1 \input texinfo @c -*-texinfo-*-
3 @setfilename gfortran.info
4 @set copyrights-gfortran 1999-2007
6 @include gcc-common.texi
8 @settitle The GNU Fortran Compiler
10 @c Create a separate index for command line options
12 @c Merge the standard indexes into a single one.
19 @c TODO: The following "Part" definitions are included here temporarily
20 @c until they are incorporated into the official Texinfo distribution.
21 @c They borrow heavily from Texinfo's \unnchapentry definitions.
28 \vglue\titlepagetopglue
30 \leftline{Part #1:@* #2}
31 \vskip4pt \hrule height 4pt width \hsize \vskip4pt
33 \writetocentry{part}{#2}{#1}
36 \writetocentry{blankpart}{}{}
38 % Part TOC-entry definition for summary contents.
39 \gdef\dosmallpartentry#1#2#3#4{%
40 \vskip .5\baselineskip plus.2\baselineskip
43 \tocentry{Part #2: #1}{\doshortpageno\bgroup#4\egroup}
46 \gdef\dosmallblankpartentry#1#2#3#4{%
47 \vskip .5\baselineskip plus.2\baselineskip
49 % Part TOC-entry definition for regular contents. This has to be
50 % equated to an existing entry to not cause problems when the PDF
52 \gdef\dopartentry#1#2#3#4{%
53 \unnchapentry{Part #2: #1}{}{#3}{#4}
55 \gdef\doblankpartentry#1#2#3#4{}
60 @c Use with @@smallbook.
62 @c %** start of document
64 @c Cause even numbered pages to be printed on the left hand side of
65 @c the page and odd numbered pages to be printed on the right hand
66 @c side of the page. Using this, you can print on both sides of a
67 @c sheet of paper and have the text on the same part of the sheet.
69 @c The text on right hand pages is pushed towards the right hand
70 @c margin and the text on left hand pages is pushed toward the left
72 @c (To provide the reverse effect, set bindingoffset to -0.75in.)
75 @c \global\bindingoffset=0.75in
76 @c \global\normaloffset =0.75in
80 Copyright @copyright{} @value{copyrights-gfortran} Free Software Foundation, Inc.
82 Permission is granted to copy, distribute and/or modify this document
83 under the terms of the GNU Free Documentation License, Version 1.1 or
84 any later version published by the Free Software Foundation; with the
85 Invariant Sections being ``GNU General Public License'' and ``Funding
86 Free Software'', the Front-Cover
87 texts being (a) (see below), and with the Back-Cover Texts being (b)
88 (see below). A copy of the license is included in the section entitled
89 ``GNU Free Documentation License''.
91 (a) The FSF's Front-Cover Text is:
95 (b) The FSF's Back-Cover Text is:
97 You have freedom to copy and modify this GNU Manual, like GNU
98 software. Copies published by the Free Software Foundation raise
99 funds for GNU development.
103 @dircategory Software development
105 * gfortran: (gfortran). The GNU Fortran Compiler.
107 This file documents the use and the internals of
108 the GNU Fortran compiler, (@command{gfortran}).
110 Published by the Free Software Foundation
111 51 Franklin Street, Fifth Floor
112 Boston, MA 02110-1301 USA
118 @setchapternewpage odd
120 @title Using GNU Fortran
122 @author The @t{gfortran} team
124 @vskip 0pt plus 1filll
125 Published by the Free Software Foundation@*
126 51 Franklin Street, Fifth Floor@*
127 Boston, MA 02110-1301, USA@*
128 @c Last printed ??ber, 19??.@*
129 @c Printed copies are available for $? each.@*
135 @c TODO: The following "Part" definitions are included here temporarily
136 @c until they are incorporated into the official Texinfo distribution.
139 \global\let\partentry=\dosmallpartentry
140 \global\let\blankpartentry=\dosmallblankpartentry
145 \global\let\partentry=\dopartentry
146 \global\let\blankpartentry=\doblankpartentry
152 @c ---------------------------------------------------------------------
153 @c TexInfo table of contents.
154 @c ---------------------------------------------------------------------
161 This manual documents the use of @command{gfortran},
162 the GNU Fortran compiler. You can find in this manual how to invoke
163 @command{gfortran}, as well as its features and incompatibilities.
166 @emph{Warning:} This document, and the compiler it describes, are still
167 under development. While efforts are made to keep it up-to-date, it might
168 not accurately reflect the status of the most recent GNU Fortran compiler.
172 @comment When you add a new menu item, please keep the right hand
173 @comment aligned to the same column. Do not use tabs. This provides
174 @comment better formatting.
179 Part I: Invoking GNU Fortran
180 * Invoking GNU Fortran:: Command options supported by @command{gfortran}.
181 * Runtime:: Influencing runtime behavior with environment variables.
183 Part II: Language Reference
184 * Fortran 2003 status:: Fortran 2003 features supported by GNU Fortran.
185 * Extensions:: Language extensions implemented by GNU Fortran.
186 * Intrinsic Procedures:: Intrinsic procedures supported by GNU Fortran.
187 * Intrinsic Modules:: Intrinsic modules supported by GNU Fortran.
189 * Contributing:: How you can help.
190 * Copying:: GNU General Public License says
191 how you can copy and share GNU Fortran.
192 * GNU Free Documentation License::
193 How you can copy and share this manual.
194 * Funding:: How to help assure continued work for free software.
195 * Option Index:: Index of command line options
196 * Keyword Index:: Index of concepts
200 @c ---------------------------------------------------------------------
202 @c ---------------------------------------------------------------------
205 @chapter Introduction
207 @c The following duplicates the text on the TexInfo table of contents.
209 This manual documents the use of @command{gfortran}, the GNU Fortran
210 compiler. You can find in this manual how to invoke @command{gfortran},
211 as well as its features and incompatibilities.
214 @emph{Warning:} This document, and the compiler it describes, are still
215 under development. While efforts are made to keep it up-to-date, it
216 might not accurately reflect the status of the most recent GNU Fortran
221 The GNU Fortran compiler front end was
222 designed initially as a free replacement for,
223 or alternative to, the unix @command{f95} command;
224 @command{gfortran} is the command you'll use to invoke the compiler.
227 * About GNU Fortran:: What you should know about the GNU Fortran compiler.
228 * GNU Fortran and GCC:: You can compile Fortran, C, or other programs.
229 * Preprocessing and conditional compilation:: The Fortran preprocessor
230 * GNU Fortran and G77:: Why we chose to start from scratch.
231 * Project Status:: Status of GNU Fortran, roadmap, proposed extensions.
232 * Standards:: Standards supported by GNU Fortran.
236 @c ---------------------------------------------------------------------
238 @c ---------------------------------------------------------------------
240 @node About GNU Fortran
241 @section About GNU Fortran
243 The GNU Fortran compiler is still in an early state of development.
244 It can generate code for most constructs and expressions,
245 but much work remains to be done.
247 When the GNU Fortran compiler is finished,
248 it will do everything you expect from any decent compiler:
252 Read a user's program,
253 stored in a file and containing instructions written
254 in Fortran 77, Fortran 90, Fortran 95 or Fortran 2003.
255 This file contains @dfn{source code}.
258 Translate the user's program into instructions a computer
259 can carry out more quickly than it takes to translate the
260 instructions in the first
261 place. The result after compilation of a program is
263 code designed to be efficiently translated and processed
264 by a machine such as your computer.
265 Humans usually aren't as good writing machine code
266 as they are at writing Fortran (or C++, Ada, or Java),
267 because is easy to make tiny mistakes writing machine code.
270 Provide the user with information about the reasons why
271 the compiler is unable to create a binary from the source code.
272 Usually this will be the case if the source code is flawed.
273 When writing Fortran, it is easy to make big mistakes.
274 The Fortran 90 requires that the compiler can point out
275 mistakes to the user.
276 An incorrect usage of the language causes an @dfn{error message}.
278 The compiler will also attempt to diagnose cases where the
279 user's program contains a correct usage of the language,
280 but instructs the computer to do something questionable.
281 This kind of diagnostics message is called a @dfn{warning message}.
284 Provide optional information about the translation passes
285 from the source code to machine code.
286 This can help a user of the compiler to find the cause of
287 certain bugs which may not be obvious in the source code,
288 but may be more easily found at a lower level compiler output.
289 It also helps developers to find bugs in the compiler itself.
292 Provide information in the generated machine code that can
293 make it easier to find bugs in the program (using a debugging tool,
294 called a @dfn{debugger}, such as the GNU Debugger @command{gdb}).
297 Locate and gather machine code already generated to
298 perform actions requested by statements in the user's program.
299 This machine code is organized into @dfn{modules} and is located
300 and @dfn{linked} to the user program.
303 The GNU Fortran compiler consists of several components:
307 A version of the @command{gcc} command
308 (which also might be installed as the system's @command{cc} command)
309 that also understands and accepts Fortran source code.
310 The @command{gcc} command is the @dfn{driver} program for
311 all the languages in the GNU Compiler Collection (GCC);
313 you can compile the source code of any language for
314 which a front end is available in GCC.
317 The @command{gfortran} command itself,
318 which also might be installed as the
319 system's @command{f95} command.
320 @command{gfortran} is just another driver program,
321 but specifically for the Fortran compiler only.
322 The difference with @command{gcc} is that @command{gfortran}
323 will automatically link the correct libraries to your program.
326 A collection of run-time libraries.
327 These libraries contain the machine code needed to support
328 capabilities of the Fortran language that are not directly
329 provided by the machine code generated by the
330 @command{gfortran} compilation phase,
331 such as intrinsic functions and subroutines,
332 and routines for interaction with files and the operating system.
333 @c and mechanisms to spawn,
334 @c unleash and pause threads in parallelized code.
337 The Fortran compiler itself, (@command{f951}).
338 This is the GNU Fortran parser and code generator,
339 linked to and interfaced with the GCC backend library.
340 @command{f951} ``translates'' the source code to
341 assembler code. You would typically not use this
343 instead, the @command{gcc} or @command{gfortran} driver
344 programs will call it for you.
348 @c ---------------------------------------------------------------------
349 @c GNU Fortran and GCC
350 @c ---------------------------------------------------------------------
352 @node GNU Fortran and GCC
353 @section GNU Fortran and GCC
354 @cindex GNU Compiler Collection
357 GNU Fortran is a part of GCC, the @dfn{GNU Compiler Collection}. GCC
358 consists of a collection of front ends for various languages, which
359 translate the source code into a language-independent form called
360 @dfn{GENERIC}. This is then processed by a common middle end which
361 provides optimization, and then passed to one of a collection of back
362 ends which generate code for different computer architectures and
365 Functionally, this is implemented with a driver program (@command{gcc})
366 which provides the command-line interface for the compiler. It calls
367 the relevant compiler front-end program (e.g., @command{f951} for
368 Fortran) for each file in the source code, and then calls the assembler
369 and linker as appropriate to produce the compiled output. In a copy of
370 GCC which has been compiled with Fortran language support enabled,
371 @command{gcc} will recognize files with @file{.f}, @file{.for}, @file{.ftn},
372 @file{.f90}, @file{.f95}, and @file{.f03} extensions as Fortran source code,
373 and compile it accordingly. A @command{gfortran} driver program is also
374 provided, which is identical to @command{gcc} except that it automatically
375 links the Fortran runtime libraries into the compiled program.
377 Source files with @file{.f}, @file{.for}, @file{.fpp}, @file{.ftn}, @file{.F},
378 @file{.FOR}, @file{.FPP}, and @file{.FTN} extensions are treated as fixed form.
379 Source files with @file{.f90}, @file{.f95}, @file{.f03}, @file{.F90},
380 @file{.F95}, and @file{.F03} extensions are treated as free form. The
381 capitalized versions of either form are run through preprocessing. Source files
382 with the lower case @file{.fpp} extension are also run through preprocessing.
384 This manual specifically documents the Fortran front end, which handles
385 the programming language's syntax and semantics. The aspects of GCC
386 which relate to the optimization passes and the back-end code generation
387 are documented in the GCC manual; see
388 @ref{Top,,Introduction,gcc,Using the GNU Compiler Collection (GCC)}.
389 The two manuals together provide a complete reference for the GNU
393 @c ---------------------------------------------------------------------
394 @c Preprocessing and conditional compilation
395 @c ---------------------------------------------------------------------
397 @node Preprocessing and conditional compilation
398 @section Preprocessing and conditional compilation
401 @cindex Conditional compilation
402 @cindex Preprocessing
404 Many Fortran compilers including GNU Fortran allow passing the source code
405 through a C preprocessor (CPP; sometimes also called the Fortran preprocessor,
406 FPP) to allow for conditional compilation. In the case of GNU Fortran,
407 this is the GNU C Preprocessor in the traditional mode. On systems with
408 case-preserving file names, the preprocessor is automatically invoked if the
409 file extension is @code{.F}, @code{.FOR}, @code{.FTN}, @code{.F90},
410 @code{.F95} or @code{.F03}; otherwise use for fixed-format code the option
411 @code{-x f77-cpp-input} and for free-format code @code{-x f95-cpp-input}.
412 Invocation of the preprocessor can be suppressed using @code{-x f77} or
415 If the GNU Fortran invoked the preprocessor, @code{__GFORTRAN__}
416 is defined and @code{__GNUC__}, @code{__GNUC_MINOR__} and
417 @code{__GNUC_PATCHLEVEL__} can be used to determine the version of the
418 compiler. See @ref{Top,,Overview,cpp,The C Preprocessor} for details.
420 While CPP is the de-facto standard for preprocessing Fortran code,
421 Part 3 of the Fortran 95 standard (ISO/IEC 1539-3:1998) defines
422 Conditional Compilation, which is not widely used and not directly
423 supported by the GNU Fortran compiler. You can use the program coco
424 to preprocess such files (@uref{http://users.erols.com/dnagle/coco.html}).
427 @c ---------------------------------------------------------------------
428 @c GNU Fortran and G77
429 @c ---------------------------------------------------------------------
431 @node GNU Fortran and G77
432 @section GNU Fortran and G77
434 @cindex @command{g77}
436 The GNU Fortran compiler is the successor to @command{g77}, the Fortran
437 77 front end included in GCC prior to version 4. It is an entirely new
438 program that has been designed to provide Fortran 95 support and
439 extensibility for future Fortran language standards, as well as providing
440 backwards compatibility for Fortran 77 and nearly all of the GNU language
441 extensions supported by @command{g77}.
444 @c ---------------------------------------------------------------------
446 @c ---------------------------------------------------------------------
449 @section Project Status
452 As soon as @command{gfortran} can parse all of the statements correctly,
453 it will be in the ``larva'' state.
454 When we generate code, the ``puppa'' state.
455 When @command{gfortran} is done,
456 we'll see if it will be a beautiful butterfly,
457 or just a big bug....
459 --Andy Vaught, April 2000
462 The start of the GNU Fortran 95 project was announced on
463 the GCC homepage in March 18, 2000
464 (even though Andy had already been working on it for a while,
467 The GNU Fortran compiler is able to compile nearly all
468 standard-compliant Fortran 95, Fortran 90, and Fortran 77 programs,
469 including a number of standard and non-standard extensions, and can be
470 used on real-world programs. In particular, the supported extensions
471 include OpenMP, Cray-style pointers, and several Fortran 2003 features
472 such as enumeration, stream I/O, and some of the enhancements to
473 allocatable array support from TR 15581. However, it is still under
474 development and has a few remaining rough edges.
476 At present, the GNU Fortran compiler passes the
477 @uref{http://www.fortran-2000.com/ArnaudRecipes/fcvs21_f95.html,
478 NIST Fortran 77 Test Suite}, and produces acceptable results on the
479 @uref{http://www.netlib.org/lapack/faq.html#1.21, LAPACK Test Suite}.
480 It also provides respectable performance on
481 the @uref{http://www.polyhedron.com/pb05.html, Polyhedron Fortran
482 compiler benchmarks} and the
483 @uref{http://www.llnl.gov/asci_benchmarks/asci/limited/lfk/README.html,
484 Livermore Fortran Kernels test}. It has been used to compile a number of
485 large real-world programs, including
486 @uref{http://mysite.verizon.net/serveall/moene.pdf, the HIRLAM
487 weather-forecasting code} and
488 @uref{http://www.theochem.uwa.edu.au/tonto/, the Tonto quantum
489 chemistry package}; see @url{http://gcc.gnu.org/wiki/GfortranApps} for an
492 Among other things, the GNU Fortran compiler is intended as a replacement
493 for G77. At this point, nearly all programs that could be compiled with
494 G77 can be compiled with GNU Fortran, although there are a few minor known
497 The primary work remaining to be done on GNU Fortran falls into three
498 categories: bug fixing (primarily regarding the treatment of invalid code
499 and providing useful error messages), improving the compiler optimizations
500 and the performance of compiled code, and extending the compiler to support
501 future standards---in particular, Fortran 2003.
504 @c ---------------------------------------------------------------------
506 @c ---------------------------------------------------------------------
512 The GNU Fortran compiler implements
513 ISO/IEC 1539:1997 (Fortran 95). As such, it can also compile essentially all
514 standard-compliant Fortran 90 and Fortran 77 programs. It also supports
515 the ISO/IEC TR-15581 enhancements to allocatable arrays, and
516 the @uref{http://www.openmp.org/drupal/mp-documents/spec25.pdf,
517 OpenMP Application Program Interface v2.5} specification.
519 In the future, the GNU Fortran compiler may also support other standard
520 variants of and extensions to the Fortran language. These include
521 ISO/IEC 1539-1:2004 (Fortran 2003).
524 @c =====================================================================
525 @c PART I: INVOCATION REFERENCE
526 @c =====================================================================
529 \part{I}{Invoking GNU Fortran}
532 @c ---------------------------------------------------------------------
534 @c ---------------------------------------------------------------------
539 @c ---------------------------------------------------------------------
541 @c ---------------------------------------------------------------------
544 @chapter Runtime: Influencing runtime behavior with environment variables
545 @cindex environment variable
547 The behavior of the @command{gfortran} can be influenced by
548 environment variables.
550 Malformed environment variables are silently ignored.
553 * GFORTRAN_STDIN_UNIT:: Unit number for standard input
554 * GFORTRAN_STDOUT_UNIT:: Unit number for standard output
555 * GFORTRAN_STDERR_UNIT:: Unit number for standard error
556 * GFORTRAN_USE_STDERR:: Send library output to standard error
557 * GFORTRAN_TMPDIR:: Directory for scratch files
558 * GFORTRAN_UNBUFFERED_ALL:: Don't buffer I/O for all units.
559 * GFORTRAN_UNBUFFERED_PRECONNECTED:: Don't buffer I/O for preconnected units.
560 * GFORTRAN_SHOW_LOCUS:: Show location for runtime errors
561 * GFORTRAN_OPTIONAL_PLUS:: Print leading + where permitted
562 * GFORTRAN_DEFAULT_RECL:: Default record length for new files
563 * GFORTRAN_LIST_SEPARATOR:: Separator for list output
564 * GFORTRAN_CONVERT_UNIT:: Set endianness for unformatted I/O
565 * GFORTRAN_ERROR_DUMPCORE:: Dump core on run-time errors
566 * GFORTRAN_ERROR_BACKTRACE:: Show backtrace on run-time errors
569 @node GFORTRAN_STDIN_UNIT
570 @section @env{GFORTRAN_STDIN_UNIT}---Unit number for standard input
572 This environment variable can be used to select the unit number
573 preconnected to standard input. This must be a positive integer.
574 The default value is 5.
576 @node GFORTRAN_STDOUT_UNIT
577 @section @env{GFORTRAN_STDOUT_UNIT}---Unit number for standard output
579 This environment variable can be used to select the unit number
580 preconnected to standard output. This must be a positive integer.
581 The default value is 6.
583 @node GFORTRAN_STDERR_UNIT
584 @section @env{GFORTRAN_STDERR_UNIT}---Unit number for standard error
586 This environment variable can be used to select the unit number
587 preconnected to standard error. This must be a positive integer.
588 The default value is 0.
590 @node GFORTRAN_USE_STDERR
591 @section @env{GFORTRAN_USE_STDERR}---Send library output to standard error
593 This environment variable controls where library output is sent.
594 If the first letter is @samp{y}, @samp{Y} or @samp{1}, standard
595 error is used. If the first letter is @samp{n}, @samp{N} or
596 @samp{0}, standard output is used.
598 @node GFORTRAN_TMPDIR
599 @section @env{GFORTRAN_TMPDIR}---Directory for scratch files
601 This environment variable controls where scratch files are
602 created. If this environment variable is missing,
603 GNU Fortran searches for the environment variable @env{TMP}. If
604 this is also missing, the default is @file{/tmp}.
606 @node GFORTRAN_UNBUFFERED_ALL
607 @section @env{GFORTRAN_UNBUFFERED_ALL}---Don't buffer I/O on all units
609 This environment variable controls whether all I/O is unbuffered. If
610 the first letter is @samp{y}, @samp{Y} or @samp{1}, all I/O is
611 unbuffered. This will slow down small sequential reads and writes. If
612 the first letter is @samp{n}, @samp{N} or @samp{0}, I/O is buffered.
615 @node GFORTRAN_UNBUFFERED_PRECONNECTED
616 @section @env{GFORTRAN_UNBUFFERED_PRECONNECTED}---Don't buffer I/O on
619 The environment variable named @env{GFORTRAN_UNBUFFERED_PRECONNECTED} controls
620 whether I/O on a preconnected unit (i.e STDOUT or STDERR) is unbuffered. If
621 the first letter is @samp{y}, @samp{Y} or @samp{1}, I/O is unbuffered. This
622 will slow down small sequential reads and writes. If the first letter
623 is @samp{n}, @samp{N} or @samp{0}, I/O is buffered. This is the default.
625 @node GFORTRAN_SHOW_LOCUS
626 @section @env{GFORTRAN_SHOW_LOCUS}---Show location for runtime errors
628 If the first letter is @samp{y}, @samp{Y} or @samp{1}, filename and
629 line numbers for runtime errors are printed. If the first letter is
630 @samp{n}, @samp{N} or @samp{0}, don't print filename and line numbers
631 for runtime errors. The default is to print the location.
633 @node GFORTRAN_OPTIONAL_PLUS
634 @section @env{GFORTRAN_OPTIONAL_PLUS}---Print leading + where permitted
636 If the first letter is @samp{y}, @samp{Y} or @samp{1},
637 a plus sign is printed
638 where permitted by the Fortran standard. If the first letter
639 is @samp{n}, @samp{N} or @samp{0}, a plus sign is not printed
640 in most cases. Default is not to print plus signs.
642 @node GFORTRAN_DEFAULT_RECL
643 @section @env{GFORTRAN_DEFAULT_RECL}---Default record length for new files
645 This environment variable specifies the default record length, in
646 bytes, for files which are opened without a @code{RECL} tag in the
647 @code{OPEN} statement. This must be a positive integer. The
648 default value is 1073741824 bytes (1 GB).
650 @node GFORTRAN_LIST_SEPARATOR
651 @section @env{GFORTRAN_LIST_SEPARATOR}---Separator for list output
653 This environment variable specifies the separator when writing
654 list-directed output. It may contain any number of spaces and
655 at most one comma. If you specify this on the command line,
656 be sure to quote spaces, as in
658 $ GFORTRAN_LIST_SEPARATOR=' , ' ./a.out
660 when @command{a.out} is the compiled Fortran program that you want to run.
661 Default is a single space.
663 @node GFORTRAN_CONVERT_UNIT
664 @section @env{GFORTRAN_CONVERT_UNIT}---Set endianness for unformatted I/O
666 By setting the @env{GFORTRAN_CONVERT_UNIT} variable, it is possible
667 to change the representation of data for unformatted files.
668 The syntax for the @env{GFORTRAN_CONVERT_UNIT} variable is:
670 GFORTRAN_CONVERT_UNIT: mode | mode ';' exception | exception ;
671 mode: 'native' | 'swap' | 'big_endian' | 'little_endian' ;
672 exception: mode ':' unit_list | unit_list ;
673 unit_list: unit_spec | unit_list unit_spec ;
674 unit_spec: INTEGER | INTEGER '-' INTEGER ;
676 The variable consists of an optional default mode, followed by
677 a list of optional exceptions, which are separated by semicolons
678 from the preceding default and each other. Each exception consists
679 of a format and a comma-separated list of units. Valid values for
680 the modes are the same as for the @code{CONVERT} specifier:
683 @item @code{NATIVE} Use the native format. This is the default.
684 @item @code{SWAP} Swap between little- and big-endian.
685 @item @code{LITTLE_ENDIAN} Use the little-endian format
686 for unformatted files.
687 @item @code{BIG_ENDIAN} Use the big-endian format for unformatted files.
689 A missing mode for an exception is taken to mean @code{BIG_ENDIAN}.
690 Examples of values for @env{GFORTRAN_CONVERT_UNIT} are:
692 @item @code{'big_endian'} Do all unformatted I/O in big_endian mode.
693 @item @code{'little_endian;native:10-20,25'} Do all unformatted I/O
694 in little_endian mode, except for units 10 to 20 and 25, which are in
696 @item @code{'10-20'} Units 10 to 20 are big-endian, the rest is native.
699 Setting the environment variables should be done on the command
700 line or via the @command{export}
701 command for @command{sh}-compatible shells and via @command{setenv}
702 for @command{csh}-compatible shells.
704 Example for @command{sh}:
707 $ GFORTRAN_CONVERT_UNIT='big_endian;native:10-20' ./a.out
710 Example code for @command{csh}:
713 % setenv GFORTRAN_CONVERT_UNIT 'big_endian;native:10-20'
717 Using anything but the native representation for unformatted data
718 carries a significant speed overhead. If speed in this area matters
719 to you, it is best if you use this only for data that needs to be
722 @xref{CONVERT specifier}, for an alternative way to specify the
723 data representation for unformatted files. @xref{Runtime Options}, for
724 setting a default data representation for the whole program. The
725 @code{CONVERT} specifier overrides the @option{-fconvert} compile options.
727 @emph{Note that the values specified via the GFORTRAN_CONVERT_UNIT
728 environment variable will override the CONVERT specifier in the
729 open statement}. This is to give control over data formats to
730 users who do not have the source code of their program available.
732 @node GFORTRAN_ERROR_DUMPCORE
733 @section @env{GFORTRAN_ERROR_DUMPCORE}---Dump core on run-time errors
735 If the @env{GFORTRAN_ERROR_DUMPCORE} variable is set to
736 @samp{y}, @samp{Y} or @samp{1} (only the first letter is relevant)
737 then library run-time errors cause core dumps. To disable the core
738 dumps, set the variable to @samp{n}, @samp{N}, @samp{0}. Default
739 is not to core dump unless the @option{-fdump-core} compile option
742 @node GFORTRAN_ERROR_BACKTRACE
743 @section @env{GFORTRAN_ERROR_BACKTRACE}---Show backtrace on run-time errors
745 If the @env{GFORTRAN_ERROR_BACKTRACE} variable is set to
746 @samp{y}, @samp{Y} or @samp{1} (only the first letter is relevant)
747 then a backtrace is printed when a run-time error occurs.
748 To disable the backtracing, set the variable to
749 @samp{n}, @samp{N}, @samp{0}. Default is not to print a backtrace
750 unless the @option{-fbacktrace} compile option
753 @c =====================================================================
754 @c PART II: LANGUAGE REFERENCE
755 @c =====================================================================
758 \part{II}{Language Reference}
761 @c ---------------------------------------------------------------------
762 @c Fortran 2003 Status
763 @c ---------------------------------------------------------------------
765 @node Fortran 2003 status
766 @chapter Fortran 2003 Status
768 Although GNU Fortran focuses on implementing the Fortran 95
769 standard for the time being, a few Fortran 2003 features are currently
774 Intrinsics @code{command_argument_count}, @code{get_command},
775 @code{get_command_argument}, @code{get_environment_variable}, and
779 @cindex array, constructors
781 Array constructors using square brackets. That is, @code{[...]} rather
785 @cindex @code{FLUSH} statement
786 @cindex statement, @code{FLUSH}
787 @code{FLUSH} statement.
790 @cindex @code{IOMSG=} specifier
791 @code{IOMSG=} specifier for I/O statements.
794 @cindex @code{ENUM} statement
795 @cindex @code{ENUMERATOR} statement
796 @cindex statement, @code{ENUM}
797 @cindex statement, @code{ENUMERATOR}
798 @opindex @code{fshort-enums}
799 Support for the declaration of enumeration constants via the
800 @code{ENUM} and @code{ENUMERATOR} statements. Interoperability with
801 @command{gcc} is guaranteed also for the case where the
802 @command{-fshort-enums} command line option is given.
809 @cindex @code{ALLOCATABLE} dummy arguments
810 @code{ALLOCATABLE} dummy arguments.
812 @cindex @code{ALLOCATABLE} function results
813 @code{ALLOCATABLE} function results
815 @cindex @code{ALLOCATABLE} components of derived types
816 @code{ALLOCATABLE} components of derived types
820 @cindex @code{STREAM} I/O
821 @cindex @code{ACCESS='STREAM'} I/O
822 The @code{OPEN} statement supports the @code{ACCESS='STREAM'} specifier,
823 allowing I/O without any record structure.
826 Namelist input/output for internal files.
829 @cindex @code{PROTECTED} statement
830 @cindex statement, @code{PROTECTED}
831 The @code{PROTECTED} statement and attribute.
834 @cindex @code{VALUE} statement
835 @cindex statement, @code{VALUE}
836 The @code{VALUE} statement and attribute.
839 @cindex @code{VOLATILE} statement
840 @cindex statement, @code{VOLATILE}
841 The @code{VOLATILE} statement and attribute.
844 @cindex @code{IMPORT} statement
845 @cindex statement, @code{IMPORT}
846 The @code{IMPORT} statement, allowing to import
847 host-associated derived types.
850 @cindex @code{USE, INTRINSIC} statement
851 @cindex statement, @code{USE, INTRINSIC}
852 @cindex @code{ISO_FORTRAN_ENV} statement
853 @cindex statement, @code{ISO_FORTRAN_ENV}
854 @code{USE} statement with @code{INTRINSIC} and @code{NON_INTRINSIC}
855 attribute; supported intrinsic modules: @code{ISO_FORTRAN_ENV},
856 @code{OMP_LIB} and @code{OMP_LIB_KINDS}.
859 Renaming of operators in the @code{USE} statement.
862 @cindex ISO C Bindings
863 Interoperability with C (ISO C Bindings)
866 BOZ as argument of INT, REAL, DBLE and CMPLX.
871 @c ---------------------------------------------------------------------
873 @c ---------------------------------------------------------------------
875 @c Maybe this chapter should be merged with the 'Standards' section,
876 @c whenever that is written :-)
882 GNU Fortran implements a number of extensions over standard
883 Fortran. This chapter contains information on their syntax and
884 meaning. There are currently two categories of GNU Fortran
885 extensions, those that provide functionality beyond that provided
886 by any standard, and those that are supported by GNU Fortran
887 purely for backward compatibility with legacy compilers. By default,
888 @option{-std=gnu} allows the compiler to accept both types of
889 extensions, but to warn about the use of the latter. Specifying
890 either @option{-std=f95} or @option{-std=f2003} disables both types
891 of extensions, and @option{-std=legacy} allows both without warning.
894 * Old-style kind specifications::
895 * Old-style variable initialization::
896 * Extensions to namelist::
897 * X format descriptor without count field::
898 * Commas in FORMAT specifications::
899 * Missing period in FORMAT specifications::
901 * BOZ literal constants::
902 * Real array indices::
904 * Implicitly convert LOGICAL and INTEGER values::
905 * Hollerith constants support::
907 * CONVERT specifier::
909 * Argument list functions::
912 @node Old-style kind specifications
913 @section Old-style kind specifications
914 @cindex kind, old-style
916 GNU Fortran allows old-style kind specifications in declarations. These
922 where @code{TYPESPEC} is a basic type (@code{INTEGER}, @code{REAL},
923 etc.), and where @code{size} is a byte count corresponding to the
924 storage size of a valid kind for that type. (For @code{COMPLEX}
925 variables, @code{size} is the total size of the real and imaginary
926 parts.) The statement then declares @code{x}, @code{y} and @code{z} to
927 be of type @code{TYPESPEC} with the appropriate kind. This is
928 equivalent to the standard-conforming declaration
933 where @code{k} is equal to @code{size} for most types, but is equal to
934 @code{size/2} for the @code{COMPLEX} type.
936 @node Old-style variable initialization
937 @section Old-style variable initialization
939 GNU Fortran allows old-style initialization of variables of the
943 REAL x(2,2) /3*0.,1./
945 The syntax for the initializers is as for the @code{DATA} statement, but
946 unlike in a @code{DATA} statement, an initializer only applies to the
947 variable immediately preceding the initialization. In other words,
948 something like @code{INTEGER I,J/2,3/} is not valid. This style of
949 initialization is only allowed in declarations without double colons
950 (@code{::}); the double colons were introduced in Fortran 90, which also
951 introduced a standard syntax for initializing variables in type
954 Examples of standard-conforming code equivalent to the above example
958 INTEGER :: i = 1, j = 2
959 REAL :: x(2,2) = RESHAPE((/0.,0.,0.,1./),SHAPE(x))
963 DATA i/1/, j/2/, x/3*0.,1./
966 Note that variables which are explicitly initialized in declarations
967 or in @code{DATA} statements automatically acquire the @code{SAVE}
970 @node Extensions to namelist
971 @section Extensions to namelist
974 GNU Fortran fully supports the Fortran 95 standard for namelist I/O
975 including array qualifiers, substrings and fully qualified derived types.
976 The output from a namelist write is compatible with namelist read. The
977 output has all names in upper case and indentation to column 1 after the
978 namelist name. Two extensions are permitted:
980 Old-style use of @samp{$} instead of @samp{&}
983 X(:)%Y(2) = 1.0 2.0 3.0
988 It should be noted that the default terminator is @samp{/} rather than
991 Querying of the namelist when inputting from stdin. After at least
992 one space, entering @samp{?} sends to stdout the namelist name and the names of
993 the variables in the namelist:
1004 Entering @samp{=?} outputs the namelist to stdout, as if
1005 @code{WRITE(*,NML = mynml)} had been called:
1010 X(1)%Y= 0.000000 , 1.000000 , 0.000000 ,
1011 X(2)%Y= 0.000000 , 2.000000 , 0.000000 ,
1012 X(3)%Y= 0.000000 , 3.000000 , 0.000000 ,
1016 To aid this dialog, when input is from stdin, errors send their
1017 messages to stderr and execution continues, even if @code{IOSTAT} is set.
1019 @code{PRINT} namelist is permitted. This causes an error if
1020 @option{-std=f95} is used.
1023 REAL, dimension (4) :: x = (/1.0, 2.0, 3.0, 4.0/)
1026 END PROGRAM test_print
1029 Expanded namelist reads are permitted. This causes an error if
1030 @option{-std=f95} is used. In the following example, the first element
1031 of the array will be given the value 0.00 and the two succeeding
1032 elements will be given the values 1.00 and 2.00.
1035 X(1,1) = 0.00 , 1.00 , 2.00
1039 @node X format descriptor without count field
1040 @section @code{X} format descriptor without count field
1042 To support legacy codes, GNU Fortran permits the count field of the
1043 @code{X} edit descriptor in @code{FORMAT} statements to be omitted.
1044 When omitted, the count is implicitly assumed to be one.
1048 10 FORMAT (I1, X, I1)
1051 @node Commas in FORMAT specifications
1052 @section Commas in @code{FORMAT} specifications
1054 To support legacy codes, GNU Fortran allows the comma separator
1055 to be omitted immediately before and after character string edit
1056 descriptors in @code{FORMAT} statements.
1060 10 FORMAT ('FOO='I1' BAR='I2)
1064 @node Missing period in FORMAT specifications
1065 @section Missing period in @code{FORMAT} specifications
1067 To support legacy codes, GNU Fortran allows missing periods in format
1068 specifications if and only if @option{-std=legacy} is given on the
1069 command line. This is considered non-conforming code and is
1078 @node I/O item lists
1079 @section I/O item lists
1080 @cindex I/O item lists
1082 To support legacy codes, GNU Fortran allows the input item list
1083 of the @code{READ} statement, and the output item lists of the
1084 @code{WRITE} and @code{PRINT} statements, to start with a comma.
1086 @node BOZ literal constants
1087 @section BOZ literal constants
1088 @cindex BOZ literal constants
1090 Besides decimal constants, Fortran also supports binary (@code{b}),
1091 octal (@code{o}) and hexadecimal (@code{z}) integer constants. The
1092 syntax is: @samp{prefix quote digits quote}, were the prefix is
1093 either @code{b}, @code{o} or @code{z}, quote is either @code{'} or
1094 @code{"} and the digits are for binary @code{0} or @code{1}, for
1095 octal between @code{0} and @code{7}, and for hexadecimal between
1096 @code{0} and @code{F}. (Example: @code{b'01011101'}.)
1098 Up to Fortran 95, BOZ literals were only allowed to initialize
1099 integer variables in DATA statements. Since Fortran 2003 BOZ literals
1100 are also allowed as argument of @code{REAL}, @code{DBLE}, @code{INT}
1101 and @code{CMPLX}; the result is the same as if the integer BOZ
1102 literal had been converted by @code{TRANSFER} to, respectively,
1103 @code{real}, @code{double precision}, @code{integer} or @code{complex}.
1104 As GNU Fortran extension the intrinsic procedures @code{FLOAT},
1105 @code{DFLOAT}, @code{COMPLEX} and @code{DCMPLX} are treated alike.
1107 As an extension, GNU Fortran allows hexadecimal BOZ literal constants to
1108 be specified using the @code{X} prefix, in addition to the standard
1109 @code{Z} prefix. The BOZ literal can also be specified by adding a
1110 suffix to the string, for example, @code{Z'ABC'} and @code{'ABC'Z} are
1113 Furthermore, GNU Fortran allows using BOZ literal constants outside
1114 DATA statements and the four intrinsic functions allowed by Fortran 2003.
1115 In DATA statements, in direct assignments, where the right-hand side
1116 only contains a BOZ literal constant, and for old-style initializers of
1117 the form @code{integer i /o'0173'/}, the constant is transferred
1118 as if @code{TRANSFER} had been used; for @code{COMPLEX} numbers, only
1119 the real part is initialized unless @code{CMPLX} is used. In all other
1120 cases, the BOZ literal constant is converted to an @code{INTEGER} value with
1121 the largest decimal representation. This value is then converted
1122 numerically to the type and kind of the variable in question.
1123 (For instance @code{real :: r = b'0000001' + 1} initializes @code{r}
1124 with @code{2.0}.) As different compilers implement the extension
1125 differently, one should be careful when doing bitwise initialization
1126 of non-integer variables.
1128 Note that initializing an @code{INTEGER} variable with a statement such
1129 as @code{DATA i/Z'FFFFFFFF'/} will give an integer overflow error rather
1130 than the desired result of @math{-1} when @code{i} is a 32-bit integer
1131 on a system that supports 64-bit integers. The @samp{-fno-range-check}
1132 option can be used as a workaround for legacy code that initializes
1133 integers in this manner.
1135 @node Real array indices
1136 @section Real array indices
1137 @cindex array, indices of type real
1139 As an extension, GNU Fortran allows the use of @code{REAL} expressions
1140 or variables as array indices.
1142 @node Unary operators
1143 @section Unary operators
1144 @cindex operators, unary
1146 As an extension, GNU Fortran allows unary plus and unary minus operators
1147 to appear as the second operand of binary arithmetic operators without
1148 the need for parenthesis.
1154 @node Implicitly convert LOGICAL and INTEGER values
1155 @section Implicitly convert @code{LOGICAL} and @code{INTEGER} values
1156 @cindex conversion, to integer
1157 @cindex conversion, to logical
1159 As an extension for backwards compatibility with other compilers, GNU
1160 Fortran allows the implicit conversion of @code{LOGICAL} values to
1161 @code{INTEGER} values and vice versa. When converting from a
1162 @code{LOGICAL} to an @code{INTEGER}, @code{.FALSE.} is interpreted as
1163 zero, and @code{.TRUE.} is interpreted as one. When converting from
1164 @code{INTEGER} to @code{LOGICAL}, the value zero is interpreted as
1165 @code{.FALSE.} and any nonzero value is interpreted as @code{.TRUE.}.
1176 However, there is no implicit conversion of @code{INTEGER} values in
1177 @code{if}-statements, nor of @code{LOGICAL} or @code{INTEGER} values
1180 @node Hollerith constants support
1181 @section Hollerith constants support
1182 @cindex Hollerith constants
1184 GNU Fortran supports Hollerith constants in assignments, function
1185 arguments, and @code{DATA} and @code{ASSIGN} statements. A Hollerith
1186 constant is written as a string of characters preceded by an integer
1187 constant indicating the character count, and the letter @code{H} or
1188 @code{h}, and stored in bytewise fashion in a numeric (@code{INTEGER},
1189 @code{REAL}, or @code{complex}) or @code{LOGICAL} variable. The
1190 constant will be padded or truncated to fit the size of the variable in
1193 Examples of valid uses of Hollerith constants:
1196 data x /16Habcdefghijklmnop, 16Hqrstuvwxyz012345/
1197 x(1) = 16HABCDEFGHIJKLMNOP
1201 Invalid Hollerith constants examples:
1204 a = 8H12345678 ! Valid, but the Hollerith constant will be truncated.
1205 a = 0H ! At least one character is needed.
1208 In general, Hollerith constants were used to provide a rudimentary
1209 facility for handling character strings in early Fortran compilers,
1210 prior to the introduction of @code{CHARACTER} variables in Fortran 77;
1211 in those cases, the standard-compliant equivalent is to convert the
1212 program to use proper character strings. On occasion, there may be a
1213 case where the intent is specifically to initialize a numeric variable
1214 with a given byte sequence. In these cases, the same result can be
1215 obtained by using the @code{TRANSFER} statement, as in this example.
1217 INTEGER(KIND=4) :: a
1218 a = TRANSFER ("abcd", a) ! equivalent to: a = 4Habcd
1223 @section Cray pointers
1224 @cindex pointer, cray
1226 Cray pointers are part of a non-standard extension that provides a
1227 C-like pointer in Fortran. This is accomplished through a pair of
1228 variables: an integer "pointer" that holds a memory address, and a
1229 "pointee" that is used to dereference the pointer.
1231 Pointer/pointee pairs are declared in statements of the form:
1233 pointer ( <pointer> , <pointee> )
1237 pointer ( <pointer1> , <pointee1> ), ( <pointer2> , <pointee2> ), ...
1239 The pointer is an integer that is intended to hold a memory address.
1240 The pointee may be an array or scalar. A pointee can be an assumed
1241 size array---that is, the last dimension may be left unspecified by
1242 using a @code{*} in place of a value---but a pointee cannot be an
1243 assumed shape array. No space is allocated for the pointee.
1245 The pointee may have its type declared before or after the pointer
1246 statement, and its array specification (if any) may be declared
1247 before, during, or after the pointer statement. The pointer may be
1248 declared as an integer prior to the pointer statement. However, some
1249 machines have default integer sizes that are different than the size
1250 of a pointer, and so the following code is not portable:
1255 If a pointer is declared with a kind that is too small, the compiler
1256 will issue a warning; the resulting binary will probably not work
1257 correctly, because the memory addresses stored in the pointers may be
1258 truncated. It is safer to omit the first line of the above example;
1259 if explicit declaration of ipt's type is omitted, then the compiler
1260 will ensure that ipt is an integer variable large enough to hold a
1263 Pointer arithmetic is valid with Cray pointers, but it is not the same
1264 as C pointer arithmetic. Cray pointers are just ordinary integers, so
1265 the user is responsible for determining how many bytes to add to a
1266 pointer in order to increment it. Consider the following example:
1270 pointer (ipt, pointee)
1274 The last statement does not set @code{ipt} to the address of
1275 @code{target(1)}, as it would in C pointer arithmetic. Adding @code{1}
1276 to @code{ipt} just adds one byte to the address stored in @code{ipt}.
1278 Any expression involving the pointee will be translated to use the
1279 value stored in the pointer as the base address.
1281 To get the address of elements, this extension provides an intrinsic
1282 function @code{LOC()}. The @code{LOC()} function is equivalent to the
1283 @code{&} operator in C, except the address is cast to an integer type:
1286 pointer(ipt, arpte(10))
1288 ipt = loc(ar) ! Makes arpte is an alias for ar
1289 arpte(1) = 1.0 ! Sets ar(1) to 1.0
1291 The pointer can also be set by a call to the @code{MALLOC} intrinsic
1294 Cray pointees often are used to alias an existing variable. For
1302 As long as @code{ipt} remains unchanged, @code{iarr} is now an alias for
1303 @code{target}. The optimizer, however, will not detect this aliasing, so
1304 it is unsafe to use @code{iarr} and @code{target} simultaneously. Using
1305 a pointee in any way that violates the Fortran aliasing rules or
1306 assumptions is illegal. It is the user's responsibility to avoid doing
1307 this; the compiler works under the assumption that no such aliasing
1310 Cray pointers will work correctly when there is no aliasing (i.e., when
1311 they are used to access a dynamically allocated block of memory), and
1312 also in any routine where a pointee is used, but any variable with which
1313 it shares storage is not used. Code that violates these rules may not
1314 run as the user intends. This is not a bug in the optimizer; any code
1315 that violates the aliasing rules is illegal. (Note that this is not
1316 unique to GNU Fortran; any Fortran compiler that supports Cray pointers
1317 will ``incorrectly'' optimize code with illegal aliasing.)
1319 There are a number of restrictions on the attributes that can be applied
1320 to Cray pointers and pointees. Pointees may not have the
1321 @code{ALLOCATABLE}, @code{INTENT}, @code{OPTIONAL}, @code{DUMMY},
1322 @code{TARGET}, @code{INTRINSIC}, or @code{POINTER} attributes. Pointers
1323 may not have the @code{DIMENSION}, @code{POINTER}, @code{TARGET},
1324 @code{ALLOCATABLE}, @code{EXTERNAL}, or @code{INTRINSIC} attributes.
1325 Pointees may not occur in more than one pointer statement. A pointee
1326 cannot be a pointer. Pointees cannot occur in equivalence, common, or
1329 A Cray pointer may also point to a function or a subroutine. For
1330 example, the following excerpt is valid:
1334 pointer (subptr,subpte)
1344 A pointer may be modified during the course of a program, and this
1345 will change the location to which the pointee refers. However, when
1346 pointees are passed as arguments, they are treated as ordinary
1347 variables in the invoked function. Subsequent changes to the pointer
1348 will not change the base address of the array that was passed.
1350 @node CONVERT specifier
1351 @section CONVERT specifier
1352 @cindex CONVERT specifier
1354 GNU Fortran allows the conversion of unformatted data between little-
1355 and big-endian representation to facilitate moving of data
1356 between different systems. The conversion can be indicated with
1357 the @code{CONVERT} specifier on the @code{OPEN} statement.
1358 @xref{GFORTRAN_CONVERT_UNIT}, for an alternative way of specifying
1359 the data format via an environment variable.
1361 Valid values for @code{CONVERT} are:
1363 @item @code{CONVERT='NATIVE'} Use the native format. This is the default.
1364 @item @code{CONVERT='SWAP'} Swap between little- and big-endian.
1365 @item @code{CONVERT='LITTLE_ENDIAN'} Use the little-endian representation
1366 for unformatted files.
1367 @item @code{CONVERT='BIG_ENDIAN'} Use the big-endian representation for
1371 Using the option could look like this:
1373 open(file='big.dat',form='unformatted',access='sequential', &
1374 convert='big_endian')
1377 The value of the conversion can be queried by using
1378 @code{INQUIRE(CONVERT=ch)}. The values returned are
1379 @code{'BIG_ENDIAN'} and @code{'LITTLE_ENDIAN'}.
1381 @code{CONVERT} works between big- and little-endian for
1382 @code{INTEGER} values of all supported kinds and for @code{REAL}
1383 on IEEE systems of kinds 4 and 8. Conversion between different
1384 ``extended double'' types on different architectures such as
1385 m68k and x86_64, which GNU Fortran
1386 supports as @code{REAL(KIND=10)} and @code{REAL(KIND=16)}, will
1389 @emph{Note that the values specified via the GFORTRAN_CONVERT_UNIT
1390 environment variable will override the CONVERT specifier in the
1391 open statement}. This is to give control over data formats to
1392 users who do not have the source code of their program available.
1394 Using anything but the native representation for unformatted data
1395 carries a significant speed overhead. If speed in this area matters
1396 to you, it is best if you use this only for data that needs to be
1403 GNU Fortran attempts to be OpenMP Application Program Interface v2.5
1404 compatible when invoked with the @option{-fopenmp} option. GNU Fortran
1405 then generates parallelized code according to the OpenMP directives
1406 used in the source. The OpenMP Fortran runtime library
1407 routines are provided both in a form of a Fortran 90 module named
1408 @code{omp_lib} and in a form of a Fortran @code{include} file named
1411 For details refer to the actual
1412 @uref{http://www.openmp.org/drupal/mp-documents/spec25.pdf,
1413 OpenMP Application Program Interface v2.5} specification and to the
1414 @ref{Top,,Introduction,libgomp,GNU OpenMP runtime library}.
1416 @node Argument list functions
1417 @section Argument list functions %VAL, %REF and %LOC
1418 @cindex argument list functions
1423 GNU Fortran supports argument list functions @code{%VAL}, @code{%REF}
1424 and @code{%LOC} statements, for backward compatibility with g77.
1425 It is recommended that these should be used only for code that is
1426 accessing facilities outside of GNU Fortran, such as operating system
1427 or windowing facilities. It is best to constrain such uses to isolated
1428 portions of a program--portions that deal specifically and exclusively
1429 with low-level, system-dependent facilities. Such portions might well
1430 provide a portable interface for use by the program as a whole, but are
1431 themselves not portable, and should be thoroughly tested each time they
1432 are rebuilt using a new compiler or version of a compiler.
1434 @code{%VAL} passes a scalar argument by value, @code{%REF} passes it by
1435 reference and @code{%LOC} passes its memory location. Since gfortran
1436 already passes scalar arguments by reference, @code{%REF} is in effect
1437 a do-nothing. @code{%LOC} has the same effect as a fortran pointer.
1439 An example of passing an argument by value to a C subroutine foo.:
1442 C prototype void foo_ (float x);
1451 For details refer to the g77 manual
1452 @uref{http://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/index.html#Top}.
1454 Also, the gfortran testsuite c_by_val.f and its partner c_by_val.c are
1457 @c ---------------------------------------------------------------------
1458 @c Intrinsic Procedures
1459 @c ---------------------------------------------------------------------
1461 @include intrinsic.texi
1468 @c ---------------------------------------------------------------------
1470 @c ---------------------------------------------------------------------
1473 @unnumbered Contributing
1474 @cindex Contributing
1476 Free software is only possible if people contribute to efforts
1478 We're always in need of more people helping out with ideas
1479 and comments, writing documentation and contributing code.
1481 If you want to contribute to GNU Fortran,
1482 have a look at the long lists of projects you can take on.
1483 Some of these projects are small,
1484 some of them are large;
1485 some are completely orthogonal to the rest of what is
1486 happening on GNU Fortran,
1487 but others are ``mainstream'' projects in need of enthusiastic hackers.
1488 All of these projects are important!
1489 We'll eventually get around to the things here,
1490 but they are also things doable by someone who is willing and able.
1495 * Proposed Extensions::
1500 @section Contributors to GNU Fortran
1501 @cindex Contributors
1505 Most of the parser was hand-crafted by @emph{Andy Vaught}, who is
1506 also the initiator of the whole project. Thanks Andy!
1507 Most of the interface with GCC was written by @emph{Paul Brook}.
1509 The following individuals have contributed code and/or
1510 ideas and significant help to the GNU Fortran project
1511 (in no particular order):
1515 @item Katherine Holcomb
1516 @item Tobias Schl@"uter
1517 @item Steven Bosscher
1520 @item Niels Kristian Bech Jensen
1521 @item Steven Johnson
1526 @item Fran@,{c}ois-Xavier Coudert
1527 @item Steven G. Kargl
1529 @item Janne Blomqvist
1536 @item Richard Henderson
1537 @item Richard Sandiford
1538 @item Richard Guenther
1539 @item Bernhard Fischer
1542 The following people have contributed bug reports,
1543 smaller or larger patches,
1544 and much needed feedback and encouragement for the
1545 GNU Fortran project:
1548 @item Erik Schnetter
1553 Many other individuals have helped debug,
1554 test and improve the GNU Fortran compiler over the past few years,
1555 and we welcome you to do the same!
1556 If you already have done so,
1557 and you would like to see your name listed in the
1558 list above, please contact us.
1566 @item Help build the test suite
1567 Solicit more code for donation to the test suite.
1568 We can keep code private on request.
1570 @item Bug hunting/squishing
1571 Find bugs and write more test cases!
1572 Test cases are especially very welcome,
1573 because it allows us to concentrate on fixing bugs
1574 instead of isolating them.
1576 @item Smaller projects (``bug'' fixes):
1578 @item Allow init exprs to be numbers raised to integer powers.
1579 @item Implement correct rounding.
1580 @item Implement F restrictions on Fortran 95 syntax.
1581 @item See about making Emacs-parsable error messages.
1585 If you wish to work on the runtime libraries,
1586 please contact a project maintainer.
1590 @node Proposed Extensions
1591 @section Proposed Extensions
1593 Here's a list of proposed extensions for the GNU Fortran compiler, in no particular
1594 order. Most of these are necessary to be fully compatible with
1595 existing Fortran compilers, but they are not part of the official
1596 J3 Fortran 95 standard.
1598 @subsection Compiler extensions:
1601 User-specified alignment rules for structures.
1604 Flag to generate @code{Makefile} info.
1607 Automatically extend single precision constants to double.
1610 Compile code that conserves memory by dynamically allocating common and
1611 module storage either on stack or heap.
1614 Compile flag to generate code for array conformance checking (suggest -CC).
1617 User control of symbol names (underscores, etc).
1620 Compile setting for maximum size of stack frame size before spilling
1621 parts to static or heap.
1624 Flag to force local variables into static space.
1627 Flag to force local variables onto stack.
1630 Flag for maximum errors before ending compile.
1633 Option to initialize otherwise uninitialized integer and floating
1638 @subsection Environment Options
1641 Pluggable library modules for random numbers, linear algebra.
1642 LA should use BLAS calling conventions.
1645 Environment variables controlling actions on arithmetic exceptions like
1646 overflow, underflow, precision loss---Generate NaN, abort, default.
1650 Set precision for fp units that support it (i387).
1653 Variable for setting fp rounding mode.
1656 Variable to fill uninitialized variables with a user-defined bit
1660 Environment variable controlling filename that is opened for that unit
1664 Environment variable to clear/trash memory being freed.
1667 Environment variable to control tracing of allocations and frees.
1670 Environment variable to display allocated memory at normal program end.
1673 Environment variable for filename for * IO-unit.
1676 Environment variable for temporary file directory.
1679 Environment variable forcing standard output to be line buffered (unix).
1684 @c ---------------------------------------------------------------------
1685 @c GNU General Public License
1686 @c ---------------------------------------------------------------------
1692 @c ---------------------------------------------------------------------
1693 @c GNU Free Documentation License
1694 @c ---------------------------------------------------------------------
1700 @c ---------------------------------------------------------------------
1701 @c Funding Free Software
1702 @c ---------------------------------------------------------------------
1704 @include funding.texi
1706 @c ---------------------------------------------------------------------
1708 @c ---------------------------------------------------------------------
1711 @unnumbered Option Index
1712 @command{gfortran}'s command line options are indexed here without any
1713 initial @samp{-} or @samp{--}. Where an option has both positive and
1714 negative forms (such as -foption and -fno-option), relevant entries in
1715 the manual are indexed under the most appropriate form; it may sometimes
1716 be useful to look up both forms.
1720 @unnumbered Keyword Index