1 \input texinfo @c -*-texinfo-*-
3 @setfilename gfortran.info
4 @set copyrights-gfortran 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011
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.
19 @c TODO: The following "Part" definitions are included here temporarily
20 @c until they are incorporated into the official Texinfo distribution.
21 @c They borrow heavily from Texinfo's \unnchapentry definitions.
28 \vglue\titlepagetopglue
30 \leftline{Part #1:@* #2}
31 \vskip4pt \hrule height 4pt width \hsize \vskip4pt
33 \writetocentry{part}{#2}{#1}
36 \writetocentry{blankpart}{}{}
38 % Part TOC-entry definition for summary contents.
39 \gdef\dosmallpartentry#1#2#3#4{%
40 \vskip .5\baselineskip plus.2\baselineskip
43 \tocentry{Part #2: #1}{\doshortpageno\bgroup#4\egroup}
46 \gdef\dosmallblankpartentry#1#2#3#4{%
47 \vskip .5\baselineskip plus.2\baselineskip
49 % Part TOC-entry definition for regular contents. This has to be
50 % equated to an existing entry to not cause problems when the PDF
52 \gdef\dopartentry#1#2#3#4{%
53 \unnchapentry{Part #2: #1}{}{#3}{#4}
55 \gdef\doblankpartentry#1#2#3#4{}
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 1.3 or
84 any later version published by the Free Software Foundation; with the
85 Invariant Sections being ``Funding Free Software'', the Front-Cover
86 Texts being (a) (see below), and with the Back-Cover Texts being (b)
87 (see below). A copy of the license is included in the section entitled
88 ``GNU Free Documentation License''.
90 (a) The FSF's Front-Cover Text is:
94 (b) The FSF's Back-Cover Text is:
96 You have freedom to copy and modify this GNU Manual, like GNU
97 software. Copies published by the Free Software Foundation raise
98 funds for GNU development.
102 @dircategory Software development
104 * gfortran: (gfortran). The GNU Fortran Compiler.
106 This file documents the use and the internals of
107 the GNU Fortran compiler, (@command{gfortran}).
109 Published by the Free Software Foundation
110 51 Franklin Street, Fifth Floor
111 Boston, MA 02110-1301 USA
117 @setchapternewpage odd
119 @title Using GNU Fortran
121 @author The @t{gfortran} team
123 @vskip 0pt plus 1filll
124 Published by the Free Software Foundation@*
125 51 Franklin Street, Fifth Floor@*
126 Boston, MA 02110-1301, USA@*
127 @c Last printed ??ber, 19??.@*
128 @c Printed copies are available for $? each.@*
134 @c TODO: The following "Part" definitions are included here temporarily
135 @c until they are incorporated into the official Texinfo distribution.
138 \global\let\partentry=\dosmallpartentry
139 \global\let\blankpartentry=\dosmallblankpartentry
144 \global\let\partentry=\dopartentry
145 \global\let\blankpartentry=\doblankpartentry
151 @c ---------------------------------------------------------------------
152 @c TexInfo table of contents.
153 @c ---------------------------------------------------------------------
160 This manual documents the use of @command{gfortran},
161 the GNU Fortran compiler. You can find in this manual how to invoke
162 @command{gfortran}, as well as its features and incompatibilities.
165 @emph{Warning:} This document, and the compiler it describes, are still
166 under development. While efforts are made to keep it up-to-date, it might
167 not accurately reflect the status of the most recent GNU Fortran compiler.
171 @comment When you add a new menu item, please keep the right hand
172 @comment aligned to the same column. Do not use tabs. This provides
173 @comment better formatting.
178 Part I: Invoking GNU Fortran
179 * Invoking GNU Fortran:: Command options supported by @command{gfortran}.
180 * Runtime:: Influencing runtime behavior with environment variables.
182 Part II: Language Reference
183 * Fortran 2003 and 2008 status:: Fortran 2003 and 2008 features supported by GNU Fortran.
184 * Compiler Characteristics:: User-visible implementation details.
185 * Mixed-Language Programming:: Interoperability with C
186 * Extensions:: Language extensions implemented by GNU Fortran.
187 * Intrinsic Procedures:: Intrinsic procedures supported by GNU Fortran.
188 * Intrinsic Modules:: Intrinsic modules supported by GNU Fortran.
190 * Contributing:: How you can help.
191 * Copying:: GNU General Public License says
192 how you can copy and share GNU Fortran.
193 * GNU Free Documentation License::
194 How you can copy and share this manual.
195 * Funding:: How to help assure continued work for free software.
196 * Option Index:: Index of command line options
197 * Keyword Index:: Index of concepts
201 @c ---------------------------------------------------------------------
203 @c ---------------------------------------------------------------------
206 @chapter Introduction
208 @c The following duplicates the text on the TexInfo table of contents.
210 This manual documents the use of @command{gfortran}, the GNU Fortran
211 compiler. You can find in this manual how to invoke @command{gfortran},
212 as well as its features and incompatibilities.
215 @emph{Warning:} This document, and the compiler it describes, are still
216 under development. While efforts are made to keep it up-to-date, it
217 might not accurately reflect the status of the most recent GNU Fortran
222 The GNU Fortran compiler front end was
223 designed initially as a free replacement for,
224 or alternative to, the unix @command{f95} command;
225 @command{gfortran} is the command you'll use to invoke the compiler.
228 * About GNU Fortran:: What you should know about the GNU Fortran compiler.
229 * GNU Fortran and GCC:: You can compile Fortran, C, or other programs.
230 * Preprocessing and conditional compilation:: The Fortran preprocessor
231 * GNU Fortran and G77:: Why we chose to start from scratch.
232 * Project Status:: Status of GNU Fortran, roadmap, proposed extensions.
233 * Standards:: Standards supported by GNU Fortran.
237 @c ---------------------------------------------------------------------
239 @c ---------------------------------------------------------------------
241 @node About GNU Fortran
242 @section About GNU Fortran
244 The GNU Fortran compiler supports the Fortran 77, 90 and 95 standards
245 completely, parts of the Fortran 2003 and Fortran 2008 standards, and
246 several vendor extensions. The development goal is to provide the
251 Read a user's program,
252 stored in a file and containing instructions written
253 in Fortran 77, Fortran 90, Fortran 95, Fortran 2003 or Fortran 2008.
254 This file contains @dfn{source code}.
257 Translate the user's program into instructions a computer
258 can carry out more quickly than it takes to translate the
259 instructions in the first
260 place. The result after compilation of a program is
262 code designed to be efficiently translated and processed
263 by a machine such as your computer.
264 Humans usually aren't as good writing machine code
265 as they are at writing Fortran (or C++, Ada, or Java),
266 because it is easy to make tiny mistakes writing machine code.
269 Provide the user with information about the reasons why
270 the compiler is unable to create a binary from the source code.
271 Usually this will be the case if the source code is flawed.
272 The Fortran 90 standard requires that the compiler can point out
273 mistakes to the user.
274 An incorrect usage of the language causes an @dfn{error message}.
276 The compiler will also attempt to diagnose cases where the
277 user's program contains a correct usage of the language,
278 but instructs the computer to do something questionable.
279 This kind of diagnostics message is called a @dfn{warning message}.
282 Provide optional information about the translation passes
283 from the source code to machine code.
284 This can help a user of the compiler to find the cause of
285 certain bugs which may not be obvious in the source code,
286 but may be more easily found at a lower level compiler output.
287 It also helps developers to find bugs in the compiler itself.
290 Provide information in the generated machine code that can
291 make it easier to find bugs in the program (using a debugging tool,
292 called a @dfn{debugger}, such as the GNU Debugger @command{gdb}).
295 Locate and gather machine code already generated to
296 perform actions requested by statements in the user's program.
297 This machine code is organized into @dfn{modules} and is located
298 and @dfn{linked} to the user program.
301 The GNU Fortran compiler consists of several components:
305 A version of the @command{gcc} command
306 (which also might be installed as the system's @command{cc} command)
307 that also understands and accepts Fortran source code.
308 The @command{gcc} command is the @dfn{driver} program for
309 all the languages in the GNU Compiler Collection (GCC);
311 you can compile the source code of any language for
312 which a front end is available in GCC.
315 The @command{gfortran} command itself,
316 which also might be installed as the
317 system's @command{f95} command.
318 @command{gfortran} is just another driver program,
319 but specifically for the Fortran compiler only.
320 The difference with @command{gcc} is that @command{gfortran}
321 will automatically link the correct libraries to your program.
324 A collection of run-time libraries.
325 These libraries contain the machine code needed to support
326 capabilities of the Fortran language that are not directly
327 provided by the machine code generated by the
328 @command{gfortran} compilation phase,
329 such as intrinsic functions and subroutines,
330 and routines for interaction with files and the operating system.
331 @c and mechanisms to spawn,
332 @c unleash and pause threads in parallelized code.
335 The Fortran compiler itself, (@command{f951}).
336 This is the GNU Fortran parser and code generator,
337 linked to and interfaced with the GCC backend library.
338 @command{f951} ``translates'' the source code to
339 assembler code. You would typically not use this
341 instead, the @command{gcc} or @command{gfortran} driver
342 programs will call it for you.
346 @c ---------------------------------------------------------------------
347 @c GNU Fortran and GCC
348 @c ---------------------------------------------------------------------
350 @node GNU Fortran and GCC
351 @section GNU Fortran and GCC
352 @cindex GNU Compiler Collection
355 GNU Fortran is a part of GCC, the @dfn{GNU Compiler Collection}. GCC
356 consists of a collection of front ends for various languages, which
357 translate the source code into a language-independent form called
358 @dfn{GENERIC}. This is then processed by a common middle end which
359 provides optimization, and then passed to one of a collection of back
360 ends which generate code for different computer architectures and
363 Functionally, this is implemented with a driver program (@command{gcc})
364 which provides the command-line interface for the compiler. It calls
365 the relevant compiler front-end program (e.g., @command{f951} for
366 Fortran) for each file in the source code, and then calls the assembler
367 and linker as appropriate to produce the compiled output. In a copy of
368 GCC which has been compiled with Fortran language support enabled,
369 @command{gcc} will recognize files with @file{.f}, @file{.for}, @file{.ftn},
370 @file{.f90}, @file{.f95}, @file{.f03} and @file{.f08} extensions as
371 Fortran source code, and compile it accordingly. A @command{gfortran}
372 driver program is also provided, which is identical to @command{gcc}
373 except that it automatically links the Fortran runtime libraries into the
376 Source files with @file{.f}, @file{.for}, @file{.fpp}, @file{.ftn}, @file{.F},
377 @file{.FOR}, @file{.FPP}, and @file{.FTN} extensions are treated as fixed form.
378 Source files with @file{.f90}, @file{.f95}, @file{.f03}, @file{.f08},
379 @file{.F90}, @file{.F95}, @file{.F03} and @file{.F08} extensions are
380 treated as free form. The capitalized versions of either form are run
381 through preprocessing. Source files with the lower case @file{.fpp}
382 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
403 @cindex preprocessor, include file handling
405 Many Fortran compilers including GNU Fortran allow passing the source code
406 through a C preprocessor (CPP; sometimes also called the Fortran preprocessor,
407 FPP) to allow for conditional compilation. In the case of GNU Fortran,
408 this is the GNU C Preprocessor in the traditional mode. On systems with
409 case-preserving file names, the preprocessor is automatically invoked if the
410 filename extension is @file{.F}, @file{.FOR}, @file{.FTN}, @file{.fpp},
411 @file{.FPP}, @file{.F90}, @file{.F95}, @file{.F03} or @file{.F08}. To manually
412 invoke the preprocessor on any file, use @option{-cpp}, to disable
413 preprocessing on files where the preprocessor is run automatically, use
416 If a preprocessed file includes another file with the Fortran @code{INCLUDE}
417 statement, the included file is not preprocessed. To preprocess included
418 files, use the equivalent preprocessor statement @code{#include}.
420 If GNU Fortran invokes the preprocessor, @code{__GFORTRAN__}
421 is defined and @code{__GNUC__}, @code{__GNUC_MINOR__} and
422 @code{__GNUC_PATCHLEVEL__} can be used to determine the version of the
423 compiler. See @ref{Top,,Overview,cpp,The C Preprocessor} for details.
425 While CPP is the de-facto standard for preprocessing Fortran code,
426 Part 3 of the Fortran 95 standard (ISO/IEC 1539-3:1998) defines
427 Conditional Compilation, which is not widely used and not directly
428 supported by the GNU Fortran compiler. You can use the program coco
429 to preprocess such files (@uref{http://www.daniellnagle.com/coco.html}).
432 @c ---------------------------------------------------------------------
433 @c GNU Fortran and G77
434 @c ---------------------------------------------------------------------
436 @node GNU Fortran and G77
437 @section GNU Fortran and G77
439 @cindex @command{g77}
441 The GNU Fortran compiler is the successor to @command{g77}, the Fortran
442 77 front end included in GCC prior to version 4. It is an entirely new
443 program that has been designed to provide Fortran 95 support and
444 extensibility for future Fortran language standards, as well as providing
445 backwards compatibility for Fortran 77 and nearly all of the GNU language
446 extensions supported by @command{g77}.
449 @c ---------------------------------------------------------------------
451 @c ---------------------------------------------------------------------
454 @section Project Status
457 As soon as @command{gfortran} can parse all of the statements correctly,
458 it will be in the ``larva'' state.
459 When we generate code, the ``puppa'' state.
460 When @command{gfortran} is done,
461 we'll see if it will be a beautiful butterfly,
462 or just a big bug....
464 --Andy Vaught, April 2000
467 The start of the GNU Fortran 95 project was announced on
468 the GCC homepage in March 18, 2000
469 (even though Andy had already been working on it for a while,
472 The GNU Fortran compiler is able to compile nearly all
473 standard-compliant Fortran 95, Fortran 90, and Fortran 77 programs,
474 including a number of standard and non-standard extensions, and can be
475 used on real-world programs. In particular, the supported extensions
476 include OpenMP, Cray-style pointers, and several Fortran 2003 and Fortran
477 2008 features, including TR 15581. However, it is still under
478 development and has a few remaining rough edges.
480 At present, the GNU Fortran compiler passes the
481 @uref{http://www.fortran-2000.com/ArnaudRecipes/fcvs21_f95.html,
482 NIST Fortran 77 Test Suite}, and produces acceptable results on the
483 @uref{http://www.netlib.org/lapack/faq.html#1.21, LAPACK Test Suite}.
484 It also provides respectable performance on
485 the @uref{http://www.polyhedron.com/pb05.html, Polyhedron Fortran
486 compiler benchmarks} and the
487 @uref{http://www.llnl.gov/asci_benchmarks/asci/limited/lfk/README.html,
488 Livermore Fortran Kernels test}. It has been used to compile a number of
489 large real-world programs, including
490 @uref{http://mysite.verizon.net/serveall/moene.pdf, the HIRLAM
491 weather-forecasting code} and
492 @uref{http://www.theochem.uwa.edu.au/tonto/, the Tonto quantum
493 chemistry package}; see @url{http://gcc.gnu.org/@/wiki/@/GfortranApps} for an
496 Among other things, the GNU Fortran compiler is intended as a replacement
497 for G77. At this point, nearly all programs that could be compiled with
498 G77 can be compiled with GNU Fortran, although there are a few minor known
501 The primary work remaining to be done on GNU Fortran falls into three
502 categories: bug fixing (primarily regarding the treatment of invalid code
503 and providing useful error messages), improving the compiler optimizations
504 and the performance of compiled code, and extending the compiler to support
505 future standards---in particular, Fortran 2003 and Fortran 2008.
508 @c ---------------------------------------------------------------------
510 @c ---------------------------------------------------------------------
517 * Varying Length Character Strings::
520 The GNU Fortran compiler implements
521 ISO/IEC 1539:1997 (Fortran 95). As such, it can also compile essentially all
522 standard-compliant Fortran 90 and Fortran 77 programs. It also supports
523 the ISO/IEC TR-15581 enhancements to allocatable arrays.
525 In the future, the GNU Fortran compiler will also support ISO/IEC
526 1539-1:2004 (Fortran 2003), ISO/IEC 1539-1:2010 (Fortran 2008) and
527 future Fortran standards. Partial support of the Fortran 2003 and
528 Fortran 2008 standard is already provided; the current status of the
529 support is reported in the @ref{Fortran 2003 status} and
530 @ref{Fortran 2008 status} sections of the documentation.
532 Additionally, the GNU Fortran compilers supports the OpenMP specification
533 (version 3.0, @url{http://openmp.org/@/wp/@/openmp-specifications/}).
535 @node Varying Length Character Strings
536 @subsection Varying Length Character Strings
537 @cindex Varying length character strings
538 @cindex Varying length strings
539 @cindex strings, varying length
541 The Fortran 95 standard specifies in Part 2 (ISO/IEC 1539-2:2000)
542 varying length character strings. While GNU Fortran currently does not
543 support such strings directly, there exist two Fortran implementations
544 for them, which work with GNU Fortran. They can be found at
545 @uref{http://www.fortran.com/@/iso_varying_string.f95} and at
546 @uref{ftp://ftp.nag.co.uk/@/sc22wg5/@/ISO_VARYING_STRING/}.
550 @c =====================================================================
551 @c PART I: INVOCATION REFERENCE
552 @c =====================================================================
555 \part{I}{Invoking GNU Fortran}
558 @c ---------------------------------------------------------------------
560 @c ---------------------------------------------------------------------
565 @c ---------------------------------------------------------------------
567 @c ---------------------------------------------------------------------
570 @chapter Runtime: Influencing runtime behavior with environment variables
571 @cindex environment variable
573 The behavior of the @command{gfortran} can be influenced by
574 environment variables.
576 Malformed environment variables are silently ignored.
579 * GFORTRAN_STDIN_UNIT:: Unit number for standard input
580 * GFORTRAN_STDOUT_UNIT:: Unit number for standard output
581 * GFORTRAN_STDERR_UNIT:: Unit number for standard error
582 * GFORTRAN_USE_STDERR:: Send library output to standard error
583 * GFORTRAN_TMPDIR:: Directory for scratch files
584 * GFORTRAN_UNBUFFERED_ALL:: Don't buffer I/O for all units.
585 * GFORTRAN_UNBUFFERED_PRECONNECTED:: Don't buffer I/O for preconnected units.
586 * GFORTRAN_SHOW_LOCUS:: Show location for runtime errors
587 * GFORTRAN_OPTIONAL_PLUS:: Print leading + where permitted
588 * GFORTRAN_DEFAULT_RECL:: Default record length for new files
589 * GFORTRAN_LIST_SEPARATOR:: Separator for list output
590 * GFORTRAN_CONVERT_UNIT:: Set endianness for unformatted I/O
591 * GFORTRAN_ERROR_DUMPCORE:: Dump core on run-time errors
592 * GFORTRAN_ERROR_BACKTRACE:: Show backtrace on run-time errors
595 @node GFORTRAN_STDIN_UNIT
596 @section @env{GFORTRAN_STDIN_UNIT}---Unit number for standard input
598 This environment variable can be used to select the unit number
599 preconnected to standard input. This must be a positive integer.
600 The default value is 5.
602 @node GFORTRAN_STDOUT_UNIT
603 @section @env{GFORTRAN_STDOUT_UNIT}---Unit number for standard output
605 This environment variable can be used to select the unit number
606 preconnected to standard output. This must be a positive integer.
607 The default value is 6.
609 @node GFORTRAN_STDERR_UNIT
610 @section @env{GFORTRAN_STDERR_UNIT}---Unit number for standard error
612 This environment variable can be used to select the unit number
613 preconnected to standard error. This must be a positive integer.
614 The default value is 0.
616 @node GFORTRAN_USE_STDERR
617 @section @env{GFORTRAN_USE_STDERR}---Send library output to standard error
619 This environment variable controls where library output is sent.
620 If the first letter is @samp{y}, @samp{Y} or @samp{1}, standard
621 error is used. If the first letter is @samp{n}, @samp{N} or
622 @samp{0}, standard output is used.
624 @node GFORTRAN_TMPDIR
625 @section @env{GFORTRAN_TMPDIR}---Directory for scratch files
627 This environment variable controls where scratch files are
628 created. If this environment variable is missing,
629 GNU Fortran searches for the environment variable @env{TMP}, then @env{TEMP}.
630 If these are missing, the default is @file{/tmp}.
632 @node GFORTRAN_UNBUFFERED_ALL
633 @section @env{GFORTRAN_UNBUFFERED_ALL}---Don't buffer I/O on all units
635 This environment variable controls whether all I/O is unbuffered. If
636 the first letter is @samp{y}, @samp{Y} or @samp{1}, all I/O is
637 unbuffered. This will slow down small sequential reads and writes. If
638 the first letter is @samp{n}, @samp{N} or @samp{0}, I/O is buffered.
641 @node GFORTRAN_UNBUFFERED_PRECONNECTED
642 @section @env{GFORTRAN_UNBUFFERED_PRECONNECTED}---Don't buffer I/O on preconnected units
644 The environment variable named @env{GFORTRAN_UNBUFFERED_PRECONNECTED} controls
645 whether I/O on a preconnected unit (i.e.@: STDOUT or STDERR) is unbuffered. If
646 the first letter is @samp{y}, @samp{Y} or @samp{1}, I/O is unbuffered. This
647 will slow down small sequential reads and writes. If the first letter
648 is @samp{n}, @samp{N} or @samp{0}, I/O is buffered. This is the default.
650 @node GFORTRAN_SHOW_LOCUS
651 @section @env{GFORTRAN_SHOW_LOCUS}---Show location for runtime errors
653 If the first letter is @samp{y}, @samp{Y} or @samp{1}, filename and
654 line numbers for runtime errors are printed. If the first letter is
655 @samp{n}, @samp{N} or @samp{0}, don't print filename and line numbers
656 for runtime errors. The default is to print the location.
658 @node GFORTRAN_OPTIONAL_PLUS
659 @section @env{GFORTRAN_OPTIONAL_PLUS}---Print leading + where permitted
661 If the first letter is @samp{y}, @samp{Y} or @samp{1},
662 a plus sign is printed
663 where permitted by the Fortran standard. If the first letter
664 is @samp{n}, @samp{N} or @samp{0}, a plus sign is not printed
665 in most cases. Default is not to print plus signs.
667 @node GFORTRAN_DEFAULT_RECL
668 @section @env{GFORTRAN_DEFAULT_RECL}---Default record length for new files
670 This environment variable specifies the default record length, in
671 bytes, for files which are opened without a @code{RECL} tag in the
672 @code{OPEN} statement. This must be a positive integer. The
673 default value is 1073741824 bytes (1 GB).
675 @node GFORTRAN_LIST_SEPARATOR
676 @section @env{GFORTRAN_LIST_SEPARATOR}---Separator for list output
678 This environment variable specifies the separator when writing
679 list-directed output. It may contain any number of spaces and
680 at most one comma. If you specify this on the command line,
681 be sure to quote spaces, as in
683 $ GFORTRAN_LIST_SEPARATOR=' , ' ./a.out
685 when @command{a.out} is the compiled Fortran program that you want to run.
686 Default is a single space.
688 @node GFORTRAN_CONVERT_UNIT
689 @section @env{GFORTRAN_CONVERT_UNIT}---Set endianness for unformatted I/O
691 By setting the @env{GFORTRAN_CONVERT_UNIT} variable, it is possible
692 to change the representation of data for unformatted files.
693 The syntax for the @env{GFORTRAN_CONVERT_UNIT} variable is:
695 GFORTRAN_CONVERT_UNIT: mode | mode ';' exception | exception ;
696 mode: 'native' | 'swap' | 'big_endian' | 'little_endian' ;
697 exception: mode ':' unit_list | unit_list ;
698 unit_list: unit_spec | unit_list unit_spec ;
699 unit_spec: INTEGER | INTEGER '-' INTEGER ;
701 The variable consists of an optional default mode, followed by
702 a list of optional exceptions, which are separated by semicolons
703 from the preceding default and each other. Each exception consists
704 of a format and a comma-separated list of units. Valid values for
705 the modes are the same as for the @code{CONVERT} specifier:
708 @item @code{NATIVE} Use the native format. This is the default.
709 @item @code{SWAP} Swap between little- and big-endian.
710 @item @code{LITTLE_ENDIAN} Use the little-endian format
711 for unformatted files.
712 @item @code{BIG_ENDIAN} Use the big-endian format for unformatted files.
714 A missing mode for an exception is taken to mean @code{BIG_ENDIAN}.
715 Examples of values for @env{GFORTRAN_CONVERT_UNIT} are:
717 @item @code{'big_endian'} Do all unformatted I/O in big_endian mode.
718 @item @code{'little_endian;native:10-20,25'} Do all unformatted I/O
719 in little_endian mode, except for units 10 to 20 and 25, which are in
721 @item @code{'10-20'} Units 10 to 20 are big-endian, the rest is native.
724 Setting the environment variables should be done on the command
725 line or via the @command{export}
726 command for @command{sh}-compatible shells and via @command{setenv}
727 for @command{csh}-compatible shells.
729 Example for @command{sh}:
732 $ GFORTRAN_CONVERT_UNIT='big_endian;native:10-20' ./a.out
735 Example code for @command{csh}:
738 % setenv GFORTRAN_CONVERT_UNIT 'big_endian;native:10-20'
742 Using anything but the native representation for unformatted data
743 carries a significant speed overhead. If speed in this area matters
744 to you, it is best if you use this only for data that needs to be
747 @xref{CONVERT specifier}, for an alternative way to specify the
748 data representation for unformatted files. @xref{Runtime Options}, for
749 setting a default data representation for the whole program. The
750 @code{CONVERT} specifier overrides the @option{-fconvert} compile options.
752 @emph{Note that the values specified via the GFORTRAN_CONVERT_UNIT
753 environment variable will override the CONVERT specifier in the
754 open statement}. This is to give control over data formats to
755 users who do not have the source code of their program available.
757 @node GFORTRAN_ERROR_DUMPCORE
758 @section @env{GFORTRAN_ERROR_DUMPCORE}---Dump core on run-time errors
760 If the @env{GFORTRAN_ERROR_DUMPCORE} variable is set to
761 @samp{y}, @samp{Y} or @samp{1} (only the first letter is relevant)
762 then library run-time errors cause core dumps. To disable the core
763 dumps, set the variable to @samp{n}, @samp{N}, @samp{0}. Default
764 is not to core dump unless the @option{-fdump-core} compile option
767 @node GFORTRAN_ERROR_BACKTRACE
768 @section @env{GFORTRAN_ERROR_BACKTRACE}---Show backtrace on run-time errors
770 If the @env{GFORTRAN_ERROR_BACKTRACE} variable is set to
771 @samp{y}, @samp{Y} or @samp{1} (only the first letter is relevant)
772 then a backtrace is printed when a run-time error occurs.
773 To disable the backtracing, set the variable to
774 @samp{n}, @samp{N}, @samp{0}. Default is not to print a backtrace
775 unless the @option{-fbacktrace} compile option
778 @c =====================================================================
779 @c PART II: LANGUAGE REFERENCE
780 @c =====================================================================
783 \part{II}{Language Reference}
786 @c ---------------------------------------------------------------------
787 @c Fortran 2003 and 2008 Status
788 @c ---------------------------------------------------------------------
790 @node Fortran 2003 and 2008 status
791 @chapter Fortran 2003 and 2008 Status
794 * Fortran 2003 status::
795 * Fortran 2008 status::
798 @node Fortran 2003 status
799 @section Fortran 2003 status
801 GNU Fortran supports several Fortran 2003 features; an incomplete
802 list can be found below. See also the
803 @uref{http://gcc.gnu.org/wiki/Fortran2003, wiki page} about Fortran 2003.
806 @item Procedure pointers including procedure-pointer components with
807 @code{PASS} attribute.
809 @item Procedures which are bound to a derived type (type-bound procedures)
810 including @code{PASS}, @code{PROCEDURE} and @code{GENERIC}, and
811 operators bound to a type.
813 @item Abstract interfaces and type extension with the possibility to
814 override type-bound procedures or to have deferred binding.
816 @item Polymorphic entities (``@code{CLASS}'') for derived types -- including
817 @code{SAME_TYPE_AS}, @code{EXTENDS_TYPE_OF} and @code{SELECT TYPE}.
818 Note that the support for array-valued polymorphic entities is incomplete
819 and unlimited polymophism is currently not supported.
821 @item The @code{ASSOCIATE} construct.
823 @item Interoperability with C including enumerations,
825 @item In structure constructors the components with default values may be
828 @item Extensions to the @code{ALLOCATE} statement, allowing for a
829 type-specification with type parameter and for allocation and initialization
830 from a @code{SOURCE=} expression; @code{ALLOCATE} and @code{DEALLOCATE}
831 optionally return an error message string via @code{ERRMSG=}.
833 @item Reallocation on assignment: If an intrinsic assignment is
834 used, an allocatable variable on the left-hand side is automatically allocated
835 (if unallocated) or reallocated (if the shape is different). Currently, scalar
836 deferred character length left-hand sides are correctly handled but arrays
837 are not yet fully implemented.
839 @item Transferring of allocations via @code{MOVE_ALLOC}.
841 @item The @code{PRIVATE} and @code{PUBLIC} attributes may be given individually
842 to derived-type components.
844 @item In pointer assignments, the lower bound may be specified and
845 the remapping of elements is supported.
847 @item For pointers an @code{INTENT} may be specified which affect the
848 association status not the value of the pointer target.
850 @item Intrinsics @code{command_argument_count}, @code{get_command},
851 @code{get_command_argument}, and @code{get_environment_variable}.
853 @item Support for unicode characters (ISO 10646) and UTF-8, including
854 the @code{SELECTED_CHAR_KIND} and @code{NEW_LINE} intrinsic functions.
856 @item Support for binary, octal and hexadecimal (BOZ) constants in the
857 intrinsic functions @code{INT}, @code{REAL}, @code{CMPLX} and @code{DBLE}.
859 @item Support for namelist variables with allocatable and pointer
860 attribute and nonconstant length type parameter.
863 @cindex array, constructors
865 Array constructors using square brackets. That is, @code{[...]} rather
866 than @code{(/.../)}. Type-specification for array constructors like
867 @code{(/ some-type :: ... /)}.
869 @item Extensions to the specification and initialization expressions,
870 including the support for intrinsics with real and complex arguments.
872 @item Support for the asynchronous input/output syntax; however, the
873 data transfer is currently always synchronously performed.
876 @cindex @code{FLUSH} statement
877 @cindex statement, @code{FLUSH}
878 @code{FLUSH} statement.
881 @cindex @code{IOMSG=} specifier
882 @code{IOMSG=} specifier for I/O statements.
885 @cindex @code{ENUM} statement
886 @cindex @code{ENUMERATOR} statement
887 @cindex statement, @code{ENUM}
888 @cindex statement, @code{ENUMERATOR}
889 @opindex @code{fshort-enums}
890 Support for the declaration of enumeration constants via the
891 @code{ENUM} and @code{ENUMERATOR} statements. Interoperability with
892 @command{gcc} is guaranteed also for the case where the
893 @command{-fshort-enums} command line option is given.
900 @cindex @code{ALLOCATABLE} dummy arguments
901 @code{ALLOCATABLE} dummy arguments.
903 @cindex @code{ALLOCATABLE} function results
904 @code{ALLOCATABLE} function results
906 @cindex @code{ALLOCATABLE} components of derived types
907 @code{ALLOCATABLE} components of derived types
911 @cindex @code{STREAM} I/O
912 @cindex @code{ACCESS='STREAM'} I/O
913 The @code{OPEN} statement supports the @code{ACCESS='STREAM'} specifier,
914 allowing I/O without any record structure.
917 Namelist input/output for internal files.
919 @item Further I/O extensions: Rounding during formatted output, using of
920 a decimal comma instead of a decimal point, setting whether a plus sign
921 should appear for positive numbers.
924 @cindex @code{PROTECTED} statement
925 @cindex statement, @code{PROTECTED}
926 The @code{PROTECTED} statement and attribute.
929 @cindex @code{VALUE} statement
930 @cindex statement, @code{VALUE}
931 The @code{VALUE} statement and attribute.
934 @cindex @code{VOLATILE} statement
935 @cindex statement, @code{VOLATILE}
936 The @code{VOLATILE} statement and attribute.
939 @cindex @code{IMPORT} statement
940 @cindex statement, @code{IMPORT}
941 The @code{IMPORT} statement, allowing to import
942 host-associated derived types.
944 @item The intrinsic modules @code{ISO_FORTRAN_ENVIRONMENT} is supported,
945 which contains parameters of the I/O units, storage sizes. Additionally,
946 procedures for C interoperability are available in the @code{ISO_C_BINDING}
950 @cindex @code{USE, INTRINSIC} statement
951 @cindex statement, @code{USE, INTRINSIC}
952 @cindex @code{ISO_FORTRAN_ENV} statement
953 @cindex statement, @code{ISO_FORTRAN_ENV}
954 @code{USE} statement with @code{INTRINSIC} and @code{NON_INTRINSIC}
955 attribute; supported intrinsic modules: @code{ISO_FORTRAN_ENV},
956 @code{ISO_C_BINDING}, @code{OMP_LIB} and @code{OMP_LIB_KINDS}.
959 Renaming of operators in the @code{USE} statement.
964 @node Fortran 2008 status
965 @section Fortran 2008 status
967 The latest version of the Fortran standard is ISO/IEC 1539-1:2010, informally
968 known as Fortran 2008. The official version is available from International
969 Organization for Standardization (ISO) or its national member organizations.
970 The the final draft (FDIS) can be downloaded free of charge from
971 @url{http://www.nag.co.uk/@/sc22wg5/@/links.html}. Fortran is developed by the
972 Working Group 5 of Sub-Committee 22 of the Joint Technical Committee 1 of the
973 International Organization for Standardization and the International
974 Electrotechnical Commission (IEC). This group is known as
975 @uref{http://www.nag.co.uk/sc22wg5/, WG5}.
977 The GNU Fortran supports several of the new features of Fortran 2008; the
978 @uref{http://gcc.gnu.org/wiki/Fortran2008Status, wiki} has some information
979 about the current Fortran 2008 implementation status. In particular, the
980 following is implemented.
983 @item The @option{-std=f2008} option and support for the file extensions
984 @file{.f08} and @file{.F08}.
986 @item The @code{OPEN} statement now supports the @code{NEWUNIT=} option,
987 which returns a unique file unit, thus preventing inadvertent use of the
988 same unit in different parts of the program.
990 @item The @code{g0} format descriptor and unlimited format items.
992 @item The mathematical intrinsics @code{ASINH}, @code{ACOSH}, @code{ATANH},
993 @code{ERF}, @code{ERFC}, @code{GAMMA}, @code{LOG_GAMMA}, @code{BESSEL_J0},
994 @code{BESSEL_J1}, @code{BESSEL_JN}, @code{BESSEL_Y0}, @code{BESSEL_Y1},
995 @code{BESSEL_YN}, @code{HYPOT}, @code{NORM2}, and @code{ERFC_SCALED}.
997 @item Using complex arguments with @code{TAN}, @code{SINH}, @code{COSH},
998 @code{TANH}, @code{ASIN}, @code{ACOS}, and @code{ATAN} is now possible;
999 @code{ATAN}(@var{Y},@var{X}) is now an alias for @code{ATAN2}(@var{Y},@var{X}).
1001 @item Support of the @code{PARITY} intrinsic functions.
1003 @item The following bit intrinsics: @code{LEADZ} and @code{TRAILZ} for
1004 counting the number of leading and trailing zero bits, @code{POPCNT} and
1005 @code{POPPAR} for counting the number of one bits and returning the parity;
1006 @code{BGE}, @code{BGT}, @code{BLE}, and @code{BLT} for bitwise comparisons;
1007 @code{DSHIFTL} and @code{DSHIFTR} for combined left and right shifts,
1008 @code{MASKL} and @code{MASKR} for simple left and right justified masks,
1009 @code{MERGE_BITS} for a bitwise merge using a mask, @code{SHIFTA},
1010 @code{SHIFTL} and @code{SHIFTR} for shift operations, and the
1011 transformational bit intrinsics @code{IALL}, @code{IANY} and @code{IPARITY}.
1013 @item Support of the @code{EXECUTE_COMMAND_LINE} intrinsic subroutine.
1015 @item Support for the @code{STORAGE_SIZE} intrinsic inquiry function.
1017 @item The @code{INT@{8,16,32@}} and @code{REAL@{32,64,128@}} kind type
1018 parameters and the array-valued named constants @code{INTEGER_KINDS},
1019 @code{LOGICAL_KINDS}, @code{REAL_KINDS} and @code{CHARACTER_KINDS} of
1020 the intrinsic module @code{ISO_FORTRAN_ENV}.
1022 @item The module procedures @code{C_SIZEOF} of the intrinsic module
1023 @code{ISO_C_BINDINGS} and @code{COMPILER_VERSION} and @code{COMPILER_OPTIONS}
1024 of @code{ISO_FORTRAN_ENV}.
1026 @item Experimental coarray support (for one image only), use the
1027 @option{-fcoarray=single} flag to enable it.
1029 @item The @code{BLOCK} construct is supported.
1031 @item The @code{STOP} and the new @code{ERROR STOP} statements now
1032 support all constant expressions.
1034 @item Support for the @code{CONTIGUOUS} attribute.
1036 @item Support for @code{ALLOCATE} with @code{MOLD}.
1038 @item Support for the @code{IMPURE} attribute for procedures, which
1039 allows for @code{ELEMENTAL} procedures without the restrictions of
1042 @item Null pointers (including @code{NULL()}) and not-allocated variables
1043 can be used as actual argument to optional non-pointer, non-allocatable
1044 dummy arguments, denoting an absent argument.
1046 @item Non-pointer variables with @code{TARGET} attribute can be used as
1047 actual argument to @code{POINTER} dummies with @code{INTENT(IN)}.
1049 @item Pointers including procedure pointers and those in a derived
1050 type (pointer components) can now be initialized by a target instead
1051 of only by @code{NULL}.
1053 @item The @code{EXIT} statement (with construct-name) can be now be
1054 used to leave not only the @code{DO} but also the @code{ASSOCIATE},
1055 @code{BLOCK}, @code{IF}, @code{SELECT CASE} and @code{SELECT TYPE}
1058 @item Internal procedures can now be used as actual argument.
1060 @item Minor features: obsolesce diagnostics for @code{ENTRY} with
1061 @option{-std=f2008}; a line may start with a semicolon; for internal
1062 and module procedures @code{END} can be used instead of
1063 @code{END SUBROUTINE} and @code{END FUNCTION}; @code{SELECTED_REAL_KIND}
1064 now also takes a @code{RADIX} argument; intrinsic types are supported
1065 for @code{TYPE}(@var{intrinsic-type-spec}); multiple type-bound procedures
1066 can be declared in a single @code{PROCEDURE} statement; implied-shape
1067 arrays are supported for named constants (@code{PARAMETER}).
1072 @c ---------------------------------------------------------------------
1073 @c Compiler Characteristics
1074 @c ---------------------------------------------------------------------
1076 @node Compiler Characteristics
1077 @chapter Compiler Characteristics
1079 This chapter describes certain characteristics of the GNU Fortran
1080 compiler, that are not specified by the Fortran standard, but which
1081 might in some way or another become visible to the programmer.
1084 * KIND Type Parameters::
1085 * Internal representation of LOGICAL variables::
1086 * Thread-safety of the runtime library::
1090 @node KIND Type Parameters
1091 @section KIND Type Parameters
1094 The @code{KIND} type parameters supported by GNU Fortran for the primitive
1100 1, 2, 4, 8*, 16*, default: 4 (1)
1103 1, 2, 4, 8*, 16*, default: 4 (1)
1106 4, 8, 10*, 16*, default: 4 (2)
1109 4, 8, 10*, 16*, default: 4 (2)
1117 * = not available on all systems @*
1118 (1) Unless -fdefault-integer-8 is used @*
1119 (2) Unless -fdefault-real-8 is used
1122 The @code{KIND} value matches the storage size in bytes, except for
1123 @code{COMPLEX} where the storage size is twice as much (or both real and
1124 imaginary part are a real value of the given size). It is recommended to use
1125 the @code{SELECTED_CHAR_KIND}, @code{SELECTED_INT_KIND} and
1126 @code{SELECTED_REAL_KIND} intrinsics or the @code{INT8}, @code{INT16},
1127 @code{INT32}, @code{INT64}, @code{REAL32}, @code{REAL64}, and @code{REAL128}
1128 parameters of the @code{ISO_FORTRAN_ENV} module instead of the concrete values.
1129 The available kind parameters can be found in the constant arrays
1130 @code{CHARACTER_KINDS}, @code{INTEGER_KINDS}, @code{LOGICAL_KINDS} and
1131 @code{REAL_KINDS} in the @code{ISO_FORTRAN_ENV} module
1132 (see @ref{ISO_FORTRAN_ENV}).
1135 @node Internal representation of LOGICAL variables
1136 @section Internal representation of LOGICAL variables
1137 @cindex logical, variable representation
1139 The Fortran standard does not specify how variables of @code{LOGICAL}
1140 type are represented, beyond requiring that @code{LOGICAL} variables
1141 of default kind have the same storage size as default @code{INTEGER}
1142 and @code{REAL} variables. The GNU Fortran internal representation is
1145 A @code{LOGICAL(KIND=N)} variable is represented as an
1146 @code{INTEGER(KIND=N)} variable, however, with only two permissible
1147 values: @code{1} for @code{.TRUE.} and @code{0} for
1148 @code{.FALSE.}. Any other integer value results in undefined behavior.
1150 Note that for mixed-language programming using the
1151 @code{ISO_C_BINDING} feature, there is a @code{C_BOOL} kind that can
1152 be used to create @code{LOGICAL(KIND=C_BOOL)} variables which are
1153 interoperable with the C99 _Bool type. The C99 _Bool type has an
1154 internal representation described in the C99 standard, which is
1155 identical to the above description, i.e. with 1 for true and 0 for
1156 false being the only permissible values. Thus the internal
1157 representation of @code{LOGICAL} variables in GNU Fortran is identical
1158 to C99 _Bool, except for a possible difference in storage size
1159 depending on the kind.
1162 @node Thread-safety of the runtime library
1163 @section Thread-safety of the runtime library
1164 @cindex thread-safety, threads
1166 GNU Fortran can be used in programs with multiple threads, e.g.@: by
1167 using OpenMP, by calling OS thread handling functions via the
1168 @code{ISO_C_BINDING} facility, or by GNU Fortran compiled library code
1169 being called from a multi-threaded program.
1171 The GNU Fortran runtime library, (@code{libgfortran}), supports being
1172 called concurrently from multiple threads with the following
1175 During library initialization, the C @code{getenv} function is used,
1176 which need not be thread-safe. Similarly, the @code{getenv}
1177 function is used to implement the @code{GET_ENVIRONMENT_VARIABLE} and
1178 @code{GETENV} intrinsics. It is the responsibility of the user to
1179 ensure that the environment is not being updated concurrently when any
1180 of these actions are taking place.
1182 The @code{EXECUTE_COMMAND_LINE} and @code{SYSTEM} intrinsics are
1183 implemented with the @code{system} function, which need not be
1184 thread-safe. It is the responsibility of the user to ensure that
1185 @code{system} is not called concurrently.
1187 Finally, for platforms not supporting thread-safe POSIX functions,
1188 further functionality might not be thread-safe. For details, please
1189 consult the documentation for your operating system.
1191 @c ---------------------------------------------------------------------
1193 @c ---------------------------------------------------------------------
1195 @c Maybe this chapter should be merged with the 'Standards' section,
1196 @c whenever that is written :-)
1202 The two sections below detail the extensions to standard Fortran that are
1203 implemented in GNU Fortran, as well as some of the popular or
1204 historically important extensions that are not (or not yet) implemented.
1205 For the latter case, we explain the alternatives available to GNU Fortran
1206 users, including replacement by standard-conforming code or GNU
1210 * Extensions implemented in GNU Fortran::
1211 * Extensions not implemented in GNU Fortran::
1215 @node Extensions implemented in GNU Fortran
1216 @section Extensions implemented in GNU Fortran
1217 @cindex extensions, implemented
1219 GNU Fortran implements a number of extensions over standard
1220 Fortran. This chapter contains information on their syntax and
1221 meaning. There are currently two categories of GNU Fortran
1222 extensions, those that provide functionality beyond that provided
1223 by any standard, and those that are supported by GNU Fortran
1224 purely for backward compatibility with legacy compilers. By default,
1225 @option{-std=gnu} allows the compiler to accept both types of
1226 extensions, but to warn about the use of the latter. Specifying
1227 either @option{-std=f95}, @option{-std=f2003} or @option{-std=f2008}
1228 disables both types of extensions, and @option{-std=legacy} allows both
1232 * Old-style kind specifications::
1233 * Old-style variable initialization::
1234 * Extensions to namelist::
1235 * X format descriptor without count field::
1236 * Commas in FORMAT specifications::
1237 * Missing period in FORMAT specifications::
1239 * BOZ literal constants::
1240 * @code{Q} exponent-letter::
1241 * Real array indices::
1243 * Implicitly convert LOGICAL and INTEGER values::
1244 * Hollerith constants support::
1246 * CONVERT specifier::
1248 * Argument list functions::
1251 @node Old-style kind specifications
1252 @subsection Old-style kind specifications
1253 @cindex kind, old-style
1255 GNU Fortran allows old-style kind specifications in declarations. These
1261 where @code{TYPESPEC} is a basic type (@code{INTEGER}, @code{REAL},
1262 etc.), and where @code{size} is a byte count corresponding to the
1263 storage size of a valid kind for that type. (For @code{COMPLEX}
1264 variables, @code{size} is the total size of the real and imaginary
1265 parts.) The statement then declares @code{x}, @code{y} and @code{z} to
1266 be of type @code{TYPESPEC} with the appropriate kind. This is
1267 equivalent to the standard-conforming declaration
1272 where @code{k} is the kind parameter suitable for the intended precision. As
1273 kind parameters are implementation-dependent, use the @code{KIND},
1274 @code{SELECTED_INT_KIND} and @code{SELECTED_REAL_KIND} intrinsics to retrieve
1275 the correct value, for instance @code{REAL*8 x} can be replaced by:
1277 INTEGER, PARAMETER :: dbl = KIND(1.0d0)
1281 @node Old-style variable initialization
1282 @subsection Old-style variable initialization
1284 GNU Fortran allows old-style initialization of variables of the
1288 REAL x(2,2) /3*0.,1./
1290 The syntax for the initializers is as for the @code{DATA} statement, but
1291 unlike in a @code{DATA} statement, an initializer only applies to the
1292 variable immediately preceding the initialization. In other words,
1293 something like @code{INTEGER I,J/2,3/} is not valid. This style of
1294 initialization is only allowed in declarations without double colons
1295 (@code{::}); the double colons were introduced in Fortran 90, which also
1296 introduced a standard syntax for initializing variables in type
1299 Examples of standard-conforming code equivalent to the above example
1303 INTEGER :: i = 1, j = 2
1304 REAL :: x(2,2) = RESHAPE((/0.,0.,0.,1./),SHAPE(x))
1308 DATA i/1/, j/2/, x/3*0.,1./
1311 Note that variables which are explicitly initialized in declarations
1312 or in @code{DATA} statements automatically acquire the @code{SAVE}
1315 @node Extensions to namelist
1316 @subsection Extensions to namelist
1319 GNU Fortran fully supports the Fortran 95 standard for namelist I/O
1320 including array qualifiers, substrings and fully qualified derived types.
1321 The output from a namelist write is compatible with namelist read. The
1322 output has all names in upper case and indentation to column 1 after the
1323 namelist name. Two extensions are permitted:
1325 Old-style use of @samp{$} instead of @samp{&}
1328 X(:)%Y(2) = 1.0 2.0 3.0
1333 It should be noted that the default terminator is @samp{/} rather than
1336 Querying of the namelist when inputting from stdin. After at least
1337 one space, entering @samp{?} sends to stdout the namelist name and the names of
1338 the variables in the namelist:
1349 Entering @samp{=?} outputs the namelist to stdout, as if
1350 @code{WRITE(*,NML = mynml)} had been called:
1355 X(1)%Y= 0.000000 , 1.000000 , 0.000000 ,
1356 X(2)%Y= 0.000000 , 2.000000 , 0.000000 ,
1357 X(3)%Y= 0.000000 , 3.000000 , 0.000000 ,
1361 To aid this dialog, when input is from stdin, errors send their
1362 messages to stderr and execution continues, even if @code{IOSTAT} is set.
1364 @code{PRINT} namelist is permitted. This causes an error if
1365 @option{-std=f95} is used.
1368 REAL, dimension (4) :: x = (/1.0, 2.0, 3.0, 4.0/)
1371 END PROGRAM test_print
1374 Expanded namelist reads are permitted. This causes an error if
1375 @option{-std=f95} is used. In the following example, the first element
1376 of the array will be given the value 0.00 and the two succeeding
1377 elements will be given the values 1.00 and 2.00.
1380 X(1,1) = 0.00 , 1.00 , 2.00
1384 @node X format descriptor without count field
1385 @subsection @code{X} format descriptor without count field
1387 To support legacy codes, GNU Fortran permits the count field of the
1388 @code{X} edit descriptor in @code{FORMAT} statements to be omitted.
1389 When omitted, the count is implicitly assumed to be one.
1393 10 FORMAT (I1, X, I1)
1396 @node Commas in FORMAT specifications
1397 @subsection Commas in @code{FORMAT} specifications
1399 To support legacy codes, GNU Fortran allows the comma separator
1400 to be omitted immediately before and after character string edit
1401 descriptors in @code{FORMAT} statements.
1405 10 FORMAT ('FOO='I1' BAR='I2)
1409 @node Missing period in FORMAT specifications
1410 @subsection Missing period in @code{FORMAT} specifications
1412 To support legacy codes, GNU Fortran allows missing periods in format
1413 specifications if and only if @option{-std=legacy} is given on the
1414 command line. This is considered non-conforming code and is
1423 @node I/O item lists
1424 @subsection I/O item lists
1425 @cindex I/O item lists
1427 To support legacy codes, GNU Fortran allows the input item list
1428 of the @code{READ} statement, and the output item lists of the
1429 @code{WRITE} and @code{PRINT} statements, to start with a comma.
1431 @node @code{Q} exponent-letter
1432 @subsection @code{Q} exponent-letter
1433 @cindex @code{Q} exponent-letter
1435 GNU Fortran accepts real literal constants with an exponent-letter
1436 of @code{Q}, for example, @code{1.23Q45}. The constant is interpreted
1437 as a @code{REAL(16)} entity on targets that suppports this type. If
1438 the target does not support @code{REAL(16)} but has a @code{REAL(10)}
1439 type, then the real-literal-constant will be interpreted as a
1440 @code{REAL(10)} entity. In the absence of @code{REAL(16)} and
1441 @code{REAL(10)}, an error will occur.
1443 @node BOZ literal constants
1444 @subsection BOZ literal constants
1445 @cindex BOZ literal constants
1447 Besides decimal constants, Fortran also supports binary (@code{b}),
1448 octal (@code{o}) and hexadecimal (@code{z}) integer constants. The
1449 syntax is: @samp{prefix quote digits quote}, were the prefix is
1450 either @code{b}, @code{o} or @code{z}, quote is either @code{'} or
1451 @code{"} and the digits are for binary @code{0} or @code{1}, for
1452 octal between @code{0} and @code{7}, and for hexadecimal between
1453 @code{0} and @code{F}. (Example: @code{b'01011101'}.)
1455 Up to Fortran 95, BOZ literals were only allowed to initialize
1456 integer variables in DATA statements. Since Fortran 2003 BOZ literals
1457 are also allowed as argument of @code{REAL}, @code{DBLE}, @code{INT}
1458 and @code{CMPLX}; the result is the same as if the integer BOZ
1459 literal had been converted by @code{TRANSFER} to, respectively,
1460 @code{real}, @code{double precision}, @code{integer} or @code{complex}.
1461 As GNU Fortran extension the intrinsic procedures @code{FLOAT},
1462 @code{DFLOAT}, @code{COMPLEX} and @code{DCMPLX} are treated alike.
1464 As an extension, GNU Fortran allows hexadecimal BOZ literal constants to
1465 be specified using the @code{X} prefix, in addition to the standard
1466 @code{Z} prefix. The BOZ literal can also be specified by adding a
1467 suffix to the string, for example, @code{Z'ABC'} and @code{'ABC'Z} are
1470 Furthermore, GNU Fortran allows using BOZ literal constants outside
1471 DATA statements and the four intrinsic functions allowed by Fortran 2003.
1472 In DATA statements, in direct assignments, where the right-hand side
1473 only contains a BOZ literal constant, and for old-style initializers of
1474 the form @code{integer i /o'0173'/}, the constant is transferred
1475 as if @code{TRANSFER} had been used; for @code{COMPLEX} numbers, only
1476 the real part is initialized unless @code{CMPLX} is used. In all other
1477 cases, the BOZ literal constant is converted to an @code{INTEGER} value with
1478 the largest decimal representation. This value is then converted
1479 numerically to the type and kind of the variable in question.
1480 (For instance, @code{real :: r = b'0000001' + 1} initializes @code{r}
1481 with @code{2.0}.) As different compilers implement the extension
1482 differently, one should be careful when doing bitwise initialization
1483 of non-integer variables.
1485 Note that initializing an @code{INTEGER} variable with a statement such
1486 as @code{DATA i/Z'FFFFFFFF'/} will give an integer overflow error rather
1487 than the desired result of @math{-1} when @code{i} is a 32-bit integer
1488 on a system that supports 64-bit integers. The @samp{-fno-range-check}
1489 option can be used as a workaround for legacy code that initializes
1490 integers in this manner.
1492 @node Real array indices
1493 @subsection Real array indices
1494 @cindex array, indices of type real
1496 As an extension, GNU Fortran allows the use of @code{REAL} expressions
1497 or variables as array indices.
1499 @node Unary operators
1500 @subsection Unary operators
1501 @cindex operators, unary
1503 As an extension, GNU Fortran allows unary plus and unary minus operators
1504 to appear as the second operand of binary arithmetic operators without
1505 the need for parenthesis.
1511 @node Implicitly convert LOGICAL and INTEGER values
1512 @subsection Implicitly convert @code{LOGICAL} and @code{INTEGER} values
1513 @cindex conversion, to integer
1514 @cindex conversion, to logical
1516 As an extension for backwards compatibility with other compilers, GNU
1517 Fortran allows the implicit conversion of @code{LOGICAL} values to
1518 @code{INTEGER} values and vice versa. When converting from a
1519 @code{LOGICAL} to an @code{INTEGER}, @code{.FALSE.} is interpreted as
1520 zero, and @code{.TRUE.} is interpreted as one. When converting from
1521 @code{INTEGER} to @code{LOGICAL}, the value zero is interpreted as
1522 @code{.FALSE.} and any nonzero value is interpreted as @code{.TRUE.}.
1533 However, there is no implicit conversion of @code{INTEGER} values in
1534 @code{if}-statements, nor of @code{LOGICAL} or @code{INTEGER} values
1537 @node Hollerith constants support
1538 @subsection Hollerith constants support
1539 @cindex Hollerith constants
1541 GNU Fortran supports Hollerith constants in assignments, function
1542 arguments, and @code{DATA} and @code{ASSIGN} statements. A Hollerith
1543 constant is written as a string of characters preceded by an integer
1544 constant indicating the character count, and the letter @code{H} or
1545 @code{h}, and stored in bytewise fashion in a numeric (@code{INTEGER},
1546 @code{REAL}, or @code{complex}) or @code{LOGICAL} variable. The
1547 constant will be padded or truncated to fit the size of the variable in
1550 Examples of valid uses of Hollerith constants:
1553 data x /16Habcdefghijklmnop, 16Hqrstuvwxyz012345/
1554 x(1) = 16HABCDEFGHIJKLMNOP
1558 Invalid Hollerith constants examples:
1561 a = 8H12345678 ! Valid, but the Hollerith constant will be truncated.
1562 a = 0H ! At least one character is needed.
1565 In general, Hollerith constants were used to provide a rudimentary
1566 facility for handling character strings in early Fortran compilers,
1567 prior to the introduction of @code{CHARACTER} variables in Fortran 77;
1568 in those cases, the standard-compliant equivalent is to convert the
1569 program to use proper character strings. On occasion, there may be a
1570 case where the intent is specifically to initialize a numeric variable
1571 with a given byte sequence. In these cases, the same result can be
1572 obtained by using the @code{TRANSFER} statement, as in this example.
1574 INTEGER(KIND=4) :: a
1575 a = TRANSFER ("abcd", a) ! equivalent to: a = 4Habcd
1580 @subsection Cray pointers
1581 @cindex pointer, Cray
1583 Cray pointers are part of a non-standard extension that provides a
1584 C-like pointer in Fortran. This is accomplished through a pair of
1585 variables: an integer "pointer" that holds a memory address, and a
1586 "pointee" that is used to dereference the pointer.
1588 Pointer/pointee pairs are declared in statements of the form:
1590 pointer ( <pointer> , <pointee> )
1594 pointer ( <pointer1> , <pointee1> ), ( <pointer2> , <pointee2> ), ...
1596 The pointer is an integer that is intended to hold a memory address.
1597 The pointee may be an array or scalar. A pointee can be an assumed
1598 size array---that is, the last dimension may be left unspecified by
1599 using a @code{*} in place of a value---but a pointee cannot be an
1600 assumed shape array. No space is allocated for the pointee.
1602 The pointee may have its type declared before or after the pointer
1603 statement, and its array specification (if any) may be declared
1604 before, during, or after the pointer statement. The pointer may be
1605 declared as an integer prior to the pointer statement. However, some
1606 machines have default integer sizes that are different than the size
1607 of a pointer, and so the following code is not portable:
1612 If a pointer is declared with a kind that is too small, the compiler
1613 will issue a warning; the resulting binary will probably not work
1614 correctly, because the memory addresses stored in the pointers may be
1615 truncated. It is safer to omit the first line of the above example;
1616 if explicit declaration of ipt's type is omitted, then the compiler
1617 will ensure that ipt is an integer variable large enough to hold a
1620 Pointer arithmetic is valid with Cray pointers, but it is not the same
1621 as C pointer arithmetic. Cray pointers are just ordinary integers, so
1622 the user is responsible for determining how many bytes to add to a
1623 pointer in order to increment it. Consider the following example:
1627 pointer (ipt, pointee)
1631 The last statement does not set @code{ipt} to the address of
1632 @code{target(1)}, as it would in C pointer arithmetic. Adding @code{1}
1633 to @code{ipt} just adds one byte to the address stored in @code{ipt}.
1635 Any expression involving the pointee will be translated to use the
1636 value stored in the pointer as the base address.
1638 To get the address of elements, this extension provides an intrinsic
1639 function @code{LOC()}. The @code{LOC()} function is equivalent to the
1640 @code{&} operator in C, except the address is cast to an integer type:
1643 pointer(ipt, arpte(10))
1645 ipt = loc(ar) ! Makes arpte is an alias for ar
1646 arpte(1) = 1.0 ! Sets ar(1) to 1.0
1648 The pointer can also be set by a call to the @code{MALLOC} intrinsic
1651 Cray pointees often are used to alias an existing variable. For
1659 As long as @code{ipt} remains unchanged, @code{iarr} is now an alias for
1660 @code{target}. The optimizer, however, will not detect this aliasing, so
1661 it is unsafe to use @code{iarr} and @code{target} simultaneously. Using
1662 a pointee in any way that violates the Fortran aliasing rules or
1663 assumptions is illegal. It is the user's responsibility to avoid doing
1664 this; the compiler works under the assumption that no such aliasing
1667 Cray pointers will work correctly when there is no aliasing (i.e., when
1668 they are used to access a dynamically allocated block of memory), and
1669 also in any routine where a pointee is used, but any variable with which
1670 it shares storage is not used. Code that violates these rules may not
1671 run as the user intends. This is not a bug in the optimizer; any code
1672 that violates the aliasing rules is illegal. (Note that this is not
1673 unique to GNU Fortran; any Fortran compiler that supports Cray pointers
1674 will ``incorrectly'' optimize code with illegal aliasing.)
1676 There are a number of restrictions on the attributes that can be applied
1677 to Cray pointers and pointees. Pointees may not have the
1678 @code{ALLOCATABLE}, @code{INTENT}, @code{OPTIONAL}, @code{DUMMY},
1679 @code{TARGET}, @code{INTRINSIC}, or @code{POINTER} attributes. Pointers
1680 may not have the @code{DIMENSION}, @code{POINTER}, @code{TARGET},
1681 @code{ALLOCATABLE}, @code{EXTERNAL}, or @code{INTRINSIC} attributes, nor
1682 may they be function results. Pointees may not occur in more than one
1683 pointer statement. A pointee cannot be a pointer. Pointees cannot occur
1684 in equivalence, common, or data statements.
1686 A Cray pointer may also point to a function or a subroutine. For
1687 example, the following excerpt is valid:
1691 pointer (subptr,subpte)
1701 A pointer may be modified during the course of a program, and this
1702 will change the location to which the pointee refers. However, when
1703 pointees are passed as arguments, they are treated as ordinary
1704 variables in the invoked function. Subsequent changes to the pointer
1705 will not change the base address of the array that was passed.
1707 @node CONVERT specifier
1708 @subsection @code{CONVERT} specifier
1709 @cindex @code{CONVERT} specifier
1711 GNU Fortran allows the conversion of unformatted data between little-
1712 and big-endian representation to facilitate moving of data
1713 between different systems. The conversion can be indicated with
1714 the @code{CONVERT} specifier on the @code{OPEN} statement.
1715 @xref{GFORTRAN_CONVERT_UNIT}, for an alternative way of specifying
1716 the data format via an environment variable.
1718 Valid values for @code{CONVERT} are:
1720 @item @code{CONVERT='NATIVE'} Use the native format. This is the default.
1721 @item @code{CONVERT='SWAP'} Swap between little- and big-endian.
1722 @item @code{CONVERT='LITTLE_ENDIAN'} Use the little-endian representation
1723 for unformatted files.
1724 @item @code{CONVERT='BIG_ENDIAN'} Use the big-endian representation for
1728 Using the option could look like this:
1730 open(file='big.dat',form='unformatted',access='sequential', &
1731 convert='big_endian')
1734 The value of the conversion can be queried by using
1735 @code{INQUIRE(CONVERT=ch)}. The values returned are
1736 @code{'BIG_ENDIAN'} and @code{'LITTLE_ENDIAN'}.
1738 @code{CONVERT} works between big- and little-endian for
1739 @code{INTEGER} values of all supported kinds and for @code{REAL}
1740 on IEEE systems of kinds 4 and 8. Conversion between different
1741 ``extended double'' types on different architectures such as
1742 m68k and x86_64, which GNU Fortran
1743 supports as @code{REAL(KIND=10)} and @code{REAL(KIND=16)}, will
1746 @emph{Note that the values specified via the GFORTRAN_CONVERT_UNIT
1747 environment variable will override the CONVERT specifier in the
1748 open statement}. This is to give control over data formats to
1749 users who do not have the source code of their program available.
1751 Using anything but the native representation for unformatted data
1752 carries a significant speed overhead. If speed in this area matters
1753 to you, it is best if you use this only for data that needs to be
1760 OpenMP (Open Multi-Processing) is an application programming
1761 interface (API) that supports multi-platform shared memory
1762 multiprocessing programming in C/C++ and Fortran on many
1763 architectures, including Unix and Microsoft Windows platforms.
1764 It consists of a set of compiler directives, library routines,
1765 and environment variables that influence run-time behavior.
1767 GNU Fortran strives to be compatible to the
1768 @uref{http://www.openmp.org/mp-documents/spec30.pdf,
1769 OpenMP Application Program Interface v3.0}.
1771 To enable the processing of the OpenMP directive @code{!$omp} in
1772 free-form source code; the @code{c$omp}, @code{*$omp} and @code{!$omp}
1773 directives in fixed form; the @code{!$} conditional compilation sentinels
1774 in free form; and the @code{c$}, @code{*$} and @code{!$} sentinels
1775 in fixed form, @command{gfortran} needs to be invoked with the
1776 @option{-fopenmp}. This also arranges for automatic linking of the
1777 GNU OpenMP runtime library @ref{Top,,libgomp,libgomp,GNU OpenMP
1780 The OpenMP Fortran runtime library routines are provided both in a
1781 form of a Fortran 90 module named @code{omp_lib} and in a form of
1782 a Fortran @code{include} file named @file{omp_lib.h}.
1784 An example of a parallelized loop taken from Appendix A.1 of
1785 the OpenMP Application Program Interface v2.5:
1787 SUBROUTINE A1(N, A, B)
1790 !$OMP PARALLEL DO !I is private by default
1792 B(I) = (A(I) + A(I-1)) / 2.0
1794 !$OMP END PARALLEL DO
1801 @option{-fopenmp} implies @option{-frecursive}, i.e., all local arrays
1802 will be allocated on the stack. When porting existing code to OpenMP,
1803 this may lead to surprising results, especially to segmentation faults
1804 if the stacksize is limited.
1807 On glibc-based systems, OpenMP enabled applications cannot be statically
1808 linked due to limitations of the underlying pthreads-implementation. It
1809 might be possible to get a working solution if
1810 @command{-Wl,--whole-archive -lpthread -Wl,--no-whole-archive} is added
1811 to the command line. However, this is not supported by @command{gcc} and
1812 thus not recommended.
1815 @node Argument list functions
1816 @subsection Argument list functions @code{%VAL}, @code{%REF} and @code{%LOC}
1817 @cindex argument list functions
1822 GNU Fortran supports argument list functions @code{%VAL}, @code{%REF}
1823 and @code{%LOC} statements, for backward compatibility with g77.
1824 It is recommended that these should be used only for code that is
1825 accessing facilities outside of GNU Fortran, such as operating system
1826 or windowing facilities. It is best to constrain such uses to isolated
1827 portions of a program--portions that deal specifically and exclusively
1828 with low-level, system-dependent facilities. Such portions might well
1829 provide a portable interface for use by the program as a whole, but are
1830 themselves not portable, and should be thoroughly tested each time they
1831 are rebuilt using a new compiler or version of a compiler.
1833 @code{%VAL} passes a scalar argument by value, @code{%REF} passes it by
1834 reference and @code{%LOC} passes its memory location. Since gfortran
1835 already passes scalar arguments by reference, @code{%REF} is in effect
1836 a do-nothing. @code{%LOC} has the same effect as a Fortran pointer.
1838 An example of passing an argument by value to a C subroutine foo.:
1841 C prototype void foo_ (float x);
1850 For details refer to the g77 manual
1851 @uref{http://gcc.gnu.org/@/onlinedocs/@/gcc-3.4.6/@/g77/@/index.html#Top}.
1853 Also, @code{c_by_val.f} and its partner @code{c_by_val.c} of the
1854 GNU Fortran testsuite are worth a look.
1857 @node Extensions not implemented in GNU Fortran
1858 @section Extensions not implemented in GNU Fortran
1859 @cindex extensions, not implemented
1861 The long history of the Fortran language, its wide use and broad
1862 userbase, the large number of different compiler vendors and the lack of
1863 some features crucial to users in the first standards have lead to the
1864 existence of a number of important extensions to the language. While
1865 some of the most useful or popular extensions are supported by the GNU
1866 Fortran compiler, not all existing extensions are supported. This section
1867 aims at listing these extensions and offering advice on how best make
1868 code that uses them running with the GNU Fortran compiler.
1870 @c More can be found here:
1871 @c -- http://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/Missing-Features.html
1872 @c -- the list of Fortran and libgfortran bugs closed as WONTFIX:
1873 @c http://tinyurl.com/2u4h5y
1876 * STRUCTURE and RECORD::
1877 @c * UNION and MAP::
1878 * ENCODE and DECODE statements::
1879 * Variable FORMAT expressions::
1880 @c * Q edit descriptor::
1881 @c * AUTOMATIC statement::
1882 @c * TYPE and ACCEPT I/O Statements::
1883 @c * .XOR. operator::
1884 @c * CARRIAGECONTROL, DEFAULTFILE, DISPOSE and RECORDTYPE I/O specifiers::
1885 @c * Omitted arguments in procedure call::
1886 * Alternate complex function syntax::
1890 @node STRUCTURE and RECORD
1891 @subsection @code{STRUCTURE} and @code{RECORD}
1892 @cindex @code{STRUCTURE}
1893 @cindex @code{RECORD}
1895 Structures are user-defined aggregate data types; this functionality was
1896 standardized in Fortran 90 with an different syntax, under the name of
1897 ``derived types''. Here is an example of code using the non portable
1901 ! Declaring a structure named ``item'' and containing three fields:
1902 ! an integer ID, an description string and a floating-point price.
1905 CHARACTER(LEN=200) description
1909 ! Define two variables, an single record of type ``item''
1910 ! named ``pear'', and an array of items named ``store_catalog''
1911 RECORD /item/ pear, store_catalog(100)
1913 ! We can directly access the fields of both variables
1915 pear.description = "juicy D'Anjou pear"
1917 store_catalog(7).id = 7831
1918 store_catalog(7).description = "milk bottle"
1919 store_catalog(7).price = 1.2
1921 ! We can also manipulate the whole structure
1922 store_catalog(12) = pear
1923 print *, store_catalog(12)
1927 This code can easily be rewritten in the Fortran 90 syntax as following:
1930 ! ``STRUCTURE /name/ ... END STRUCTURE'' becomes
1931 ! ``TYPE name ... END TYPE''
1934 CHARACTER(LEN=200) description
1938 ! ``RECORD /name/ variable'' becomes ``TYPE(name) variable''
1939 TYPE(item) pear, store_catalog(100)
1941 ! Instead of using a dot (.) to access fields of a record, the
1942 ! standard syntax uses a percent sign (%)
1944 pear%description = "juicy D'Anjou pear"
1946 store_catalog(7)%id = 7831
1947 store_catalog(7)%description = "milk bottle"
1948 store_catalog(7)%price = 1.2
1950 ! Assignments of a whole variable don't change
1951 store_catalog(12) = pear
1952 print *, store_catalog(12)
1956 @c @node UNION and MAP
1957 @c @subsection @code{UNION} and @code{MAP}
1958 @c @cindex @code{UNION}
1959 @c @cindex @code{MAP}
1961 @c For help writing this one, see
1962 @c http://www.eng.umd.edu/~nsw/ench250/fortran1.htm#UNION and
1963 @c http://www.tacc.utexas.edu/services/userguides/pgi/pgiws_ug/pgi32u06.htm
1966 @node ENCODE and DECODE statements
1967 @subsection @code{ENCODE} and @code{DECODE} statements
1968 @cindex @code{ENCODE}
1969 @cindex @code{DECODE}
1971 GNU Fortran doesn't support the @code{ENCODE} and @code{DECODE}
1972 statements. These statements are best replaced by @code{READ} and
1973 @code{WRITE} statements involving internal files (@code{CHARACTER}
1974 variables and arrays), which have been part of the Fortran standard since
1975 Fortran 77. For example, replace a code fragment like
1980 c ... Code that sets LINE
1981 DECODE (80, 9000, LINE) A, B, C
1982 9000 FORMAT (1X, 3(F10.5))
1989 CHARACTER(LEN=80) LINE
1991 c ... Code that sets LINE
1992 READ (UNIT=LINE, FMT=9000) A, B, C
1993 9000 FORMAT (1X, 3(F10.5))
1996 Similarly, replace a code fragment like
2001 c ... Code that sets A, B and C
2002 ENCODE (80, 9000, LINE) A, B, C
2003 9000 FORMAT (1X, 'OUTPUT IS ', 3(F10.5))
2010 CHARACTER(LEN=80) LINE
2012 c ... Code that sets A, B and C
2013 WRITE (UNIT=LINE, FMT=9000) A, B, C
2014 9000 FORMAT (1X, 'OUTPUT IS ', 3(F10.5))
2018 @node Variable FORMAT expressions
2019 @subsection Variable @code{FORMAT} expressions
2020 @cindex @code{FORMAT}
2022 A variable @code{FORMAT} expression is format statement which includes
2023 angle brackets enclosing a Fortran expression: @code{FORMAT(I<N>)}. GNU
2024 Fortran does not support this legacy extension. The effect of variable
2025 format expressions can be reproduced by using the more powerful (and
2026 standard) combination of internal output and string formats. For example,
2027 replace a code fragment like this:
2038 c Variable declaration
2039 CHARACTER(LEN=20) FMT
2041 c Other code here...
2043 WRITE(FMT,'("(I", I0, ")")') N+1
2051 c Variable declaration
2052 CHARACTER(LEN=20) FMT
2054 c Other code here...
2057 WRITE(6,"(I" // ADJUSTL(FMT) // ")") INT1
2061 @node Alternate complex function syntax
2062 @subsection Alternate complex function syntax
2063 @cindex Complex function
2065 Some Fortran compilers, including @command{g77}, let the user declare
2066 complex functions with the syntax @code{COMPLEX FUNCTION name*16()}, as
2067 well as @code{COMPLEX*16 FUNCTION name()}. Both are non-standard, legacy
2068 extensions. @command{gfortran} accepts the latter form, which is more
2069 common, but not the former.
2073 @c ---------------------------------------------------------------------
2074 @c Mixed-Language Programming
2075 @c ---------------------------------------------------------------------
2077 @node Mixed-Language Programming
2078 @chapter Mixed-Language Programming
2079 @cindex Interoperability
2080 @cindex Mixed-language programming
2083 * Interoperability with C::
2084 * GNU Fortran Compiler Directives::
2085 * Non-Fortran Main Program::
2088 This chapter is about mixed-language interoperability, but also applies
2089 if one links Fortran code compiled by different compilers. In most cases,
2090 use of the C Binding features of the Fortran 2003 standard is sufficient,
2091 and their use is highly recommended.
2094 @node Interoperability with C
2095 @section Interoperability with C
2099 * Derived Types and struct::
2100 * Interoperable Global Variables::
2101 * Interoperable Subroutines and Functions::
2102 * Working with Pointers::
2103 * Further Interoperability of Fortran with C::
2106 Since Fortran 2003 (ISO/IEC 1539-1:2004(E)) there is a
2107 standardized way to generate procedure and derived-type
2108 declarations and global variables which are interoperable with C
2109 (ISO/IEC 9899:1999). The @code{bind(C)} attribute has been added
2110 to inform the compiler that a symbol shall be interoperable with C;
2111 also, some constraints are added. Note, however, that not
2112 all C features have a Fortran equivalent or vice versa. For instance,
2113 neither C's unsigned integers nor C's functions with variable number
2114 of arguments have an equivalent in Fortran.
2116 Note that array dimensions are reversely ordered in C and that arrays in
2117 C always start with index 0 while in Fortran they start by default with
2118 1. Thus, an array declaration @code{A(n,m)} in Fortran matches
2119 @code{A[m][n]} in C and accessing the element @code{A(i,j)} matches
2120 @code{A[j-1][i-1]}. The element following @code{A(i,j)} (C: @code{A[j-1][i-1]};
2121 assuming @math{i < n}) in memory is @code{A(i+1,j)} (C: @code{A[j-1][i]}).
2123 @node Intrinsic Types
2124 @subsection Intrinsic Types
2126 In order to ensure that exactly the same variable type and kind is used
2127 in C and Fortran, the named constants shall be used which are defined in the
2128 @code{ISO_C_BINDING} intrinsic module. That module contains named constants
2129 for kind parameters and character named constants for the escape sequences
2130 in C. For a list of the constants, see @ref{ISO_C_BINDING}.
2132 @node Derived Types and struct
2133 @subsection Derived Types and struct
2135 For compatibility of derived types with @code{struct}, one needs to use
2136 the @code{BIND(C)} attribute in the type declaration. For instance, the
2137 following type declaration
2141 TYPE, BIND(C) :: myType
2142 INTEGER(C_INT) :: i1, i2
2143 INTEGER(C_SIGNED_CHAR) :: i3
2144 REAL(C_DOUBLE) :: d1
2145 COMPLEX(C_FLOAT_COMPLEX) :: c1
2146 CHARACTER(KIND=C_CHAR) :: str(5)
2150 matches the following @code{struct} declaration in C
2155 /* Note: "char" might be signed or unsigned. */
2163 Derived types with the C binding attribute shall not have the @code{sequence}
2164 attribute, type parameters, the @code{extends} attribute, nor type-bound
2165 procedures. Every component must be of interoperable type and kind and may not
2166 have the @code{pointer} or @code{allocatable} attribute. The names of the
2167 variables are irrelevant for interoperability.
2169 As there exist no direct Fortran equivalents, neither unions nor structs
2170 with bit field or variable-length array members are interoperable.
2172 @node Interoperable Global Variables
2173 @subsection Interoperable Global Variables
2175 Variables can be made accessible from C using the C binding attribute,
2176 optionally together with specifying a binding name. Those variables
2177 have to be declared in the declaration part of a @code{MODULE},
2178 be of interoperable type, and have neither the @code{pointer} nor
2179 the @code{allocatable} attribute.
2185 integer(C_INT), bind(C, name="_MyProject_flags") :: global_flag
2186 type(myType), bind(C) :: tp
2190 Here, @code{_MyProject_flags} is the case-sensitive name of the variable
2191 as seen from C programs while @code{global_flag} is the case-insensitive
2192 name as seen from Fortran. If no binding name is specified, as for
2193 @var{tp}, the C binding name is the (lowercase) Fortran binding name.
2194 If a binding name is specified, only a single variable may be after the
2195 double colon. Note of warning: You cannot use a global variable to
2196 access @var{errno} of the C library as the C standard allows it to be
2197 a macro. Use the @code{IERRNO} intrinsic (GNU extension) instead.
2199 @node Interoperable Subroutines and Functions
2200 @subsection Interoperable Subroutines and Functions
2202 Subroutines and functions have to have the @code{BIND(C)} attribute to
2203 be compatible with C. The dummy argument declaration is relatively
2204 straightforward. However, one needs to be careful because C uses
2205 call-by-value by default while Fortran behaves usually similar to
2206 call-by-reference. Furthermore, strings and pointers are handled
2207 differently. Note that only explicit size and assumed-size arrays are
2208 supported but not assumed-shape or allocatable arrays.
2210 To pass a variable by value, use the @code{VALUE} attribute.
2211 Thus the following C prototype
2214 @code{int func(int i, int *j)}
2217 matches the Fortran declaration
2220 integer(c_int) function func(i,j)
2221 use iso_c_binding, only: c_int
2222 integer(c_int), VALUE :: i
2226 Note that pointer arguments also frequently need the @code{VALUE} attribute,
2227 see @ref{Working with Pointers}.
2229 Strings are handled quite differently in C and Fortran. In C a string
2230 is a @code{NUL}-terminated array of characters while in Fortran each string
2231 has a length associated with it and is thus not terminated (by e.g.
2232 @code{NUL}). For example, if one wants to use the following C function,
2236 void print_C(char *string) /* equivalent: char string[] */
2238 printf("%s\n", string);
2242 to print ``Hello World'' from Fortran, one can call it using
2245 use iso_c_binding, only: C_CHAR, C_NULL_CHAR
2247 subroutine print_c(string) bind(C, name="print_C")
2248 use iso_c_binding, only: c_char
2249 character(kind=c_char) :: string(*)
2250 end subroutine print_c
2252 call print_c(C_CHAR_"Hello World"//C_NULL_CHAR)
2255 As the example shows, one needs to ensure that the
2256 string is @code{NUL} terminated. Additionally, the dummy argument
2257 @var{string} of @code{print_C} is a length-one assumed-size
2258 array; using @code{character(len=*)} is not allowed. The example
2259 above uses @code{c_char_"Hello World"} to ensure the string
2260 literal has the right type; typically the default character
2261 kind and @code{c_char} are the same and thus @code{"Hello World"}
2262 is equivalent. However, the standard does not guarantee this.
2264 The use of strings is now further illustrated using the C library
2265 function @code{strncpy}, whose prototype is
2268 char *strncpy(char *restrict s1, const char *restrict s2, size_t n);
2271 The function @code{strncpy} copies at most @var{n} characters from
2272 string @var{s2} to @var{s1} and returns @var{s1}. In the following
2273 example, we ignore the return value:
2278 character(len=30) :: str,str2
2280 ! Ignore the return value of strncpy -> subroutine
2281 ! "restrict" is always assumed if we do not pass a pointer
2282 subroutine strncpy(dest, src, n) bind(C)
2284 character(kind=c_char), intent(out) :: dest(*)
2285 character(kind=c_char), intent(in) :: src(*)
2286 integer(c_size_t), value, intent(in) :: n
2287 end subroutine strncpy
2289 str = repeat('X',30) ! Initialize whole string with 'X'
2290 call strncpy(str, c_char_"Hello World"//C_NULL_CHAR, &
2291 len(c_char_"Hello World",kind=c_size_t))
2292 print '(a)', str ! prints: "Hello WorldXXXXXXXXXXXXXXXXXXX"
2296 The intrinsic procedures are described in @ref{Intrinsic Procedures}.
2298 @node Working with Pointers
2299 @subsection Working with Pointers
2301 C pointers are represented in Fortran via the special opaque derived type
2302 @code{type(c_ptr)} (with private components). Thus one needs to
2303 use intrinsic conversion procedures to convert from or to C pointers.
2308 type(c_ptr) :: cptr1, cptr2
2309 integer, target :: array(7), scalar
2310 integer, pointer :: pa(:), ps
2311 cptr1 = c_loc(array(1)) ! The programmer needs to ensure that the
2312 ! array is contiguous if required by the C
2314 cptr2 = c_loc(scalar)
2315 call c_f_pointer(cptr2, ps)
2316 call c_f_pointer(cptr2, pa, shape=[7])
2319 When converting C to Fortran arrays, the one-dimensional @code{SHAPE} argument
2322 If a pointer is a dummy-argument of an interoperable procedure, it usually
2323 has to be declared using the @code{VALUE} attribute. @code{void*}
2324 matches @code{TYPE(C_PTR), VALUE}, while @code{TYPE(C_PTR)} alone
2325 matches @code{void**}.
2327 Procedure pointers are handled analogously to pointers; the C type is
2328 @code{TYPE(C_FUNPTR)} and the intrinsic conversion procedures are
2329 @code{C_F_PROCPOINTER} and @code{C_FUNLOC}.
2331 Let's consider two examples of actually passing a procedure pointer from
2332 C to Fortran and vice versa. Note that these examples are also very
2333 similar to passing ordinary pointers between both languages.
2334 First, consider this code in C:
2337 /* Procedure implemented in Fortran. */
2338 void get_values (void (*)(double));
2340 /* Call-back routine we want called from Fortran. */
2344 printf ("Number is %f.\n", x);
2347 /* Call Fortran routine and pass call-back to it. */
2351 get_values (&print_it);
2355 A matching implementation for @code{get_values} in Fortran, that correctly
2356 receives the procedure pointer from C and is able to call it, is given
2357 in the following @code{MODULE}:
2363 ! Define interface of call-back routine.
2365 SUBROUTINE callback (x)
2366 USE, INTRINSIC :: ISO_C_BINDING
2367 REAL(KIND=C_DOUBLE), INTENT(IN), VALUE :: x
2368 END SUBROUTINE callback
2373 ! Define C-bound procedure.
2374 SUBROUTINE get_values (cproc) BIND(C)
2375 USE, INTRINSIC :: ISO_C_BINDING
2376 TYPE(C_FUNPTR), INTENT(IN), VALUE :: cproc
2378 PROCEDURE(callback), POINTER :: proc
2380 ! Convert C to Fortran procedure pointer.
2381 CALL C_F_PROCPOINTER (cproc, proc)
2384 CALL proc (1.0_C_DOUBLE)
2385 CALL proc (-42.0_C_DOUBLE)
2386 CALL proc (18.12_C_DOUBLE)
2387 END SUBROUTINE get_values
2392 Next, we want to call a C routine that expects a procedure pointer argument
2393 and pass it a Fortran procedure (which clearly must be interoperable!).
2394 Again, the C function may be:
2398 call_it (int (*func)(int), int arg)
2404 It can be used as in the following Fortran code:
2408 USE, INTRINSIC :: ISO_C_BINDING
2411 ! Define interface of C function.
2413 INTEGER(KIND=C_INT) FUNCTION call_it (func, arg) BIND(C)
2414 USE, INTRINSIC :: ISO_C_BINDING
2415 TYPE(C_FUNPTR), INTENT(IN), VALUE :: func
2416 INTEGER(KIND=C_INT), INTENT(IN), VALUE :: arg
2417 END FUNCTION call_it
2422 ! Define procedure passed to C function.
2423 ! It must be interoperable!
2424 INTEGER(KIND=C_INT) FUNCTION double_it (arg) BIND(C)
2425 INTEGER(KIND=C_INT), INTENT(IN), VALUE :: arg
2426 double_it = arg + arg
2427 END FUNCTION double_it
2430 SUBROUTINE foobar ()
2431 TYPE(C_FUNPTR) :: cproc
2432 INTEGER(KIND=C_INT) :: i
2434 ! Get C procedure pointer.
2435 cproc = C_FUNLOC (double_it)
2438 DO i = 1_C_INT, 10_C_INT
2439 PRINT *, call_it (cproc, i)
2441 END SUBROUTINE foobar
2446 @node Further Interoperability of Fortran with C
2447 @subsection Further Interoperability of Fortran with C
2449 Assumed-shape and allocatable arrays are passed using an array descriptor
2450 (dope vector). The internal structure of the array descriptor used
2451 by GNU Fortran is not yet documented and will change. There will also be
2452 a Technical Report (TR 29113) which standardizes an interoperable
2453 array descriptor. Until then, you can use the Chasm Language
2454 Interoperability Tools, @url{http://chasm-interop.sourceforge.net/},
2455 which provide an interface to GNU Fortran's array descriptor.
2457 The technical report 29113 will presumably also include support for
2458 C-interoperable @code{OPTIONAL} and for assumed-rank and assumed-type
2459 dummy arguments. However, the TR has neither been approved nor implemented
2460 in GNU Fortran; therefore, these features are not yet available.
2464 @node GNU Fortran Compiler Directives
2465 @section GNU Fortran Compiler Directives
2467 The Fortran standard standard describes how a conforming program shall
2468 behave; however, the exact implementation is not standardized. In order
2469 to allow the user to choose specific implementation details, compiler
2470 directives can be used to set attributes of variables and procedures
2471 which are not part of the standard. Whether a given attribute is
2472 supported and its exact effects depend on both the operating system and
2473 on the processor; see
2474 @ref{Top,,C Extensions,gcc,Using the GNU Compiler Collection (GCC)}
2477 For procedures and procedure pointers, the following attributes can
2478 be used to change the calling convention:
2481 @item @code{CDECL} -- standard C calling convention
2482 @item @code{STDCALL} -- convention where the called procedure pops the stack
2483 @item @code{FASTCALL} -- part of the arguments are passed via registers
2484 instead using the stack
2487 Besides changing the calling convention, the attributes also influence
2488 the decoration of the symbol name, e.g., by a leading underscore or by
2489 a trailing at-sign followed by the number of bytes on the stack. When
2490 assigning a procedure to a procedure pointer, both should use the same
2493 On some systems, procedures and global variables (module variables and
2494 @code{COMMON} blocks) need special handling to be accessible when they
2495 are in a shared library. The following attributes are available:
2498 @item @code{DLLEXPORT} -- provide a global pointer to a pointer in the DLL
2499 @item @code{DLLIMPORT} -- reference the function or variable using a global pointer
2502 The attributes are specified using the syntax
2504 @code{!GCC$ ATTRIBUTES} @var{attribute-list} @code{::} @var{variable-list}
2506 where in free-form source code only whitespace is allowed before @code{!GCC$}
2507 and in fixed-form source code @code{!GCC$}, @code{cGCC$} or @code{*GCC$} shall
2508 start in the first column.
2510 For procedures, the compiler directives shall be placed into the body
2511 of the procedure; for variables and procedure pointers, they shall be in
2512 the same declaration part as the variable or procedure pointer.
2516 @node Non-Fortran Main Program
2517 @section Non-Fortran Main Program
2520 * _gfortran_set_args:: Save command-line arguments
2521 * _gfortran_set_options:: Set library option flags
2522 * _gfortran_set_convert:: Set endian conversion
2523 * _gfortran_set_record_marker:: Set length of record markers
2524 * _gfortran_set_max_subrecord_length:: Set subrecord length
2525 * _gfortran_set_fpe:: Set when a Floating Point Exception should be raised
2528 Even if you are doing mixed-language programming, it is very
2529 likely that you do not need to know or use the information in this
2530 section. Since it is about the internal structure of GNU Fortran,
2531 it may also change in GCC minor releases.
2533 When you compile a @code{PROGRAM} with GNU Fortran, a function
2534 with the name @code{main} (in the symbol table of the object file)
2535 is generated, which initializes the libgfortran library and then
2536 calls the actual program which uses the name @code{MAIN__}, for
2537 historic reasons. If you link GNU Fortran compiled procedures
2538 to, e.g., a C or C++ program or to a Fortran program compiled by
2539 a different compiler, the libgfortran library is not initialized
2540 and thus a few intrinsic procedures do not work properly, e.g.
2541 those for obtaining the command-line arguments.
2543 Therefore, if your @code{PROGRAM} is not compiled with
2544 GNU Fortran and the GNU Fortran compiled procedures require
2545 intrinsics relying on the library initialization, you need to
2546 initialize the library yourself. Using the default options,
2547 gfortran calls @code{_gfortran_set_args} and
2548 @code{_gfortran_set_options}. The initialization of the former
2549 is needed if the called procedures access the command line
2550 (and for backtracing); the latter sets some flags based on the
2551 standard chosen or to enable backtracing. In typical programs,
2552 it is not necessary to call any initialization function.
2554 If your @code{PROGRAM} is compiled with GNU Fortran, you shall
2555 not call any of the following functions. The libgfortran
2556 initialization functions are shown in C syntax but using C
2557 bindings they are also accessible from Fortran.
2560 @node _gfortran_set_args
2561 @subsection @code{_gfortran_set_args} --- Save command-line arguments
2562 @fnindex _gfortran_set_args
2563 @cindex libgfortran initialization, set_args
2566 @item @emph{Description}:
2567 @code{_gfortran_set_args} saves the command-line arguments; this
2568 initialization is required if any of the command-line intrinsics
2569 is called. Additionally, it shall be called if backtracing is
2570 enabled (see @code{_gfortran_set_options}).
2572 @item @emph{Syntax}:
2573 @code{void _gfortran_set_args (int argc, char *argv[])}
2575 @item @emph{Arguments}:
2576 @multitable @columnfractions .15 .70
2577 @item @var{argc} @tab number of command line argument strings
2578 @item @var{argv} @tab the command-line argument strings; argv[0]
2579 is the pathname of the executable itself.
2582 @item @emph{Example}:
2584 int main (int argc, char *argv[])
2586 /* Initialize libgfortran. */
2587 _gfortran_set_args (argc, argv);
2594 @node _gfortran_set_options
2595 @subsection @code{_gfortran_set_options} --- Set library option flags
2596 @fnindex _gfortran_set_options
2597 @cindex libgfortran initialization, set_options
2600 @item @emph{Description}:
2601 @code{_gfortran_set_options} sets several flags related to the Fortran
2602 standard to be used, whether backtracing or core dumps should be enabled
2603 and whether range checks should be performed. The syntax allows for
2604 upward compatibility since the number of passed flags is specified; for
2605 non-passed flags, the default value is used. See also
2606 @pxref{Code Gen Options}. Please note that not all flags are actually
2609 @item @emph{Syntax}:
2610 @code{void _gfortran_set_options (int num, int options[])}
2612 @item @emph{Arguments}:
2613 @multitable @columnfractions .15 .70
2614 @item @var{num} @tab number of options passed
2615 @item @var{argv} @tab The list of flag values
2618 @item @emph{option flag list}:
2619 @multitable @columnfractions .15 .70
2620 @item @var{option}[0] @tab Allowed standard; can give run-time errors
2621 if e.g. an input-output edit descriptor is invalid in a given standard.
2622 Possible values are (bitwise or-ed) @code{GFC_STD_F77} (1),
2623 @code{GFC_STD_F95_OBS} (2), @code{GFC_STD_F95_DEL} (4), @code{GFC_STD_F95}
2624 (8), @code{GFC_STD_F2003} (16), @code{GFC_STD_GNU} (32),
2625 @code{GFC_STD_LEGACY} (64), @code{GFC_STD_F2008} (128), and
2626 @code{GFC_STD_F2008_OBS} (256). Default: @code{GFC_STD_F95_OBS
2627 | GFC_STD_F95_DEL | GFC_STD_F95 | GFC_STD_F2003 | GFC_STD_F2008
2628 | GFC_STD_F2008_OBS | GFC_STD_F77 | GFC_STD_GNU | GFC_STD_LEGACY}.
2629 @item @var{option}[1] @tab Standard-warning flag; prints a warning to
2630 standard error. Default: @code{GFC_STD_F95_DEL | GFC_STD_LEGACY}.
2631 @item @var{option}[2] @tab If non zero, enable pedantic checking.
2633 @item @var{option}[3] @tab If non zero, enable core dumps on run-time
2634 errors. Default: off.
2635 @item @var{option}[4] @tab If non zero, enable backtracing on run-time
2636 errors. Default: off.
2637 Note: Installs a signal handler and requires command-line
2638 initialization using @code{_gfortran_set_args}.
2639 @item @var{option}[5] @tab If non zero, supports signed zeros.
2641 @item @var{option}[6] @tab Enables run-time checking. Possible values
2642 are (bitwise or-ed): GFC_RTCHECK_BOUNDS (1), GFC_RTCHECK_ARRAY_TEMPS (2),
2643 GFC_RTCHECK_RECURSION (4), GFC_RTCHECK_DO (16), GFC_RTCHECK_POINTER (32).
2645 @item @var{option}[7] @tab If non zero, range checking is enabled.
2646 Default: enabled. See -frange-check (@pxref{Code Gen Options}).
2649 @item @emph{Example}:
2651 /* Use gfortran 4.5 default options. */
2652 static int options[] = @{68, 255, 0, 0, 0, 1, 0, 1@};
2653 _gfortran_set_options (8, &options);
2658 @node _gfortran_set_convert
2659 @subsection @code{_gfortran_set_convert} --- Set endian conversion
2660 @fnindex _gfortran_set_convert
2661 @cindex libgfortran initialization, set_convert
2664 @item @emph{Description}:
2665 @code{_gfortran_set_convert} set the representation of data for
2668 @item @emph{Syntax}:
2669 @code{void _gfortran_set_convert (int conv)}
2671 @item @emph{Arguments}:
2672 @multitable @columnfractions .15 .70
2673 @item @var{conv} @tab Endian conversion, possible values:
2674 GFC_CONVERT_NATIVE (0, default), GFC_CONVERT_SWAP (1),
2675 GFC_CONVERT_BIG (2), GFC_CONVERT_LITTLE (3).
2678 @item @emph{Example}:
2680 int main (int argc, char *argv[])
2682 /* Initialize libgfortran. */
2683 _gfortran_set_args (argc, argv);
2684 _gfortran_set_convert (1);
2691 @node _gfortran_set_record_marker
2692 @subsection @code{_gfortran_set_record_marker} --- Set length of record markers
2693 @fnindex _gfortran_set_record_marker
2694 @cindex libgfortran initialization, set_record_marker
2697 @item @emph{Description}:
2698 @code{_gfortran_set_record_marker} sets the length of record markers
2699 for unformatted files.
2701 @item @emph{Syntax}:
2702 @code{void _gfortran_set_record_marker (int val)}
2704 @item @emph{Arguments}:
2705 @multitable @columnfractions .15 .70
2706 @item @var{val} @tab Length of the record marker; valid values
2707 are 4 and 8. Default is 4.
2710 @item @emph{Example}:
2712 int main (int argc, char *argv[])
2714 /* Initialize libgfortran. */
2715 _gfortran_set_args (argc, argv);
2716 _gfortran_set_record_marker (8);
2723 @node _gfortran_set_fpe
2724 @subsection @code{_gfortran_set_fpe} --- Set when a Floating Point Exception should be raised
2725 @fnindex _gfortran_set_fpe
2726 @cindex libgfortran initialization, set_fpe
2729 @item @emph{Description}:
2730 @code{_gfortran_set_fpe} sets the IEEE exceptions for which a
2731 Floating Point Exception (FPE) should be raised. On most systems,
2732 this will result in a SIGFPE signal being sent and the program
2735 @item @emph{Syntax}:
2736 @code{void _gfortran_set_fpe (int val)}
2738 @item @emph{Arguments}:
2739 @multitable @columnfractions .15 .70
2740 @item @var{option}[0] @tab IEEE exceptions. Possible values are
2741 (bitwise or-ed) zero (0, default) no trapping,
2742 @code{GFC_FPE_INVALID} (1), @code{GFC_FPE_DENORMAL} (2),
2743 @code{GFC_FPE_ZERO} (4), @code{GFC_FPE_OVERFLOW} (8),
2744 @code{GFC_FPE_UNDERFLOW} (16), and @code{GFC_FPE_PRECISION} (32).
2747 @item @emph{Example}:
2749 int main (int argc, char *argv[])
2751 /* Initialize libgfortran. */
2752 _gfortran_set_args (argc, argv);
2753 /* FPE for invalid operations such as SQRT(-1.0). */
2754 _gfortran_set_fpe (1);
2761 @node _gfortran_set_max_subrecord_length
2762 @subsection @code{_gfortran_set_max_subrecord_length} --- Set subrecord length
2763 @fnindex _gfortran_set_max_subrecord_length
2764 @cindex libgfortran initialization, set_max_subrecord_length
2767 @item @emph{Description}:
2768 @code{_gfortran_set_max_subrecord_length} set the maximum length
2769 for a subrecord. This option only makes sense for testing and
2770 debugging of unformatted I/O.
2772 @item @emph{Syntax}:
2773 @code{void _gfortran_set_max_subrecord_length (int val)}
2775 @item @emph{Arguments}:
2776 @multitable @columnfractions .15 .70
2777 @item @var{val} @tab the maximum length for a subrecord;
2778 the maximum permitted value is 2147483639, which is also
2782 @item @emph{Example}:
2784 int main (int argc, char *argv[])
2786 /* Initialize libgfortran. */
2787 _gfortran_set_args (argc, argv);
2788 _gfortran_set_max_subrecord_length (8);
2796 @c Intrinsic Procedures
2797 @c ---------------------------------------------------------------------
2799 @include intrinsic.texi
2806 @c ---------------------------------------------------------------------
2808 @c ---------------------------------------------------------------------
2811 @unnumbered Contributing
2812 @cindex Contributing
2814 Free software is only possible if people contribute to efforts
2816 We're always in need of more people helping out with ideas
2817 and comments, writing documentation and contributing code.
2819 If you want to contribute to GNU Fortran,
2820 have a look at the long lists of projects you can take on.
2821 Some of these projects are small,
2822 some of them are large;
2823 some are completely orthogonal to the rest of what is
2824 happening on GNU Fortran,
2825 but others are ``mainstream'' projects in need of enthusiastic hackers.
2826 All of these projects are important!
2827 We'll eventually get around to the things here,
2828 but they are also things doable by someone who is willing and able.
2833 * Proposed Extensions::
2838 @section Contributors to GNU Fortran
2839 @cindex Contributors
2843 Most of the parser was hand-crafted by @emph{Andy Vaught}, who is
2844 also the initiator of the whole project. Thanks Andy!
2845 Most of the interface with GCC was written by @emph{Paul Brook}.
2847 The following individuals have contributed code and/or
2848 ideas and significant help to the GNU Fortran project
2849 (in alphabetical order):
2852 @item Janne Blomqvist
2853 @item Steven Bosscher
2856 @item Fran@,{c}ois-Xavier Coudert
2860 @item Bernhard Fischer
2862 @item Richard Guenther
2863 @item Richard Henderson
2864 @item Katherine Holcomb
2866 @item Niels Kristian Bech Jensen
2867 @item Steven Johnson
2868 @item Steven G. Kargl
2876 @item Christopher D. Rickett
2877 @item Richard Sandiford
2878 @item Tobias Schl@"uter
2887 The following people have contributed bug reports,
2888 smaller or larger patches,
2889 and much needed feedback and encouragement for the
2890 GNU Fortran project:
2894 @item Dominique d'Humi@`eres
2896 @item Erik Schnetter
2897 @item Joost VandeVondele
2900 Many other individuals have helped debug,
2901 test and improve the GNU Fortran compiler over the past few years,
2902 and we welcome you to do the same!
2903 If you already have done so,
2904 and you would like to see your name listed in the
2905 list above, please contact us.
2913 @item Help build the test suite
2914 Solicit more code for donation to the test suite: the more extensive the
2915 testsuite, the smaller the risk of breaking things in the future! We can
2916 keep code private on request.
2918 @item Bug hunting/squishing
2919 Find bugs and write more test cases! Test cases are especially very
2920 welcome, because it allows us to concentrate on fixing bugs instead of
2921 isolating them. Going through the bugzilla database at
2922 @url{http://gcc.gnu.org/@/bugzilla/} to reduce testcases posted there and
2923 add more information (for example, for which version does the testcase
2924 work, for which versions does it fail?) is also very helpful.
2929 @node Proposed Extensions
2930 @section Proposed Extensions
2932 Here's a list of proposed extensions for the GNU Fortran compiler, in no particular
2933 order. Most of these are necessary to be fully compatible with
2934 existing Fortran compilers, but they are not part of the official
2935 J3 Fortran 95 standard.
2937 @subsection Compiler extensions:
2940 User-specified alignment rules for structures.
2943 Automatically extend single precision constants to double.
2946 Compile code that conserves memory by dynamically allocating common and
2947 module storage either on stack or heap.
2950 Compile flag to generate code for array conformance checking (suggest -CC).
2953 User control of symbol names (underscores, etc).
2956 Compile setting for maximum size of stack frame size before spilling
2957 parts to static or heap.
2960 Flag to force local variables into static space.
2963 Flag to force local variables onto stack.
2967 @subsection Environment Options
2970 Pluggable library modules for random numbers, linear algebra.
2971 LA should use BLAS calling conventions.
2974 Environment variables controlling actions on arithmetic exceptions like
2975 overflow, underflow, precision loss---Generate NaN, abort, default.
2979 Set precision for fp units that support it (i387).
2982 Variable for setting fp rounding mode.
2985 Variable to fill uninitialized variables with a user-defined bit
2989 Environment variable controlling filename that is opened for that unit
2993 Environment variable to clear/trash memory being freed.
2996 Environment variable to control tracing of allocations and frees.
2999 Environment variable to display allocated memory at normal program end.
3002 Environment variable for filename for * IO-unit.
3005 Environment variable for temporary file directory.
3008 Environment variable forcing standard output to be line buffered (unix).
3013 @c ---------------------------------------------------------------------
3014 @c GNU General Public License
3015 @c ---------------------------------------------------------------------
3017 @include gpl_v3.texi
3021 @c ---------------------------------------------------------------------
3022 @c GNU Free Documentation License
3023 @c ---------------------------------------------------------------------
3029 @c ---------------------------------------------------------------------
3030 @c Funding Free Software
3031 @c ---------------------------------------------------------------------
3033 @include funding.texi
3035 @c ---------------------------------------------------------------------
3037 @c ---------------------------------------------------------------------
3040 @unnumbered Option Index
3041 @command{gfortran}'s command line options are indexed here without any
3042 initial @samp{-} or @samp{--}. Where an option has both positive and
3043 negative forms (such as -foption and -fno-option), relevant entries in
3044 the manual are indexed under the most appropriate form; it may sometimes
3045 be useful to look up both forms.
3049 @unnumbered Keyword Index