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.
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20 @c until they are incorporated into the official Texinfo distribution.
21 @c They borrow heavily from Texinfo's \unnchapentry definitions.
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60 @c Use with @@smallbook.
62 @c %** start of document
64 @c Cause even numbered pages to be printed on the left hand side of
65 @c the page and odd numbered pages to be printed on the right hand
66 @c side of the page. Using this, you can print on both sides of a
67 @c sheet of paper and have the text on the same part of the sheet.
69 @c The text on right hand pages is pushed towards the right hand
70 @c margin and the text on left hand pages is pushed toward the left
72 @c (To provide the reverse effect, set bindingoffset to -0.75in.)
75 @c \global\bindingoffset=0.75in
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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.
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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_TMPDIR:: Directory for scratch files
583 * GFORTRAN_UNBUFFERED_ALL:: Don't buffer I/O for all units.
584 * GFORTRAN_UNBUFFERED_PRECONNECTED:: Don't buffer I/O for preconnected units.
585 * GFORTRAN_SHOW_LOCUS:: Show location for runtime errors
586 * GFORTRAN_OPTIONAL_PLUS:: Print leading + where permitted
587 * GFORTRAN_DEFAULT_RECL:: Default record length for new files
588 * GFORTRAN_LIST_SEPARATOR:: Separator for list output
589 * GFORTRAN_CONVERT_UNIT:: Set endianness for unformatted I/O
590 * GFORTRAN_ERROR_BACKTRACE:: Show backtrace on run-time errors
593 @node GFORTRAN_STDIN_UNIT
594 @section @env{GFORTRAN_STDIN_UNIT}---Unit number for standard input
596 This environment variable can be used to select the unit number
597 preconnected to standard input. This must be a positive integer.
598 The default value is 5.
600 @node GFORTRAN_STDOUT_UNIT
601 @section @env{GFORTRAN_STDOUT_UNIT}---Unit number for standard output
603 This environment variable can be used to select the unit number
604 preconnected to standard output. This must be a positive integer.
605 The default value is 6.
607 @node GFORTRAN_STDERR_UNIT
608 @section @env{GFORTRAN_STDERR_UNIT}---Unit number for standard error
610 This environment variable can be used to select the unit number
611 preconnected to standard error. This must be a positive integer.
612 The default value is 0.
614 @node GFORTRAN_TMPDIR
615 @section @env{GFORTRAN_TMPDIR}---Directory for scratch files
617 This environment variable controls where scratch files are
618 created. If this environment variable is missing,
619 GNU Fortran searches for the environment variable @env{TMP}, then @env{TEMP}.
620 If these are missing, the default is @file{/tmp}.
622 @node GFORTRAN_UNBUFFERED_ALL
623 @section @env{GFORTRAN_UNBUFFERED_ALL}---Don't buffer I/O on all units
625 This environment variable controls whether all I/O is unbuffered. If
626 the first letter is @samp{y}, @samp{Y} or @samp{1}, all I/O is
627 unbuffered. This will slow down small sequential reads and writes. If
628 the first letter is @samp{n}, @samp{N} or @samp{0}, I/O is buffered.
631 @node GFORTRAN_UNBUFFERED_PRECONNECTED
632 @section @env{GFORTRAN_UNBUFFERED_PRECONNECTED}---Don't buffer I/O on preconnected units
634 The environment variable named @env{GFORTRAN_UNBUFFERED_PRECONNECTED} controls
635 whether I/O on a preconnected unit (i.e.@: STDOUT or STDERR) is unbuffered. If
636 the first letter is @samp{y}, @samp{Y} or @samp{1}, I/O is unbuffered. This
637 will slow down small sequential reads and writes. If the first letter
638 is @samp{n}, @samp{N} or @samp{0}, I/O is buffered. This is the default.
640 @node GFORTRAN_SHOW_LOCUS
641 @section @env{GFORTRAN_SHOW_LOCUS}---Show location for runtime errors
643 If the first letter is @samp{y}, @samp{Y} or @samp{1}, filename and
644 line numbers for runtime errors are printed. If the first letter is
645 @samp{n}, @samp{N} or @samp{0}, don't print filename and line numbers
646 for runtime errors. The default is to print the location.
648 @node GFORTRAN_OPTIONAL_PLUS
649 @section @env{GFORTRAN_OPTIONAL_PLUS}---Print leading + where permitted
651 If the first letter is @samp{y}, @samp{Y} or @samp{1},
652 a plus sign is printed
653 where permitted by the Fortran standard. If the first letter
654 is @samp{n}, @samp{N} or @samp{0}, a plus sign is not printed
655 in most cases. Default is not to print plus signs.
657 @node GFORTRAN_DEFAULT_RECL
658 @section @env{GFORTRAN_DEFAULT_RECL}---Default record length for new files
660 This environment variable specifies the default record length, in
661 bytes, for files which are opened without a @code{RECL} tag in the
662 @code{OPEN} statement. This must be a positive integer. The
663 default value is 1073741824 bytes (1 GB).
665 @node GFORTRAN_LIST_SEPARATOR
666 @section @env{GFORTRAN_LIST_SEPARATOR}---Separator for list output
668 This environment variable specifies the separator when writing
669 list-directed output. It may contain any number of spaces and
670 at most one comma. If you specify this on the command line,
671 be sure to quote spaces, as in
673 $ GFORTRAN_LIST_SEPARATOR=' , ' ./a.out
675 when @command{a.out} is the compiled Fortran program that you want to run.
676 Default is a single space.
678 @node GFORTRAN_CONVERT_UNIT
679 @section @env{GFORTRAN_CONVERT_UNIT}---Set endianness for unformatted I/O
681 By setting the @env{GFORTRAN_CONVERT_UNIT} variable, it is possible
682 to change the representation of data for unformatted files.
683 The syntax for the @env{GFORTRAN_CONVERT_UNIT} variable is:
685 GFORTRAN_CONVERT_UNIT: mode | mode ';' exception | exception ;
686 mode: 'native' | 'swap' | 'big_endian' | 'little_endian' ;
687 exception: mode ':' unit_list | unit_list ;
688 unit_list: unit_spec | unit_list unit_spec ;
689 unit_spec: INTEGER | INTEGER '-' INTEGER ;
691 The variable consists of an optional default mode, followed by
692 a list of optional exceptions, which are separated by semicolons
693 from the preceding default and each other. Each exception consists
694 of a format and a comma-separated list of units. Valid values for
695 the modes are the same as for the @code{CONVERT} specifier:
698 @item @code{NATIVE} Use the native format. This is the default.
699 @item @code{SWAP} Swap between little- and big-endian.
700 @item @code{LITTLE_ENDIAN} Use the little-endian format
701 for unformatted files.
702 @item @code{BIG_ENDIAN} Use the big-endian format for unformatted files.
704 A missing mode for an exception is taken to mean @code{BIG_ENDIAN}.
705 Examples of values for @env{GFORTRAN_CONVERT_UNIT} are:
707 @item @code{'big_endian'} Do all unformatted I/O in big_endian mode.
708 @item @code{'little_endian;native:10-20,25'} Do all unformatted I/O
709 in little_endian mode, except for units 10 to 20 and 25, which are in
711 @item @code{'10-20'} Units 10 to 20 are big-endian, the rest is native.
714 Setting the environment variables should be done on the command
715 line or via the @command{export}
716 command for @command{sh}-compatible shells and via @command{setenv}
717 for @command{csh}-compatible shells.
719 Example for @command{sh}:
722 $ GFORTRAN_CONVERT_UNIT='big_endian;native:10-20' ./a.out
725 Example code for @command{csh}:
728 % setenv GFORTRAN_CONVERT_UNIT 'big_endian;native:10-20'
732 Using anything but the native representation for unformatted data
733 carries a significant speed overhead. If speed in this area matters
734 to you, it is best if you use this only for data that needs to be
737 @xref{CONVERT specifier}, for an alternative way to specify the
738 data representation for unformatted files. @xref{Runtime Options}, for
739 setting a default data representation for the whole program. The
740 @code{CONVERT} specifier overrides the @option{-fconvert} compile options.
742 @emph{Note that the values specified via the GFORTRAN_CONVERT_UNIT
743 environment variable will override the CONVERT specifier in the
744 open statement}. This is to give control over data formats to
745 users who do not have the source code of their program available.
747 @node GFORTRAN_ERROR_BACKTRACE
748 @section @env{GFORTRAN_ERROR_BACKTRACE}---Show backtrace on run-time errors
750 If the @env{GFORTRAN_ERROR_BACKTRACE} variable is set to @samp{y},
751 @samp{Y} or @samp{1} (only the first letter is relevant) then a
752 backtrace is printed when a serious run-time error occurs. To disable
753 the backtracing, set the variable to @samp{n}, @samp{N}, @samp{0}.
754 Default is to print a backtrace unless the @option{-fno-backtrace}
755 compile option was used.
757 @c =====================================================================
758 @c PART II: LANGUAGE REFERENCE
759 @c =====================================================================
762 \part{II}{Language Reference}
765 @c ---------------------------------------------------------------------
766 @c Fortran 2003 and 2008 Status
767 @c ---------------------------------------------------------------------
769 @node Fortran 2003 and 2008 status
770 @chapter Fortran 2003 and 2008 Status
773 * Fortran 2003 status::
774 * Fortran 2008 status::
777 @node Fortran 2003 status
778 @section Fortran 2003 status
780 GNU Fortran supports several Fortran 2003 features; an incomplete
781 list can be found below. See also the
782 @uref{http://gcc.gnu.org/wiki/Fortran2003, wiki page} about Fortran 2003.
785 @item Procedure pointers including procedure-pointer components with
786 @code{PASS} attribute.
788 @item Procedures which are bound to a derived type (type-bound procedures)
789 including @code{PASS}, @code{PROCEDURE} and @code{GENERIC}, and
790 operators bound to a type.
792 @item Abstract interfaces and type extension with the possibility to
793 override type-bound procedures or to have deferred binding.
795 @item Polymorphic entities (``@code{CLASS}'') for derived types -- including
796 @code{SAME_TYPE_AS}, @code{EXTENDS_TYPE_OF} and @code{SELECT TYPE}.
797 Note that the support for array-valued polymorphic entities is incomplete
798 and unlimited polymophism is currently not supported.
800 @item The @code{ASSOCIATE} construct.
802 @item Interoperability with C including enumerations,
804 @item In structure constructors the components with default values may be
807 @item Extensions to the @code{ALLOCATE} statement, allowing for a
808 type-specification with type parameter and for allocation and initialization
809 from a @code{SOURCE=} expression; @code{ALLOCATE} and @code{DEALLOCATE}
810 optionally return an error message string via @code{ERRMSG=}.
812 @item Reallocation on assignment: If an intrinsic assignment is
813 used, an allocatable variable on the left-hand side is automatically allocated
814 (if unallocated) or reallocated (if the shape is different). Currently, scalar
815 deferred character length left-hand sides are correctly handled but arrays
816 are not yet fully implemented.
818 @item Transferring of allocations via @code{MOVE_ALLOC}.
820 @item The @code{PRIVATE} and @code{PUBLIC} attributes may be given individually
821 to derived-type components.
823 @item In pointer assignments, the lower bound may be specified and
824 the remapping of elements is supported.
826 @item For pointers an @code{INTENT} may be specified which affect the
827 association status not the value of the pointer target.
829 @item Intrinsics @code{command_argument_count}, @code{get_command},
830 @code{get_command_argument}, and @code{get_environment_variable}.
832 @item Support for unicode characters (ISO 10646) and UTF-8, including
833 the @code{SELECTED_CHAR_KIND} and @code{NEW_LINE} intrinsic functions.
835 @item Support for binary, octal and hexadecimal (BOZ) constants in the
836 intrinsic functions @code{INT}, @code{REAL}, @code{CMPLX} and @code{DBLE}.
838 @item Support for namelist variables with allocatable and pointer
839 attribute and nonconstant length type parameter.
842 @cindex array, constructors
844 Array constructors using square brackets. That is, @code{[...]} rather
845 than @code{(/.../)}. Type-specification for array constructors like
846 @code{(/ some-type :: ... /)}.
848 @item Extensions to the specification and initialization expressions,
849 including the support for intrinsics with real and complex arguments.
851 @item Support for the asynchronous input/output syntax; however, the
852 data transfer is currently always synchronously performed.
855 @cindex @code{FLUSH} statement
856 @cindex statement, @code{FLUSH}
857 @code{FLUSH} statement.
860 @cindex @code{IOMSG=} specifier
861 @code{IOMSG=} specifier for I/O statements.
864 @cindex @code{ENUM} statement
865 @cindex @code{ENUMERATOR} statement
866 @cindex statement, @code{ENUM}
867 @cindex statement, @code{ENUMERATOR}
868 @opindex @code{fshort-enums}
869 Support for the declaration of enumeration constants via the
870 @code{ENUM} and @code{ENUMERATOR} statements. Interoperability with
871 @command{gcc} is guaranteed also for the case where the
872 @command{-fshort-enums} command line option is given.
879 @cindex @code{ALLOCATABLE} dummy arguments
880 @code{ALLOCATABLE} dummy arguments.
882 @cindex @code{ALLOCATABLE} function results
883 @code{ALLOCATABLE} function results
885 @cindex @code{ALLOCATABLE} components of derived types
886 @code{ALLOCATABLE} components of derived types
890 @cindex @code{STREAM} I/O
891 @cindex @code{ACCESS='STREAM'} I/O
892 The @code{OPEN} statement supports the @code{ACCESS='STREAM'} specifier,
893 allowing I/O without any record structure.
896 Namelist input/output for internal files.
898 @item Further I/O extensions: Rounding during formatted output, using of
899 a decimal comma instead of a decimal point, setting whether a plus sign
900 should appear for positive numbers.
903 @cindex @code{PROTECTED} statement
904 @cindex statement, @code{PROTECTED}
905 The @code{PROTECTED} statement and attribute.
908 @cindex @code{VALUE} statement
909 @cindex statement, @code{VALUE}
910 The @code{VALUE} statement and attribute.
913 @cindex @code{VOLATILE} statement
914 @cindex statement, @code{VOLATILE}
915 The @code{VOLATILE} statement and attribute.
918 @cindex @code{IMPORT} statement
919 @cindex statement, @code{IMPORT}
920 The @code{IMPORT} statement, allowing to import
921 host-associated derived types.
923 @item The intrinsic modules @code{ISO_FORTRAN_ENVIRONMENT} is supported,
924 which contains parameters of the I/O units, storage sizes. Additionally,
925 procedures for C interoperability are available in the @code{ISO_C_BINDING}
929 @cindex @code{USE, INTRINSIC} statement
930 @cindex statement, @code{USE, INTRINSIC}
931 @cindex @code{ISO_FORTRAN_ENV} statement
932 @cindex statement, @code{ISO_FORTRAN_ENV}
933 @code{USE} statement with @code{INTRINSIC} and @code{NON_INTRINSIC}
934 attribute; supported intrinsic modules: @code{ISO_FORTRAN_ENV},
935 @code{ISO_C_BINDING}, @code{OMP_LIB} and @code{OMP_LIB_KINDS}.
938 Renaming of operators in the @code{USE} statement.
943 @node Fortran 2008 status
944 @section Fortran 2008 status
946 The latest version of the Fortran standard is ISO/IEC 1539-1:2010, informally
947 known as Fortran 2008. The official version is available from International
948 Organization for Standardization (ISO) or its national member organizations.
949 The the final draft (FDIS) can be downloaded free of charge from
950 @url{http://www.nag.co.uk/@/sc22wg5/@/links.html}. Fortran is developed by the
951 Working Group 5 of Sub-Committee 22 of the Joint Technical Committee 1 of the
952 International Organization for Standardization and the International
953 Electrotechnical Commission (IEC). This group is known as
954 @uref{http://www.nag.co.uk/sc22wg5/, WG5}.
956 The GNU Fortran supports several of the new features of Fortran 2008; the
957 @uref{http://gcc.gnu.org/wiki/Fortran2008Status, wiki} has some information
958 about the current Fortran 2008 implementation status. In particular, the
959 following is implemented.
962 @item The @option{-std=f2008} option and support for the file extensions
963 @file{.f08} and @file{.F08}.
965 @item The @code{OPEN} statement now supports the @code{NEWUNIT=} option,
966 which returns a unique file unit, thus preventing inadvertent use of the
967 same unit in different parts of the program.
969 @item The @code{g0} format descriptor and unlimited format items.
971 @item The mathematical intrinsics @code{ASINH}, @code{ACOSH}, @code{ATANH},
972 @code{ERF}, @code{ERFC}, @code{GAMMA}, @code{LOG_GAMMA}, @code{BESSEL_J0},
973 @code{BESSEL_J1}, @code{BESSEL_JN}, @code{BESSEL_Y0}, @code{BESSEL_Y1},
974 @code{BESSEL_YN}, @code{HYPOT}, @code{NORM2}, and @code{ERFC_SCALED}.
976 @item Using complex arguments with @code{TAN}, @code{SINH}, @code{COSH},
977 @code{TANH}, @code{ASIN}, @code{ACOS}, and @code{ATAN} is now possible;
978 @code{ATAN}(@var{Y},@var{X}) is now an alias for @code{ATAN2}(@var{Y},@var{X}).
980 @item Support of the @code{PARITY} intrinsic functions.
982 @item The following bit intrinsics: @code{LEADZ} and @code{TRAILZ} for
983 counting the number of leading and trailing zero bits, @code{POPCNT} and
984 @code{POPPAR} for counting the number of one bits and returning the parity;
985 @code{BGE}, @code{BGT}, @code{BLE}, and @code{BLT} for bitwise comparisons;
986 @code{DSHIFTL} and @code{DSHIFTR} for combined left and right shifts,
987 @code{MASKL} and @code{MASKR} for simple left and right justified masks,
988 @code{MERGE_BITS} for a bitwise merge using a mask, @code{SHIFTA},
989 @code{SHIFTL} and @code{SHIFTR} for shift operations, and the
990 transformational bit intrinsics @code{IALL}, @code{IANY} and @code{IPARITY}.
992 @item Support of the @code{EXECUTE_COMMAND_LINE} intrinsic subroutine.
994 @item Support for the @code{STORAGE_SIZE} intrinsic inquiry function.
996 @item The @code{INT@{8,16,32@}} and @code{REAL@{32,64,128@}} kind type
997 parameters and the array-valued named constants @code{INTEGER_KINDS},
998 @code{LOGICAL_KINDS}, @code{REAL_KINDS} and @code{CHARACTER_KINDS} of
999 the intrinsic module @code{ISO_FORTRAN_ENV}.
1001 @item The module procedures @code{C_SIZEOF} of the intrinsic module
1002 @code{ISO_C_BINDINGS} and @code{COMPILER_VERSION} and @code{COMPILER_OPTIONS}
1003 of @code{ISO_FORTRAN_ENV}.
1005 @item Experimental coarray support (for one image only), use the
1006 @option{-fcoarray=single} flag to enable it.
1008 @item The @code{BLOCK} construct is supported.
1010 @item The @code{STOP} and the new @code{ERROR STOP} statements now
1011 support all constant expressions.
1013 @item Support for the @code{CONTIGUOUS} attribute.
1015 @item Support for @code{ALLOCATE} with @code{MOLD}.
1017 @item Support for the @code{IMPURE} attribute for procedures, which
1018 allows for @code{ELEMENTAL} procedures without the restrictions of
1021 @item Null pointers (including @code{NULL()}) and not-allocated variables
1022 can be used as actual argument to optional non-pointer, non-allocatable
1023 dummy arguments, denoting an absent argument.
1025 @item Non-pointer variables with @code{TARGET} attribute can be used as
1026 actual argument to @code{POINTER} dummies with @code{INTENT(IN)}.
1028 @item Pointers including procedure pointers and those in a derived
1029 type (pointer components) can now be initialized by a target instead
1030 of only by @code{NULL}.
1032 @item The @code{EXIT} statement (with construct-name) can be now be
1033 used to leave not only the @code{DO} but also the @code{ASSOCIATE},
1034 @code{BLOCK}, @code{IF}, @code{SELECT CASE} and @code{SELECT TYPE}
1037 @item Internal procedures can now be used as actual argument.
1039 @item Minor features: obsolesce diagnostics for @code{ENTRY} with
1040 @option{-std=f2008}; a line may start with a semicolon; for internal
1041 and module procedures @code{END} can be used instead of
1042 @code{END SUBROUTINE} and @code{END FUNCTION}; @code{SELECTED_REAL_KIND}
1043 now also takes a @code{RADIX} argument; intrinsic types are supported
1044 for @code{TYPE}(@var{intrinsic-type-spec}); multiple type-bound procedures
1045 can be declared in a single @code{PROCEDURE} statement; implied-shape
1046 arrays are supported for named constants (@code{PARAMETER}).
1051 @c ---------------------------------------------------------------------
1052 @c Compiler Characteristics
1053 @c ---------------------------------------------------------------------
1055 @node Compiler Characteristics
1056 @chapter Compiler Characteristics
1058 This chapter describes certain characteristics of the GNU Fortran
1059 compiler, that are not specified by the Fortran standard, but which
1060 might in some way or another become visible to the programmer.
1063 * KIND Type Parameters::
1064 * Internal representation of LOGICAL variables::
1065 * Thread-safety of the runtime library::
1069 @node KIND Type Parameters
1070 @section KIND Type Parameters
1073 The @code{KIND} type parameters supported by GNU Fortran for the primitive
1079 1, 2, 4, 8*, 16*, default: 4 (1)
1082 1, 2, 4, 8*, 16*, default: 4 (1)
1085 4, 8, 10*, 16*, default: 4 (2)
1088 4, 8, 10*, 16*, default: 4 (2)
1096 * = not available on all systems @*
1097 (1) Unless -fdefault-integer-8 is used @*
1098 (2) Unless -fdefault-real-8 is used
1101 The @code{KIND} value matches the storage size in bytes, except for
1102 @code{COMPLEX} where the storage size is twice as much (or both real and
1103 imaginary part are a real value of the given size). It is recommended to use
1104 the @code{SELECTED_CHAR_KIND}, @code{SELECTED_INT_KIND} and
1105 @code{SELECTED_REAL_KIND} intrinsics or the @code{INT8}, @code{INT16},
1106 @code{INT32}, @code{INT64}, @code{REAL32}, @code{REAL64}, and @code{REAL128}
1107 parameters of the @code{ISO_FORTRAN_ENV} module instead of the concrete values.
1108 The available kind parameters can be found in the constant arrays
1109 @code{CHARACTER_KINDS}, @code{INTEGER_KINDS}, @code{LOGICAL_KINDS} and
1110 @code{REAL_KINDS} in the @code{ISO_FORTRAN_ENV} module
1111 (see @ref{ISO_FORTRAN_ENV}).
1114 @node Internal representation of LOGICAL variables
1115 @section Internal representation of LOGICAL variables
1116 @cindex logical, variable representation
1118 The Fortran standard does not specify how variables of @code{LOGICAL}
1119 type are represented, beyond requiring that @code{LOGICAL} variables
1120 of default kind have the same storage size as default @code{INTEGER}
1121 and @code{REAL} variables. The GNU Fortran internal representation is
1124 A @code{LOGICAL(KIND=N)} variable is represented as an
1125 @code{INTEGER(KIND=N)} variable, however, with only two permissible
1126 values: @code{1} for @code{.TRUE.} and @code{0} for
1127 @code{.FALSE.}. Any other integer value results in undefined behavior.
1129 Note that for mixed-language programming using the
1130 @code{ISO_C_BINDING} feature, there is a @code{C_BOOL} kind that can
1131 be used to create @code{LOGICAL(KIND=C_BOOL)} variables which are
1132 interoperable with the C99 _Bool type. The C99 _Bool type has an
1133 internal representation described in the C99 standard, which is
1134 identical to the above description, i.e. with 1 for true and 0 for
1135 false being the only permissible values. Thus the internal
1136 representation of @code{LOGICAL} variables in GNU Fortran is identical
1137 to C99 _Bool, except for a possible difference in storage size
1138 depending on the kind.
1141 @node Thread-safety of the runtime library
1142 @section Thread-safety of the runtime library
1143 @cindex thread-safety, threads
1145 GNU Fortran can be used in programs with multiple threads, e.g.@: by
1146 using OpenMP, by calling OS thread handling functions via the
1147 @code{ISO_C_BINDING} facility, or by GNU Fortran compiled library code
1148 being called from a multi-threaded program.
1150 The GNU Fortran runtime library, (@code{libgfortran}), supports being
1151 called concurrently from multiple threads with the following
1154 During library initialization, the C @code{getenv} function is used,
1155 which need not be thread-safe. Similarly, the @code{getenv}
1156 function is used to implement the @code{GET_ENVIRONMENT_VARIABLE} and
1157 @code{GETENV} intrinsics. It is the responsibility of the user to
1158 ensure that the environment is not being updated concurrently when any
1159 of these actions are taking place.
1161 The @code{EXECUTE_COMMAND_LINE} and @code{SYSTEM} intrinsics are
1162 implemented with the @code{system} function, which need not be
1163 thread-safe. It is the responsibility of the user to ensure that
1164 @code{system} is not called concurrently.
1166 Finally, for platforms not supporting thread-safe POSIX functions,
1167 further functionality might not be thread-safe. For details, please
1168 consult the documentation for your operating system.
1170 @c ---------------------------------------------------------------------
1172 @c ---------------------------------------------------------------------
1174 @c Maybe this chapter should be merged with the 'Standards' section,
1175 @c whenever that is written :-)
1181 The two sections below detail the extensions to standard Fortran that are
1182 implemented in GNU Fortran, as well as some of the popular or
1183 historically important extensions that are not (or not yet) implemented.
1184 For the latter case, we explain the alternatives available to GNU Fortran
1185 users, including replacement by standard-conforming code or GNU
1189 * Extensions implemented in GNU Fortran::
1190 * Extensions not implemented in GNU Fortran::
1194 @node Extensions implemented in GNU Fortran
1195 @section Extensions implemented in GNU Fortran
1196 @cindex extensions, implemented
1198 GNU Fortran implements a number of extensions over standard
1199 Fortran. This chapter contains information on their syntax and
1200 meaning. There are currently two categories of GNU Fortran
1201 extensions, those that provide functionality beyond that provided
1202 by any standard, and those that are supported by GNU Fortran
1203 purely for backward compatibility with legacy compilers. By default,
1204 @option{-std=gnu} allows the compiler to accept both types of
1205 extensions, but to warn about the use of the latter. Specifying
1206 either @option{-std=f95}, @option{-std=f2003} or @option{-std=f2008}
1207 disables both types of extensions, and @option{-std=legacy} allows both
1211 * Old-style kind specifications::
1212 * Old-style variable initialization::
1213 * Extensions to namelist::
1214 * X format descriptor without count field::
1215 * Commas in FORMAT specifications::
1216 * Missing period in FORMAT specifications::
1218 * BOZ literal constants::
1219 * @code{Q} exponent-letter::
1220 * Real array indices::
1222 * Implicitly convert LOGICAL and INTEGER values::
1223 * Hollerith constants support::
1225 * CONVERT specifier::
1227 * Argument list functions::
1230 @node Old-style kind specifications
1231 @subsection Old-style kind specifications
1232 @cindex kind, old-style
1234 GNU Fortran allows old-style kind specifications in declarations. These
1240 where @code{TYPESPEC} is a basic type (@code{INTEGER}, @code{REAL},
1241 etc.), and where @code{size} is a byte count corresponding to the
1242 storage size of a valid kind for that type. (For @code{COMPLEX}
1243 variables, @code{size} is the total size of the real and imaginary
1244 parts.) The statement then declares @code{x}, @code{y} and @code{z} to
1245 be of type @code{TYPESPEC} with the appropriate kind. This is
1246 equivalent to the standard-conforming declaration
1251 where @code{k} is the kind parameter suitable for the intended precision. As
1252 kind parameters are implementation-dependent, use the @code{KIND},
1253 @code{SELECTED_INT_KIND} and @code{SELECTED_REAL_KIND} intrinsics to retrieve
1254 the correct value, for instance @code{REAL*8 x} can be replaced by:
1256 INTEGER, PARAMETER :: dbl = KIND(1.0d0)
1260 @node Old-style variable initialization
1261 @subsection Old-style variable initialization
1263 GNU Fortran allows old-style initialization of variables of the
1267 REAL x(2,2) /3*0.,1./
1269 The syntax for the initializers is as for the @code{DATA} statement, but
1270 unlike in a @code{DATA} statement, an initializer only applies to the
1271 variable immediately preceding the initialization. In other words,
1272 something like @code{INTEGER I,J/2,3/} is not valid. This style of
1273 initialization is only allowed in declarations without double colons
1274 (@code{::}); the double colons were introduced in Fortran 90, which also
1275 introduced a standard syntax for initializing variables in type
1278 Examples of standard-conforming code equivalent to the above example
1282 INTEGER :: i = 1, j = 2
1283 REAL :: x(2,2) = RESHAPE((/0.,0.,0.,1./),SHAPE(x))
1287 DATA i/1/, j/2/, x/3*0.,1./
1290 Note that variables which are explicitly initialized in declarations
1291 or in @code{DATA} statements automatically acquire the @code{SAVE}
1294 @node Extensions to namelist
1295 @subsection Extensions to namelist
1298 GNU Fortran fully supports the Fortran 95 standard for namelist I/O
1299 including array qualifiers, substrings and fully qualified derived types.
1300 The output from a namelist write is compatible with namelist read. The
1301 output has all names in upper case and indentation to column 1 after the
1302 namelist name. Two extensions are permitted:
1304 Old-style use of @samp{$} instead of @samp{&}
1307 X(:)%Y(2) = 1.0 2.0 3.0
1312 It should be noted that the default terminator is @samp{/} rather than
1315 Querying of the namelist when inputting from stdin. After at least
1316 one space, entering @samp{?} sends to stdout the namelist name and the names of
1317 the variables in the namelist:
1328 Entering @samp{=?} outputs the namelist to stdout, as if
1329 @code{WRITE(*,NML = mynml)} had been called:
1334 X(1)%Y= 0.000000 , 1.000000 , 0.000000 ,
1335 X(2)%Y= 0.000000 , 2.000000 , 0.000000 ,
1336 X(3)%Y= 0.000000 , 3.000000 , 0.000000 ,
1340 To aid this dialog, when input is from stdin, errors send their
1341 messages to stderr and execution continues, even if @code{IOSTAT} is set.
1343 @code{PRINT} namelist is permitted. This causes an error if
1344 @option{-std=f95} is used.
1347 REAL, dimension (4) :: x = (/1.0, 2.0, 3.0, 4.0/)
1350 END PROGRAM test_print
1353 Expanded namelist reads are permitted. This causes an error if
1354 @option{-std=f95} is used. In the following example, the first element
1355 of the array will be given the value 0.00 and the two succeeding
1356 elements will be given the values 1.00 and 2.00.
1359 X(1,1) = 0.00 , 1.00 , 2.00
1363 @node X format descriptor without count field
1364 @subsection @code{X} format descriptor without count field
1366 To support legacy codes, GNU Fortran permits the count field of the
1367 @code{X} edit descriptor in @code{FORMAT} statements to be omitted.
1368 When omitted, the count is implicitly assumed to be one.
1372 10 FORMAT (I1, X, I1)
1375 @node Commas in FORMAT specifications
1376 @subsection Commas in @code{FORMAT} specifications
1378 To support legacy codes, GNU Fortran allows the comma separator
1379 to be omitted immediately before and after character string edit
1380 descriptors in @code{FORMAT} statements.
1384 10 FORMAT ('FOO='I1' BAR='I2)
1388 @node Missing period in FORMAT specifications
1389 @subsection Missing period in @code{FORMAT} specifications
1391 To support legacy codes, GNU Fortran allows missing periods in format
1392 specifications if and only if @option{-std=legacy} is given on the
1393 command line. This is considered non-conforming code and is
1402 @node I/O item lists
1403 @subsection I/O item lists
1404 @cindex I/O item lists
1406 To support legacy codes, GNU Fortran allows the input item list
1407 of the @code{READ} statement, and the output item lists of the
1408 @code{WRITE} and @code{PRINT} statements, to start with a comma.
1410 @node @code{Q} exponent-letter
1411 @subsection @code{Q} exponent-letter
1412 @cindex @code{Q} exponent-letter
1414 GNU Fortran accepts real literal constants with an exponent-letter
1415 of @code{Q}, for example, @code{1.23Q45}. The constant is interpreted
1416 as a @code{REAL(16)} entity on targets that suppports this type. If
1417 the target does not support @code{REAL(16)} but has a @code{REAL(10)}
1418 type, then the real-literal-constant will be interpreted as a
1419 @code{REAL(10)} entity. In the absence of @code{REAL(16)} and
1420 @code{REAL(10)}, an error will occur.
1422 @node BOZ literal constants
1423 @subsection BOZ literal constants
1424 @cindex BOZ literal constants
1426 Besides decimal constants, Fortran also supports binary (@code{b}),
1427 octal (@code{o}) and hexadecimal (@code{z}) integer constants. The
1428 syntax is: @samp{prefix quote digits quote}, were the prefix is
1429 either @code{b}, @code{o} or @code{z}, quote is either @code{'} or
1430 @code{"} and the digits are for binary @code{0} or @code{1}, for
1431 octal between @code{0} and @code{7}, and for hexadecimal between
1432 @code{0} and @code{F}. (Example: @code{b'01011101'}.)
1434 Up to Fortran 95, BOZ literals were only allowed to initialize
1435 integer variables in DATA statements. Since Fortran 2003 BOZ literals
1436 are also allowed as argument of @code{REAL}, @code{DBLE}, @code{INT}
1437 and @code{CMPLX}; the result is the same as if the integer BOZ
1438 literal had been converted by @code{TRANSFER} to, respectively,
1439 @code{real}, @code{double precision}, @code{integer} or @code{complex}.
1440 As GNU Fortran extension the intrinsic procedures @code{FLOAT},
1441 @code{DFLOAT}, @code{COMPLEX} and @code{DCMPLX} are treated alike.
1443 As an extension, GNU Fortran allows hexadecimal BOZ literal constants to
1444 be specified using the @code{X} prefix, in addition to the standard
1445 @code{Z} prefix. The BOZ literal can also be specified by adding a
1446 suffix to the string, for example, @code{Z'ABC'} and @code{'ABC'Z} are
1449 Furthermore, GNU Fortran allows using BOZ literal constants outside
1450 DATA statements and the four intrinsic functions allowed by Fortran 2003.
1451 In DATA statements, in direct assignments, where the right-hand side
1452 only contains a BOZ literal constant, and for old-style initializers of
1453 the form @code{integer i /o'0173'/}, the constant is transferred
1454 as if @code{TRANSFER} had been used; for @code{COMPLEX} numbers, only
1455 the real part is initialized unless @code{CMPLX} is used. In all other
1456 cases, the BOZ literal constant is converted to an @code{INTEGER} value with
1457 the largest decimal representation. This value is then converted
1458 numerically to the type and kind of the variable in question.
1459 (For instance, @code{real :: r = b'0000001' + 1} initializes @code{r}
1460 with @code{2.0}.) As different compilers implement the extension
1461 differently, one should be careful when doing bitwise initialization
1462 of non-integer variables.
1464 Note that initializing an @code{INTEGER} variable with a statement such
1465 as @code{DATA i/Z'FFFFFFFF'/} will give an integer overflow error rather
1466 than the desired result of @math{-1} when @code{i} is a 32-bit integer
1467 on a system that supports 64-bit integers. The @samp{-fno-range-check}
1468 option can be used as a workaround for legacy code that initializes
1469 integers in this manner.
1471 @node Real array indices
1472 @subsection Real array indices
1473 @cindex array, indices of type real
1475 As an extension, GNU Fortran allows the use of @code{REAL} expressions
1476 or variables as array indices.
1478 @node Unary operators
1479 @subsection Unary operators
1480 @cindex operators, unary
1482 As an extension, GNU Fortran allows unary plus and unary minus operators
1483 to appear as the second operand of binary arithmetic operators without
1484 the need for parenthesis.
1490 @node Implicitly convert LOGICAL and INTEGER values
1491 @subsection Implicitly convert @code{LOGICAL} and @code{INTEGER} values
1492 @cindex conversion, to integer
1493 @cindex conversion, to logical
1495 As an extension for backwards compatibility with other compilers, GNU
1496 Fortran allows the implicit conversion of @code{LOGICAL} values to
1497 @code{INTEGER} values and vice versa. When converting from a
1498 @code{LOGICAL} to an @code{INTEGER}, @code{.FALSE.} is interpreted as
1499 zero, and @code{.TRUE.} is interpreted as one. When converting from
1500 @code{INTEGER} to @code{LOGICAL}, the value zero is interpreted as
1501 @code{.FALSE.} and any nonzero value is interpreted as @code{.TRUE.}.
1512 However, there is no implicit conversion of @code{INTEGER} values in
1513 @code{if}-statements, nor of @code{LOGICAL} or @code{INTEGER} values
1516 @node Hollerith constants support
1517 @subsection Hollerith constants support
1518 @cindex Hollerith constants
1520 GNU Fortran supports Hollerith constants in assignments, function
1521 arguments, and @code{DATA} and @code{ASSIGN} statements. A Hollerith
1522 constant is written as a string of characters preceded by an integer
1523 constant indicating the character count, and the letter @code{H} or
1524 @code{h}, and stored in bytewise fashion in a numeric (@code{INTEGER},
1525 @code{REAL}, or @code{complex}) or @code{LOGICAL} variable. The
1526 constant will be padded or truncated to fit the size of the variable in
1529 Examples of valid uses of Hollerith constants:
1532 data x /16Habcdefghijklmnop, 16Hqrstuvwxyz012345/
1533 x(1) = 16HABCDEFGHIJKLMNOP
1537 Invalid Hollerith constants examples:
1540 a = 8H12345678 ! Valid, but the Hollerith constant will be truncated.
1541 a = 0H ! At least one character is needed.
1544 In general, Hollerith constants were used to provide a rudimentary
1545 facility for handling character strings in early Fortran compilers,
1546 prior to the introduction of @code{CHARACTER} variables in Fortran 77;
1547 in those cases, the standard-compliant equivalent is to convert the
1548 program to use proper character strings. On occasion, there may be a
1549 case where the intent is specifically to initialize a numeric variable
1550 with a given byte sequence. In these cases, the same result can be
1551 obtained by using the @code{TRANSFER} statement, as in this example.
1553 INTEGER(KIND=4) :: a
1554 a = TRANSFER ("abcd", a) ! equivalent to: a = 4Habcd
1559 @subsection Cray pointers
1560 @cindex pointer, Cray
1562 Cray pointers are part of a non-standard extension that provides a
1563 C-like pointer in Fortran. This is accomplished through a pair of
1564 variables: an integer "pointer" that holds a memory address, and a
1565 "pointee" that is used to dereference the pointer.
1567 Pointer/pointee pairs are declared in statements of the form:
1569 pointer ( <pointer> , <pointee> )
1573 pointer ( <pointer1> , <pointee1> ), ( <pointer2> , <pointee2> ), ...
1575 The pointer is an integer that is intended to hold a memory address.
1576 The pointee may be an array or scalar. A pointee can be an assumed
1577 size array---that is, the last dimension may be left unspecified by
1578 using a @code{*} in place of a value---but a pointee cannot be an
1579 assumed shape array. No space is allocated for the pointee.
1581 The pointee may have its type declared before or after the pointer
1582 statement, and its array specification (if any) may be declared
1583 before, during, or after the pointer statement. The pointer may be
1584 declared as an integer prior to the pointer statement. However, some
1585 machines have default integer sizes that are different than the size
1586 of a pointer, and so the following code is not portable:
1591 If a pointer is declared with a kind that is too small, the compiler
1592 will issue a warning; the resulting binary will probably not work
1593 correctly, because the memory addresses stored in the pointers may be
1594 truncated. It is safer to omit the first line of the above example;
1595 if explicit declaration of ipt's type is omitted, then the compiler
1596 will ensure that ipt is an integer variable large enough to hold a
1599 Pointer arithmetic is valid with Cray pointers, but it is not the same
1600 as C pointer arithmetic. Cray pointers are just ordinary integers, so
1601 the user is responsible for determining how many bytes to add to a
1602 pointer in order to increment it. Consider the following example:
1606 pointer (ipt, pointee)
1610 The last statement does not set @code{ipt} to the address of
1611 @code{target(1)}, as it would in C pointer arithmetic. Adding @code{1}
1612 to @code{ipt} just adds one byte to the address stored in @code{ipt}.
1614 Any expression involving the pointee will be translated to use the
1615 value stored in the pointer as the base address.
1617 To get the address of elements, this extension provides an intrinsic
1618 function @code{LOC()}. The @code{LOC()} function is equivalent to the
1619 @code{&} operator in C, except the address is cast to an integer type:
1622 pointer(ipt, arpte(10))
1624 ipt = loc(ar) ! Makes arpte is an alias for ar
1625 arpte(1) = 1.0 ! Sets ar(1) to 1.0
1627 The pointer can also be set by a call to the @code{MALLOC} intrinsic
1630 Cray pointees often are used to alias an existing variable. For
1638 As long as @code{ipt} remains unchanged, @code{iarr} is now an alias for
1639 @code{target}. The optimizer, however, will not detect this aliasing, so
1640 it is unsafe to use @code{iarr} and @code{target} simultaneously. Using
1641 a pointee in any way that violates the Fortran aliasing rules or
1642 assumptions is illegal. It is the user's responsibility to avoid doing
1643 this; the compiler works under the assumption that no such aliasing
1646 Cray pointers will work correctly when there is no aliasing (i.e., when
1647 they are used to access a dynamically allocated block of memory), and
1648 also in any routine where a pointee is used, but any variable with which
1649 it shares storage is not used. Code that violates these rules may not
1650 run as the user intends. This is not a bug in the optimizer; any code
1651 that violates the aliasing rules is illegal. (Note that this is not
1652 unique to GNU Fortran; any Fortran compiler that supports Cray pointers
1653 will ``incorrectly'' optimize code with illegal aliasing.)
1655 There are a number of restrictions on the attributes that can be applied
1656 to Cray pointers and pointees. Pointees may not have the
1657 @code{ALLOCATABLE}, @code{INTENT}, @code{OPTIONAL}, @code{DUMMY},
1658 @code{TARGET}, @code{INTRINSIC}, or @code{POINTER} attributes. Pointers
1659 may not have the @code{DIMENSION}, @code{POINTER}, @code{TARGET},
1660 @code{ALLOCATABLE}, @code{EXTERNAL}, or @code{INTRINSIC} attributes, nor
1661 may they be function results. Pointees may not occur in more than one
1662 pointer statement. A pointee cannot be a pointer. Pointees cannot occur
1663 in equivalence, common, or data statements.
1665 A Cray pointer may also point to a function or a subroutine. For
1666 example, the following excerpt is valid:
1670 pointer (subptr,subpte)
1680 A pointer may be modified during the course of a program, and this
1681 will change the location to which the pointee refers. However, when
1682 pointees are passed as arguments, they are treated as ordinary
1683 variables in the invoked function. Subsequent changes to the pointer
1684 will not change the base address of the array that was passed.
1686 @node CONVERT specifier
1687 @subsection @code{CONVERT} specifier
1688 @cindex @code{CONVERT} specifier
1690 GNU Fortran allows the conversion of unformatted data between little-
1691 and big-endian representation to facilitate moving of data
1692 between different systems. The conversion can be indicated with
1693 the @code{CONVERT} specifier on the @code{OPEN} statement.
1694 @xref{GFORTRAN_CONVERT_UNIT}, for an alternative way of specifying
1695 the data format via an environment variable.
1697 Valid values for @code{CONVERT} are:
1699 @item @code{CONVERT='NATIVE'} Use the native format. This is the default.
1700 @item @code{CONVERT='SWAP'} Swap between little- and big-endian.
1701 @item @code{CONVERT='LITTLE_ENDIAN'} Use the little-endian representation
1702 for unformatted files.
1703 @item @code{CONVERT='BIG_ENDIAN'} Use the big-endian representation for
1707 Using the option could look like this:
1709 open(file='big.dat',form='unformatted',access='sequential', &
1710 convert='big_endian')
1713 The value of the conversion can be queried by using
1714 @code{INQUIRE(CONVERT=ch)}. The values returned are
1715 @code{'BIG_ENDIAN'} and @code{'LITTLE_ENDIAN'}.
1717 @code{CONVERT} works between big- and little-endian for
1718 @code{INTEGER} values of all supported kinds and for @code{REAL}
1719 on IEEE systems of kinds 4 and 8. Conversion between different
1720 ``extended double'' types on different architectures such as
1721 m68k and x86_64, which GNU Fortran
1722 supports as @code{REAL(KIND=10)} and @code{REAL(KIND=16)}, will
1725 @emph{Note that the values specified via the GFORTRAN_CONVERT_UNIT
1726 environment variable will override the CONVERT specifier in the
1727 open statement}. This is to give control over data formats to
1728 users who do not have the source code of their program available.
1730 Using anything but the native representation for unformatted data
1731 carries a significant speed overhead. If speed in this area matters
1732 to you, it is best if you use this only for data that needs to be
1739 OpenMP (Open Multi-Processing) is an application programming
1740 interface (API) that supports multi-platform shared memory
1741 multiprocessing programming in C/C++ and Fortran on many
1742 architectures, including Unix and Microsoft Windows platforms.
1743 It consists of a set of compiler directives, library routines,
1744 and environment variables that influence run-time behavior.
1746 GNU Fortran strives to be compatible to the
1747 @uref{http://www.openmp.org/mp-documents/spec30.pdf,
1748 OpenMP Application Program Interface v3.0}.
1750 To enable the processing of the OpenMP directive @code{!$omp} in
1751 free-form source code; the @code{c$omp}, @code{*$omp} and @code{!$omp}
1752 directives in fixed form; the @code{!$} conditional compilation sentinels
1753 in free form; and the @code{c$}, @code{*$} and @code{!$} sentinels
1754 in fixed form, @command{gfortran} needs to be invoked with the
1755 @option{-fopenmp}. This also arranges for automatic linking of the
1756 GNU OpenMP runtime library @ref{Top,,libgomp,libgomp,GNU OpenMP
1759 The OpenMP Fortran runtime library routines are provided both in a
1760 form of a Fortran 90 module named @code{omp_lib} and in a form of
1761 a Fortran @code{include} file named @file{omp_lib.h}.
1763 An example of a parallelized loop taken from Appendix A.1 of
1764 the OpenMP Application Program Interface v2.5:
1766 SUBROUTINE A1(N, A, B)
1769 !$OMP PARALLEL DO !I is private by default
1771 B(I) = (A(I) + A(I-1)) / 2.0
1773 !$OMP END PARALLEL DO
1780 @option{-fopenmp} implies @option{-frecursive}, i.e., all local arrays
1781 will be allocated on the stack. When porting existing code to OpenMP,
1782 this may lead to surprising results, especially to segmentation faults
1783 if the stacksize is limited.
1786 On glibc-based systems, OpenMP enabled applications cannot be statically
1787 linked due to limitations of the underlying pthreads-implementation. It
1788 might be possible to get a working solution if
1789 @command{-Wl,--whole-archive -lpthread -Wl,--no-whole-archive} is added
1790 to the command line. However, this is not supported by @command{gcc} and
1791 thus not recommended.
1794 @node Argument list functions
1795 @subsection Argument list functions @code{%VAL}, @code{%REF} and @code{%LOC}
1796 @cindex argument list functions
1801 GNU Fortran supports argument list functions @code{%VAL}, @code{%REF}
1802 and @code{%LOC} statements, for backward compatibility with g77.
1803 It is recommended that these should be used only for code that is
1804 accessing facilities outside of GNU Fortran, such as operating system
1805 or windowing facilities. It is best to constrain such uses to isolated
1806 portions of a program--portions that deal specifically and exclusively
1807 with low-level, system-dependent facilities. Such portions might well
1808 provide a portable interface for use by the program as a whole, but are
1809 themselves not portable, and should be thoroughly tested each time they
1810 are rebuilt using a new compiler or version of a compiler.
1812 @code{%VAL} passes a scalar argument by value, @code{%REF} passes it by
1813 reference and @code{%LOC} passes its memory location. Since gfortran
1814 already passes scalar arguments by reference, @code{%REF} is in effect
1815 a do-nothing. @code{%LOC} has the same effect as a Fortran pointer.
1817 An example of passing an argument by value to a C subroutine foo.:
1820 C prototype void foo_ (float x);
1829 For details refer to the g77 manual
1830 @uref{http://gcc.gnu.org/@/onlinedocs/@/gcc-3.4.6/@/g77/@/index.html#Top}.
1832 Also, @code{c_by_val.f} and its partner @code{c_by_val.c} of the
1833 GNU Fortran testsuite are worth a look.
1836 @node Extensions not implemented in GNU Fortran
1837 @section Extensions not implemented in GNU Fortran
1838 @cindex extensions, not implemented
1840 The long history of the Fortran language, its wide use and broad
1841 userbase, the large number of different compiler vendors and the lack of
1842 some features crucial to users in the first standards have lead to the
1843 existence of a number of important extensions to the language. While
1844 some of the most useful or popular extensions are supported by the GNU
1845 Fortran compiler, not all existing extensions are supported. This section
1846 aims at listing these extensions and offering advice on how best make
1847 code that uses them running with the GNU Fortran compiler.
1849 @c More can be found here:
1850 @c -- http://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/Missing-Features.html
1851 @c -- the list of Fortran and libgfortran bugs closed as WONTFIX:
1852 @c http://tinyurl.com/2u4h5y
1855 * STRUCTURE and RECORD::
1856 @c * UNION and MAP::
1857 * ENCODE and DECODE statements::
1858 * Variable FORMAT expressions::
1859 @c * Q edit descriptor::
1860 @c * AUTOMATIC statement::
1861 @c * TYPE and ACCEPT I/O Statements::
1862 @c * .XOR. operator::
1863 @c * CARRIAGECONTROL, DEFAULTFILE, DISPOSE and RECORDTYPE I/O specifiers::
1864 @c * Omitted arguments in procedure call::
1865 * Alternate complex function syntax::
1869 @node STRUCTURE and RECORD
1870 @subsection @code{STRUCTURE} and @code{RECORD}
1871 @cindex @code{STRUCTURE}
1872 @cindex @code{RECORD}
1874 Structures are user-defined aggregate data types; this functionality was
1875 standardized in Fortran 90 with an different syntax, under the name of
1876 ``derived types''. Here is an example of code using the non portable
1880 ! Declaring a structure named ``item'' and containing three fields:
1881 ! an integer ID, an description string and a floating-point price.
1884 CHARACTER(LEN=200) description
1888 ! Define two variables, an single record of type ``item''
1889 ! named ``pear'', and an array of items named ``store_catalog''
1890 RECORD /item/ pear, store_catalog(100)
1892 ! We can directly access the fields of both variables
1894 pear.description = "juicy D'Anjou pear"
1896 store_catalog(7).id = 7831
1897 store_catalog(7).description = "milk bottle"
1898 store_catalog(7).price = 1.2
1900 ! We can also manipulate the whole structure
1901 store_catalog(12) = pear
1902 print *, store_catalog(12)
1906 This code can easily be rewritten in the Fortran 90 syntax as following:
1909 ! ``STRUCTURE /name/ ... END STRUCTURE'' becomes
1910 ! ``TYPE name ... END TYPE''
1913 CHARACTER(LEN=200) description
1917 ! ``RECORD /name/ variable'' becomes ``TYPE(name) variable''
1918 TYPE(item) pear, store_catalog(100)
1920 ! Instead of using a dot (.) to access fields of a record, the
1921 ! standard syntax uses a percent sign (%)
1923 pear%description = "juicy D'Anjou pear"
1925 store_catalog(7)%id = 7831
1926 store_catalog(7)%description = "milk bottle"
1927 store_catalog(7)%price = 1.2
1929 ! Assignments of a whole variable don't change
1930 store_catalog(12) = pear
1931 print *, store_catalog(12)
1935 @c @node UNION and MAP
1936 @c @subsection @code{UNION} and @code{MAP}
1937 @c @cindex @code{UNION}
1938 @c @cindex @code{MAP}
1940 @c For help writing this one, see
1941 @c http://www.eng.umd.edu/~nsw/ench250/fortran1.htm#UNION and
1942 @c http://www.tacc.utexas.edu/services/userguides/pgi/pgiws_ug/pgi32u06.htm
1945 @node ENCODE and DECODE statements
1946 @subsection @code{ENCODE} and @code{DECODE} statements
1947 @cindex @code{ENCODE}
1948 @cindex @code{DECODE}
1950 GNU Fortran doesn't support the @code{ENCODE} and @code{DECODE}
1951 statements. These statements are best replaced by @code{READ} and
1952 @code{WRITE} statements involving internal files (@code{CHARACTER}
1953 variables and arrays), which have been part of the Fortran standard since
1954 Fortran 77. For example, replace a code fragment like
1959 c ... Code that sets LINE
1960 DECODE (80, 9000, LINE) A, B, C
1961 9000 FORMAT (1X, 3(F10.5))
1968 CHARACTER(LEN=80) LINE
1970 c ... Code that sets LINE
1971 READ (UNIT=LINE, FMT=9000) A, B, C
1972 9000 FORMAT (1X, 3(F10.5))
1975 Similarly, replace a code fragment like
1980 c ... Code that sets A, B and C
1981 ENCODE (80, 9000, LINE) A, B, C
1982 9000 FORMAT (1X, 'OUTPUT IS ', 3(F10.5))
1989 CHARACTER(LEN=80) LINE
1991 c ... Code that sets A, B and C
1992 WRITE (UNIT=LINE, FMT=9000) A, B, C
1993 9000 FORMAT (1X, 'OUTPUT IS ', 3(F10.5))
1997 @node Variable FORMAT expressions
1998 @subsection Variable @code{FORMAT} expressions
1999 @cindex @code{FORMAT}
2001 A variable @code{FORMAT} expression is format statement which includes
2002 angle brackets enclosing a Fortran expression: @code{FORMAT(I<N>)}. GNU
2003 Fortran does not support this legacy extension. The effect of variable
2004 format expressions can be reproduced by using the more powerful (and
2005 standard) combination of internal output and string formats. For example,
2006 replace a code fragment like this:
2017 c Variable declaration
2018 CHARACTER(LEN=20) FMT
2020 c Other code here...
2022 WRITE(FMT,'("(I", I0, ")")') N+1
2030 c Variable declaration
2031 CHARACTER(LEN=20) FMT
2033 c Other code here...
2036 WRITE(6,"(I" // ADJUSTL(FMT) // ")") INT1
2040 @node Alternate complex function syntax
2041 @subsection Alternate complex function syntax
2042 @cindex Complex function
2044 Some Fortran compilers, including @command{g77}, let the user declare
2045 complex functions with the syntax @code{COMPLEX FUNCTION name*16()}, as
2046 well as @code{COMPLEX*16 FUNCTION name()}. Both are non-standard, legacy
2047 extensions. @command{gfortran} accepts the latter form, which is more
2048 common, but not the former.
2052 @c ---------------------------------------------------------------------
2053 @c Mixed-Language Programming
2054 @c ---------------------------------------------------------------------
2056 @node Mixed-Language Programming
2057 @chapter Mixed-Language Programming
2058 @cindex Interoperability
2059 @cindex Mixed-language programming
2062 * Interoperability with C::
2063 * GNU Fortran Compiler Directives::
2064 * Non-Fortran Main Program::
2067 This chapter is about mixed-language interoperability, but also applies
2068 if one links Fortran code compiled by different compilers. In most cases,
2069 use of the C Binding features of the Fortran 2003 standard is sufficient,
2070 and their use is highly recommended.
2073 @node Interoperability with C
2074 @section Interoperability with C
2078 * Derived Types and struct::
2079 * Interoperable Global Variables::
2080 * Interoperable Subroutines and Functions::
2081 * Working with Pointers::
2082 * Further Interoperability of Fortran with C::
2085 Since Fortran 2003 (ISO/IEC 1539-1:2004(E)) there is a
2086 standardized way to generate procedure and derived-type
2087 declarations and global variables which are interoperable with C
2088 (ISO/IEC 9899:1999). The @code{bind(C)} attribute has been added
2089 to inform the compiler that a symbol shall be interoperable with C;
2090 also, some constraints are added. Note, however, that not
2091 all C features have a Fortran equivalent or vice versa. For instance,
2092 neither C's unsigned integers nor C's functions with variable number
2093 of arguments have an equivalent in Fortran.
2095 Note that array dimensions are reversely ordered in C and that arrays in
2096 C always start with index 0 while in Fortran they start by default with
2097 1. Thus, an array declaration @code{A(n,m)} in Fortran matches
2098 @code{A[m][n]} in C and accessing the element @code{A(i,j)} matches
2099 @code{A[j-1][i-1]}. The element following @code{A(i,j)} (C: @code{A[j-1][i-1]};
2100 assuming @math{i < n}) in memory is @code{A(i+1,j)} (C: @code{A[j-1][i]}).
2102 @node Intrinsic Types
2103 @subsection Intrinsic Types
2105 In order to ensure that exactly the same variable type and kind is used
2106 in C and Fortran, the named constants shall be used which are defined in the
2107 @code{ISO_C_BINDING} intrinsic module. That module contains named constants
2108 for kind parameters and character named constants for the escape sequences
2109 in C. For a list of the constants, see @ref{ISO_C_BINDING}.
2111 @node Derived Types and struct
2112 @subsection Derived Types and struct
2114 For compatibility of derived types with @code{struct}, one needs to use
2115 the @code{BIND(C)} attribute in the type declaration. For instance, the
2116 following type declaration
2120 TYPE, BIND(C) :: myType
2121 INTEGER(C_INT) :: i1, i2
2122 INTEGER(C_SIGNED_CHAR) :: i3
2123 REAL(C_DOUBLE) :: d1
2124 COMPLEX(C_FLOAT_COMPLEX) :: c1
2125 CHARACTER(KIND=C_CHAR) :: str(5)
2129 matches the following @code{struct} declaration in C
2134 /* Note: "char" might be signed or unsigned. */
2142 Derived types with the C binding attribute shall not have the @code{sequence}
2143 attribute, type parameters, the @code{extends} attribute, nor type-bound
2144 procedures. Every component must be of interoperable type and kind and may not
2145 have the @code{pointer} or @code{allocatable} attribute. The names of the
2146 variables are irrelevant for interoperability.
2148 As there exist no direct Fortran equivalents, neither unions nor structs
2149 with bit field or variable-length array members are interoperable.
2151 @node Interoperable Global Variables
2152 @subsection Interoperable Global Variables
2154 Variables can be made accessible from C using the C binding attribute,
2155 optionally together with specifying a binding name. Those variables
2156 have to be declared in the declaration part of a @code{MODULE},
2157 be of interoperable type, and have neither the @code{pointer} nor
2158 the @code{allocatable} attribute.
2164 integer(C_INT), bind(C, name="_MyProject_flags") :: global_flag
2165 type(myType), bind(C) :: tp
2169 Here, @code{_MyProject_flags} is the case-sensitive name of the variable
2170 as seen from C programs while @code{global_flag} is the case-insensitive
2171 name as seen from Fortran. If no binding name is specified, as for
2172 @var{tp}, the C binding name is the (lowercase) Fortran binding name.
2173 If a binding name is specified, only a single variable may be after the
2174 double colon. Note of warning: You cannot use a global variable to
2175 access @var{errno} of the C library as the C standard allows it to be
2176 a macro. Use the @code{IERRNO} intrinsic (GNU extension) instead.
2178 @node Interoperable Subroutines and Functions
2179 @subsection Interoperable Subroutines and Functions
2181 Subroutines and functions have to have the @code{BIND(C)} attribute to
2182 be compatible with C. The dummy argument declaration is relatively
2183 straightforward. However, one needs to be careful because C uses
2184 call-by-value by default while Fortran behaves usually similar to
2185 call-by-reference. Furthermore, strings and pointers are handled
2186 differently. Note that only explicit size and assumed-size arrays are
2187 supported but not assumed-shape or allocatable arrays.
2189 To pass a variable by value, use the @code{VALUE} attribute.
2190 Thus the following C prototype
2193 @code{int func(int i, int *j)}
2196 matches the Fortran declaration
2199 integer(c_int) function func(i,j)
2200 use iso_c_binding, only: c_int
2201 integer(c_int), VALUE :: i
2205 Note that pointer arguments also frequently need the @code{VALUE} attribute,
2206 see @ref{Working with Pointers}.
2208 Strings are handled quite differently in C and Fortran. In C a string
2209 is a @code{NUL}-terminated array of characters while in Fortran each string
2210 has a length associated with it and is thus not terminated (by e.g.
2211 @code{NUL}). For example, if one wants to use the following C function,
2215 void print_C(char *string) /* equivalent: char string[] */
2217 printf("%s\n", string);
2221 to print ``Hello World'' from Fortran, one can call it using
2224 use iso_c_binding, only: C_CHAR, C_NULL_CHAR
2226 subroutine print_c(string) bind(C, name="print_C")
2227 use iso_c_binding, only: c_char
2228 character(kind=c_char) :: string(*)
2229 end subroutine print_c
2231 call print_c(C_CHAR_"Hello World"//C_NULL_CHAR)
2234 As the example shows, one needs to ensure that the
2235 string is @code{NUL} terminated. Additionally, the dummy argument
2236 @var{string} of @code{print_C} is a length-one assumed-size
2237 array; using @code{character(len=*)} is not allowed. The example
2238 above uses @code{c_char_"Hello World"} to ensure the string
2239 literal has the right type; typically the default character
2240 kind and @code{c_char} are the same and thus @code{"Hello World"}
2241 is equivalent. However, the standard does not guarantee this.
2243 The use of strings is now further illustrated using the C library
2244 function @code{strncpy}, whose prototype is
2247 char *strncpy(char *restrict s1, const char *restrict s2, size_t n);
2250 The function @code{strncpy} copies at most @var{n} characters from
2251 string @var{s2} to @var{s1} and returns @var{s1}. In the following
2252 example, we ignore the return value:
2257 character(len=30) :: str,str2
2259 ! Ignore the return value of strncpy -> subroutine
2260 ! "restrict" is always assumed if we do not pass a pointer
2261 subroutine strncpy(dest, src, n) bind(C)
2263 character(kind=c_char), intent(out) :: dest(*)
2264 character(kind=c_char), intent(in) :: src(*)
2265 integer(c_size_t), value, intent(in) :: n
2266 end subroutine strncpy
2268 str = repeat('X',30) ! Initialize whole string with 'X'
2269 call strncpy(str, c_char_"Hello World"//C_NULL_CHAR, &
2270 len(c_char_"Hello World",kind=c_size_t))
2271 print '(a)', str ! prints: "Hello WorldXXXXXXXXXXXXXXXXXXX"
2275 The intrinsic procedures are described in @ref{Intrinsic Procedures}.
2277 @node Working with Pointers
2278 @subsection Working with Pointers
2280 C pointers are represented in Fortran via the special opaque derived type
2281 @code{type(c_ptr)} (with private components). Thus one needs to
2282 use intrinsic conversion procedures to convert from or to C pointers.
2287 type(c_ptr) :: cptr1, cptr2
2288 integer, target :: array(7), scalar
2289 integer, pointer :: pa(:), ps
2290 cptr1 = c_loc(array(1)) ! The programmer needs to ensure that the
2291 ! array is contiguous if required by the C
2293 cptr2 = c_loc(scalar)
2294 call c_f_pointer(cptr2, ps)
2295 call c_f_pointer(cptr2, pa, shape=[7])
2298 When converting C to Fortran arrays, the one-dimensional @code{SHAPE} argument
2301 If a pointer is a dummy-argument of an interoperable procedure, it usually
2302 has to be declared using the @code{VALUE} attribute. @code{void*}
2303 matches @code{TYPE(C_PTR), VALUE}, while @code{TYPE(C_PTR)} alone
2304 matches @code{void**}.
2306 Procedure pointers are handled analogously to pointers; the C type is
2307 @code{TYPE(C_FUNPTR)} and the intrinsic conversion procedures are
2308 @code{C_F_PROCPOINTER} and @code{C_FUNLOC}.
2310 Let's consider two examples of actually passing a procedure pointer from
2311 C to Fortran and vice versa. Note that these examples are also very
2312 similar to passing ordinary pointers between both languages.
2313 First, consider this code in C:
2316 /* Procedure implemented in Fortran. */
2317 void get_values (void (*)(double));
2319 /* Call-back routine we want called from Fortran. */
2323 printf ("Number is %f.\n", x);
2326 /* Call Fortran routine and pass call-back to it. */
2330 get_values (&print_it);
2334 A matching implementation for @code{get_values} in Fortran, that correctly
2335 receives the procedure pointer from C and is able to call it, is given
2336 in the following @code{MODULE}:
2342 ! Define interface of call-back routine.
2344 SUBROUTINE callback (x)
2345 USE, INTRINSIC :: ISO_C_BINDING
2346 REAL(KIND=C_DOUBLE), INTENT(IN), VALUE :: x
2347 END SUBROUTINE callback
2352 ! Define C-bound procedure.
2353 SUBROUTINE get_values (cproc) BIND(C)
2354 USE, INTRINSIC :: ISO_C_BINDING
2355 TYPE(C_FUNPTR), INTENT(IN), VALUE :: cproc
2357 PROCEDURE(callback), POINTER :: proc
2359 ! Convert C to Fortran procedure pointer.
2360 CALL C_F_PROCPOINTER (cproc, proc)
2363 CALL proc (1.0_C_DOUBLE)
2364 CALL proc (-42.0_C_DOUBLE)
2365 CALL proc (18.12_C_DOUBLE)
2366 END SUBROUTINE get_values
2371 Next, we want to call a C routine that expects a procedure pointer argument
2372 and pass it a Fortran procedure (which clearly must be interoperable!).
2373 Again, the C function may be:
2377 call_it (int (*func)(int), int arg)
2383 It can be used as in the following Fortran code:
2387 USE, INTRINSIC :: ISO_C_BINDING
2390 ! Define interface of C function.
2392 INTEGER(KIND=C_INT) FUNCTION call_it (func, arg) BIND(C)
2393 USE, INTRINSIC :: ISO_C_BINDING
2394 TYPE(C_FUNPTR), INTENT(IN), VALUE :: func
2395 INTEGER(KIND=C_INT), INTENT(IN), VALUE :: arg
2396 END FUNCTION call_it
2401 ! Define procedure passed to C function.
2402 ! It must be interoperable!
2403 INTEGER(KIND=C_INT) FUNCTION double_it (arg) BIND(C)
2404 INTEGER(KIND=C_INT), INTENT(IN), VALUE :: arg
2405 double_it = arg + arg
2406 END FUNCTION double_it
2409 SUBROUTINE foobar ()
2410 TYPE(C_FUNPTR) :: cproc
2411 INTEGER(KIND=C_INT) :: i
2413 ! Get C procedure pointer.
2414 cproc = C_FUNLOC (double_it)
2417 DO i = 1_C_INT, 10_C_INT
2418 PRINT *, call_it (cproc, i)
2420 END SUBROUTINE foobar
2425 @node Further Interoperability of Fortran with C
2426 @subsection Further Interoperability of Fortran with C
2428 Assumed-shape and allocatable arrays are passed using an array descriptor
2429 (dope vector). The internal structure of the array descriptor used
2430 by GNU Fortran is not yet documented and will change. There will also be
2431 a Technical Report (TR 29113) which standardizes an interoperable
2432 array descriptor. Until then, you can use the Chasm Language
2433 Interoperability Tools, @url{http://chasm-interop.sourceforge.net/},
2434 which provide an interface to GNU Fortran's array descriptor.
2436 The technical report 29113 will presumably also include support for
2437 C-interoperable @code{OPTIONAL} and for assumed-rank and assumed-type
2438 dummy arguments. However, the TR has neither been approved nor implemented
2439 in GNU Fortran; therefore, these features are not yet available.
2443 @node GNU Fortran Compiler Directives
2444 @section GNU Fortran Compiler Directives
2446 The Fortran standard standard describes how a conforming program shall
2447 behave; however, the exact implementation is not standardized. In order
2448 to allow the user to choose specific implementation details, compiler
2449 directives can be used to set attributes of variables and procedures
2450 which are not part of the standard. Whether a given attribute is
2451 supported and its exact effects depend on both the operating system and
2452 on the processor; see
2453 @ref{Top,,C Extensions,gcc,Using the GNU Compiler Collection (GCC)}
2456 For procedures and procedure pointers, the following attributes can
2457 be used to change the calling convention:
2460 @item @code{CDECL} -- standard C calling convention
2461 @item @code{STDCALL} -- convention where the called procedure pops the stack
2462 @item @code{FASTCALL} -- part of the arguments are passed via registers
2463 instead using the stack
2466 Besides changing the calling convention, the attributes also influence
2467 the decoration of the symbol name, e.g., by a leading underscore or by
2468 a trailing at-sign followed by the number of bytes on the stack. When
2469 assigning a procedure to a procedure pointer, both should use the same
2472 On some systems, procedures and global variables (module variables and
2473 @code{COMMON} blocks) need special handling to be accessible when they
2474 are in a shared library. The following attributes are available:
2477 @item @code{DLLEXPORT} -- provide a global pointer to a pointer in the DLL
2478 @item @code{DLLIMPORT} -- reference the function or variable using a global pointer
2481 The attributes are specified using the syntax
2483 @code{!GCC$ ATTRIBUTES} @var{attribute-list} @code{::} @var{variable-list}
2485 where in free-form source code only whitespace is allowed before @code{!GCC$}
2486 and in fixed-form source code @code{!GCC$}, @code{cGCC$} or @code{*GCC$} shall
2487 start in the first column.
2489 For procedures, the compiler directives shall be placed into the body
2490 of the procedure; for variables and procedure pointers, they shall be in
2491 the same declaration part as the variable or procedure pointer.
2495 @node Non-Fortran Main Program
2496 @section Non-Fortran Main Program
2499 * _gfortran_set_args:: Save command-line arguments
2500 * _gfortran_set_options:: Set library option flags
2501 * _gfortran_set_convert:: Set endian conversion
2502 * _gfortran_set_record_marker:: Set length of record markers
2503 * _gfortran_set_max_subrecord_length:: Set subrecord length
2504 * _gfortran_set_fpe:: Set when a Floating Point Exception should be raised
2507 Even if you are doing mixed-language programming, it is very
2508 likely that you do not need to know or use the information in this
2509 section. Since it is about the internal structure of GNU Fortran,
2510 it may also change in GCC minor releases.
2512 When you compile a @code{PROGRAM} with GNU Fortran, a function
2513 with the name @code{main} (in the symbol table of the object file)
2514 is generated, which initializes the libgfortran library and then
2515 calls the actual program which uses the name @code{MAIN__}, for
2516 historic reasons. If you link GNU Fortran compiled procedures
2517 to, e.g., a C or C++ program or to a Fortran program compiled by
2518 a different compiler, the libgfortran library is not initialized
2519 and thus a few intrinsic procedures do not work properly, e.g.
2520 those for obtaining the command-line arguments.
2522 Therefore, if your @code{PROGRAM} is not compiled with
2523 GNU Fortran and the GNU Fortran compiled procedures require
2524 intrinsics relying on the library initialization, you need to
2525 initialize the library yourself. Using the default options,
2526 gfortran calls @code{_gfortran_set_args} and
2527 @code{_gfortran_set_options}. The initialization of the former
2528 is needed if the called procedures access the command line
2529 (and for backtracing); the latter sets some flags based on the
2530 standard chosen or to enable backtracing. In typical programs,
2531 it is not necessary to call any initialization function.
2533 If your @code{PROGRAM} is compiled with GNU Fortran, you shall
2534 not call any of the following functions. The libgfortran
2535 initialization functions are shown in C syntax but using C
2536 bindings they are also accessible from Fortran.
2539 @node _gfortran_set_args
2540 @subsection @code{_gfortran_set_args} --- Save command-line arguments
2541 @fnindex _gfortran_set_args
2542 @cindex libgfortran initialization, set_args
2545 @item @emph{Description}:
2546 @code{_gfortran_set_args} saves the command-line arguments; this
2547 initialization is required if any of the command-line intrinsics
2548 is called. Additionally, it shall be called if backtracing is
2549 enabled (see @code{_gfortran_set_options}).
2551 @item @emph{Syntax}:
2552 @code{void _gfortran_set_args (int argc, char *argv[])}
2554 @item @emph{Arguments}:
2555 @multitable @columnfractions .15 .70
2556 @item @var{argc} @tab number of command line argument strings
2557 @item @var{argv} @tab the command-line argument strings; argv[0]
2558 is the pathname of the executable itself.
2561 @item @emph{Example}:
2563 int main (int argc, char *argv[])
2565 /* Initialize libgfortran. */
2566 _gfortran_set_args (argc, argv);
2573 @node _gfortran_set_options
2574 @subsection @code{_gfortran_set_options} --- Set library option flags
2575 @fnindex _gfortran_set_options
2576 @cindex libgfortran initialization, set_options
2579 @item @emph{Description}:
2580 @code{_gfortran_set_options} sets several flags related to the Fortran
2581 standard to be used, whether backtracing should be enabled
2582 and whether range checks should be performed. The syntax allows for
2583 upward compatibility since the number of passed flags is specified; for
2584 non-passed flags, the default value is used. See also
2585 @pxref{Code Gen Options}. Please note that not all flags are actually
2588 @item @emph{Syntax}:
2589 @code{void _gfortran_set_options (int num, int options[])}
2591 @item @emph{Arguments}:
2592 @multitable @columnfractions .15 .70
2593 @item @var{num} @tab number of options passed
2594 @item @var{argv} @tab The list of flag values
2597 @item @emph{option flag list}:
2598 @multitable @columnfractions .15 .70
2599 @item @var{option}[0] @tab Allowed standard; can give run-time errors
2600 if e.g. an input-output edit descriptor is invalid in a given standard.
2601 Possible values are (bitwise or-ed) @code{GFC_STD_F77} (1),
2602 @code{GFC_STD_F95_OBS} (2), @code{GFC_STD_F95_DEL} (4), @code{GFC_STD_F95}
2603 (8), @code{GFC_STD_F2003} (16), @code{GFC_STD_GNU} (32),
2604 @code{GFC_STD_LEGACY} (64), @code{GFC_STD_F2008} (128), and
2605 @code{GFC_STD_F2008_OBS} (256). Default: @code{GFC_STD_F95_OBS
2606 | GFC_STD_F95_DEL | GFC_STD_F95 | GFC_STD_F2003 | GFC_STD_F2008
2607 | GFC_STD_F2008_OBS | GFC_STD_F77 | GFC_STD_GNU | GFC_STD_LEGACY}.
2608 @item @var{option}[1] @tab Standard-warning flag; prints a warning to
2609 standard error. Default: @code{GFC_STD_F95_DEL | GFC_STD_LEGACY}.
2610 @item @var{option}[2] @tab If non zero, enable pedantic checking.
2612 @item @var{option}[3] @tab Unused.
2613 @item @var{option}[4] @tab If non zero, enable backtracing on run-time
2614 errors. Default: off.
2615 Note: Installs a signal handler and requires command-line
2616 initialization using @code{_gfortran_set_args}.
2617 @item @var{option}[5] @tab If non zero, supports signed zeros.
2619 @item @var{option}[6] @tab Enables run-time checking. Possible values
2620 are (bitwise or-ed): GFC_RTCHECK_BOUNDS (1), GFC_RTCHECK_ARRAY_TEMPS (2),
2621 GFC_RTCHECK_RECURSION (4), GFC_RTCHECK_DO (16), GFC_RTCHECK_POINTER (32).
2623 @item @var{option}[7] @tab If non zero, range checking is enabled.
2624 Default: enabled. See -frange-check (@pxref{Code Gen Options}).
2627 @item @emph{Example}:
2629 /* Use gfortran 4.7 default options. */
2630 static int options[] = @{68, 255, 0, 0, 1, 1, 0, 1@};
2631 _gfortran_set_options (8, &options);
2636 @node _gfortran_set_convert
2637 @subsection @code{_gfortran_set_convert} --- Set endian conversion
2638 @fnindex _gfortran_set_convert
2639 @cindex libgfortran initialization, set_convert
2642 @item @emph{Description}:
2643 @code{_gfortran_set_convert} set the representation of data for
2646 @item @emph{Syntax}:
2647 @code{void _gfortran_set_convert (int conv)}
2649 @item @emph{Arguments}:
2650 @multitable @columnfractions .15 .70
2651 @item @var{conv} @tab Endian conversion, possible values:
2652 GFC_CONVERT_NATIVE (0, default), GFC_CONVERT_SWAP (1),
2653 GFC_CONVERT_BIG (2), GFC_CONVERT_LITTLE (3).
2656 @item @emph{Example}:
2658 int main (int argc, char *argv[])
2660 /* Initialize libgfortran. */
2661 _gfortran_set_args (argc, argv);
2662 _gfortran_set_convert (1);
2669 @node _gfortran_set_record_marker
2670 @subsection @code{_gfortran_set_record_marker} --- Set length of record markers
2671 @fnindex _gfortran_set_record_marker
2672 @cindex libgfortran initialization, set_record_marker
2675 @item @emph{Description}:
2676 @code{_gfortran_set_record_marker} sets the length of record markers
2677 for unformatted files.
2679 @item @emph{Syntax}:
2680 @code{void _gfortran_set_record_marker (int val)}
2682 @item @emph{Arguments}:
2683 @multitable @columnfractions .15 .70
2684 @item @var{val} @tab Length of the record marker; valid values
2685 are 4 and 8. Default is 4.
2688 @item @emph{Example}:
2690 int main (int argc, char *argv[])
2692 /* Initialize libgfortran. */
2693 _gfortran_set_args (argc, argv);
2694 _gfortran_set_record_marker (8);
2701 @node _gfortran_set_fpe
2702 @subsection @code{_gfortran_set_fpe} --- Set when a Floating Point Exception should be raised
2703 @fnindex _gfortran_set_fpe
2704 @cindex libgfortran initialization, set_fpe
2707 @item @emph{Description}:
2708 @code{_gfortran_set_fpe} sets the IEEE exceptions for which a
2709 Floating Point Exception (FPE) should be raised. On most systems,
2710 this will result in a SIGFPE signal being sent and the program
2713 @item @emph{Syntax}:
2714 @code{void _gfortran_set_fpe (int val)}
2716 @item @emph{Arguments}:
2717 @multitable @columnfractions .15 .70
2718 @item @var{option}[0] @tab IEEE exceptions. Possible values are
2719 (bitwise or-ed) zero (0, default) no trapping,
2720 @code{GFC_FPE_INVALID} (1), @code{GFC_FPE_DENORMAL} (2),
2721 @code{GFC_FPE_ZERO} (4), @code{GFC_FPE_OVERFLOW} (8),
2722 @code{GFC_FPE_UNDERFLOW} (16), and @code{GFC_FPE_PRECISION} (32).
2725 @item @emph{Example}:
2727 int main (int argc, char *argv[])
2729 /* Initialize libgfortran. */
2730 _gfortran_set_args (argc, argv);
2731 /* FPE for invalid operations such as SQRT(-1.0). */
2732 _gfortran_set_fpe (1);
2739 @node _gfortran_set_max_subrecord_length
2740 @subsection @code{_gfortran_set_max_subrecord_length} --- Set subrecord length
2741 @fnindex _gfortran_set_max_subrecord_length
2742 @cindex libgfortran initialization, set_max_subrecord_length
2745 @item @emph{Description}:
2746 @code{_gfortran_set_max_subrecord_length} set the maximum length
2747 for a subrecord. This option only makes sense for testing and
2748 debugging of unformatted I/O.
2750 @item @emph{Syntax}:
2751 @code{void _gfortran_set_max_subrecord_length (int val)}
2753 @item @emph{Arguments}:
2754 @multitable @columnfractions .15 .70
2755 @item @var{val} @tab the maximum length for a subrecord;
2756 the maximum permitted value is 2147483639, which is also
2760 @item @emph{Example}:
2762 int main (int argc, char *argv[])
2764 /* Initialize libgfortran. */
2765 _gfortran_set_args (argc, argv);
2766 _gfortran_set_max_subrecord_length (8);
2774 @c Intrinsic Procedures
2775 @c ---------------------------------------------------------------------
2777 @include intrinsic.texi
2784 @c ---------------------------------------------------------------------
2786 @c ---------------------------------------------------------------------
2789 @unnumbered Contributing
2790 @cindex Contributing
2792 Free software is only possible if people contribute to efforts
2794 We're always in need of more people helping out with ideas
2795 and comments, writing documentation and contributing code.
2797 If you want to contribute to GNU Fortran,
2798 have a look at the long lists of projects you can take on.
2799 Some of these projects are small,
2800 some of them are large;
2801 some are completely orthogonal to the rest of what is
2802 happening on GNU Fortran,
2803 but others are ``mainstream'' projects in need of enthusiastic hackers.
2804 All of these projects are important!
2805 We'll eventually get around to the things here,
2806 but they are also things doable by someone who is willing and able.
2811 * Proposed Extensions::
2816 @section Contributors to GNU Fortran
2817 @cindex Contributors
2821 Most of the parser was hand-crafted by @emph{Andy Vaught}, who is
2822 also the initiator of the whole project. Thanks Andy!
2823 Most of the interface with GCC was written by @emph{Paul Brook}.
2825 The following individuals have contributed code and/or
2826 ideas and significant help to the GNU Fortran project
2827 (in alphabetical order):
2830 @item Janne Blomqvist
2831 @item Steven Bosscher
2834 @item Fran@,{c}ois-Xavier Coudert
2838 @item Bernhard Fischer
2840 @item Richard Guenther
2841 @item Richard Henderson
2842 @item Katherine Holcomb
2844 @item Niels Kristian Bech Jensen
2845 @item Steven Johnson
2846 @item Steven G. Kargl
2854 @item Christopher D. Rickett
2855 @item Richard Sandiford
2856 @item Tobias Schl@"uter
2865 The following people have contributed bug reports,
2866 smaller or larger patches,
2867 and much needed feedback and encouragement for the
2868 GNU Fortran project:
2872 @item Dominique d'Humi@`eres
2874 @item Erik Schnetter
2875 @item Joost VandeVondele
2878 Many other individuals have helped debug,
2879 test and improve the GNU Fortran compiler over the past few years,
2880 and we welcome you to do the same!
2881 If you already have done so,
2882 and you would like to see your name listed in the
2883 list above, please contact us.
2891 @item Help build the test suite
2892 Solicit more code for donation to the test suite: the more extensive the
2893 testsuite, the smaller the risk of breaking things in the future! We can
2894 keep code private on request.
2896 @item Bug hunting/squishing
2897 Find bugs and write more test cases! Test cases are especially very
2898 welcome, because it allows us to concentrate on fixing bugs instead of
2899 isolating them. Going through the bugzilla database at
2900 @url{http://gcc.gnu.org/@/bugzilla/} to reduce testcases posted there and
2901 add more information (for example, for which version does the testcase
2902 work, for which versions does it fail?) is also very helpful.
2907 @node Proposed Extensions
2908 @section Proposed Extensions
2910 Here's a list of proposed extensions for the GNU Fortran compiler, in no particular
2911 order. Most of these are necessary to be fully compatible with
2912 existing Fortran compilers, but they are not part of the official
2913 J3 Fortran 95 standard.
2915 @subsection Compiler extensions:
2918 User-specified alignment rules for structures.
2921 Automatically extend single precision constants to double.
2924 Compile code that conserves memory by dynamically allocating common and
2925 module storage either on stack or heap.
2928 Compile flag to generate code for array conformance checking (suggest -CC).
2931 User control of symbol names (underscores, etc).
2934 Compile setting for maximum size of stack frame size before spilling
2935 parts to static or heap.
2938 Flag to force local variables into static space.
2941 Flag to force local variables onto stack.
2945 @subsection Environment Options
2948 Pluggable library modules for random numbers, linear algebra.
2949 LA should use BLAS calling conventions.
2952 Environment variables controlling actions on arithmetic exceptions like
2953 overflow, underflow, precision loss---Generate NaN, abort, default.
2957 Set precision for fp units that support it (i387).
2960 Variable for setting fp rounding mode.
2963 Variable to fill uninitialized variables with a user-defined bit
2967 Environment variable controlling filename that is opened for that unit
2971 Environment variable to clear/trash memory being freed.
2974 Environment variable to control tracing of allocations and frees.
2977 Environment variable to display allocated memory at normal program end.
2980 Environment variable for filename for * IO-unit.
2983 Environment variable for temporary file directory.
2986 Environment variable forcing standard output to be line buffered (unix).
2991 @c ---------------------------------------------------------------------
2992 @c GNU General Public License
2993 @c ---------------------------------------------------------------------
2995 @include gpl_v3.texi
2999 @c ---------------------------------------------------------------------
3000 @c GNU Free Documentation License
3001 @c ---------------------------------------------------------------------
3007 @c ---------------------------------------------------------------------
3008 @c Funding Free Software
3009 @c ---------------------------------------------------------------------
3011 @include funding.texi
3013 @c ---------------------------------------------------------------------
3015 @c ---------------------------------------------------------------------
3018 @unnumbered Option Index
3019 @command{gfortran}'s command line options are indexed here without any
3020 initial @samp{-} or @samp{--}. Where an option has both positive and
3021 negative forms (such as -foption and -fno-option), relevant entries in
3022 the manual are indexed under the most appropriate form; it may sometimes
3023 be useful to look up both forms.
3027 @unnumbered Keyword Index