads})
14808 @cindex @code{GNAT.UTF_32} (@file{g-table.ads})
14809 @cindex Wide character codes
14812 This is a package intended to be used in conjunction with the
14813 @code{Wide_Character} type in Ada 95 and the
14814 @code{Wide_Wide_Character} type in Ada 2005 (available
14815 in @code{GNAT} in Ada 2005 mode). This package contains
14816 Unicode categorization routines, as well as lexical
14817 categorization routines corresponding to the Ada 2005
14818 lexical rules for identifiers and strings, and also a
14819 lower case to upper case fold routine corresponding to
14820 the Ada 2005 rules for identifier equivalence.
14822 @node GNAT.UTF_32_Spelling_Checker (g-u3spch.ads)
14823 @section @code{GNAT.Wide_Spelling_Checker} (@file{g-u3spch.ads})
14824 @cindex @code{GNAT.Wide_Spelling_Checker} (@file{g-u3spch.ads})
14825 @cindex Spell checking
14828 Provides a function for determining whether one wide wide string is a plausible
14829 near misspelling of another wide wide string, where the strings are represented
14830 using the UTF_32_String type defined in System.Wch_Cnv.
14832 @node GNAT.Wide_Spelling_Checker (g-wispch.ads)
14833 @section @code{GNAT.Wide_Spelling_Checker} (@file{g-wispch.ads})
14834 @cindex @code{GNAT.Wide_Spelling_Checker} (@file{g-wispch.ads})
14835 @cindex Spell checking
14838 Provides a function for determining whether one wide string is a plausible
14839 near misspelling of another wide string.
14841 @node GNAT.Wide_String_Split (g-wistsp.ads)
14842 @section @code{GNAT.Wide_String_Split} (@file{g-wistsp.ads})
14843 @cindex @code{GNAT.Wide_String_Split} (@file{g-wistsp.ads})
14844 @cindex Wide_String splitter
14847 Useful wide string manipulation routines: given a set of separators, split
14848 a wide string wherever the separators appear, and provide direct access
14849 to the resulting slices. This package is instantiated from
14850 @code{GNAT.Array_Split}.
14852 @node GNAT.Wide_Wide_Spelling_Checker (g-zspche.ads)
14853 @section @code{GNAT.Wide_Wide_Spelling_Checker} (@file{g-zspche.ads})
14854 @cindex @code{GNAT.Wide_Wide_Spelling_Checker} (@file{g-zspche.ads})
14855 @cindex Spell checking
14858 Provides a function for determining whether one wide wide string is a plausible
14859 near misspelling of another wide wide string.
14861 @node GNAT.Wide_Wide_String_Split (g-zistsp.ads)
14862 @section @code{GNAT.Wide_Wide_String_Split} (@file{g-zistsp.ads})
14863 @cindex @code{GNAT.Wide_Wide_String_Split} (@file{g-zistsp.ads})
14864 @cindex Wide_Wide_String splitter
14867 Useful wide wide string manipulation routines: given a set of separators, split
14868 a wide wide string wherever the separators appear, and provide direct access
14869 to the resulting slices. This package is instantiated from
14870 @code{GNAT.Array_Split}.
14872 @node Interfaces.C.Extensions (i-cexten.ads)
14873 @section @code{Interfaces.C.Extensions} (@file{i-cexten.ads})
14874 @cindex @code{Interfaces.C.Extensions} (@file{i-cexten.ads})
14877 This package contains additional C-related definitions, intended
14878 for use with either manually or automatically generated bindings
14881 @node Interfaces.C.Streams (i-cstrea.ads)
14882 @section @code{Interfaces.C.Streams} (@file{i-cstrea.ads})
14883 @cindex @code{Interfaces.C.Streams} (@file{i-cstrea.ads})
14884 @cindex C streams, interfacing
14887 This package is a binding for the most commonly used operations
14890 @node Interfaces.CPP (i-cpp.ads)
14891 @section @code{Interfaces.CPP} (@file{i-cpp.ads})
14892 @cindex @code{Interfaces.CPP} (@file{i-cpp.ads})
14893 @cindex C++ interfacing
14894 @cindex Interfacing, to C++
14897 This package provides facilities for use in interfacing to C++. It
14898 is primarily intended to be used in connection with automated tools
14899 for the generation of C++ interfaces.
14901 @node Interfaces.Packed_Decimal (i-pacdec.ads)
14902 @section @code{Interfaces.Packed_Decimal} (@file{i-pacdec.ads})
14903 @cindex @code{Interfaces.Packed_Decimal} (@file{i-pacdec.ads})
14904 @cindex IBM Packed Format
14905 @cindex Packed Decimal
14908 This package provides a set of routines for conversions to and
14909 from a packed decimal format compatible with that used on IBM
14912 @node Interfaces.VxWorks (i-vxwork.ads)
14913 @section @code{Interfaces.VxWorks} (@file{i-vxwork.ads})
14914 @cindex @code{Interfaces.VxWorks} (@file{i-vxwork.ads})
14915 @cindex Interfacing to VxWorks
14916 @cindex VxWorks, interfacing
14919 This package provides a limited binding to the VxWorks API.
14920 In particular, it interfaces with the
14921 VxWorks hardware interrupt facilities.
14923 @node Interfaces.VxWorks.IO (i-vxwoio.ads)
14924 @section @code{Interfaces.VxWorks.IO} (@file{i-vxwoio.ads})
14925 @cindex @code{Interfaces.VxWorks.IO} (@file{i-vxwoio.ads})
14926 @cindex Interfacing to VxWorks' I/O
14927 @cindex VxWorks, I/O interfacing
14928 @cindex VxWorks, Get_Immediate
14929 @cindex Get_Immediate, VxWorks
14932 This package provides a binding to the ioctl (IO/Control)
14933 function of VxWorks, defining a set of option values and
14934 function codes. A particular use of this package is
14935 to enable the use of Get_Immediate under VxWorks.
14937 @node System.Address_Image (s-addima.ads)
14938 @section @code{System.Address_Image} (@file{s-addima.ads})
14939 @cindex @code{System.Address_Image} (@file{s-addima.ads})
14940 @cindex Address image
14941 @cindex Image, of an address
14944 This function provides a useful debugging
14945 function that gives an (implementation dependent)
14946 string which identifies an address.
14948 @node System.Assertions (s-assert.ads)
14949 @section @code{System.Assertions} (@file{s-assert.ads})
14950 @cindex @code{System.Assertions} (@file{s-assert.ads})
14952 @cindex Assert_Failure, exception
14955 This package provides the declaration of the exception raised
14956 by an run-time assertion failure, as well as the routine that
14957 is used internally to raise this assertion.
14959 @node System.Memory (s-memory.ads)
14960 @section @code{System.Memory} (@file{s-memory.ads})
14961 @cindex @code{System.Memory} (@file{s-memory.ads})
14962 @cindex Memory allocation
14965 This package provides the interface to the low level routines used
14966 by the generated code for allocation and freeing storage for the
14967 default storage pool (analogous to the C routines malloc and free.
14968 It also provides a reallocation interface analogous to the C routine
14969 realloc. The body of this unit may be modified to provide alternative
14970 allocation mechanisms for the default pool, and in addition, direct
14971 calls to this unit may be made for low level allocation uses (for
14972 example see the body of @code{GNAT.Tables}).
14974 @node System.Partition_Interface (s-parint.ads)
14975 @section @code{System.Partition_Interface} (@file{s-parint.ads})
14976 @cindex @code{System.Partition_Interface} (@file{s-parint.ads})
14977 @cindex Partition interfacing functions
14980 This package provides facilities for partition interfacing. It
14981 is used primarily in a distribution context when using Annex E
14984 @node System.Pool_Global (s-pooglo.ads)
14985 @section @code{System.Pool_Global} (@file{s-pooglo.ads})
14986 @cindex @code{System.Pool_Global} (@file{s-pooglo.ads})
14987 @cindex Storage pool, global
14988 @cindex Global storage pool
14991 This package provides a storage pool that is equivalent to the default
14992 storage pool used for access types for which no pool is specifically
14993 declared. It uses malloc/free to allocate/free and does not attempt to
14994 do any automatic reclamation.
14996 @node System.Pool_Local (s-pooloc.ads)
14997 @section @code{System.Pool_Local} (@file{s-pooloc.ads})
14998 @cindex @code{System.Pool_Local} (@file{s-pooloc.ads})
14999 @cindex Storage pool, local
15000 @cindex Local storage pool
15003 This package provides a storage pool that is intended for use with locally
15004 defined access types. It uses malloc/free for allocate/free, and maintains
15005 a list of allocated blocks, so that all storage allocated for the pool can
15006 be freed automatically when the pool is finalized.
15008 @node System.Restrictions (s-restri.ads)
15009 @section @code{System.Restrictions} (@file{s-restri.ads})
15010 @cindex @code{System.Restrictions} (@file{s-restri.ads})
15011 @cindex Run-time restrictions access
15014 This package provides facilities for accessing at run time
15015 the status of restrictions specified at compile time for
15016 the partition. Information is available both with regard
15017 to actual restrictions specified, and with regard to
15018 compiler determined information on which restrictions
15019 are violated by one or more packages in the partition.
15021 @node System.Rident (s-rident.ads)
15022 @section @code{System.Rident} (@file{s-rident.ads})
15023 @cindex @code{System.Rident} (@file{s-rident.ads})
15024 @cindex Restrictions definitions
15027 This package provides definitions of the restrictions
15028 identifiers supported by GNAT, and also the format of
15029 the restrictions provided in package System.Restrictions.
15030 It is not normally necessary to @code{with} this generic package
15031 since the necessary instantiation is included in
15032 package System.Restrictions.
15034 @node System.Strings.Stream_Ops (s-ststop.ads)
15035 @section @code{System.Strings.Stream_Ops} (@file{s-ststop.ads})
15036 @cindex @code{System.Strings.Stream_Ops} (@file{s-ststop.ads})
15037 @cindex Stream operations
15038 @cindex String stream operations
15041 This package provides a set of stream subprograms for standard string types.
15042 It is intended primarily to support implicit use of such subprograms when
15043 stream attributes are applied to string types, but the subprograms in this
15044 package can be used directly by application programs.
15046 @node System.Task_Info (s-tasinf.ads)
15047 @section @code{System.Task_Info} (@file{s-tasinf.ads})
15048 @cindex @code{System.Task_Info} (@file{s-tasinf.ads})
15049 @cindex Task_Info pragma
15052 This package provides target dependent functionality that is used
15053 to support the @code{Task_Info} pragma
15055 @node System.Wch_Cnv (s-wchcnv.ads)
15056 @section @code{System.Wch_Cnv} (@file{s-wchcnv.ads})
15057 @cindex @code{System.Wch_Cnv} (@file{s-wchcnv.ads})
15058 @cindex Wide Character, Representation
15059 @cindex Wide String, Conversion
15060 @cindex Representation of wide characters
15063 This package provides routines for converting between
15064 wide and wide wide characters and a representation as a value of type
15065 @code{Standard.String}, using a specified wide character
15066 encoding method. It uses definitions in
15067 package @code{System.Wch_Con}.
15069 @node System.Wch_Con (s-wchcon.ads)
15070 @section @code{System.Wch_Con} (@file{s-wchcon.ads})
15071 @cindex @code{System.Wch_Con} (@file{s-wchcon.ads})
15074 This package provides definitions and descriptions of
15075 the various methods used for encoding wide characters
15076 in ordinary strings. These definitions are used by
15077 the package @code{System.Wch_Cnv}.
15079 @node Interfacing to Other Languages
15080 @chapter Interfacing to Other Languages
15082 The facilities in annex B of the Ada Reference Manual are fully
15083 implemented in GNAT, and in addition, a full interface to C++ is
15087 * Interfacing to C::
15088 * Interfacing to C++::
15089 * Interfacing to COBOL::
15090 * Interfacing to Fortran::
15091 * Interfacing to non-GNAT Ada code::
15094 @node Interfacing to C
15095 @section Interfacing to C
15098 Interfacing to C with GNAT can use one of two approaches:
15102 The types in the package @code{Interfaces.C} may be used.
15104 Standard Ada types may be used directly. This may be less portable to
15105 other compilers, but will work on all GNAT compilers, which guarantee
15106 correspondence between the C and Ada types.
15110 Pragma @code{Convention C} may be applied to Ada types, but mostly has no
15111 effect, since this is the default. The following table shows the
15112 correspondence between Ada scalar types and the corresponding C types.
15117 @item Short_Integer
15119 @item Short_Short_Integer
15123 @item Long_Long_Integer
15131 @item Long_Long_Float
15132 This is the longest floating-point type supported by the hardware.
15136 Additionally, there are the following general correspondences between Ada
15140 Ada enumeration types map to C enumeration types directly if pragma
15141 @code{Convention C} is specified, which causes them to have int
15142 length. Without pragma @code{Convention C}, Ada enumeration types map to
15143 8, 16, or 32 bits (i.e.@: C types @code{signed char}, @code{short},
15144 @code{int}, respectively) depending on the number of values passed.
15145 This is the only case in which pragma @code{Convention C} affects the
15146 representation of an Ada type.
15149 Ada access types map to C pointers, except for the case of pointers to
15150 unconstrained types in Ada, which have no direct C equivalent.
15153 Ada arrays map directly to C arrays.
15156 Ada records map directly to C structures.
15159 Packed Ada records map to C structures where all members are bit fields
15160 of the length corresponding to the @code{@var{type}'Size} value in Ada.
15163 @node Interfacing to C++
15164 @section Interfacing to C++
15167 The interface to C++ makes use of the following pragmas, which are
15168 primarily intended to be constructed automatically using a binding generator
15169 tool, although it is possible to construct them by hand. No suitable binding
15170 generator tool is supplied with GNAT though.
15172 Using these pragmas it is possible to achieve complete
15173 inter-operability between Ada tagged types and C++ class definitions.
15174 See @ref{Implementation Defined Pragmas}, for more details.
15177 @item pragma CPP_Class ([Entity =>] @var{LOCAL_NAME})
15178 The argument denotes an entity in the current declarative region that is
15179 declared as a tagged or untagged record type. It indicates that the type
15180 corresponds to an externally declared C++ class type, and is to be laid
15181 out the same way that C++ would lay out the type.
15183 Note: Pragma @code{CPP_Class} is currently obsolete. It is supported
15184 for backward compatibility but its functionality is available
15185 using pragma @code{Import} with @code{Convention} = @code{CPP}.
15187 @item pragma CPP_Constructor ([Entity =>] @var{LOCAL_NAME})
15188 This pragma identifies an imported function (imported in the usual way
15189 with pragma @code{Import}) as corresponding to a C++ constructor.
15192 @node Interfacing to COBOL
15193 @section Interfacing to COBOL
15196 Interfacing to COBOL is achieved as described in section B.4 of
15197 the Ada Reference Manual.
15199 @node Interfacing to Fortran
15200 @section Interfacing to Fortran
15203 Interfacing to Fortran is achieved as described in section B.5 of the
15204 Ada Reference Manual. The pragma @code{Convention Fortran}, applied to a
15205 multi-dimensional array causes the array to be stored in column-major
15206 order as required for convenient interface to Fortran.
15208 @node Interfacing to non-GNAT Ada code
15209 @section Interfacing to non-GNAT Ada code
15211 It is possible to specify the convention @code{Ada} in a pragma
15212 @code{Import} or pragma @code{Export}. However this refers to
15213 the calling conventions used by GNAT, which may or may not be
15214 similar enough to those used by some other Ada 83 / Ada 95 / Ada 2005
15215 compiler to allow interoperation.
15217 If arguments types are kept simple, and if the foreign compiler generally
15218 follows system calling conventions, then it may be possible to integrate
15219 files compiled by other Ada compilers, provided that the elaboration
15220 issues are adequately addressed (for example by eliminating the
15221 need for any load time elaboration).
15223 In particular, GNAT running on VMS is designed to
15224 be highly compatible with the DEC Ada 83 compiler, so this is one
15225 case in which it is possible to import foreign units of this type,
15226 provided that the data items passed are restricted to simple scalar
15227 values or simple record types without variants, or simple array
15228 types with fixed bounds.
15230 @node Specialized Needs Annexes
15231 @chapter Specialized Needs Annexes
15234 Ada 95 and Ada 2005 define a number of Specialized Needs Annexes, which are not
15235 required in all implementations. However, as described in this chapter,
15236 GNAT implements all of these annexes:
15239 @item Systems Programming (Annex C)
15240 The Systems Programming Annex is fully implemented.
15242 @item Real-Time Systems (Annex D)
15243 The Real-Time Systems Annex is fully implemented.
15245 @item Distributed Systems (Annex E)
15246 Stub generation is fully implemented in the GNAT compiler. In addition,
15247 a complete compatible PCS is available as part of the GLADE system,
15248 a separate product. When the two
15249 products are used in conjunction, this annex is fully implemented.
15251 @item Information Systems (Annex F)
15252 The Information Systems annex is fully implemented.
15254 @item Numerics (Annex G)
15255 The Numerics Annex is fully implemented.
15257 @item Safety and Security / High-Integrity Systems (Annex H)
15258 The Safety and Security Annex (termed the High-Integrity Systems Annex
15259 in Ada 2005) is fully implemented.
15262 @node Implementation of Specific Ada Features
15263 @chapter Implementation of Specific Ada Features
15266 This chapter describes the GNAT implementation of several Ada language
15270 * Machine Code Insertions::
15271 * GNAT Implementation of Tasking::
15272 * GNAT Implementation of Shared Passive Packages::
15273 * Code Generation for Array Aggregates::
15274 * The Size of Discriminated Records with Default Discriminants::
15275 * Strict Conformance to the Ada Reference Manual::
15278 @node Machine Code Insertions
15279 @section Machine Code Insertions
15280 @cindex Machine Code insertions
15283 Package @code{Machine_Code} provides machine code support as described
15284 in the Ada Reference Manual in two separate forms:
15287 Machine code statements, consisting of qualified expressions that
15288 fit the requirements of RM section 13.8.
15290 An intrinsic callable procedure, providing an alternative mechanism of
15291 including machine instructions in a subprogram.
15295 The two features are similar, and both are closely related to the mechanism
15296 provided by the asm instruction in the GNU C compiler. Full understanding
15297 and use of the facilities in this package requires understanding the asm
15298 instruction, see @ref{Extended Asm,, Assembler Instructions with C Expression
15299 Operands, gcc, Using the GNU Compiler Collection (GCC)}.
15301 Calls to the function @code{Asm} and the procedure @code{Asm} have identical
15302 semantic restrictions and effects as described below. Both are provided so
15303 that the procedure call can be used as a statement, and the function call
15304 can be used to form a code_statement.
15306 The first example given in the GCC documentation is the C @code{asm}
15309 asm ("fsinx %1 %0" : "=f" (result) : "f" (angle));
15313 The equivalent can be written for GNAT as:
15315 @smallexample @c ada
15316 Asm ("fsinx %1 %0",
15317 My_Float'Asm_Output ("=f", result),
15318 My_Float'Asm_Input ("f", angle));
15322 The first argument to @code{Asm} is the assembler template, and is
15323 identical to what is used in GNU C@. This string must be a static
15324 expression. The second argument is the output operand list. It is
15325 either a single @code{Asm_Output} attribute reference, or a list of such
15326 references enclosed in parentheses (technically an array aggregate of
15329 The @code{Asm_Output} attribute denotes a function that takes two
15330 parameters. The first is a string, the second is the name of a variable
15331 of the type designated by the attribute prefix. The first (string)
15332 argument is required to be a static expression and designates the
15333 constraint for the parameter (e.g.@: what kind of register is
15334 required). The second argument is the variable to be updated with the
15335 result. The possible values for constraint are the same as those used in
15336 the RTL, and are dependent on the configuration file used to build the
15337 GCC back end. If there are no output operands, then this argument may
15338 either be omitted, or explicitly given as @code{No_Output_Operands}.
15340 The second argument of @code{@var{my_float}'Asm_Output} functions as
15341 though it were an @code{out} parameter, which is a little curious, but
15342 all names have the form of expressions, so there is no syntactic
15343 irregularity, even though normally functions would not be permitted
15344 @code{out} parameters. The third argument is the list of input
15345 operands. It is either a single @code{Asm_Input} attribute reference, or
15346 a list of such references enclosed in parentheses (technically an array
15347 aggregate of such references).
15349 The @code{Asm_Input} attribute denotes a function that takes two
15350 parameters. The first is a string, the second is an expression of the
15351 type designated by the prefix. The first (string) argument is required
15352 to be a static expression, and is the constraint for the parameter,
15353 (e.g.@: what kind of register is required). The second argument is the
15354 value to be used as the input argument. The possible values for the
15355 constant are the same as those used in the RTL, and are dependent on
15356 the configuration file used to built the GCC back end.
15358 If there are no input operands, this argument may either be omitted, or
15359 explicitly given as @code{No_Input_Operands}. The fourth argument, not
15360 present in the above example, is a list of register names, called the
15361 @dfn{clobber} argument. This argument, if given, must be a static string
15362 expression, and is a space or comma separated list of names of registers
15363 that must be considered destroyed as a result of the @code{Asm} call. If
15364 this argument is the null string (the default value), then the code
15365 generator assumes that no additional registers are destroyed.
15367 The fifth argument, not present in the above example, called the
15368 @dfn{volatile} argument, is by default @code{False}. It can be set to
15369 the literal value @code{True} to indicate to the code generator that all
15370 optimizations with respect to the instruction specified should be
15371 suppressed, and that in particular, for an instruction that has outputs,
15372 the instruction will still be generated, even if none of the outputs are
15373 used. @xref{Extended Asm,, Assembler Instructions with C Expression Operands,
15374 gcc, Using the GNU Compiler Collection (GCC)}, for the full description.
15375 Generally it is strongly advisable to use Volatile for any ASM statement
15376 that is missing either input or output operands, or when two or more ASM
15377 statements appear in sequence, to avoid unwanted optimizations. A warning
15378 is generated if this advice is not followed.
15380 The @code{Asm} subprograms may be used in two ways. First the procedure
15381 forms can be used anywhere a procedure call would be valid, and
15382 correspond to what the RM calls ``intrinsic'' routines. Such calls can
15383 be used to intersperse machine instructions with other Ada statements.
15384 Second, the function forms, which return a dummy value of the limited
15385 private type @code{Asm_Insn}, can be used in code statements, and indeed
15386 this is the only context where such calls are allowed. Code statements
15387 appear as aggregates of the form:
15389 @smallexample @c ada
15390 Asm_Insn'(Asm (@dots{}));
15391 Asm_Insn'(Asm_Volatile (@dots{}));
15395 In accordance with RM rules, such code statements are allowed only
15396 within subprograms whose entire body consists of such statements. It is
15397 not permissible to intermix such statements with other Ada statements.
15399 Typically the form using intrinsic procedure calls is more convenient
15400 and more flexible. The code statement form is provided to meet the RM
15401 suggestion that such a facility should be made available. The following
15402 is the exact syntax of the call to @code{Asm}. As usual, if named notation
15403 is used, the arguments may be given in arbitrary order, following the
15404 normal rules for use of positional and named arguments)
15408 [Template =>] static_string_EXPRESSION
15409 [,[Outputs =>] OUTPUT_OPERAND_LIST ]
15410 [,[Inputs =>] INPUT_OPERAND_LIST ]
15411 [,[Clobber =>] static_string_EXPRESSION ]
15412 [,[Volatile =>] static_boolean_EXPRESSION] )
15414 OUTPUT_OPERAND_LIST ::=
15415 [PREFIX.]No_Output_Operands
15416 | OUTPUT_OPERAND_ATTRIBUTE
15417 | (OUTPUT_OPERAND_ATTRIBUTE @{,OUTPUT_OPERAND_ATTRIBUTE@})
15419 OUTPUT_OPERAND_ATTRIBUTE ::=
15420 SUBTYPE_MARK'Asm_Output (static_string_EXPRESSION, NAME)
15422 INPUT_OPERAND_LIST ::=
15423 [PREFIX.]No_Input_Operands
15424 | INPUT_OPERAND_ATTRIBUTE
15425 | (INPUT_OPERAND_ATTRIBUTE @{,INPUT_OPERAND_ATTRIBUTE@})
15427 INPUT_OPERAND_ATTRIBUTE ::=
15428 SUBTYPE_MARK'Asm_Input (static_string_EXPRESSION, EXPRESSION)
15432 The identifiers @code{No_Input_Operands} and @code{No_Output_Operands}
15433 are declared in the package @code{Machine_Code} and must be referenced
15434 according to normal visibility rules. In particular if there is no
15435 @code{use} clause for this package, then appropriate package name
15436 qualification is required.
15438 @node GNAT Implementation of Tasking
15439 @section GNAT Implementation of Tasking
15442 This chapter outlines the basic GNAT approach to tasking (in particular,
15443 a multi-layered library for portability) and discusses issues related
15444 to compliance with the Real-Time Systems Annex.
15447 * Mapping Ada Tasks onto the Underlying Kernel Threads::
15448 * Ensuring Compliance with the Real-Time Annex::
15451 @node Mapping Ada Tasks onto the Underlying Kernel Threads
15452 @subsection Mapping Ada Tasks onto the Underlying Kernel Threads
15455 GNAT's run-time support comprises two layers:
15458 @item GNARL (GNAT Run-time Layer)
15459 @item GNULL (GNAT Low-level Library)
15463 In GNAT, Ada's tasking services rely on a platform and OS independent
15464 layer known as GNARL@. This code is responsible for implementing the
15465 correct semantics of Ada's task creation, rendezvous, protected
15468 GNARL decomposes Ada's tasking semantics into simpler lower level
15469 operations such as create a thread, set the priority of a thread,
15470 yield, create a lock, lock/unlock, etc. The spec for these low-level
15471 operations constitutes GNULLI, the GNULL Interface. This interface is
15472 directly inspired from the POSIX real-time API@.
15474 If the underlying executive or OS implements the POSIX standard
15475 faithfully, the GNULL Interface maps as is to the services offered by
15476 the underlying kernel. Otherwise, some target dependent glue code maps
15477 the services offered by the underlying kernel to the semantics expected
15480 Whatever the underlying OS (VxWorks, UNIX, OS/2, Windows NT, etc.) the
15481 key point is that each Ada task is mapped on a thread in the underlying
15482 kernel. For example, in the case of VxWorks, one Ada task = one VxWorks task.
15484 In addition Ada task priorities map onto the underlying thread priorities.
15485 Mapping Ada tasks onto the underlying kernel threads has several advantages:
15489 The underlying scheduler is used to schedule the Ada tasks. This
15490 makes Ada tasks as efficient as kernel threads from a scheduling
15494 Interaction with code written in C containing threads is eased
15495 since at the lowest level Ada tasks and C threads map onto the same
15496 underlying kernel concept.
15499 When an Ada task is blocked during I/O the remaining Ada tasks are
15503 On multiprocessor systems Ada tasks can execute in parallel.
15507 Some threads libraries offer a mechanism to fork a new process, with the
15508 child process duplicating the threads from the parent.
15510 support this functionality when the parent contains more than one task.
15511 @cindex Forking a new process
15513 @node Ensuring Compliance with the Real-Time Annex
15514 @subsection Ensuring Compliance with the Real-Time Annex
15515 @cindex Real-Time Systems Annex compliance
15518 Although mapping Ada tasks onto
15519 the underlying threads has significant advantages, it does create some
15520 complications when it comes to respecting the scheduling semantics
15521 specified in the real-time annex (Annex D).
15523 For instance the Annex D requirement for the @code{FIFO_Within_Priorities}
15524 scheduling policy states:
15527 @emph{When the active priority of a ready task that is not running
15528 changes, or the setting of its base priority takes effect, the
15529 task is removed from the ready queue for its old active priority
15530 and is added at the tail of the ready queue for its new active
15531 priority, except in the case where the active priority is lowered
15532 due to the loss of inherited priority, in which case the task is
15533 added at the head of the ready queue for its new active priority.}
15537 While most kernels do put tasks at the end of the priority queue when
15538 a task changes its priority, (which respects the main
15539 FIFO_Within_Priorities requirement), almost none keep a thread at the
15540 beginning of its priority queue when its priority drops from the loss
15541 of inherited priority.
15543 As a result most vendors have provided incomplete Annex D implementations.
15545 The GNAT run-time, has a nice cooperative solution to this problem
15546 which ensures that accurate FIFO_Within_Priorities semantics are
15549 The principle is as follows. When an Ada task T is about to start
15550 running, it checks whether some other Ada task R with the same
15551 priority as T has been suspended due to the loss of priority
15552 inheritance. If this is the case, T yields and is placed at the end of
15553 its priority queue. When R arrives at the front of the queue it
15556 Note that this simple scheme preserves the relative order of the tasks
15557 that were ready to execute in the priority queue where R has been
15560 @node GNAT Implementation of Shared Passive Packages
15561 @section GNAT Implementation of Shared Passive Packages
15562 @cindex Shared passive packages
15565 GNAT fully implements the pragma @code{Shared_Passive} for
15566 @cindex pragma @code{Shared_Passive}
15567 the purpose of designating shared passive packages.
15568 This allows the use of passive partitions in the
15569 context described in the Ada Reference Manual; i.e., for communication
15570 between separate partitions of a distributed application using the
15571 features in Annex E.
15573 @cindex Distribution Systems Annex
15575 However, the implementation approach used by GNAT provides for more
15576 extensive usage as follows:
15579 @item Communication between separate programs
15581 This allows separate programs to access the data in passive
15582 partitions, using protected objects for synchronization where
15583 needed. The only requirement is that the two programs have a
15584 common shared file system. It is even possible for programs
15585 running on different machines with different architectures
15586 (e.g.@: different endianness) to communicate via the data in
15587 a passive partition.
15589 @item Persistence between program runs
15591 The data in a passive package can persist from one run of a
15592 program to another, so that a later program sees the final
15593 values stored by a previous run of the same program.
15598 The implementation approach used is to store the data in files. A
15599 separate stream file is created for each object in the package, and
15600 an access to an object causes the corresponding file to be read or
15603 The environment variable @code{SHARED_MEMORY_DIRECTORY} should be
15604 @cindex @code{SHARED_MEMORY_DIRECTORY} environment variable
15605 set to the directory to be used for these files.
15606 The files in this directory
15607 have names that correspond to their fully qualified names. For
15608 example, if we have the package
15610 @smallexample @c ada
15612 pragma Shared_Passive (X);
15619 and the environment variable is set to @code{/stemp/}, then the files created
15620 will have the names:
15628 These files are created when a value is initially written to the object, and
15629 the files are retained until manually deleted. This provides the persistence
15630 semantics. If no file exists, it means that no partition has assigned a value
15631 to the variable; in this case the initial value declared in the package
15632 will be used. This model ensures that there are no issues in synchronizing
15633 the elaboration process, since elaboration of passive packages elaborates the
15634 initial values, but does not create the files.
15636 The files are written using normal @code{Stream_IO} access.
15637 If you want to be able
15638 to communicate between programs or partitions running on different
15639 architectures, then you should use the XDR versions of the stream attribute
15640 routines, since these are architecture independent.
15642 If active synchronization is required for access to the variables in the
15643 shared passive package, then as described in the Ada Reference Manual, the
15644 package may contain protected objects used for this purpose. In this case
15645 a lock file (whose name is @file{___lock} (three underscores)
15646 is created in the shared memory directory.
15647 @cindex @file{___lock} file (for shared passive packages)
15648 This is used to provide the required locking
15649 semantics for proper protected object synchronization.
15651 As of January 2003, GNAT supports shared passive packages on all platforms
15652 except for OpenVMS.
15654 @node Code Generation for Array Aggregates
15655 @section Code Generation for Array Aggregates
15658 * Static constant aggregates with static bounds::
15659 * Constant aggregates with unconstrained nominal types::
15660 * Aggregates with static bounds::
15661 * Aggregates with non-static bounds::
15662 * Aggregates in assignment statements::
15666 Aggregates have a rich syntax and allow the user to specify the values of
15667 complex data structures by means of a single construct. As a result, the
15668 code generated for aggregates can be quite complex and involve loops, case
15669 statements and multiple assignments. In the simplest cases, however, the
15670 compiler will recognize aggregates whose components and constraints are
15671 fully static, and in those cases the compiler will generate little or no
15672 executable code. The following is an outline of the code that GNAT generates
15673 for various aggregate constructs. For further details, you will find it
15674 useful to examine the output produced by the -gnatG flag to see the expanded
15675 source that is input to the code generator. You may also want to examine
15676 the assembly code generated at various levels of optimization.
15678 The code generated for aggregates depends on the context, the component values,
15679 and the type. In the context of an object declaration the code generated is
15680 generally simpler than in the case of an assignment. As a general rule, static
15681 component values and static subtypes also lead to simpler code.
15683 @node Static constant aggregates with static bounds
15684 @subsection Static constant aggregates with static bounds
15687 For the declarations:
15688 @smallexample @c ada
15689 type One_Dim is array (1..10) of integer;
15690 ar0 : constant One_Dim := (1, 2, 3, 4, 5, 6, 7, 8, 9, 0);
15694 GNAT generates no executable code: the constant ar0 is placed in static memory.
15695 The same is true for constant aggregates with named associations:
15697 @smallexample @c ada
15698 Cr1 : constant One_Dim := (4 => 16, 2 => 4, 3 => 9, 1 => 1, 5 .. 10 => 0);
15699 Cr3 : constant One_Dim := (others => 7777);
15703 The same is true for multidimensional constant arrays such as:
15705 @smallexample @c ada
15706 type two_dim is array (1..3, 1..3) of integer;
15707 Unit : constant two_dim := ( (1,0,0), (0,1,0), (0,0,1));
15711 The same is true for arrays of one-dimensional arrays: the following are
15714 @smallexample @c ada
15715 type ar1b is array (1..3) of boolean;
15716 type ar_ar is array (1..3) of ar1b;
15717 None : constant ar1b := (others => false); -- fully static
15718 None2 : constant ar_ar := (1..3 => None); -- fully static
15722 However, for multidimensional aggregates with named associations, GNAT will
15723 generate assignments and loops, even if all associations are static. The
15724 following two declarations generate a loop for the first dimension, and
15725 individual component assignments for the second dimension:
15727 @smallexample @c ada
15728 Zero1: constant two_dim := (1..3 => (1..3 => 0));
15729 Zero2: constant two_dim := (others => (others => 0));
15732 @node Constant aggregates with unconstrained nominal types
15733 @subsection Constant aggregates with unconstrained nominal types
15736 In such cases the aggregate itself establishes the subtype, so that
15737 associations with @code{others} cannot be used. GNAT determines the
15738 bounds for the actual subtype of the aggregate, and allocates the
15739 aggregate statically as well. No code is generated for the following:
15741 @smallexample @c ada
15742 type One_Unc is array (natural range <>) of integer;
15743 Cr_Unc : constant One_Unc := (12,24,36);
15746 @node Aggregates with static bounds
15747 @subsection Aggregates with static bounds
15750 In all previous examples the aggregate was the initial (and immutable) value
15751 of a constant. If the aggregate initializes a variable, then code is generated
15752 for it as a combination of individual assignments and loops over the target
15753 object. The declarations
15755 @smallexample @c ada
15756 Cr_Var1 : One_Dim := (2, 5, 7, 11, 0, 0, 0, 0, 0, 0);
15757 Cr_Var2 : One_Dim := (others > -1);
15761 generate the equivalent of
15763 @smallexample @c ada
15769 for I in Cr_Var2'range loop
15774 @node Aggregates with non-static bounds
15775 @subsection Aggregates with non-static bounds
15778 If the bounds of the aggregate are not statically compatible with the bounds
15779 of the nominal subtype of the target, then constraint checks have to be
15780 generated on the bounds. For a multidimensional array, constraint checks may
15781 have to be applied to sub-arrays individually, if they do not have statically
15782 compatible subtypes.
15784 @node Aggregates in assignment statements
15785 @subsection Aggregates in assignment statements
15788 In general, aggregate assignment requires the construction of a temporary,
15789 and a copy from the temporary to the target of the assignment. This is because
15790 it is not always possible to convert the assignment into a series of individual
15791 component assignments. For example, consider the simple case:
15793 @smallexample @c ada
15798 This cannot be converted into:
15800 @smallexample @c ada
15806 So the aggregate has to be built first in a separate location, and then
15807 copied into the target. GNAT recognizes simple cases where this intermediate
15808 step is not required, and the assignments can be performed in place, directly
15809 into the target. The following sufficient criteria are applied:
15813 The bounds of the aggregate are static, and the associations are static.
15815 The components of the aggregate are static constants, names of
15816 simple variables that are not renamings, or expressions not involving
15817 indexed components whose operands obey these rules.
15821 If any of these conditions are violated, the aggregate will be built in
15822 a temporary (created either by the front-end or the code generator) and then
15823 that temporary will be copied onto the target.
15826 @node The Size of Discriminated Records with Default Discriminants
15827 @section The Size of Discriminated Records with Default Discriminants
15830 If a discriminated type @code{T} has discriminants with default values, it is
15831 possible to declare an object of this type without providing an explicit
15834 @smallexample @c ada
15836 type Size is range 1..100;
15838 type Rec (D : Size := 15) is record
15839 Name : String (1..D);
15847 Such an object is said to be @emph{unconstrained}.
15848 The discriminant of the object
15849 can be modified by a full assignment to the object, as long as it preserves the
15850 relation between the value of the discriminant, and the value of the components
15853 @smallexample @c ada
15855 Word := (3, "yes");
15857 Word := (5, "maybe");
15859 Word := (5, "no"); -- raises Constraint_Error
15864 In order to support this behavior efficiently, an unconstrained object is
15865 given the maximum size that any value of the type requires. In the case
15866 above, @code{Word} has storage for the discriminant and for
15867 a @code{String} of length 100.
15868 It is important to note that unconstrained objects do not require dynamic
15869 allocation. It would be an improper implementation to place on the heap those
15870 components whose size depends on discriminants. (This improper implementation
15871 was used by some Ada83 compilers, where the @code{Name} component above
15873 been stored as a pointer to a dynamic string). Following the principle that
15874 dynamic storage management should never be introduced implicitly,
15875 an Ada compiler should reserve the full size for an unconstrained declared
15876 object, and place it on the stack.
15878 This maximum size approach
15879 has been a source of surprise to some users, who expect the default
15880 values of the discriminants to determine the size reserved for an
15881 unconstrained object: ``If the default is 15, why should the object occupy
15883 The answer, of course, is that the discriminant may be later modified,
15884 and its full range of values must be taken into account. This is why the
15889 type Rec (D : Positive := 15) is record
15890 Name : String (1..D);
15898 is flagged by the compiler with a warning:
15899 an attempt to create @code{Too_Large} will raise @code{Storage_Error},
15900 because the required size includes @code{Positive'Last}
15901 bytes. As the first example indicates, the proper approach is to declare an
15902 index type of ``reasonable'' range so that unconstrained objects are not too
15905 One final wrinkle: if the object is declared to be @code{aliased}, or if it is
15906 created in the heap by means of an allocator, then it is @emph{not}
15908 it is constrained by the default values of the discriminants, and those values
15909 cannot be modified by full assignment. This is because in the presence of
15910 aliasing all views of the object (which may be manipulated by different tasks,
15911 say) must be consistent, so it is imperative that the object, once created,
15914 @node Strict Conformance to the Ada Reference Manual
15915 @section Strict Conformance to the Ada Reference Manual
15918 The dynamic semantics defined by the Ada Reference Manual impose a set of
15919 run-time checks to be generated. By default, the GNAT compiler will insert many
15920 run-time checks into the compiled code, including most of those required by the
15921 Ada Reference Manual. However, there are three checks that are not enabled
15922 in the default mode for efficiency reasons: arithmetic overflow checking for
15923 integer operations (including division by zero), checks for access before
15924 elaboration on subprogram calls, and stack overflow checking (most operating
15925 systems do not perform this check by default).
15927 Strict conformance to the Ada Reference Manual can be achieved by adding
15928 three compiler options for overflow checking for integer operations
15929 (@option{-gnato}), dynamic checks for access-before-elaboration on subprogram
15930 calls and generic instantiations (@option{-gnatE}), and stack overflow
15931 checking (@option{-fstack-check}).
15933 Note that the result of a floating point arithmetic operation in overflow and
15934 invalid situations, when the @code{Machine_Overflows} attribute of the result
15935 type is @code{False}, is to generate IEEE NaN and infinite values. This is the
15936 case for machines compliant with the IEEE floating-point standard, but on
15937 machines that are not fully compliant with this standard, such as Alpha, the
15938 @option{-mieee} compiler flag must be used for achieving IEEE confirming
15939 behavior (although at the cost of a significant performance penalty), so
15940 infinite and and NaN values are properly generated.
15943 @node Project File Reference
15944 @chapter Project File Reference
15947 This chapter describes the syntax and semantics of project files.
15948 Project files specify the options to be used when building a system.
15949 Project files can specify global settings for all tools,
15950 as well as tool-specific settings.
15951 @xref{Examples of Project Files,,, gnat_ugn, @value{EDITION} User's Guide},
15952 for examples of use.
15956 * Lexical Elements::
15958 * Empty declarations::
15959 * Typed string declarations::
15963 * Project Attributes::
15964 * Attribute References::
15965 * External Values::
15966 * Case Construction::
15968 * Package Renamings::
15970 * Project Extensions::
15971 * Project File Elaboration::
15974 @node Reserved Words
15975 @section Reserved Words
15978 All Ada reserved words are reserved in project files, and cannot be used
15979 as variable names or project names. In addition, the following are
15980 also reserved in project files:
15983 @item @code{extends}
15985 @item @code{external}
15987 @item @code{project}
15991 @node Lexical Elements
15992 @section Lexical Elements
15995 Rules for identifiers are the same as in Ada. Identifiers
15996 are case-insensitive. Strings are case sensitive, except where noted.
15997 Comments have the same form as in Ada.
16007 simple_name @{. simple_name@}
16011 @section Declarations
16014 Declarations introduce new entities that denote types, variables, attributes,
16015 and packages. Some declarations can only appear immediately within a project
16016 declaration. Others can appear within a project or within a package.
16020 declarative_item ::=
16021 simple_declarative_item |
16022 typed_string_declaration |
16023 package_declaration
16025 simple_declarative_item ::=
16026 variable_declaration |
16027 typed_variable_declaration |
16028 attribute_declaration |
16029 case_construction |
16033 @node Empty declarations
16034 @section Empty declarations
16037 empty_declaration ::=
16041 An empty declaration is allowed anywhere a declaration is allowed.
16044 @node Typed string declarations
16045 @section Typed string declarations
16048 Typed strings are sequences of string literals. Typed strings are the only
16049 named types in project files. They are used in case constructions, where they
16050 provide support for conditional attribute definitions.
16054 typed_string_declaration ::=
16055 @b{type} <typed_string_>_simple_name @b{is}
16056 ( string_literal @{, string_literal@} );
16060 A typed string declaration can only appear immediately within a project
16063 All the string literals in a typed string declaration must be distinct.
16069 Variables denote values, and appear as constituents of expressions.
16072 typed_variable_declaration ::=
16073 <typed_variable_>simple_name : <typed_string_>name := string_expression ;
16075 variable_declaration ::=
16076 <variable_>simple_name := expression;
16080 The elaboration of a variable declaration introduces the variable and
16081 assigns to it the value of the expression. The name of the variable is
16082 available after the assignment symbol.
16085 A typed_variable can only be declare once.
16088 a non-typed variable can be declared multiple times.
16091 Before the completion of its first declaration, the value of variable
16092 is the null string.
16095 @section Expressions
16098 An expression is a formula that defines a computation or retrieval of a value.
16099 In a project file the value of an expression is either a string or a list
16100 of strings. A string value in an expression is either a literal, the current
16101 value of a variable, an external value, an attribute reference, or a
16102 concatenation operation.
16115 attribute_reference
16121 ( <string_>expression @{ , <string_>expression @} )
16124 @subsection Concatenation
16126 The following concatenation functions are defined:
16128 @smallexample @c ada
16129 function "&" (X : String; Y : String) return String;
16130 function "&" (X : String_List; Y : String) return String_List;
16131 function "&" (X : String_List; Y : String_List) return String_List;
16135 @section Attributes
16138 An attribute declaration defines a property of a project or package. This
16139 property can later be queried by means of an attribute reference.
16140 Attribute values are strings or string lists.
16142 Some attributes are associative arrays. These attributes are mappings whose
16143 domain is a set of strings. These attributes are declared one association
16144 at a time, by specifying a point in the domain and the corresponding image
16145 of the attribute. They may also be declared as a full associative array,
16146 getting the same associations as the corresponding attribute in an imported
16147 or extended project.
16149 Attributes that are not associative arrays are called simple attributes.
16153 attribute_declaration ::=
16154 full_associative_array_declaration |
16155 @b{for} attribute_designator @b{use} expression ;
16157 full_associative_array_declaration ::=
16158 @b{for} <associative_array_attribute_>simple_name @b{use}
16159 <project_>simple_name [ . <package_>simple_Name ] ' <attribute_>simple_name ;
16161 attribute_designator ::=
16162 <simple_attribute_>simple_name |
16163 <associative_array_attribute_>simple_name ( string_literal )
16167 Some attributes are project-specific, and can only appear immediately within
16168 a project declaration. Others are package-specific, and can only appear within
16169 the proper package.
16171 The expression in an attribute definition must be a string or a string_list.
16172 The string literal appearing in the attribute_designator of an associative
16173 array attribute is case-insensitive.
16175 @node Project Attributes
16176 @section Project Attributes
16179 The following attributes apply to a project. All of them are simple
16184 Expression must be a path name. The attribute defines the
16185 directory in which the object files created by the build are to be placed. If
16186 not specified, object files are placed in the project directory.
16189 Expression must be a path name. The attribute defines the
16190 directory in which the executables created by the build are to be placed.
16191 If not specified, executables are placed in the object directory.
16194 Expression must be a list of path names. The attribute
16195 defines the directories in which the source files for the project are to be
16196 found. If not specified, source files are found in the project directory.
16197 If a string in the list ends with "/**", then the directory that precedes
16198 "/**" and all of its subdirectories (recursively) are included in the list
16199 of source directories.
16201 @item Excluded_Source_Dirs
16202 Expression must be a list of strings. Each entry designates a directory that
16203 is not to be included in the list of source directories of the project.
16204 This is normally used when there are strings ending with "/**" in the value
16205 of attribute Source_Dirs.
16208 Expression must be a list of file names. The attribute
16209 defines the individual files, in the project directory, which are to be used
16210 as sources for the project. File names are path_names that contain no directory
16211 information. If the project has no sources the attribute must be declared
16212 explicitly with an empty list.
16214 @item Excluded_Source_Files (Locally_Removed_Files)
16215 Expression must be a list of strings that are legal file names.
16216 Each file name must designate a source that would normally be a source file
16217 in the source directories of the project or, if the project file is an
16218 extending project file, inherited by the current project file. It cannot
16219 designate an immediate source that is not inherited. Each of the source files
16220 in the list are not considered to be sources of the project file: they are not
16221 inherited. Attribute Locally_Removed_Files is obsolescent, attribute
16222 Excluded_Source_Files is preferred.
16224 @item Source_List_File
16225 Expression must a single path name. The attribute
16226 defines a text file that contains a list of source file names to be used
16227 as sources for the project
16230 Expression must be a path name. The attribute defines the
16231 directory in which a library is to be built. The directory must exist, must
16232 be distinct from the project's object directory, and must be writable.
16235 Expression must be a string that is a legal file name,
16236 without extension. The attribute defines a string that is used to generate
16237 the name of the library to be built by the project.
16240 Argument must be a string value that must be one of the
16241 following @code{"static"}, @code{"dynamic"} or @code{"relocatable"}. This
16242 string is case-insensitive. If this attribute is not specified, the library is
16243 a static library. Otherwise, the library may be dynamic or relocatable. This
16244 distinction is operating-system dependent.
16246 @item Library_Version
16247 Expression must be a string value whose interpretation
16248 is platform dependent. On UNIX, it is used only for dynamic/relocatable
16249 libraries as the internal name of the library (the @code{"soname"}). If the
16250 library file name (built from the @code{Library_Name}) is different from the
16251 @code{Library_Version}, then the library file will be a symbolic link to the
16252 actual file whose name will be @code{Library_Version}.
16254 @item Library_Interface
16255 Expression must be a string list. Each element of the string list
16256 must designate a unit of the project.
16257 If this attribute is present in a Library Project File, then the project
16258 file is a Stand-alone Library_Project_File.
16260 @item Library_Auto_Init
16261 Expression must be a single string "true" or "false", case-insensitive.
16262 If this attribute is present in a Stand-alone Library Project File,
16263 it indicates if initialization is automatic when the dynamic library
16266 @item Library_Options
16267 Expression must be a string list. Indicates additional switches that
16268 are to be used when building a shared library.
16271 Expression must be a single string. Designates an alternative to "gcc"
16272 for building shared libraries.
16274 @item Library_Src_Dir
16275 Expression must be a path name. The attribute defines the
16276 directory in which the sources of the interfaces of a Stand-alone Library will
16277 be copied. The directory must exist, must be distinct from the project's
16278 object directory and source directories of all projects in the project tree,
16279 and must be writable.
16281 @item Library_Src_Dir
16282 Expression must be a path name. The attribute defines the
16283 directory in which the ALI files of a Library will
16284 be copied. The directory must exist, must be distinct from the project's
16285 object directory and source directories of all projects in the project tree,
16286 and must be writable.
16288 @item Library_Symbol_File
16289 Expression must be a single string. Its value is the single file name of a
16290 symbol file to be created when building a stand-alone library when the
16291 symbol policy is either "compliant", "controlled" or "restricted",
16292 on platforms that support symbol control, such as VMS. When symbol policy
16293 is "direct", then a file with this name must exist in the object directory.
16295 @item Library_Reference_Symbol_File
16296 Expression must be a single string. Its value is the path name of a
16297 reference symbol file that is read when the symbol policy is either
16298 "compliant" or "controlled", on platforms that support symbol control,
16299 such as VMS, when building a stand-alone library. The path may be an absolute
16300 path or a path relative to the project directory.
16302 @item Library_Symbol_Policy
16303 Expression must be a single string. Its case-insensitive value can only be
16304 "autonomous", "default", "compliant", "controlled", "restricted" or "direct".
16306 This attribute is not taken into account on all platforms. It controls the
16307 policy for exported symbols and, on some platforms (like VMS) that have the
16308 notions of major and minor IDs built in the library files, it controls
16309 the setting of these IDs.
16311 "autonomous" or "default": exported symbols are not controlled.
16313 "compliant": if attribute Library_Reference_Symbol_File is not defined, then
16314 it is equivalent to policy "autonomous". If there are exported symbols in
16315 the reference symbol file that are not in the object files of the interfaces,
16316 the major ID of the library is increased. If there are symbols in the
16317 object files of the interfaces that are not in the reference symbol file,
16318 these symbols are put at the end of the list in the newly created symbol file
16319 and the minor ID is increased.
16321 "controlled": the attribute Library_Reference_Symbol_File must be defined.
16322 The library will fail to build if the exported symbols in the object files of
16323 the interfaces do not match exactly the symbol in the symbol file.
16325 "restricted": The attribute Library_Symbol_File must be defined. The library
16326 will fail to build if there are symbols in the symbol file that are not in
16327 the exported symbols of the object files of the interfaces. Additional symbols
16328 in the object files are not added to the symbol file.
16330 "direct": The attribute Library_Symbol_File must be defined and must designate
16331 an existing file in the object directory. This symbol file is passed directly
16332 to the underlying linker without any symbol processing.
16335 Expression must be a list of strings that are legal file names.
16336 These file names designate existing compilation units in the source directory
16337 that are legal main subprograms.
16339 When a project file is elaborated, as part of the execution of a gnatmake
16340 command, one or several executables are built and placed in the Exec_Dir.
16341 If the gnatmake command does not include explicit file names, the executables
16342 that are built correspond to the files specified by this attribute.
16344 @item Externally_Built
16345 Expression must be a single string. Its value must be either "true" of "false",
16346 case-insensitive. The default is "false". When the value of this attribute is
16347 "true", no attempt is made to compile the sources or to build the library,
16348 when the project is a library project.
16350 @item Main_Language
16351 This is a simple attribute. Its value is a string that specifies the
16352 language of the main program.
16355 Expression must be a string list. Each string designates
16356 a programming language that is known to GNAT. The strings are case-insensitive.
16360 @node Attribute References
16361 @section Attribute References
16364 Attribute references are used to retrieve the value of previously defined
16365 attribute for a package or project.
16368 attribute_reference ::=
16369 attribute_prefix ' <simple_attribute_>simple_name [ ( string_literal ) ]
16371 attribute_prefix ::=
16373 <project_simple_name | package_identifier |
16374 <project_>simple_name . package_identifier
16378 If an attribute has not been specified for a given package or project, its
16379 value is the null string or the empty list.
16381 @node External Values
16382 @section External Values
16385 An external value is an expression whose value is obtained from the command
16386 that invoked the processing of the current project file (typically a
16392 @b{external} ( string_literal [, string_literal] )
16396 The first string_literal is the string to be used on the command line or
16397 in the environment to specify the external value. The second string_literal,
16398 if present, is the default to use if there is no specification for this
16399 external value either on the command line or in the environment.
16401 @node Case Construction
16402 @section Case Construction
16405 A case construction supports attribute and variable declarations that depend
16406 on the value of a previously declared variable.
16410 case_construction ::=
16411 @b{case} <typed_variable_>name @b{is}
16416 @b{when} discrete_choice_list =>
16417 @{case_construction |
16418 attribute_declaration |
16419 variable_declaration |
16420 empty_declaration@}
16422 discrete_choice_list ::=
16423 string_literal @{| string_literal@} |
16428 Inside a case construction, variable declarations must be for variables that
16429 have already been declared before the case construction.
16431 All choices in a choice list must be distinct. The choice lists of two
16432 distinct alternatives must be disjoint. Unlike Ada, the choice lists of all
16433 alternatives do not need to include all values of the type. An @code{others}
16434 choice must appear last in the list of alternatives.
16440 A package provides a grouping of variable declarations and attribute
16441 declarations to be used when invoking various GNAT tools. The name of
16442 the package indicates the tool(s) to which it applies.
16446 package_declaration ::=
16447 package_spec | package_renaming
16450 @b{package} package_identifier @b{is}
16451 @{simple_declarative_item@}
16452 @b{end} package_identifier ;
16454 package_identifier ::=
16455 @code{Naming} | @code{Builder} | @code{Compiler} | @code{Binder} |
16456 @code{Linker} | @code{Finder} | @code{Cross_Reference} |
16457 @code{gnatls} | @code{IDE} | @code{Pretty_Printer} | @code{Check}
16460 @subsection Package Naming
16463 The attributes of a @code{Naming} package specifies the naming conventions
16464 that apply to the source files in a project. When invoking other GNAT tools,
16465 they will use the sources in the source directories that satisfy these
16466 naming conventions.
16468 The following attributes apply to a @code{Naming} package:
16472 This is a simple attribute whose value is a string. Legal values of this
16473 string are @code{"lowercase"}, @code{"uppercase"} or @code{"mixedcase"}.
16474 These strings are themselves case insensitive.
16477 If @code{Casing} is not specified, then the default is @code{"lowercase"}.
16479 @item Dot_Replacement
16480 This is a simple attribute whose string value satisfies the following
16484 @item It must not be empty
16485 @item It cannot start or end with an alphanumeric character
16486 @item It cannot be a single underscore
16487 @item It cannot start with an underscore followed by an alphanumeric
16488 @item It cannot contain a dot @code{'.'} if longer than one character
16492 If @code{Dot_Replacement} is not specified, then the default is @code{"-"}.
16495 This is an associative array attribute, defined on language names,
16496 whose image is a string that must satisfy the following
16500 @item It must not be empty
16501 @item It cannot start with an alphanumeric character
16502 @item It cannot start with an underscore followed by an alphanumeric character
16506 For Ada, the attribute denotes the suffix used in file names that contain
16507 library unit declarations, that is to say units that are package and
16508 subprogram declarations. If @code{Spec_Suffix ("Ada")} is not
16509 specified, then the default is @code{".ads"}.
16511 For C and C++, the attribute denotes the suffix used in file names that
16512 contain prototypes.
16515 This is an associative array attribute defined on language names,
16516 whose image is a string that must satisfy the following
16520 @item It must not be empty
16521 @item It cannot start with an alphanumeric character
16522 @item It cannot start with an underscore followed by an alphanumeric character
16523 @item It cannot be a suffix of @code{Spec_Suffix}
16527 For Ada, the attribute denotes the suffix used in file names that contain
16528 library bodies, that is to say units that are package and subprogram bodies.
16529 If @code{Body_Suffix ("Ada")} is not specified, then the default is
16532 For C and C++, the attribute denotes the suffix used in file names that contain
16535 @item Separate_Suffix
16536 This is a simple attribute whose value satisfies the same conditions as
16537 @code{Body_Suffix}.
16539 This attribute is specific to Ada. It denotes the suffix used in file names
16540 that contain separate bodies. If it is not specified, then it defaults to same
16541 value as @code{Body_Suffix ("Ada")}.
16544 This is an associative array attribute, specific to Ada, defined over
16545 compilation unit names. The image is a string that is the name of the file
16546 that contains that library unit. The file name is case sensitive if the
16547 conventions of the host operating system require it.
16550 This is an associative array attribute, specific to Ada, defined over
16551 compilation unit names. The image is a string that is the name of the file
16552 that contains the library unit body for the named unit. The file name is case
16553 sensitive if the conventions of the host operating system require it.
16555 @item Specification_Exceptions
16556 This is an associative array attribute defined on language names,
16557 whose value is a list of strings.
16559 This attribute is not significant for Ada.
16561 For C and C++, each string in the list denotes the name of a file that
16562 contains prototypes, but whose suffix is not necessarily the
16563 @code{Spec_Suffix} for the language.
16565 @item Implementation_Exceptions
16566 This is an associative array attribute defined on language names,
16567 whose value is a list of strings.
16569 This attribute is not significant for Ada.
16571 For C and C++, each string in the list denotes the name of a file that
16572 contains source code, but whose suffix is not necessarily the
16573 @code{Body_Suffix} for the language.
16576 The following attributes of package @code{Naming} are obsolescent. They are
16577 kept as synonyms of other attributes for compatibility with previous versions
16578 of the Project Manager.
16581 @item Specification_Suffix
16582 This is a synonym of @code{Spec_Suffix}.
16584 @item Implementation_Suffix
16585 This is a synonym of @code{Body_Suffix}.
16587 @item Specification
16588 This is a synonym of @code{Spec}.
16590 @item Implementation
16591 This is a synonym of @code{Body}.
16594 @subsection package Compiler
16597 The attributes of the @code{Compiler} package specify the compilation options
16598 to be used by the underlying compiler.
16601 @item Default_Switches
16602 This is an associative array attribute. Its
16603 domain is a set of language names. Its range is a string list that
16604 specifies the compilation options to be used when compiling a component
16605 written in that language, for which no file-specific switches have been
16609 This is an associative array attribute. Its domain is
16610 a set of file names. Its range is a string list that specifies the
16611 compilation options to be used when compiling the named file. If a file
16612 is not specified in the Switches attribute, it is compiled with the
16613 options specified by Default_Switches of its language, if defined.
16615 @item Local_Configuration_Pragmas.
16616 This is a simple attribute, whose
16617 value is a path name that designates a file containing configuration pragmas
16618 to be used for all invocations of the compiler for immediate sources of the
16622 @subsection package Builder
16625 The attributes of package @code{Builder} specify the compilation, binding, and
16626 linking options to be used when building an executable for a project. The
16627 following attributes apply to package @code{Builder}:
16630 @item Default_Switches
16631 This is an associative array attribute. Its
16632 domain is a set of language names. Its range is a string list that
16633 specifies options to be used when building a main
16634 written in that language, for which no file-specific switches have been
16638 This is an associative array attribute. Its domain is
16639 a set of file names. Its range is a string list that specifies
16640 options to be used when building the named main file. If a main file
16641 is not specified in the Switches attribute, it is built with the
16642 options specified by Default_Switches of its language, if defined.
16644 @item Global_Configuration_Pragmas
16645 This is a simple attribute, whose
16646 value is a path name that designates a file that contains configuration pragmas
16647 to be used in every build of an executable. If both local and global
16648 configuration pragmas are specified, a compilation makes use of both sets.
16652 This is an associative array attribute. Its domain is
16653 a set of main source file names. Its range is a simple string that specifies
16654 the executable file name to be used when linking the specified main source.
16655 If a main source is not specified in the Executable attribute, the executable
16656 file name is deducted from the main source file name.
16657 This attribute has no effect if its value is the empty string.
16659 @item Executable_Suffix
16660 This is a simple attribute whose value is the suffix to be added to
16661 the executables that don't have an attribute Executable specified.
16664 @subsection package Gnatls
16667 The attributes of package @code{Gnatls} specify the tool options to be used
16668 when invoking the library browser @command{gnatls}.
16669 The following attributes apply to package @code{Gnatls}:
16673 This is a single attribute with a string list value. Each nonempty string
16674 in the list is an option when invoking @code{gnatls}.
16677 @subsection package Binder
16680 The attributes of package @code{Binder} specify the options to be used
16681 when invoking the binder in the construction of an executable.
16682 The following attributes apply to package @code{Binder}:
16685 @item Default_Switches
16686 This is an associative array attribute. Its
16687 domain is a set of language names. Its range is a string list that
16688 specifies options to be used when binding a main
16689 written in that language, for which no file-specific switches have been
16693 This is an associative array attribute. Its domain is
16694 a set of file names. Its range is a string list that specifies
16695 options to be used when binding the named main file. If a main file
16696 is not specified in the Switches attribute, it is bound with the
16697 options specified by Default_Switches of its language, if defined.
16700 @subsection package Linker
16703 The attributes of package @code{Linker} specify the options to be used when
16704 invoking the linker in the construction of an executable.
16705 The following attributes apply to package @code{Linker}:
16708 @item Default_Switches
16709 This is an associative array attribute. Its
16710 domain is a set of language names. Its range is a string list that
16711 specifies options to be used when linking a main
16712 written in that language, for which no file-specific switches have been
16716 This is an associative array attribute. Its domain is
16717 a set of file names. Its range is a string list that specifies
16718 options to be used when linking the named main file. If a main file
16719 is not specified in the Switches attribute, it is linked with the
16720 options specified by Default_Switches of its language, if defined.
16722 @item Linker_Options
16723 This is a string list attribute. Its value specifies additional options that
16724 be given to the linker when linking an executable. This attribute is not
16725 used in the main project, only in projects imported directly or indirectly.
16729 @subsection package Cross_Reference
16732 The attributes of package @code{Cross_Reference} specify the tool options
16734 when invoking the library tool @command{gnatxref}.
16735 The following attributes apply to package @code{Cross_Reference}:
16738 @item Default_Switches
16739 This is an associative array attribute. Its
16740 domain is a set of language names. Its range is a string list that
16741 specifies options to be used when calling @command{gnatxref} on a source
16742 written in that language, for which no file-specific switches have been
16746 This is an associative array attribute. Its domain is
16747 a set of file names. Its range is a string list that specifies
16748 options to be used when calling @command{gnatxref} on the named main source.
16749 If a source is not specified in the Switches attribute, @command{gnatxref} will
16750 be called with the options specified by Default_Switches of its language,
16754 @subsection package Finder
16757 The attributes of package @code{Finder} specify the tool options to be used
16758 when invoking the search tool @command{gnatfind}.
16759 The following attributes apply to package @code{Finder}:
16762 @item Default_Switches
16763 This is an associative array attribute. Its
16764 domain is a set of language names. Its range is a string list that
16765 specifies options to be used when calling @command{gnatfind} on a source
16766 written in that language, for which no file-specific switches have been
16770 This is an associative array attribute. Its domain is
16771 a set of file names. Its range is a string list that specifies
16772 options to be used when calling @command{gnatfind} on the named main source.
16773 If a source is not specified in the Switches attribute, @command{gnatfind} will
16774 be called with the options specified by Default_Switches of its language,
16778 @subsection package Check
16781 The attributes of package @code{Check}
16782 specify the checking rule options to be used
16783 when invoking the checking tool @command{gnatcheck}.
16784 The following attributes apply to package @code{Check}:
16787 @item Default_switches
16788 This is an associative array attribute. Its
16789 domain is a set of language names. Its range is a string list that
16790 specifies options to be used when calling @command{gnatcheck} on a source
16791 written in that language. The first string in the range should always be
16792 @code{"-rules"} to specify that all the other options belong to the
16793 @code{-rules} section of the parameters of @command{gnatcheck} call.
16797 @subsection package Pretty_Printer
16800 The attributes of package @code{Pretty_Printer}
16801 specify the tool options to be used
16802 when invoking the formatting tool @command{gnatpp}.
16803 The following attributes apply to package @code{Pretty_Printer}:
16806 @item Default_switches
16807 This is an associative array attribute. Its
16808 domain is a set of language names. Its range is a string list that
16809 specifies options to be used when calling @command{gnatpp} on a source
16810 written in that language, for which no file-specific switches have been
16814 This is an associative array attribute. Its domain is
16815 a set of file names. Its range is a string list that specifies
16816 options to be used when calling @command{gnatpp} on the named main source.
16817 If a source is not specified in the Switches attribute, @command{gnatpp} will
16818 be called with the options specified by Default_Switches of its language,
16822 @subsection package gnatstub
16825 The attributes of package @code{gnatstub}
16826 specify the tool options to be used
16827 when invoking the tool @command{gnatstub}.
16828 The following attributes apply to package @code{gnatstub}:
16831 @item Default_switches
16832 This is an associative array attribute. Its
16833 domain is a set of language names. Its range is a string list that
16834 specifies options to be used when calling @command{gnatstub} on a source
16835 written in that language, for which no file-specific switches have been
16839 This is an associative array attribute. Its domain is
16840 a set of file names. Its range is a string list that specifies
16841 options to be used when calling @command{gnatstub} on the named main source.
16842 If a source is not specified in the Switches attribute, @command{gnatpp} will
16843 be called with the options specified by Default_Switches of its language,
16847 @subsection package Eliminate
16850 The attributes of package @code{Eliminate}
16851 specify the tool options to be used
16852 when invoking the tool @command{gnatelim}.
16853 The following attributes apply to package @code{Eliminate}:
16856 @item Default_switches
16857 This is an associative array attribute. Its
16858 domain is a set of language names. Its range is a string list that
16859 specifies options to be used when calling @command{gnatelim} on a source
16860 written in that language, for which no file-specific switches have been
16864 This is an associative array attribute. Its domain is
16865 a set of file names. Its range is a string list that specifies
16866 options to be used when calling @command{gnatelim} on the named main source.
16867 If a source is not specified in the Switches attribute, @command{gnatelim} will
16868 be called with the options specified by Default_Switches of its language,
16872 @subsection package Metrics
16875 The attributes of package @code{Metrics}
16876 specify the tool options to be used
16877 when invoking the tool @command{gnatmetric}.
16878 The following attributes apply to package @code{Metrics}:
16881 @item Default_switches
16882 This is an associative array attribute. Its
16883 domain is a set of language names. Its range is a string list that
16884 specifies options to be used when calling @command{gnatmetric} on a source
16885 written in that language, for which no file-specific switches have been
16889 This is an associative array attribute. Its domain is
16890 a set of file names. Its range is a string list that specifies
16891 options to be used when calling @command{gnatmetric} on the named main source.
16892 If a source is not specified in the Switches attribute, @command{gnatmetric}
16893 will be called with the options specified by Default_Switches of its language,
16897 @subsection package IDE
16900 The attributes of package @code{IDE} specify the options to be used when using
16901 an Integrated Development Environment such as @command{GPS}.
16905 This is a simple attribute. Its value is a string that designates the remote
16906 host in a cross-compilation environment, to be used for remote compilation and
16907 debugging. This field should not be specified when running on the local
16911 This is a simple attribute. Its value is a string that specifies the
16912 name of IP address of the embedded target in a cross-compilation environment,
16913 on which the program should execute.
16915 @item Communication_Protocol
16916 This is a simple string attribute. Its value is the name of the protocol
16917 to use to communicate with the target in a cross-compilation environment,
16918 e.g.@: @code{"wtx"} or @code{"vxworks"}.
16920 @item Compiler_Command
16921 This is an associative array attribute, whose domain is a language name. Its
16922 value is string that denotes the command to be used to invoke the compiler.
16923 The value of @code{Compiler_Command ("Ada")} is expected to be compatible with
16924 gnatmake, in particular in the handling of switches.
16926 @item Debugger_Command
16927 This is simple attribute, Its value is a string that specifies the name of
16928 the debugger to be used, such as gdb, powerpc-wrs-vxworks-gdb or gdb-4.
16930 @item Default_Switches
16931 This is an associative array attribute. Its indexes are the name of the
16932 external tools that the GNAT Programming System (GPS) is supporting. Its
16933 value is a list of switches to use when invoking that tool.
16936 This is a simple attribute. Its value is a string that specifies the name
16937 of the @command{gnatls} utility to be used to retrieve information about the
16938 predefined path; e.g., @code{"gnatls"}, @code{"powerpc-wrs-vxworks-gnatls"}.
16941 This is a simple attribute. Its value is a string used to specify the
16942 Version Control System (VCS) to be used for this project, e.g.@: CVS, RCS
16943 ClearCase or Perforce.
16945 @item VCS_File_Check
16946 This is a simple attribute. Its value is a string that specifies the
16947 command used by the VCS to check the validity of a file, either
16948 when the user explicitly asks for a check, or as a sanity check before
16949 doing the check-in.
16951 @item VCS_Log_Check
16952 This is a simple attribute. Its value is a string that specifies
16953 the command used by the VCS to check the validity of a log file.
16955 @item VCS_Repository_Root
16956 The VCS repository root path. This is used to create tags or branches
16957 of the repository. For subversion the value should be the @code{URL}
16958 as specified to check-out the working copy of the repository.
16960 @item VCS_Patch_Root
16961 The local root directory to use for building patch file. All patch chunks
16962 will be relative to this path. The root project directory is used if
16963 this value is not defined.
16967 @node Package Renamings
16968 @section Package Renamings
16971 A package can be defined by a renaming declaration. The new package renames
16972 a package declared in a different project file, and has the same attributes
16973 as the package it renames.
16976 package_renaming ::==
16977 @b{package} package_identifier @b{renames}
16978 <project_>simple_name.package_identifier ;
16982 The package_identifier of the renamed package must be the same as the
16983 package_identifier. The project whose name is the prefix of the renamed
16984 package must contain a package declaration with this name. This project
16985 must appear in the context_clause of the enclosing project declaration,
16986 or be the parent project of the enclosing child project.
16992 A project file specifies a set of rules for constructing a software system.
16993 A project file can be self-contained, or depend on other project files.
16994 Dependencies are expressed through a context clause that names other projects.
17000 context_clause project_declaration
17002 project_declaration ::=
17003 simple_project_declaration | project_extension
17005 simple_project_declaration ::=
17006 @b{project} <project_>simple_name @b{is}
17007 @{declarative_item@}
17008 @b{end} <project_>simple_name;
17014 [@b{limited}] @b{with} path_name @{ , path_name @} ;
17021 A path name denotes a project file. A path name can be absolute or relative.
17022 An absolute path name includes a sequence of directories, in the syntax of
17023 the host operating system, that identifies uniquely the project file in the
17024 file system. A relative path name identifies the project file, relative
17025 to the directory that contains the current project, or relative to a
17026 directory listed in the environment variable ADA_PROJECT_PATH.
17027 Path names are case sensitive if file names in the host operating system
17028 are case sensitive.
17030 The syntax of the environment variable ADA_PROJECT_PATH is a list of
17031 directory names separated by colons (semicolons on Windows).
17033 A given project name can appear only once in a context_clause.
17035 It is illegal for a project imported by a context clause to refer, directly
17036 or indirectly, to the project in which this context clause appears (the
17037 dependency graph cannot contain cycles), except when one of the with_clause
17038 in the cycle is a @code{limited with}.
17040 @node Project Extensions
17041 @section Project Extensions
17044 A project extension introduces a new project, which inherits the declarations
17045 of another project.
17049 project_extension ::=
17050 @b{project} <project_>simple_name @b{extends} path_name @b{is}
17051 @{declarative_item@}
17052 @b{end} <project_>simple_name;
17056 The project extension declares a child project. The child project inherits
17057 all the declarations and all the files of the parent project, These inherited
17058 declaration can be overridden in the child project, by means of suitable
17061 @node Project File Elaboration
17062 @section Project File Elaboration
17065 A project file is processed as part of the invocation of a gnat tool that
17066 uses the project option. Elaboration of the process file consists in the
17067 sequential elaboration of all its declarations. The computed values of
17068 attributes and variables in the project are then used to establish the
17069 environment in which the gnat tool will execute.
17071 @node Obsolescent Features
17072 @chapter Obsolescent Features
17075 This chapter describes features that are provided by GNAT, but are
17076 considered obsolescent since there are preferred ways of achieving
17077 the same effect. These features are provided solely for historical
17078 compatibility purposes.
17081 * pragma No_Run_Time::
17082 * pragma Ravenscar::
17083 * pragma Restricted_Run_Time::
17086 @node pragma No_Run_Time
17087 @section pragma No_Run_Time
17089 The pragma @code{No_Run_Time} is used to achieve an affect similar
17090 to the use of the "Zero Foot Print" configurable run time, but without
17091 requiring a specially configured run time. The result of using this
17092 pragma, which must be used for all units in a partition, is to restrict
17093 the use of any language features requiring run-time support code. The
17094 preferred usage is to use an appropriately configured run-time that
17095 includes just those features that are to be made accessible.
17097 @node pragma Ravenscar
17098 @section pragma Ravenscar
17100 The pragma @code{Ravenscar} has exactly the same effect as pragma
17101 @code{Profile (Ravenscar)}. The latter usage is preferred since it
17102 is part of the new Ada 2005 standard.
17104 @node pragma Restricted_Run_Time
17105 @section pragma Restricted_Run_Time
17107 The pragma @code{Restricted_Run_Time} has exactly the same effect as
17108 pragma @code{Profile (Restricted)}. The latter usage is
17109 preferred since the Ada 2005 pragma @code{Profile} is intended for
17110 this kind of implementation dependent addition.
17113 @c GNU Free Documentation License
17115 @node Index,,GNU Free Documentation License, Top