1 \input texinfo @c -*-texinfo-*-
3 @setfilename gfortran.info
4 @set copyrights-gfortran 1999-2008
6 @include gcc-common.texi
8 @settitle The GNU Fortran Compiler
10 @c Create a separate index for command line options
12 @c Merge the standard indexes into a single one.
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60 @c Use with @@smallbook.
62 @c %** start of document
64 @c Cause even numbered pages to be printed on the left hand side of
65 @c the page and odd numbered pages to be printed on the right hand
66 @c side of the page. Using this, you can print on both sides of a
67 @c sheet of paper and have the text on the same part of the sheet.
69 @c The text on right hand pages is pushed towards the right hand
70 @c margin and the text on left hand pages is pushed toward the left
72 @c (To provide the reverse effect, set bindingoffset to -0.75in.)
75 @c \global\bindingoffset=0.75in
76 @c \global\normaloffset =0.75in
80 Copyright @copyright{} @value{copyrights-gfortran} Free Software Foundation, Inc.
82 Permission is granted to copy, distribute and/or modify this document
83 under the terms of the GNU Free Documentation License, Version 1.1 or
84 any later version published by the Free Software Foundation; with the
85 Invariant Sections being ``GNU General Public License'' and ``Funding
86 Free Software'', the Front-Cover
87 texts being (a) (see below), and with the Back-Cover Texts being (b)
88 (see below). A copy of the license is included in the section entitled
89 ``GNU Free Documentation License''.
91 (a) The FSF's Front-Cover Text is:
95 (b) The FSF's Back-Cover Text is:
97 You have freedom to copy and modify this GNU Manual, like GNU
98 software. Copies published by the Free Software Foundation raise
99 funds for GNU development.
103 @dircategory Software development
105 * gfortran: (gfortran). The GNU Fortran Compiler.
107 This file documents the use and the internals of
108 the GNU Fortran compiler, (@command{gfortran}).
110 Published by the Free Software Foundation
111 51 Franklin Street, Fifth Floor
112 Boston, MA 02110-1301 USA
118 @setchapternewpage odd
120 @title Using GNU Fortran
122 @author The @t{gfortran} team
124 @vskip 0pt plus 1filll
125 Published by the Free Software Foundation@*
126 51 Franklin Street, Fifth Floor@*
127 Boston, MA 02110-1301, USA@*
128 @c Last printed ??ber, 19??.@*
129 @c Printed copies are available for $? each.@*
135 @c TODO: The following "Part" definitions are included here temporarily
136 @c until they are incorporated into the official Texinfo distribution.
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152 @c ---------------------------------------------------------------------
153 @c TexInfo table of contents.
154 @c ---------------------------------------------------------------------
161 This manual documents the use of @command{gfortran},
162 the GNU Fortran compiler. You can find in this manual how to invoke
163 @command{gfortran}, as well as its features and incompatibilities.
166 @emph{Warning:} This document, and the compiler it describes, are still
167 under development. While efforts are made to keep it up-to-date, it might
168 not accurately reflect the status of the most recent GNU Fortran compiler.
172 @comment When you add a new menu item, please keep the right hand
173 @comment aligned to the same column. Do not use tabs. This provides
174 @comment better formatting.
179 Part I: Invoking GNU Fortran
180 * Invoking GNU Fortran:: Command options supported by @command{gfortran}.
181 * Runtime:: Influencing runtime behavior with environment variables.
183 Part II: Language Reference
184 * Fortran 2003 status:: Fortran 2003 features supported by GNU Fortran.
185 * Extensions:: Language extensions implemented by GNU Fortran.
186 * Intrinsic Procedures:: Intrinsic procedures supported by GNU Fortran.
187 * Intrinsic Modules:: Intrinsic modules supported by GNU Fortran.
189 * Contributing:: How you can help.
190 * Copying:: GNU General Public License says
191 how you can copy and share GNU Fortran.
192 * GNU Free Documentation License::
193 How you can copy and share this manual.
194 * Funding:: How to help assure continued work for free software.
195 * Option Index:: Index of command line options
196 * Keyword Index:: Index of concepts
200 @c ---------------------------------------------------------------------
202 @c ---------------------------------------------------------------------
205 @chapter Introduction
207 @c The following duplicates the text on the TexInfo table of contents.
209 This manual documents the use of @command{gfortran}, the GNU Fortran
210 compiler. You can find in this manual how to invoke @command{gfortran},
211 as well as its features and incompatibilities.
214 @emph{Warning:} This document, and the compiler it describes, are still
215 under development. While efforts are made to keep it up-to-date, it
216 might not accurately reflect the status of the most recent GNU Fortran
221 The GNU Fortran compiler front end was
222 designed initially as a free replacement for,
223 or alternative to, the unix @command{f95} command;
224 @command{gfortran} is the command you'll use to invoke the compiler.
227 * About GNU Fortran:: What you should know about the GNU Fortran compiler.
228 * GNU Fortran and GCC:: You can compile Fortran, C, or other programs.
229 * Preprocessing and conditional compilation:: The Fortran preprocessor
230 * GNU Fortran and G77:: Why we chose to start from scratch.
231 * Project Status:: Status of GNU Fortran, roadmap, proposed extensions.
232 * Standards:: Standards supported by GNU Fortran.
236 @c ---------------------------------------------------------------------
238 @c ---------------------------------------------------------------------
240 @node About GNU Fortran
241 @section About GNU Fortran
243 The GNU Fortran compiler is still in an early state of development.
244 It can generate code for most constructs and expressions,
245 but much work remains to be done.
247 When the GNU Fortran compiler is finished,
248 it will do everything you expect from any decent compiler:
252 Read a user's program,
253 stored in a file and containing instructions written
254 in Fortran 77, Fortran 90, Fortran 95 or Fortran 2003.
255 This file contains @dfn{source code}.
258 Translate the user's program into instructions a computer
259 can carry out more quickly than it takes to translate the
260 instructions in the first
261 place. The result after compilation of a program is
263 code designed to be efficiently translated and processed
264 by a machine such as your computer.
265 Humans usually aren't as good writing machine code
266 as they are at writing Fortran (or C++, Ada, or Java),
267 because is easy to make tiny mistakes writing machine code.
270 Provide the user with information about the reasons why
271 the compiler is unable to create a binary from the source code.
272 Usually this will be the case if the source code is flawed.
273 When writing Fortran, it is easy to make big mistakes.
274 The Fortran 90 requires that the compiler can point out
275 mistakes to the user.
276 An incorrect usage of the language causes an @dfn{error message}.
278 The compiler will also attempt to diagnose cases where the
279 user's program contains a correct usage of the language,
280 but instructs the computer to do something questionable.
281 This kind of diagnostics message is called a @dfn{warning message}.
284 Provide optional information about the translation passes
285 from the source code to machine code.
286 This can help a user of the compiler to find the cause of
287 certain bugs which may not be obvious in the source code,
288 but may be more easily found at a lower level compiler output.
289 It also helps developers to find bugs in the compiler itself.
292 Provide information in the generated machine code that can
293 make it easier to find bugs in the program (using a debugging tool,
294 called a @dfn{debugger}, such as the GNU Debugger @command{gdb}).
297 Locate and gather machine code already generated to
298 perform actions requested by statements in the user's program.
299 This machine code is organized into @dfn{modules} and is located
300 and @dfn{linked} to the user program.
303 The GNU Fortran compiler consists of several components:
307 A version of the @command{gcc} command
308 (which also might be installed as the system's @command{cc} command)
309 that also understands and accepts Fortran source code.
310 The @command{gcc} command is the @dfn{driver} program for
311 all the languages in the GNU Compiler Collection (GCC);
313 you can compile the source code of any language for
314 which a front end is available in GCC.
317 The @command{gfortran} command itself,
318 which also might be installed as the
319 system's @command{f95} command.
320 @command{gfortran} is just another driver program,
321 but specifically for the Fortran compiler only.
322 The difference with @command{gcc} is that @command{gfortran}
323 will automatically link the correct libraries to your program.
326 A collection of run-time libraries.
327 These libraries contain the machine code needed to support
328 capabilities of the Fortran language that are not directly
329 provided by the machine code generated by the
330 @command{gfortran} compilation phase,
331 such as intrinsic functions and subroutines,
332 and routines for interaction with files and the operating system.
333 @c and mechanisms to spawn,
334 @c unleash and pause threads in parallelized code.
337 The Fortran compiler itself, (@command{f951}).
338 This is the GNU Fortran parser and code generator,
339 linked to and interfaced with the GCC backend library.
340 @command{f951} ``translates'' the source code to
341 assembler code. You would typically not use this
343 instead, the @command{gcc} or @command{gfortran} driver
344 programs will call it for you.
348 @c ---------------------------------------------------------------------
349 @c GNU Fortran and GCC
350 @c ---------------------------------------------------------------------
352 @node GNU Fortran and GCC
353 @section GNU Fortran and GCC
354 @cindex GNU Compiler Collection
357 GNU Fortran is a part of GCC, the @dfn{GNU Compiler Collection}. GCC
358 consists of a collection of front ends for various languages, which
359 translate the source code into a language-independent form called
360 @dfn{GENERIC}. This is then processed by a common middle end which
361 provides optimization, and then passed to one of a collection of back
362 ends which generate code for different computer architectures and
365 Functionally, this is implemented with a driver program (@command{gcc})
366 which provides the command-line interface for the compiler. It calls
367 the relevant compiler front-end program (e.g., @command{f951} for
368 Fortran) for each file in the source code, and then calls the assembler
369 and linker as appropriate to produce the compiled output. In a copy of
370 GCC which has been compiled with Fortran language support enabled,
371 @command{gcc} will recognize files with @file{.f}, @file{.for}, @file{.ftn},
372 @file{.f90}, @file{.f95}, and @file{.f03} extensions as Fortran source code,
373 and compile it accordingly. A @command{gfortran} driver program is also
374 provided, which is identical to @command{gcc} except that it automatically
375 links the Fortran runtime libraries into the compiled program.
377 Source files with @file{.f}, @file{.for}, @file{.fpp}, @file{.ftn}, @file{.F},
378 @file{.FOR}, @file{.FPP}, and @file{.FTN} extensions are treated as fixed form.
379 Source files with @file{.f90}, @file{.f95}, @file{.f03}, @file{.F90},
380 @file{.F95}, and @file{.F03} extensions are treated as free form. The
381 capitalized versions of either form are run through preprocessing. Source files
382 with the lower case @file{.fpp} extension are also run through preprocessing.
384 This manual specifically documents the Fortran front end, which handles
385 the programming language's syntax and semantics. The aspects of GCC
386 which relate to the optimization passes and the back-end code generation
387 are documented in the GCC manual; see
388 @ref{Top,,Introduction,gcc,Using the GNU Compiler Collection (GCC)}.
389 The two manuals together provide a complete reference for the GNU
393 @c ---------------------------------------------------------------------
394 @c Preprocessing and conditional compilation
395 @c ---------------------------------------------------------------------
397 @node Preprocessing and conditional compilation
398 @section Preprocessing and conditional compilation
401 @cindex Conditional compilation
402 @cindex Preprocessing
404 Many Fortran compilers including GNU Fortran allow passing the source code
405 through a C preprocessor (CPP; sometimes also called the Fortran preprocessor,
406 FPP) to allow for conditional compilation. In the case of GNU Fortran,
407 this is the GNU C Preprocessor in the traditional mode. On systems with
408 case-preserving file names, the preprocessor is automatically invoked if the
409 file extension is @code{.F}, @code{.FOR}, @code{.FTN}, @code{.F90},
410 @code{.F95} or @code{.F03}; otherwise use for fixed-format code the option
411 @code{-x f77-cpp-input} and for free-format code @code{-x f95-cpp-input}.
412 Invocation of the preprocessor can be suppressed using @code{-x f77} or
415 If the GNU Fortran invoked the preprocessor, @code{__GFORTRAN__}
416 is defined and @code{__GNUC__}, @code{__GNUC_MINOR__} and
417 @code{__GNUC_PATCHLEVEL__} can be used to determine the version of the
418 compiler. See @ref{Top,,Overview,cpp,The C Preprocessor} for details.
420 While CPP is the de-facto standard for preprocessing Fortran code,
421 Part 3 of the Fortran 95 standard (ISO/IEC 1539-3:1998) defines
422 Conditional Compilation, which is not widely used and not directly
423 supported by the GNU Fortran compiler. You can use the program coco
424 to preprocess such files (@uref{http://users.erols.com/dnagle/coco.html}).
427 @c ---------------------------------------------------------------------
428 @c GNU Fortran and G77
429 @c ---------------------------------------------------------------------
431 @node GNU Fortran and G77
432 @section GNU Fortran and G77
434 @cindex @command{g77}
436 The GNU Fortran compiler is the successor to @command{g77}, the Fortran
437 77 front end included in GCC prior to version 4. It is an entirely new
438 program that has been designed to provide Fortran 95 support and
439 extensibility for future Fortran language standards, as well as providing
440 backwards compatibility for Fortran 77 and nearly all of the GNU language
441 extensions supported by @command{g77}.
444 @c ---------------------------------------------------------------------
446 @c ---------------------------------------------------------------------
449 @section Project Status
452 As soon as @command{gfortran} can parse all of the statements correctly,
453 it will be in the ``larva'' state.
454 When we generate code, the ``puppa'' state.
455 When @command{gfortran} is done,
456 we'll see if it will be a beautiful butterfly,
457 or just a big bug....
459 --Andy Vaught, April 2000
462 The start of the GNU Fortran 95 project was announced on
463 the GCC homepage in March 18, 2000
464 (even though Andy had already been working on it for a while,
467 The GNU Fortran compiler is able to compile nearly all
468 standard-compliant Fortran 95, Fortran 90, and Fortran 77 programs,
469 including a number of standard and non-standard extensions, and can be
470 used on real-world programs. In particular, the supported extensions
471 include OpenMP, Cray-style pointers, and several Fortran 2003 features
472 such as enumeration, stream I/O, and some of the enhancements to
473 allocatable array support from TR 15581. However, it is still under
474 development and has a few remaining rough edges.
476 At present, the GNU Fortran compiler passes the
477 @uref{http://www.fortran-2000.com/ArnaudRecipes/fcvs21_f95.html,
478 NIST Fortran 77 Test Suite}, and produces acceptable results on the
479 @uref{http://www.netlib.org/lapack/faq.html#1.21, LAPACK Test Suite}.
480 It also provides respectable performance on
481 the @uref{http://www.polyhedron.com/pb05.html, Polyhedron Fortran
482 compiler benchmarks} and the
483 @uref{http://www.llnl.gov/asci_benchmarks/asci/limited/lfk/README.html,
484 Livermore Fortran Kernels test}. It has been used to compile a number of
485 large real-world programs, including
486 @uref{http://mysite.verizon.net/serveall/moene.pdf, the HIRLAM
487 weather-forecasting code} and
488 @uref{http://www.theochem.uwa.edu.au/tonto/, the Tonto quantum
489 chemistry package}; see @url{http://gcc.gnu.org/wiki/GfortranApps} for an
492 Among other things, the GNU Fortran compiler is intended as a replacement
493 for G77. At this point, nearly all programs that could be compiled with
494 G77 can be compiled with GNU Fortran, although there are a few minor known
497 The primary work remaining to be done on GNU Fortran falls into three
498 categories: bug fixing (primarily regarding the treatment of invalid code
499 and providing useful error messages), improving the compiler optimizations
500 and the performance of compiled code, and extending the compiler to support
501 future standards---in particular, Fortran 2003.
504 @c ---------------------------------------------------------------------
506 @c ---------------------------------------------------------------------
512 The GNU Fortran compiler implements
513 ISO/IEC 1539:1997 (Fortran 95). As such, it can also compile essentially all
514 standard-compliant Fortran 90 and Fortran 77 programs. It also supports
515 the ISO/IEC TR-15581 enhancements to allocatable arrays, and
516 the @uref{http://www.openmp.org/drupal/mp-documents/spec25.pdf,
517 OpenMP Application Program Interface v2.5} specification.
519 In the future, the GNU Fortran compiler may also support other standard
520 variants of and extensions to the Fortran language. These include
521 ISO/IEC 1539-1:2004 (Fortran 2003).
524 @c =====================================================================
525 @c PART I: INVOCATION REFERENCE
526 @c =====================================================================
529 \part{I}{Invoking GNU Fortran}
532 @c ---------------------------------------------------------------------
534 @c ---------------------------------------------------------------------
539 @c ---------------------------------------------------------------------
541 @c ---------------------------------------------------------------------
544 @chapter Runtime: Influencing runtime behavior with environment variables
545 @cindex environment variable
547 The behavior of the @command{gfortran} can be influenced by
548 environment variables.
550 Malformed environment variables are silently ignored.
553 * GFORTRAN_STDIN_UNIT:: Unit number for standard input
554 * GFORTRAN_STDOUT_UNIT:: Unit number for standard output
555 * GFORTRAN_STDERR_UNIT:: Unit number for standard error
556 * GFORTRAN_USE_STDERR:: Send library output to standard error
557 * GFORTRAN_TMPDIR:: Directory for scratch files
558 * GFORTRAN_UNBUFFERED_ALL:: Don't buffer I/O for all units.
559 * GFORTRAN_UNBUFFERED_PRECONNECTED:: Don't buffer I/O for preconnected units.
560 * GFORTRAN_SHOW_LOCUS:: Show location for runtime errors
561 * GFORTRAN_OPTIONAL_PLUS:: Print leading + where permitted
562 * GFORTRAN_DEFAULT_RECL:: Default record length for new files
563 * GFORTRAN_LIST_SEPARATOR:: Separator for list output
564 * GFORTRAN_CONVERT_UNIT:: Set endianness for unformatted I/O
565 * GFORTRAN_ERROR_DUMPCORE:: Dump core on run-time errors
566 * GFORTRAN_ERROR_BACKTRACE:: Show backtrace on run-time errors
569 @node GFORTRAN_STDIN_UNIT
570 @section @env{GFORTRAN_STDIN_UNIT}---Unit number for standard input
572 This environment variable can be used to select the unit number
573 preconnected to standard input. This must be a positive integer.
574 The default value is 5.
576 @node GFORTRAN_STDOUT_UNIT
577 @section @env{GFORTRAN_STDOUT_UNIT}---Unit number for standard output
579 This environment variable can be used to select the unit number
580 preconnected to standard output. This must be a positive integer.
581 The default value is 6.
583 @node GFORTRAN_STDERR_UNIT
584 @section @env{GFORTRAN_STDERR_UNIT}---Unit number for standard error
586 This environment variable can be used to select the unit number
587 preconnected to standard error. This must be a positive integer.
588 The default value is 0.
590 @node GFORTRAN_USE_STDERR
591 @section @env{GFORTRAN_USE_STDERR}---Send library output to standard error
593 This environment variable controls where library output is sent.
594 If the first letter is @samp{y}, @samp{Y} or @samp{1}, standard
595 error is used. If the first letter is @samp{n}, @samp{N} or
596 @samp{0}, standard output is used.
598 @node GFORTRAN_TMPDIR
599 @section @env{GFORTRAN_TMPDIR}---Directory for scratch files
601 This environment variable controls where scratch files are
602 created. If this environment variable is missing,
603 GNU Fortran searches for the environment variable @env{TMP}. If
604 this is also missing, the default is @file{/tmp}.
606 @node GFORTRAN_UNBUFFERED_ALL
607 @section @env{GFORTRAN_UNBUFFERED_ALL}---Don't buffer I/O on all units
609 This environment variable controls whether all I/O is unbuffered. If
610 the first letter is @samp{y}, @samp{Y} or @samp{1}, all I/O is
611 unbuffered. This will slow down small sequential reads and writes. If
612 the first letter is @samp{n}, @samp{N} or @samp{0}, I/O is buffered.
615 @node GFORTRAN_UNBUFFERED_PRECONNECTED
616 @section @env{GFORTRAN_UNBUFFERED_PRECONNECTED}---Don't buffer I/O on preconnected units
618 The environment variable named @env{GFORTRAN_UNBUFFERED_PRECONNECTED} controls
619 whether I/O on a preconnected unit (i.e.@: STDOUT or STDERR) is unbuffered. If
620 the first letter is @samp{y}, @samp{Y} or @samp{1}, I/O is unbuffered. This
621 will slow down small sequential reads and writes. If the first letter
622 is @samp{n}, @samp{N} or @samp{0}, I/O is buffered. This is the default.
624 @node GFORTRAN_SHOW_LOCUS
625 @section @env{GFORTRAN_SHOW_LOCUS}---Show location for runtime errors
627 If the first letter is @samp{y}, @samp{Y} or @samp{1}, filename and
628 line numbers for runtime errors are printed. If the first letter is
629 @samp{n}, @samp{N} or @samp{0}, don't print filename and line numbers
630 for runtime errors. The default is to print the location.
632 @node GFORTRAN_OPTIONAL_PLUS
633 @section @env{GFORTRAN_OPTIONAL_PLUS}---Print leading + where permitted
635 If the first letter is @samp{y}, @samp{Y} or @samp{1},
636 a plus sign is printed
637 where permitted by the Fortran standard. If the first letter
638 is @samp{n}, @samp{N} or @samp{0}, a plus sign is not printed
639 in most cases. Default is not to print plus signs.
641 @node GFORTRAN_DEFAULT_RECL
642 @section @env{GFORTRAN_DEFAULT_RECL}---Default record length for new files
644 This environment variable specifies the default record length, in
645 bytes, for files which are opened without a @code{RECL} tag in the
646 @code{OPEN} statement. This must be a positive integer. The
647 default value is 1073741824 bytes (1 GB).
649 @node GFORTRAN_LIST_SEPARATOR
650 @section @env{GFORTRAN_LIST_SEPARATOR}---Separator for list output
652 This environment variable specifies the separator when writing
653 list-directed output. It may contain any number of spaces and
654 at most one comma. If you specify this on the command line,
655 be sure to quote spaces, as in
657 $ GFORTRAN_LIST_SEPARATOR=' , ' ./a.out
659 when @command{a.out} is the compiled Fortran program that you want to run.
660 Default is a single space.
662 @node GFORTRAN_CONVERT_UNIT
663 @section @env{GFORTRAN_CONVERT_UNIT}---Set endianness for unformatted I/O
665 By setting the @env{GFORTRAN_CONVERT_UNIT} variable, it is possible
666 to change the representation of data for unformatted files.
667 The syntax for the @env{GFORTRAN_CONVERT_UNIT} variable is:
669 GFORTRAN_CONVERT_UNIT: mode | mode ';' exception | exception ;
670 mode: 'native' | 'swap' | 'big_endian' | 'little_endian' ;
671 exception: mode ':' unit_list | unit_list ;
672 unit_list: unit_spec | unit_list unit_spec ;
673 unit_spec: INTEGER | INTEGER '-' INTEGER ;
675 The variable consists of an optional default mode, followed by
676 a list of optional exceptions, which are separated by semicolons
677 from the preceding default and each other. Each exception consists
678 of a format and a comma-separated list of units. Valid values for
679 the modes are the same as for the @code{CONVERT} specifier:
682 @item @code{NATIVE} Use the native format. This is the default.
683 @item @code{SWAP} Swap between little- and big-endian.
684 @item @code{LITTLE_ENDIAN} Use the little-endian format
685 for unformatted files.
686 @item @code{BIG_ENDIAN} Use the big-endian format for unformatted files.
688 A missing mode for an exception is taken to mean @code{BIG_ENDIAN}.
689 Examples of values for @env{GFORTRAN_CONVERT_UNIT} are:
691 @item @code{'big_endian'} Do all unformatted I/O in big_endian mode.
692 @item @code{'little_endian;native:10-20,25'} Do all unformatted I/O
693 in little_endian mode, except for units 10 to 20 and 25, which are in
695 @item @code{'10-20'} Units 10 to 20 are big-endian, the rest is native.
698 Setting the environment variables should be done on the command
699 line or via the @command{export}
700 command for @command{sh}-compatible shells and via @command{setenv}
701 for @command{csh}-compatible shells.
703 Example for @command{sh}:
706 $ GFORTRAN_CONVERT_UNIT='big_endian;native:10-20' ./a.out
709 Example code for @command{csh}:
712 % setenv GFORTRAN_CONVERT_UNIT 'big_endian;native:10-20'
716 Using anything but the native representation for unformatted data
717 carries a significant speed overhead. If speed in this area matters
718 to you, it is best if you use this only for data that needs to be
721 @xref{CONVERT specifier}, for an alternative way to specify the
722 data representation for unformatted files. @xref{Runtime Options}, for
723 setting a default data representation for the whole program. The
724 @code{CONVERT} specifier overrides the @option{-fconvert} compile options.
726 @emph{Note that the values specified via the GFORTRAN_CONVERT_UNIT
727 environment variable will override the CONVERT specifier in the
728 open statement}. This is to give control over data formats to
729 users who do not have the source code of their program available.
731 @node GFORTRAN_ERROR_DUMPCORE
732 @section @env{GFORTRAN_ERROR_DUMPCORE}---Dump core on run-time errors
734 If the @env{GFORTRAN_ERROR_DUMPCORE} variable is set to
735 @samp{y}, @samp{Y} or @samp{1} (only the first letter is relevant)
736 then library run-time errors cause core dumps. To disable the core
737 dumps, set the variable to @samp{n}, @samp{N}, @samp{0}. Default
738 is not to core dump unless the @option{-fdump-core} compile option
741 @node GFORTRAN_ERROR_BACKTRACE
742 @section @env{GFORTRAN_ERROR_BACKTRACE}---Show backtrace on run-time errors
744 If the @env{GFORTRAN_ERROR_BACKTRACE} variable is set to
745 @samp{y}, @samp{Y} or @samp{1} (only the first letter is relevant)
746 then a backtrace is printed when a run-time error occurs.
747 To disable the backtracing, set the variable to
748 @samp{n}, @samp{N}, @samp{0}. Default is not to print a backtrace
749 unless the @option{-fbacktrace} compile option
752 @c =====================================================================
753 @c PART II: LANGUAGE REFERENCE
754 @c =====================================================================
757 \part{II}{Language Reference}
760 @c ---------------------------------------------------------------------
761 @c Fortran 2003 Status
762 @c ---------------------------------------------------------------------
764 @node Fortran 2003 status
765 @chapter Fortran 2003 Status
767 Although GNU Fortran focuses on implementing the Fortran 95
768 standard for the time being, a few Fortran 2003 features are currently
773 Intrinsics @code{command_argument_count}, @code{get_command},
774 @code{get_command_argument}, @code{get_environment_variable}, and
778 @cindex array, constructors
780 Array constructors using square brackets. That is, @code{[...]} rather
784 @cindex @code{FLUSH} statement
785 @cindex statement, @code{FLUSH}
786 @code{FLUSH} statement.
789 @cindex @code{IOMSG=} specifier
790 @code{IOMSG=} specifier for I/O statements.
793 @cindex @code{ENUM} statement
794 @cindex @code{ENUMERATOR} statement
795 @cindex statement, @code{ENUM}
796 @cindex statement, @code{ENUMERATOR}
797 @opindex @code{fshort-enums}
798 Support for the declaration of enumeration constants via the
799 @code{ENUM} and @code{ENUMERATOR} statements. Interoperability with
800 @command{gcc} is guaranteed also for the case where the
801 @command{-fshort-enums} command line option is given.
808 @cindex @code{ALLOCATABLE} dummy arguments
809 @code{ALLOCATABLE} dummy arguments.
811 @cindex @code{ALLOCATABLE} function results
812 @code{ALLOCATABLE} function results
814 @cindex @code{ALLOCATABLE} components of derived types
815 @code{ALLOCATABLE} components of derived types
819 @cindex @code{STREAM} I/O
820 @cindex @code{ACCESS='STREAM'} I/O
821 The @code{OPEN} statement supports the @code{ACCESS='STREAM'} specifier,
822 allowing I/O without any record structure.
825 Namelist input/output for internal files.
828 @cindex @code{PROTECTED} statement
829 @cindex statement, @code{PROTECTED}
830 The @code{PROTECTED} statement and attribute.
833 @cindex @code{VALUE} statement
834 @cindex statement, @code{VALUE}
835 The @code{VALUE} statement and attribute.
838 @cindex @code{VOLATILE} statement
839 @cindex statement, @code{VOLATILE}
840 The @code{VOLATILE} statement and attribute.
843 @cindex @code{IMPORT} statement
844 @cindex statement, @code{IMPORT}
845 The @code{IMPORT} statement, allowing to import
846 host-associated derived types.
849 @cindex @code{USE, INTRINSIC} statement
850 @cindex statement, @code{USE, INTRINSIC}
851 @cindex @code{ISO_FORTRAN_ENV} statement
852 @cindex statement, @code{ISO_FORTRAN_ENV}
853 @code{USE} statement with @code{INTRINSIC} and @code{NON_INTRINSIC}
854 attribute; supported intrinsic modules: @code{ISO_FORTRAN_ENV},
855 @code{OMP_LIB} and @code{OMP_LIB_KINDS}.
858 Renaming of operators in the @code{USE} statement.
861 @cindex ISO C Bindings
862 Interoperability with C (ISO C Bindings)
865 BOZ as argument of INT, REAL, DBLE and CMPLX.
870 @c ---------------------------------------------------------------------
872 @c ---------------------------------------------------------------------
874 @c Maybe this chapter should be merged with the 'Standards' section,
875 @c whenever that is written :-)
881 The two sections below detail the extensions to standard Fortran that are
882 implemented in GNU Fortran, as well as some of the popular or
883 historically important extensions that are not (or not yet) implemented.
884 For the latter case, we explain the alternatives available to GNU Fortran
885 users, including replacement by standard-conforming code or GNU
889 * Extensions implemented in GNU Fortran::
890 * Extensions not implemented in GNU Fortran::
894 @node Extensions implemented in GNU Fortran
895 @section Extensions implemented in GNU Fortran
896 @cindex extensions, implemented
898 GNU Fortran implements a number of extensions over standard
899 Fortran. This chapter contains information on their syntax and
900 meaning. There are currently two categories of GNU Fortran
901 extensions, those that provide functionality beyond that provided
902 by any standard, and those that are supported by GNU Fortran
903 purely for backward compatibility with legacy compilers. By default,
904 @option{-std=gnu} allows the compiler to accept both types of
905 extensions, but to warn about the use of the latter. Specifying
906 either @option{-std=f95} or @option{-std=f2003} disables both types
907 of extensions, and @option{-std=legacy} allows both without warning.
910 * Old-style kind specifications::
911 * Old-style variable initialization::
912 * Extensions to namelist::
913 * X format descriptor without count field::
914 * Commas in FORMAT specifications::
915 * Missing period in FORMAT specifications::
917 * BOZ literal constants::
918 * Real array indices::
920 * Implicitly convert LOGICAL and INTEGER values::
921 * Hollerith constants support::
923 * CONVERT specifier::
925 * Argument list functions::
928 @node Old-style kind specifications
929 @subsection Old-style kind specifications
930 @cindex kind, old-style
932 GNU Fortran allows old-style kind specifications in declarations. These
938 where @code{TYPESPEC} is a basic type (@code{INTEGER}, @code{REAL},
939 etc.), and where @code{size} is a byte count corresponding to the
940 storage size of a valid kind for that type. (For @code{COMPLEX}
941 variables, @code{size} is the total size of the real and imaginary
942 parts.) The statement then declares @code{x}, @code{y} and @code{z} to
943 be of type @code{TYPESPEC} with the appropriate kind. This is
944 equivalent to the standard-conforming declaration
949 where @code{k} is equal to @code{size} for most types, but is equal to
950 @code{size/2} for the @code{COMPLEX} type.
952 @node Old-style variable initialization
953 @subsection Old-style variable initialization
955 GNU Fortran allows old-style initialization of variables of the
959 REAL x(2,2) /3*0.,1./
961 The syntax for the initializers is as for the @code{DATA} statement, but
962 unlike in a @code{DATA} statement, an initializer only applies to the
963 variable immediately preceding the initialization. In other words,
964 something like @code{INTEGER I,J/2,3/} is not valid. This style of
965 initialization is only allowed in declarations without double colons
966 (@code{::}); the double colons were introduced in Fortran 90, which also
967 introduced a standard syntax for initializing variables in type
970 Examples of standard-conforming code equivalent to the above example
974 INTEGER :: i = 1, j = 2
975 REAL :: x(2,2) = RESHAPE((/0.,0.,0.,1./),SHAPE(x))
979 DATA i/1/, j/2/, x/3*0.,1./
982 Note that variables which are explicitly initialized in declarations
983 or in @code{DATA} statements automatically acquire the @code{SAVE}
986 @node Extensions to namelist
987 @subsection Extensions to namelist
990 GNU Fortran fully supports the Fortran 95 standard for namelist I/O
991 including array qualifiers, substrings and fully qualified derived types.
992 The output from a namelist write is compatible with namelist read. The
993 output has all names in upper case and indentation to column 1 after the
994 namelist name. Two extensions are permitted:
996 Old-style use of @samp{$} instead of @samp{&}
999 X(:)%Y(2) = 1.0 2.0 3.0
1004 It should be noted that the default terminator is @samp{/} rather than
1007 Querying of the namelist when inputting from stdin. After at least
1008 one space, entering @samp{?} sends to stdout the namelist name and the names of
1009 the variables in the namelist:
1020 Entering @samp{=?} outputs the namelist to stdout, as if
1021 @code{WRITE(*,NML = mynml)} had been called:
1026 X(1)%Y= 0.000000 , 1.000000 , 0.000000 ,
1027 X(2)%Y= 0.000000 , 2.000000 , 0.000000 ,
1028 X(3)%Y= 0.000000 , 3.000000 , 0.000000 ,
1032 To aid this dialog, when input is from stdin, errors send their
1033 messages to stderr and execution continues, even if @code{IOSTAT} is set.
1035 @code{PRINT} namelist is permitted. This causes an error if
1036 @option{-std=f95} is used.
1039 REAL, dimension (4) :: x = (/1.0, 2.0, 3.0, 4.0/)
1042 END PROGRAM test_print
1045 Expanded namelist reads are permitted. This causes an error if
1046 @option{-std=f95} is used. In the following example, the first element
1047 of the array will be given the value 0.00 and the two succeeding
1048 elements will be given the values 1.00 and 2.00.
1051 X(1,1) = 0.00 , 1.00 , 2.00
1055 @node X format descriptor without count field
1056 @subsection @code{X} format descriptor without count field
1058 To support legacy codes, GNU Fortran permits the count field of the
1059 @code{X} edit descriptor in @code{FORMAT} statements to be omitted.
1060 When omitted, the count is implicitly assumed to be one.
1064 10 FORMAT (I1, X, I1)
1067 @node Commas in FORMAT specifications
1068 @subsection Commas in @code{FORMAT} specifications
1070 To support legacy codes, GNU Fortran allows the comma separator
1071 to be omitted immediately before and after character string edit
1072 descriptors in @code{FORMAT} statements.
1076 10 FORMAT ('FOO='I1' BAR='I2)
1080 @node Missing period in FORMAT specifications
1081 @subsection Missing period in @code{FORMAT} specifications
1083 To support legacy codes, GNU Fortran allows missing periods in format
1084 specifications if and only if @option{-std=legacy} is given on the
1085 command line. This is considered non-conforming code and is
1094 @node I/O item lists
1095 @subsection I/O item lists
1096 @cindex I/O item lists
1098 To support legacy codes, GNU Fortran allows the input item list
1099 of the @code{READ} statement, and the output item lists of the
1100 @code{WRITE} and @code{PRINT} statements, to start with a comma.
1102 @node BOZ literal constants
1103 @subsection BOZ literal constants
1104 @cindex BOZ literal constants
1106 Besides decimal constants, Fortran also supports binary (@code{b}),
1107 octal (@code{o}) and hexadecimal (@code{z}) integer constants. The
1108 syntax is: @samp{prefix quote digits quote}, were the prefix is
1109 either @code{b}, @code{o} or @code{z}, quote is either @code{'} or
1110 @code{"} and the digits are for binary @code{0} or @code{1}, for
1111 octal between @code{0} and @code{7}, and for hexadecimal between
1112 @code{0} and @code{F}. (Example: @code{b'01011101'}.)
1114 Up to Fortran 95, BOZ literals were only allowed to initialize
1115 integer variables in DATA statements. Since Fortran 2003 BOZ literals
1116 are also allowed as argument of @code{REAL}, @code{DBLE}, @code{INT}
1117 and @code{CMPLX}; the result is the same as if the integer BOZ
1118 literal had been converted by @code{TRANSFER} to, respectively,
1119 @code{real}, @code{double precision}, @code{integer} or @code{complex}.
1120 As GNU Fortran extension the intrinsic procedures @code{FLOAT},
1121 @code{DFLOAT}, @code{COMPLEX} and @code{DCMPLX} are treated alike.
1123 As an extension, GNU Fortran allows hexadecimal BOZ literal constants to
1124 be specified using the @code{X} prefix, in addition to the standard
1125 @code{Z} prefix. The BOZ literal can also be specified by adding a
1126 suffix to the string, for example, @code{Z'ABC'} and @code{'ABC'Z} are
1129 Furthermore, GNU Fortran allows using BOZ literal constants outside
1130 DATA statements and the four intrinsic functions allowed by Fortran 2003.
1131 In DATA statements, in direct assignments, where the right-hand side
1132 only contains a BOZ literal constant, and for old-style initializers of
1133 the form @code{integer i /o'0173'/}, the constant is transferred
1134 as if @code{TRANSFER} had been used; for @code{COMPLEX} numbers, only
1135 the real part is initialized unless @code{CMPLX} is used. In all other
1136 cases, the BOZ literal constant is converted to an @code{INTEGER} value with
1137 the largest decimal representation. This value is then converted
1138 numerically to the type and kind of the variable in question.
1139 (For instance @code{real :: r = b'0000001' + 1} initializes @code{r}
1140 with @code{2.0}.) As different compilers implement the extension
1141 differently, one should be careful when doing bitwise initialization
1142 of non-integer variables.
1144 Note that initializing an @code{INTEGER} variable with a statement such
1145 as @code{DATA i/Z'FFFFFFFF'/} will give an integer overflow error rather
1146 than the desired result of @math{-1} when @code{i} is a 32-bit integer
1147 on a system that supports 64-bit integers. The @samp{-fno-range-check}
1148 option can be used as a workaround for legacy code that initializes
1149 integers in this manner.
1151 @node Real array indices
1152 @subsection Real array indices
1153 @cindex array, indices of type real
1155 As an extension, GNU Fortran allows the use of @code{REAL} expressions
1156 or variables as array indices.
1158 @node Unary operators
1159 @subsection Unary operators
1160 @cindex operators, unary
1162 As an extension, GNU Fortran allows unary plus and unary minus operators
1163 to appear as the second operand of binary arithmetic operators without
1164 the need for parenthesis.
1170 @node Implicitly convert LOGICAL and INTEGER values
1171 @subsection Implicitly convert @code{LOGICAL} and @code{INTEGER} values
1172 @cindex conversion, to integer
1173 @cindex conversion, to logical
1175 As an extension for backwards compatibility with other compilers, GNU
1176 Fortran allows the implicit conversion of @code{LOGICAL} values to
1177 @code{INTEGER} values and vice versa. When converting from a
1178 @code{LOGICAL} to an @code{INTEGER}, @code{.FALSE.} is interpreted as
1179 zero, and @code{.TRUE.} is interpreted as one. When converting from
1180 @code{INTEGER} to @code{LOGICAL}, the value zero is interpreted as
1181 @code{.FALSE.} and any nonzero value is interpreted as @code{.TRUE.}.
1192 However, there is no implicit conversion of @code{INTEGER} values in
1193 @code{if}-statements, nor of @code{LOGICAL} or @code{INTEGER} values
1196 @node Hollerith constants support
1197 @subsection Hollerith constants support
1198 @cindex Hollerith constants
1200 GNU Fortran supports Hollerith constants in assignments, function
1201 arguments, and @code{DATA} and @code{ASSIGN} statements. A Hollerith
1202 constant is written as a string of characters preceded by an integer
1203 constant indicating the character count, and the letter @code{H} or
1204 @code{h}, and stored in bytewise fashion in a numeric (@code{INTEGER},
1205 @code{REAL}, or @code{complex}) or @code{LOGICAL} variable. The
1206 constant will be padded or truncated to fit the size of the variable in
1209 Examples of valid uses of Hollerith constants:
1212 data x /16Habcdefghijklmnop, 16Hqrstuvwxyz012345/
1213 x(1) = 16HABCDEFGHIJKLMNOP
1217 Invalid Hollerith constants examples:
1220 a = 8H12345678 ! Valid, but the Hollerith constant will be truncated.
1221 a = 0H ! At least one character is needed.
1224 In general, Hollerith constants were used to provide a rudimentary
1225 facility for handling character strings in early Fortran compilers,
1226 prior to the introduction of @code{CHARACTER} variables in Fortran 77;
1227 in those cases, the standard-compliant equivalent is to convert the
1228 program to use proper character strings. On occasion, there may be a
1229 case where the intent is specifically to initialize a numeric variable
1230 with a given byte sequence. In these cases, the same result can be
1231 obtained by using the @code{TRANSFER} statement, as in this example.
1233 INTEGER(KIND=4) :: a
1234 a = TRANSFER ("abcd", a) ! equivalent to: a = 4Habcd
1239 @subsection Cray pointers
1240 @cindex pointer, Cray
1242 Cray pointers are part of a non-standard extension that provides a
1243 C-like pointer in Fortran. This is accomplished through a pair of
1244 variables: an integer "pointer" that holds a memory address, and a
1245 "pointee" that is used to dereference the pointer.
1247 Pointer/pointee pairs are declared in statements of the form:
1249 pointer ( <pointer> , <pointee> )
1253 pointer ( <pointer1> , <pointee1> ), ( <pointer2> , <pointee2> ), ...
1255 The pointer is an integer that is intended to hold a memory address.
1256 The pointee may be an array or scalar. A pointee can be an assumed
1257 size array---that is, the last dimension may be left unspecified by
1258 using a @code{*} in place of a value---but a pointee cannot be an
1259 assumed shape array. No space is allocated for the pointee.
1261 The pointee may have its type declared before or after the pointer
1262 statement, and its array specification (if any) may be declared
1263 before, during, or after the pointer statement. The pointer may be
1264 declared as an integer prior to the pointer statement. However, some
1265 machines have default integer sizes that are different than the size
1266 of a pointer, and so the following code is not portable:
1271 If a pointer is declared with a kind that is too small, the compiler
1272 will issue a warning; the resulting binary will probably not work
1273 correctly, because the memory addresses stored in the pointers may be
1274 truncated. It is safer to omit the first line of the above example;
1275 if explicit declaration of ipt's type is omitted, then the compiler
1276 will ensure that ipt is an integer variable large enough to hold a
1279 Pointer arithmetic is valid with Cray pointers, but it is not the same
1280 as C pointer arithmetic. Cray pointers are just ordinary integers, so
1281 the user is responsible for determining how many bytes to add to a
1282 pointer in order to increment it. Consider the following example:
1286 pointer (ipt, pointee)
1290 The last statement does not set @code{ipt} to the address of
1291 @code{target(1)}, as it would in C pointer arithmetic. Adding @code{1}
1292 to @code{ipt} just adds one byte to the address stored in @code{ipt}.
1294 Any expression involving the pointee will be translated to use the
1295 value stored in the pointer as the base address.
1297 To get the address of elements, this extension provides an intrinsic
1298 function @code{LOC()}. The @code{LOC()} function is equivalent to the
1299 @code{&} operator in C, except the address is cast to an integer type:
1302 pointer(ipt, arpte(10))
1304 ipt = loc(ar) ! Makes arpte is an alias for ar
1305 arpte(1) = 1.0 ! Sets ar(1) to 1.0
1307 The pointer can also be set by a call to the @code{MALLOC} intrinsic
1310 Cray pointees often are used to alias an existing variable. For
1318 As long as @code{ipt} remains unchanged, @code{iarr} is now an alias for
1319 @code{target}. The optimizer, however, will not detect this aliasing, so
1320 it is unsafe to use @code{iarr} and @code{target} simultaneously. Using
1321 a pointee in any way that violates the Fortran aliasing rules or
1322 assumptions is illegal. It is the user's responsibility to avoid doing
1323 this; the compiler works under the assumption that no such aliasing
1326 Cray pointers will work correctly when there is no aliasing (i.e., when
1327 they are used to access a dynamically allocated block of memory), and
1328 also in any routine where a pointee is used, but any variable with which
1329 it shares storage is not used. Code that violates these rules may not
1330 run as the user intends. This is not a bug in the optimizer; any code
1331 that violates the aliasing rules is illegal. (Note that this is not
1332 unique to GNU Fortran; any Fortran compiler that supports Cray pointers
1333 will ``incorrectly'' optimize code with illegal aliasing.)
1335 There are a number of restrictions on the attributes that can be applied
1336 to Cray pointers and pointees. Pointees may not have the
1337 @code{ALLOCATABLE}, @code{INTENT}, @code{OPTIONAL}, @code{DUMMY},
1338 @code{TARGET}, @code{INTRINSIC}, or @code{POINTER} attributes. Pointers
1339 may not have the @code{DIMENSION}, @code{POINTER}, @code{TARGET},
1340 @code{ALLOCATABLE}, @code{EXTERNAL}, or @code{INTRINSIC} attributes.
1341 Pointees may not occur in more than one pointer statement. A pointee
1342 cannot be a pointer. Pointees cannot occur in equivalence, common, or
1345 A Cray pointer may also point to a function or a subroutine. For
1346 example, the following excerpt is valid:
1350 pointer (subptr,subpte)
1360 A pointer may be modified during the course of a program, and this
1361 will change the location to which the pointee refers. However, when
1362 pointees are passed as arguments, they are treated as ordinary
1363 variables in the invoked function. Subsequent changes to the pointer
1364 will not change the base address of the array that was passed.
1366 @node CONVERT specifier
1367 @subsection @code{CONVERT} specifier
1368 @cindex @code{CONVERT} specifier
1370 GNU Fortran allows the conversion of unformatted data between little-
1371 and big-endian representation to facilitate moving of data
1372 between different systems. The conversion can be indicated with
1373 the @code{CONVERT} specifier on the @code{OPEN} statement.
1374 @xref{GFORTRAN_CONVERT_UNIT}, for an alternative way of specifying
1375 the data format via an environment variable.
1377 Valid values for @code{CONVERT} are:
1379 @item @code{CONVERT='NATIVE'} Use the native format. This is the default.
1380 @item @code{CONVERT='SWAP'} Swap between little- and big-endian.
1381 @item @code{CONVERT='LITTLE_ENDIAN'} Use the little-endian representation
1382 for unformatted files.
1383 @item @code{CONVERT='BIG_ENDIAN'} Use the big-endian representation for
1387 Using the option could look like this:
1389 open(file='big.dat',form='unformatted',access='sequential', &
1390 convert='big_endian')
1393 The value of the conversion can be queried by using
1394 @code{INQUIRE(CONVERT=ch)}. The values returned are
1395 @code{'BIG_ENDIAN'} and @code{'LITTLE_ENDIAN'}.
1397 @code{CONVERT} works between big- and little-endian for
1398 @code{INTEGER} values of all supported kinds and for @code{REAL}
1399 on IEEE systems of kinds 4 and 8. Conversion between different
1400 ``extended double'' types on different architectures such as
1401 m68k and x86_64, which GNU Fortran
1402 supports as @code{REAL(KIND=10)} and @code{REAL(KIND=16)}, will
1405 @emph{Note that the values specified via the GFORTRAN_CONVERT_UNIT
1406 environment variable will override the CONVERT specifier in the
1407 open statement}. This is to give control over data formats to
1408 users who do not have the source code of their program available.
1410 Using anything but the native representation for unformatted data
1411 carries a significant speed overhead. If speed in this area matters
1412 to you, it is best if you use this only for data that needs to be
1419 OpenMP (Open Multi-Processing) is an application programming
1420 interface (API) that supports multi-platform shared memory
1421 multiprocessing programming in C/C++ and Fortran on many
1422 architectures, including Unix and Microsoft Windows platforms.
1423 It consists of a set of compiler directives, library routines,
1424 and environment variables that influence run-time behavior.
1426 GNU Fortran strives to be compatible to the
1427 @uref{http://www.openmp.org/drupal/mp-documents/spec25.pdf,
1428 OpenMP Application Program Interface v2.5}.
1430 To enable the processing of the OpenMP directive @code{!$omp} in
1431 free-form source code; the @code{c$omp}, @code{*$omp} and @code{!$omp}
1432 directives in fixed form; the @code{!$} conditional compilation sentinels
1433 in free form; and the @code{c$}, @code{*$} and @code{!$} sentinels
1434 in fixed form, @command{gfortran} needs to be invoked with the
1435 @option{-fopenmp}. This also arranges for automatic linking of the
1436 GNU OpenMP runtime library @ref{Top,,libgomp,libgomp,GNU OpenMP
1439 The OpenMP Fortran runtime library routines are provided both in a
1440 form of a Fortran 90 module named @code{omp_lib} and in a form of
1441 a Fortran @code{include} file named @file{omp_lib.h}.
1443 An example of a parallelized loop taken from Appendix A.1 of
1444 the OpenMP Application Program Interface v2.5:
1446 SUBROUTINE A1(N, A, B)
1449 !$OMP PARALLEL DO !I is private by default
1451 B(I) = (A(I) + A(I-1)) / 2.0
1453 !$OMP END PARALLEL DO
1460 @option{-fopenmp} implies @option{-frecursive}, i.e., all local arrays
1461 will be allocated on the stack. When porting existing code to OpenMP,
1462 this may lead to surprising results, especially to segmentation faults
1463 if the stacksize is limited.
1466 On glibc-based systems, OpenMP enabled applications can not be statically
1467 linked due to limitations of the underlying pthreads-implementation. It
1468 might be possible to get a working solution if
1469 @command{-Wl,--whole-archive -lpthread -Wl,--no-whole-archive} is added
1470 to the command line. However, this is not supported by @command{gcc} and
1471 thus not recommended.
1474 @node Argument list functions
1475 @subsection Argument list functions @code{%VAL}, @code{%REF} and @code{%LOC}
1476 @cindex argument list functions
1481 GNU Fortran supports argument list functions @code{%VAL}, @code{%REF}
1482 and @code{%LOC} statements, for backward compatibility with g77.
1483 It is recommended that these should be used only for code that is
1484 accessing facilities outside of GNU Fortran, such as operating system
1485 or windowing facilities. It is best to constrain such uses to isolated
1486 portions of a program--portions that deal specifically and exclusively
1487 with low-level, system-dependent facilities. Such portions might well
1488 provide a portable interface for use by the program as a whole, but are
1489 themselves not portable, and should be thoroughly tested each time they
1490 are rebuilt using a new compiler or version of a compiler.
1492 @code{%VAL} passes a scalar argument by value, @code{%REF} passes it by
1493 reference and @code{%LOC} passes its memory location. Since gfortran
1494 already passes scalar arguments by reference, @code{%REF} is in effect
1495 a do-nothing. @code{%LOC} has the same effect as a fortran pointer.
1497 An example of passing an argument by value to a C subroutine foo.:
1500 C prototype void foo_ (float x);
1509 For details refer to the g77 manual
1510 @uref{http://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/index.html#Top}.
1512 Also, the gfortran testsuite c_by_val.f and its partner c_by_val.c are
1517 @node Extensions not implemented in GNU Fortran
1518 @section Extensions not implemented in GNU Fortran
1519 @cindex extensions, not implemented
1521 The long history of the Fortran language, its wide use and broad
1522 userbase, the large number of different compiler vendors and the lack of
1523 some features crucial to users in the first standards have lead to the
1524 existence of an important number of extensions to the language. While
1525 some of the most useful or popular extensions are supported by the GNU
1526 Fortran compiler, not all existing extensions are supported. This section
1527 aims at listing these extensions and offering advice on how best make
1528 code that uses them running with the GNU Fortran compiler.
1530 @c More can be found here:
1531 @c -- http://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/Missing-Features.html
1532 @c -- the list of fortran and libgfortran bugs closed as WONTFIX:
1533 @c http://tinyurl.com/2u4h5y
1536 * STRUCTURE and RECORD::
1537 @c * UNION and MAP::
1538 * ENCODE and DECODE statements::
1539 @c * Expressions in FORMAT statements::
1540 @c * Q edit descriptor::
1541 @c * AUTOMATIC statement::
1542 @c * TYPE and ACCEPT I/O Statements::
1543 @c * .XOR. operator::
1544 @c * CARRIAGECONTROL, DEFAULTFILE, DISPOSE and RECORDTYPE I/O specifiers::
1545 @c * Omitted arguments in procedure call:
1549 @node STRUCTURE and RECORD
1550 @subsection @code{STRUCTURE} and @code{RECORD}
1551 @cindex @code{STRUCTURE}
1552 @cindex @code{RECORD}
1554 Structures are user-defined aggregate data types; this functionality was
1555 standardized in Fortran 90 with an different syntax, under the name of
1556 ``derived types''. Here is an example of code using the non portable
1560 ! Declaring a structure named ``item'' and containing three fields:
1561 ! an integer ID, an description string and a floating-point price.
1564 CHARACTER(LEN=200) description
1568 ! Define two variables, an single record of type ``item''
1569 ! named ``pear'', and an array of items named ``store_catalog''
1570 RECORD /item/ pear, store_catalog(100)
1572 ! We can directly access the fields of both variables
1574 pear.description = "juicy D'Anjou pear"
1576 store_catalog(7).id = 7831
1577 store_catalog(7).description = "milk bottle"
1578 store_catalog(7).price = 1.2
1580 ! We can also manipulates the whole structure
1581 store_catalog(12) = pear
1582 print *, store_catalog(12)
1586 This code can easily be rewritten in the Fortran 90 syntax as following:
1589 ! ``STRUCTURE /name/ ... END STRUCTURE'' becomes
1590 ! ``TYPE name ... END TYPE''
1593 CHARACTER(LEN=200) description
1597 ! ``RECORD /name/ variable'' becomes ``TYPE(name) variable''
1598 TYPE(item) pear, store_catalog(100)
1600 ! Instead of using a dot (.) to access fields of a record, the
1601 ! standard syntax uses a percent sign (%)
1603 pear%description = "juicy D'Anjou pear"
1605 store_catalog(7)%id = 7831
1606 store_catalog(7)%description = "milk bottle"
1607 store_catalog(7)%price = 1.2
1609 ! Assignments of a whole variable don't change
1610 store_catalog(12) = pear
1611 print *, store_catalog(12)
1615 @c @node UNION and MAP
1616 @c @subsection @code{UNION} and @code{MAP}
1617 @c @cindex @code{UNION}
1618 @c @cindex @code{MAP}
1620 @c For help writing this one, see
1621 @c http://www.eng.umd.edu/~nsw/ench250/fortran1.htm#UNION and
1622 @c http://www.tacc.utexas.edu/services/userguides/pgi/pgiws_ug/pgi32u06.htm
1625 @node ENCODE and DECODE statements
1626 @subsection @code{ENCODE} and @code{DECODE} statements
1627 @cindex @code{ENCODE}
1628 @cindex @code{DECODE}
1630 GNU Fortran doesn't support the @code{ENCODE} and @code{DECODE}
1631 statements. These statements are best replaced by @code{READ} and
1632 @code{WRITE} statements involving internal files (@code{CHARACTER}
1633 variables and arrays), which have been part of the Fortran standard since
1634 Fortran 77. For example, replace a code fragment like
1639 c ... Code that sets LINE
1640 DECODE (80, 9000, LINE) A, B, C
1641 9000 FORMAT (1X, 3(F10.5))
1648 CHARACTER(LEN=80) LINE
1650 c ... Code that sets LINE
1651 READ (UNIT=LINE, FMT=9000) A, B, C
1652 9000 FORMAT (1X, 3(F10.5))
1655 Similarly, replace a code fragment like
1660 c ... Code that sets A, B and C
1661 ENCODE (80, 9000, LINE) A, B, C
1662 9000 FORMAT (1X, 'OUTPUT IS ', 3(F10.5))
1671 c ... Code that sets A, B and C
1672 WRITE (UNIT=LINE, FMT=9000) A, B, C
1673 9000 FORMAT (1X, 'OUTPUT IS ', 3(F10.5))
1677 @c ---------------------------------------------------------------------
1678 @c Intrinsic Procedures
1679 @c ---------------------------------------------------------------------
1681 @include intrinsic.texi
1688 @c ---------------------------------------------------------------------
1690 @c ---------------------------------------------------------------------
1693 @unnumbered Contributing
1694 @cindex Contributing
1696 Free software is only possible if people contribute to efforts
1698 We're always in need of more people helping out with ideas
1699 and comments, writing documentation and contributing code.
1701 If you want to contribute to GNU Fortran,
1702 have a look at the long lists of projects you can take on.
1703 Some of these projects are small,
1704 some of them are large;
1705 some are completely orthogonal to the rest of what is
1706 happening on GNU Fortran,
1707 but others are ``mainstream'' projects in need of enthusiastic hackers.
1708 All of these projects are important!
1709 We'll eventually get around to the things here,
1710 but they are also things doable by someone who is willing and able.
1715 * Proposed Extensions::
1720 @section Contributors to GNU Fortran
1721 @cindex Contributors
1725 Most of the parser was hand-crafted by @emph{Andy Vaught}, who is
1726 also the initiator of the whole project. Thanks Andy!
1727 Most of the interface with GCC was written by @emph{Paul Brook}.
1729 The following individuals have contributed code and/or
1730 ideas and significant help to the GNU Fortran project
1731 (in alphabetical order):
1734 @item Janne Blomqvist
1735 @item Steven Bosscher
1738 @item Fran@,{c}ois-Xavier Coudert
1742 @item Bernhard Fischer
1744 @item Richard Guenther
1745 @item Richard Henderson
1746 @item Katherine Holcomb
1748 @item Niels Kristian Bech Jensen
1749 @item Steven Johnson
1750 @item Steven G. Kargl
1758 @item Christopher D. Rickett
1759 @item Richard Sandiford
1760 @item Tobias Schl@"uter
1768 The following people have contributed bug reports,
1769 smaller or larger patches,
1770 and much needed feedback and encouragement for the
1771 GNU Fortran project:
1775 @item Dominique d'Humi@`eres
1777 @item Erik Schnetter
1780 Many other individuals have helped debug,
1781 test and improve the GNU Fortran compiler over the past few years,
1782 and we welcome you to do the same!
1783 If you already have done so,
1784 and you would like to see your name listed in the
1785 list above, please contact us.
1793 @item Help build the test suite
1794 Solicit more code for donation to the test suite: the more extensive the
1795 testsuite, the smaller the risk of breaking things in the future! We can
1796 keep code private on request.
1798 @item Bug hunting/squishing
1799 Find bugs and write more test cases! Test cases are especially very
1800 welcome, because it allows us to concentrate on fixing bugs instead of
1801 isolating them. Going through the bugzilla database at
1802 @url{http://gcc.gnu.org/bugzilla/} to reduce testcases posted there and
1803 add more information (for example, for which version does the testcase
1804 work, for which versions does it fail?) is also very helpful.
1809 @node Proposed Extensions
1810 @section Proposed Extensions
1812 Here's a list of proposed extensions for the GNU Fortran compiler, in no particular
1813 order. Most of these are necessary to be fully compatible with
1814 existing Fortran compilers, but they are not part of the official
1815 J3 Fortran 95 standard.
1817 @subsection Compiler extensions:
1820 User-specified alignment rules for structures.
1823 Flag to generate @code{Makefile} info.
1826 Automatically extend single precision constants to double.
1829 Compile code that conserves memory by dynamically allocating common and
1830 module storage either on stack or heap.
1833 Compile flag to generate code for array conformance checking (suggest -CC).
1836 User control of symbol names (underscores, etc).
1839 Compile setting for maximum size of stack frame size before spilling
1840 parts to static or heap.
1843 Flag to force local variables into static space.
1846 Flag to force local variables onto stack.
1850 @subsection Environment Options
1853 Pluggable library modules for random numbers, linear algebra.
1854 LA should use BLAS calling conventions.
1857 Environment variables controlling actions on arithmetic exceptions like
1858 overflow, underflow, precision loss---Generate NaN, abort, default.
1862 Set precision for fp units that support it (i387).
1865 Variable for setting fp rounding mode.
1868 Variable to fill uninitialized variables with a user-defined bit
1872 Environment variable controlling filename that is opened for that unit
1876 Environment variable to clear/trash memory being freed.
1879 Environment variable to control tracing of allocations and frees.
1882 Environment variable to display allocated memory at normal program end.
1885 Environment variable for filename for * IO-unit.
1888 Environment variable for temporary file directory.
1891 Environment variable forcing standard output to be line buffered (unix).
1896 @c ---------------------------------------------------------------------
1897 @c GNU General Public License
1898 @c ---------------------------------------------------------------------
1904 @c ---------------------------------------------------------------------
1905 @c GNU Free Documentation License
1906 @c ---------------------------------------------------------------------
1912 @c ---------------------------------------------------------------------
1913 @c Funding Free Software
1914 @c ---------------------------------------------------------------------
1916 @include funding.texi
1918 @c ---------------------------------------------------------------------
1920 @c ---------------------------------------------------------------------
1923 @unnumbered Option Index
1924 @command{gfortran}'s command line options are indexed here without any
1925 initial @samp{-} or @samp{--}. Where an option has both positive and
1926 negative forms (such as -foption and -fno-option), relevant entries in
1927 the manual are indexed under the most appropriate form; it may sometimes
1928 be useful to look up both forms.
1932 @unnumbered Keyword Index