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.
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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 1.1 or
84 any later version published by the Free Software Foundation; with the
85 Invariant Sections being ``GNU General Public License'' and ``Funding
86 Free Software'', the Front-Cover
87 texts being (a) (see below), and with the Back-Cover Texts being (b)
88 (see below). A copy of the license is included in the section entitled
89 ``GNU Free Documentation License''.
91 (a) The FSF's Front-Cover Text is:
95 (b) The FSF's Back-Cover Text is:
97 You have freedom to copy and modify this GNU Manual, like GNU
98 software. Copies published by the Free Software Foundation raise
99 funds for GNU development.
103 @dircategory Software development
105 * gfortran: (gfortran). The GNU Fortran Compiler.
107 This file documents the use and the internals of
108 the GNU Fortran compiler, (@command{gfortran}).
110 Published by the Free Software Foundation
111 51 Franklin Street, Fifth Floor
112 Boston, MA 02110-1301 USA
118 @setchapternewpage odd
120 @title Using GNU Fortran
122 @author The @t{gfortran} team
124 @vskip 0pt plus 1filll
125 Published by the Free Software Foundation@*
126 51 Franklin Street, Fifth Floor@*
127 Boston, MA 02110-1301, USA@*
128 @c Last printed ??ber, 19??.@*
129 @c Printed copies are available for $? each.@*
135 @c TODO: The following "Part" definitions are included here temporarily
136 @c until they are incorporated into the official Texinfo distribution.
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152 @c ---------------------------------------------------------------------
153 @c TexInfo table of contents.
154 @c ---------------------------------------------------------------------
161 This manual documents the use of @command{gfortran},
162 the GNU Fortran compiler. You can find in this manual how to invoke
163 @command{gfortran}, as well as its features and incompatibilities.
166 @emph{Warning:} This document, and the compiler it describes, are still
167 under development. While efforts are made to keep it up-to-date, it might
168 not accurately reflect the status of the most recent GNU Fortran compiler.
172 @comment When you add a new menu item, please keep the right hand
173 @comment aligned to the same column. Do not use tabs. This provides
174 @comment better formatting.
179 Part I: Invoking GNU Fortran
180 * Invoking GNU Fortran:: Command options supported by @command{gfortran}.
181 * Runtime:: Influencing runtime behavior with environment variables.
183 Part II: Language Reference
184 * Fortran 2003 status:: Fortran 2003 features supported by GNU Fortran.
185 * Extensions:: Language extensions implemented by GNU Fortran.
186 * Intrinsic Procedures:: Intrinsic procedures supported by GNU Fortran.
187 * Intrinsic Modules:: Intrinsic modules supported by GNU Fortran.
189 * Contributing:: How you can help.
190 * Copying:: GNU General Public License says
191 how you can copy and share GNU Fortran.
192 * GNU Free Documentation License::
193 How you can copy and share this manual.
194 * Funding:: How to help assure continued work for free software.
195 * Option Index:: Index of command line options
196 * Keyword Index:: Index of concepts
200 @c ---------------------------------------------------------------------
202 @c ---------------------------------------------------------------------
205 @chapter Introduction
207 @c The following duplicates the text on the TexInfo table of contents.
209 This manual documents the use of @command{gfortran}, the GNU Fortran
210 compiler. You can find in this manual how to invoke @command{gfortran},
211 as well as its features and incompatibilities.
214 @emph{Warning:} This document, and the compiler it describes, are still
215 under development. While efforts are made to keep it up-to-date, it
216 might not accurately reflect the status of the most recent GNU Fortran
221 The GNU Fortran compiler front end was
222 designed initially as a free replacement for,
223 or alternative to, the unix @command{f95} command;
224 @command{gfortran} is the command you'll use to invoke the compiler.
227 * About GNU Fortran:: What you should know about the GNU Fortran compiler.
228 * GNU Fortran and GCC:: You can compile Fortran, C, or other programs.
229 * Preprocessing and conditional compilation:: The Fortran preprocessor
230 * GNU Fortran and G77:: Why we chose to start from scratch.
231 * Project Status:: Status of GNU Fortran, roadmap, proposed extensions.
232 * Standards:: Standards supported by GNU Fortran.
236 @c ---------------------------------------------------------------------
238 @c ---------------------------------------------------------------------
240 @node About GNU Fortran
241 @section About GNU Fortran
243 The GNU Fortran compiler is still in an early state of development.
244 It can generate code for most constructs and expressions,
245 but much work remains to be done.
247 When the GNU Fortran compiler is finished,
248 it will do everything you expect from any decent compiler:
252 Read a user's program,
253 stored in a file and containing instructions written
254 in Fortran 77, Fortran 90, Fortran 95 or Fortran 2003.
255 This file contains @dfn{source code}.
258 Translate the user's program into instructions a computer
259 can carry out more quickly than it takes to translate the
260 instructions in the first
261 place. The result after compilation of a program is
263 code designed to be efficiently translated and processed
264 by a machine such as your computer.
265 Humans usually aren't as good writing machine code
266 as they are at writing Fortran (or C++, Ada, or Java),
267 because is easy to make tiny mistakes writing machine code.
270 Provide the user with information about the reasons why
271 the compiler is unable to create a binary from the source code.
272 Usually this will be the case if the source code is flawed.
273 When writing Fortran, it is easy to make big mistakes.
274 The Fortran 90 requires that the compiler can point out
275 mistakes to the user.
276 An incorrect usage of the language causes an @dfn{error message}.
278 The compiler will also attempt to diagnose cases where the
279 user's program contains a correct usage of the language,
280 but instructs the computer to do something questionable.
281 This kind of diagnostics message is called a @dfn{warning message}.
284 Provide optional information about the translation passes
285 from the source code to machine code.
286 This can help a user of the compiler to find the cause of
287 certain bugs which may not be obvious in the source code,
288 but may be more easily found at a lower level compiler output.
289 It also helps developers to find bugs in the compiler itself.
292 Provide information in the generated machine code that can
293 make it easier to find bugs in the program (using a debugging tool,
294 called a @dfn{debugger}, such as the GNU Debugger @command{gdb}).
297 Locate and gather machine code already generated to
298 perform actions requested by statements in the user's program.
299 This machine code is organized into @dfn{modules} and is located
300 and @dfn{linked} to the user program.
303 The GNU Fortran compiler consists of several components:
307 A version of the @command{gcc} command
308 (which also might be installed as the system's @command{cc} command)
309 that also understands and accepts Fortran source code.
310 The @command{gcc} command is the @dfn{driver} program for
311 all the languages in the GNU Compiler Collection (GCC);
313 you can compile the source code of any language for
314 which a front end is available in GCC.
317 The @command{gfortran} command itself,
318 which also might be installed as the
319 system's @command{f95} command.
320 @command{gfortran} is just another driver program,
321 but specifically for the Fortran compiler only.
322 The difference with @command{gcc} is that @command{gfortran}
323 will automatically link the correct libraries to your program.
326 A collection of run-time libraries.
327 These libraries contain the machine code needed to support
328 capabilities of the Fortran language that are not directly
329 provided by the machine code generated by the
330 @command{gfortran} compilation phase,
331 such as intrinsic functions and subroutines,
332 and routines for interaction with files and the operating system.
333 @c and mechanisms to spawn,
334 @c unleash and pause threads in parallelized code.
337 The Fortran compiler itself, (@command{f951}).
338 This is the GNU Fortran parser and code generator,
339 linked to and interfaced with the GCC backend library.
340 @command{f951} ``translates'' the source code to
341 assembler code. You would typically not use this
343 instead, the @command{gcc} or @command{gfortran} driver
344 programs will call it for you.
348 @c ---------------------------------------------------------------------
349 @c GNU Fortran and GCC
350 @c ---------------------------------------------------------------------
352 @node GNU Fortran and GCC
353 @section GNU Fortran and GCC
354 @cindex GNU Compiler Collection
357 GNU Fortran is a part of GCC, the @dfn{GNU Compiler Collection}. GCC
358 consists of a collection of front ends for various languages, which
359 translate the source code into a language-independent form called
360 @dfn{GENERIC}. This is then processed by a common middle end which
361 provides optimization, and then passed to one of a collection of back
362 ends which generate code for different computer architectures and
365 Functionally, this is implemented with a driver program (@command{gcc})
366 which provides the command-line interface for the compiler. It calls
367 the relevant compiler front-end program (e.g., @command{f951} for
368 Fortran) for each file in the source code, and then calls the assembler
369 and linker as appropriate to produce the compiled output. In a copy of
370 GCC which has been compiled with Fortran language support enabled,
371 @command{gcc} will recognize files with @file{.f}, @file{.f90}, @file{.f95},
372 and @file{.f03} extensions as Fortran source code, and compile it
373 accordingly. A @command{gfortran} driver program is also provided,
374 which is identical to @command{gcc} except that it automatically links
375 the Fortran runtime libraries into the compiled program.
377 This manual specifically documents the Fortran front end, which handles
378 the programming language's syntax and semantics. The aspects of GCC
379 which relate to the optimization passes and the back-end code generation
380 are documented in the GCC manual; see
381 @ref{Top,,Introduction,gcc,Using the GNU Compiler Collection (GCC)}.
382 The two manuals together provide a complete reference for the GNU
386 @c ---------------------------------------------------------------------
387 @c Preprocessing and conditional compilation
388 @c ---------------------------------------------------------------------
390 @node Preprocessing and conditional compilation
391 @section Preprocessing and conditional compilation
394 @cindex Conditional compilation
395 @cindex Preprocessing
397 Many Fortran compilers including GNU Fortran allow to pass the source code
398 through a C preprocessor (CPP; sometimes also called Fortran preprocessor,
399 FPP) to allow for conditional compilation. In case of GNU Fortran
400 this is the GNU C Preprocessor in the traditional mode. On systems with
401 case-preserving file names, the preprocessor is automatically invoked if the
402 file extension is @code{.F}, @code{.F90}, @code{.F95} or @code{.F03};
403 otherwise use for fixed-format code the option @code{-x f77-cpp-input}
404 and for free-format code @code{-x f95-cpp-input}. Invocation of the
405 preprocessor can be suppressed using @code{-x f77} or @code{-x f95}.
407 If the GNU Fortran invoked the preprocessor, @code{__GFORTRAN__}
408 is defined and @code{__GNUC__}, @code{__GNUC_MINOR__} and
409 @code{__GNUC_PATCHLEVEL__} can be used to determine the version of the
410 compiler. See @ref{Top,,Overview,cpp,The C Preprocessor} for details.
412 While CPP is the de-facto standard for preprocessing Fortran code,
413 Part 3 of the Fortran 95 standard (ISO/IEC 1539-3:1998) defines
414 Conditional Compilation, which is not widely used and not directly
415 supported by the GNU Fortran compiler. You can use the program coco
416 to preprocess such files (@uref{http://users.erols.com/dnagle/coco.html}).
419 @c ---------------------------------------------------------------------
420 @c GNU Fortran and G77
421 @c ---------------------------------------------------------------------
423 @node GNU Fortran and G77
424 @section GNU Fortran and G77
426 @cindex @command{g77}
428 The GNU Fortran compiler is the successor to @command{g77}, the Fortran
429 77 front end included in GCC prior to version 4. It is an entirely new
430 program that has been designed to provide Fortran 95 support and
431 extensibility for future Fortran language standards, as well as providing
432 backwards compatibility for Fortran 77 and nearly all of the GNU language
433 extensions supported by @command{g77}.
436 @c ---------------------------------------------------------------------
438 @c ---------------------------------------------------------------------
441 @section Project Status
444 As soon as @command{gfortran} can parse all of the statements correctly,
445 it will be in the ``larva'' state.
446 When we generate code, the ``puppa'' state.
447 When @command{gfortran} is done,
448 we'll see if it will be a beautiful butterfly,
449 or just a big bug....
451 --Andy Vaught, April 2000
454 The start of the GNU Fortran 95 project was announced on
455 the GCC homepage in March 18, 2000
456 (even though Andy had already been working on it for a while,
459 The GNU Fortran compiler is able to compile nearly all
460 standard-compliant Fortran 95, Fortran 90, and Fortran 77 programs,
461 including a number of standard and non-standard extensions, and can be
462 used on real-world programs. In particular, the supported extensions
463 include OpenMP, Cray-style pointers, and several Fortran 2003 features
464 such as enumeration, stream I/O, and some of the enhancements to
465 allocatable array support from TR 15581. However, it is still under
466 development and has a few remaining rough edges.
468 At present, the GNU Fortran compiler passes the
469 @uref{http://www.fortran-2000.com/ArnaudRecipes/fcvs21_f95.html,
470 NIST Fortran 77 Test Suite}, and produces acceptable results on the
471 @uref{http://www.netlib.org/lapack/faq.html#1.21, LAPACK Test Suite}.
472 It also provides respectable performance on
473 the @uref{http://www.polyhedron.com/pb05.html, Polyhedron Fortran
474 compiler benchmarks} and the
475 @uref{http://www.llnl.gov/asci_benchmarks/asci/limited/lfk/README.html,
476 Livermore Fortran Kernels test}. It has been used to compile a number of
477 large real-world programs, including
478 @uref{http://mysite.verizon.net/serveall/moene.pdf, the HIRLAM
479 weather-forecasting code} and
480 @uref{http://www.theochem.uwa.edu.au/tonto/, the Tonto quantum
481 chemistry package}; see @url{http://gcc.gnu.org/wiki/GfortranApps} for an
484 Among other things, the GNU Fortran compiler is intended as a replacement
485 for G77. At this point, nearly all programs that could be compiled with
486 G77 can be compiled with GNU Fortran, although there are a few minor known
489 The primary work remaining to be done on GNU Fortran falls into three
490 categories: bug fixing (primarily regarding the treatment of invalid code
491 and providing useful error messages), improving the compiler optimizations
492 and the performance of compiled code, and extending the compiler to support
493 future standards---in particular, Fortran 2003.
496 @c ---------------------------------------------------------------------
498 @c ---------------------------------------------------------------------
504 The GNU Fortran compiler implements
505 ISO/IEC 1539:1997 (Fortran 95). As such, it can also compile essentially all
506 standard-compliant Fortran 90 and Fortran 77 programs. It also supports
507 the ISO/IEC TR-15581 enhancements to allocatable arrays, and
508 the @uref{http://www.openmp.org/drupal/mp-documents/spec25.pdf,
509 OpenMP Application Program Interface v2.5} specification.
511 In the future, the GNU Fortran compiler may also support other standard
512 variants of and extensions to the Fortran language. These include
513 ISO/IEC 1539-1:2004 (Fortran 2003).
516 @c =====================================================================
517 @c PART I: INVOCATION REFERENCE
518 @c =====================================================================
521 \part{I}{Invoking GNU Fortran}
524 @c ---------------------------------------------------------------------
526 @c ---------------------------------------------------------------------
531 @c ---------------------------------------------------------------------
533 @c ---------------------------------------------------------------------
536 @chapter Runtime: Influencing runtime behavior with environment variables
537 @cindex environment variable
539 The behavior of the @command{gfortran} can be influenced by
540 environment variables.
542 Malformed environment variables are silently ignored.
545 * GFORTRAN_STDIN_UNIT:: Unit number for standard input
546 * GFORTRAN_STDOUT_UNIT:: Unit number for standard output
547 * GFORTRAN_STDERR_UNIT:: Unit number for standard error
548 * GFORTRAN_USE_STDERR:: Send library output to standard error
549 * GFORTRAN_TMPDIR:: Directory for scratch files
550 * GFORTRAN_UNBUFFERED_ALL:: Don't buffer I/O for all units.
551 * GFORTRAN_UNBUFFERED_PRECONNECTED:: Don't buffer I/O for preconnected units.
552 * GFORTRAN_SHOW_LOCUS:: Show location for runtime errors
553 * GFORTRAN_OPTIONAL_PLUS:: Print leading + where permitted
554 * GFORTRAN_DEFAULT_RECL:: Default record length for new files
555 * GFORTRAN_LIST_SEPARATOR:: Separator for list output
556 * GFORTRAN_CONVERT_UNIT:: Set endianness for unformatted I/O
557 * GFORTRAN_ERROR_DUMPCORE:: Dump core on run-time errors
558 * GFORTRAN_ERROR_BACKTRACE:: Show backtrace on run-time errors
561 @node GFORTRAN_STDIN_UNIT
562 @section @env{GFORTRAN_STDIN_UNIT}---Unit number for standard input
564 This environment variable can be used to select the unit number
565 preconnected to standard input. This must be a positive integer.
566 The default value is 5.
568 @node GFORTRAN_STDOUT_UNIT
569 @section @env{GFORTRAN_STDOUT_UNIT}---Unit number for standard output
571 This environment variable can be used to select the unit number
572 preconnected to standard output. This must be a positive integer.
573 The default value is 6.
575 @node GFORTRAN_STDERR_UNIT
576 @section @env{GFORTRAN_STDERR_UNIT}---Unit number for standard error
578 This environment variable can be used to select the unit number
579 preconnected to standard error. This must be a positive integer.
580 The default value is 0.
582 @node GFORTRAN_USE_STDERR
583 @section @env{GFORTRAN_USE_STDERR}---Send library output to standard error
585 This environment variable controls where library output is sent.
586 If the first letter is @samp{y}, @samp{Y} or @samp{1}, standard
587 error is used. If the first letter is @samp{n}, @samp{N} or
588 @samp{0}, standard output is used.
590 @node GFORTRAN_TMPDIR
591 @section @env{GFORTRAN_TMPDIR}---Directory for scratch files
593 This environment variable controls where scratch files are
594 created. If this environment variable is missing,
595 GNU Fortran searches for the environment variable @env{TMP}. If
596 this is also missing, the default is @file{/tmp}.
598 @node GFORTRAN_UNBUFFERED_ALL
599 @section @env{GFORTRAN_UNBUFFERED_ALL}---Don't buffer I/O on all units
601 This environment variable controls whether all I/O is unbuffered. If
602 the first letter is @samp{y}, @samp{Y} or @samp{1}, all I/O is
603 unbuffered. This will slow down small sequential reads and writes. If
604 the first letter is @samp{n}, @samp{N} or @samp{0}, I/O is buffered.
607 @node GFORTRAN_UNBUFFERED_PRECONNECTED
608 @section @env{GFORTRAN_UNBUFFERED_PRECONNECTED}---Don't buffer I/O on
611 The environment variable named @env{GFORTRAN_UNBUFFERED_PRECONNECTED} controls
612 whether I/O on a preconnected unit (i.e STDOUT or STDERR) is unbuffered. If
613 the first letter is @samp{y}, @samp{Y} or @samp{1}, I/O is unbuffered. This
614 will slow down small sequential reads and writes. If the first letter
615 is @samp{n}, @samp{N} or @samp{0}, I/O is buffered. This is the default.
617 @node GFORTRAN_SHOW_LOCUS
618 @section @env{GFORTRAN_SHOW_LOCUS}---Show location for runtime errors
620 If the first letter is @samp{y}, @samp{Y} or @samp{1}, filename and
621 line numbers for runtime errors are printed. If the first letter is
622 @samp{n}, @samp{N} or @samp{0}, don't print filename and line numbers
623 for runtime errors. The default is to print the location.
625 @node GFORTRAN_OPTIONAL_PLUS
626 @section @env{GFORTRAN_OPTIONAL_PLUS}---Print leading + where permitted
628 If the first letter is @samp{y}, @samp{Y} or @samp{1},
629 a plus sign is printed
630 where permitted by the Fortran standard. If the first letter
631 is @samp{n}, @samp{N} or @samp{0}, a plus sign is not printed
632 in most cases. Default is not to print plus signs.
634 @node GFORTRAN_DEFAULT_RECL
635 @section @env{GFORTRAN_DEFAULT_RECL}---Default record length for new files
637 This environment variable specifies the default record length, in
638 bytes, for files which are opened without a @code{RECL} tag in the
639 @code{OPEN} statement. This must be a positive integer. The
640 default value is 1073741824 bytes (1 GB).
642 @node GFORTRAN_LIST_SEPARATOR
643 @section @env{GFORTRAN_LIST_SEPARATOR}---Separator for list output
645 This environment variable specifies the separator when writing
646 list-directed output. It may contain any number of spaces and
647 at most one comma. If you specify this on the command line,
648 be sure to quote spaces, as in
650 $ GFORTRAN_LIST_SEPARATOR=' , ' ./a.out
652 when @command{a.out} is the compiled Fortran program that you want to run.
653 Default is a single space.
655 @node GFORTRAN_CONVERT_UNIT
656 @section @env{GFORTRAN_CONVERT_UNIT}---Set endianness for unformatted I/O
658 By setting the @env{GFORTRAN_CONVERT_UNIT} variable, it is possible
659 to change the representation of data for unformatted files.
660 The syntax for the @env{GFORTRAN_CONVERT_UNIT} variable is:
662 GFORTRAN_CONVERT_UNIT: mode | mode ';' exception | exception ;
663 mode: 'native' | 'swap' | 'big_endian' | 'little_endian' ;
664 exception: mode ':' unit_list | unit_list ;
665 unit_list: unit_spec | unit_list unit_spec ;
666 unit_spec: INTEGER | INTEGER '-' INTEGER ;
668 The variable consists of an optional default mode, followed by
669 a list of optional exceptions, which are separated by semicolons
670 from the preceding default and each other. Each exception consists
671 of a format and a comma-separated list of units. Valid values for
672 the modes are the same as for the @code{CONVERT} specifier:
675 @item @code{NATIVE} Use the native format. This is the default.
676 @item @code{SWAP} Swap between little- and big-endian.
677 @item @code{LITTLE_ENDIAN} Use the little-endian format
678 for unformatted files.
679 @item @code{BIG_ENDIAN} Use the big-endian format for unformatted files.
681 A missing mode for an exception is taken to mean @code{BIG_ENDIAN}.
682 Examples of values for @env{GFORTRAN_CONVERT_UNIT} are:
684 @item @code{'big_endian'} Do all unformatted I/O in big_endian mode.
685 @item @code{'little_endian;native:10-20,25'} Do all unformatted I/O
686 in little_endian mode, except for units 10 to 20 and 25, which are in
688 @item @code{'10-20'} Units 10 to 20 are big-endian, the rest is native.
691 Setting the environment variables should be done on the command
692 line or via the @command{export}
693 command for @command{sh}-compatible shells and via @command{setenv}
694 for @command{csh}-compatible shells.
696 Example for @command{sh}:
699 $ GFORTRAN_CONVERT_UNIT='big_endian;native:10-20' ./a.out
702 Example code for @command{csh}:
705 % setenv GFORTRAN_CONVERT_UNIT 'big_endian;native:10-20'
709 Using anything but the native representation for unformatted data
710 carries a significant speed overhead. If speed in this area matters
711 to you, it is best if you use this only for data that needs to be
714 @xref{CONVERT specifier}, for an alternative way to specify the
715 data representation for unformatted files. @xref{Runtime Options}, for
716 setting a default data representation for the whole program. The
717 @code{CONVERT} specifier overrides the @option{-fconvert} compile options.
719 @emph{Note that the values specified via the GFORTRAN_CONVERT_UNIT
720 environment variable will override the CONVERT specifier in the
721 open statement}. This is to give control over data formats to
722 users who do not have the source code of their program available.
724 @node GFORTRAN_ERROR_DUMPCORE
725 @section @env{GFORTRAN_ERROR_DUMPCORE}---Dump core on run-time errors
727 If the @env{GFORTRAN_ERROR_DUMPCORE} variable is set to
728 @samp{y}, @samp{Y} or @samp{1} (only the first letter is relevant)
729 then library run-time errors cause core dumps. To disable the core
730 dumps, set the variable to @samp{n}, @samp{N}, @samp{0}. Default
731 is not to core dump unless the @option{-fdump-core} compile option
734 @node GFORTRAN_ERROR_BACKTRACE
735 @section @env{GFORTRAN_ERROR_BACKTRACE}---Show backtrace on run-time errors
737 If the @env{GFORTRAN_ERROR_BACKTRACE} variable is set to
738 @samp{y}, @samp{Y} or @samp{1} (only the first letter is relevant)
739 then a backtrace is printed when a run-time error occurs.
740 To disable the backtracing, set the variable to
741 @samp{n}, @samp{N}, @samp{0}. Default is not to print a backtrace
742 unless the @option{-fbacktrace} compile option
745 @c =====================================================================
746 @c PART II: LANGUAGE REFERENCE
747 @c =====================================================================
750 \part{II}{Language Reference}
753 @c ---------------------------------------------------------------------
754 @c Fortran 2003 Status
755 @c ---------------------------------------------------------------------
757 @node Fortran 2003 status
758 @chapter Fortran 2003 Status
760 Although GNU Fortran focuses on implementing the Fortran 95
761 standard for the time being, a few Fortran 2003 features are currently
766 Intrinsics @code{command_argument_count}, @code{get_command},
767 @code{get_command_argument}, @code{get_environment_variable}, and
771 @cindex array, constructors
773 Array constructors using square brackets. That is, @code{[...]} rather
777 @cindex @code{FLUSH} statement
778 @cindex statement, @code{FLUSH}
779 @code{FLUSH} statement.
782 @cindex @code{IOMSG=} specifier
783 @code{IOMSG=} specifier for I/O statements.
786 @cindex @code{ENUM} statement
787 @cindex @code{ENUMERATOR} statement
788 @cindex statement, @code{ENUM}
789 @cindex statement, @code{ENUMERATOR}
790 @opindex @code{fshort-enums}
791 Support for the declaration of enumeration constants via the
792 @code{ENUM} and @code{ENUMERATOR} statements. Interoperability with
793 @command{gcc} is guaranteed also for the case where the
794 @command{-fshort-enums} command line option is given.
801 @cindex @code{ALLOCATABLE} dummy arguments
802 @code{ALLOCATABLE} dummy arguments.
804 @cindex @code{ALLOCATABLE} function results
805 @code{ALLOCATABLE} function results
807 @cindex @code{ALLOCATABLE} components of derived types
808 @code{ALLOCATABLE} components of derived types
812 @cindex @code{STREAM} I/O
813 @cindex @code{ACCESS='STREAM'} I/O
814 The @code{OPEN} statement supports the @code{ACCESS='STREAM'} specifier,
815 allowing I/O without any record structure.
818 Namelist input/output for internal files.
821 @cindex @code{PROTECTED} statement
822 @cindex statement, @code{PROTECTED}
823 The @code{PROTECTED} statement and attribute.
826 @cindex @code{VALUE} statement
827 @cindex statement, @code{VALUE}
828 The @code{VALUE} statement and attribute.
831 @cindex @code{VOLATILE} statement
832 @cindex statement, @code{VOLATILE}
833 The @code{VOLATILE} statement and attribute.
836 @cindex @code{IMPORT} statement
837 @cindex statement, @code{IMPORT}
838 The @code{IMPORT} statement, allowing to import
839 host-associated derived types.
842 @cindex @code{USE, INTRINSIC} statement
843 @cindex statement, @code{USE, INTRINSIC}
844 @cindex @code{ISO_FORTRAN_ENV} statement
845 @cindex statement, @code{ISO_FORTRAN_ENV}
846 @code{USE} statement with @code{INTRINSIC} and @code{NON_INTRINSIC}
847 attribute; supported intrinsic modules: @code{ISO_FORTRAN_ENV},
848 @code{OMP_LIB} and @code{OMP_LIB_KINDS}.
851 Renaming of operators in the @code{USE} statement.
854 @cindex ISO C Bindings
855 Interoperability with C (ISO C Bindings)
860 @c ---------------------------------------------------------------------
862 @c ---------------------------------------------------------------------
864 @c Maybe this chapter should be merged with the 'Standards' section,
865 @c whenever that is written :-)
871 GNU Fortran implements a number of extensions over standard
872 Fortran. This chapter contains information on their syntax and
873 meaning. There are currently two categories of GNU Fortran
874 extensions, those that provide functionality beyond that provided
875 by any standard, and those that are supported by GNU Fortran
876 purely for backward compatibility with legacy compilers. By default,
877 @option{-std=gnu} allows the compiler to accept both types of
878 extensions, but to warn about the use of the latter. Specifying
879 either @option{-std=f95} or @option{-std=f2003} disables both types
880 of extensions, and @option{-std=legacy} allows both without warning.
883 * Old-style kind specifications::
884 * Old-style variable initialization::
885 * Extensions to namelist::
886 * X format descriptor without count field::
887 * Commas in FORMAT specifications::
888 * Missing period in FORMAT specifications::
890 * BOZ literal constants::
891 * Real array indices::
893 * Implicitly convert LOGICAL and INTEGER values::
894 * Hollerith constants support::
896 * CONVERT specifier::
898 * Argument list functions::
901 @node Old-style kind specifications
902 @section Old-style kind specifications
903 @cindex kind, old-style
905 GNU Fortran allows old-style kind specifications in declarations. These
911 where @code{TYPESPEC} is a basic type (@code{INTEGER}, @code{REAL},
912 etc.), and where @code{size} is a byte count corresponding to the
913 storage size of a valid kind for that type. (For @code{COMPLEX}
914 variables, @code{size} is the total size of the real and imaginary
915 parts.) The statement then declares @code{x}, @code{y} and @code{z} to
916 be of type @code{TYPESPEC} with the appropriate kind. This is
917 equivalent to the standard-conforming declaration
922 where @code{k} is equal to @code{size} for most types, but is equal to
923 @code{size/2} for the @code{COMPLEX} type.
925 @node Old-style variable initialization
926 @section Old-style variable initialization
928 GNU Fortran allows old-style initialization of variables of the
932 REAL x(2,2) /3*0.,1./
934 The syntax for the initializers is as for the @code{DATA} statement, but
935 unlike in a @code{DATA} statement, an initializer only applies to the
936 variable immediately preceding the initialization. In other words,
937 something like @code{INTEGER I,J/2,3/} is not valid. This style of
938 initialization is only allowed in declarations without double colons
939 (@code{::}); the double colons were introduced in Fortran 90, which also
940 introduced a standard syntax for initializing variables in type
943 Examples of standard-conforming code equivalent to the above example
947 INTEGER :: i = 1, j = 2
948 REAL :: x(2,2) = RESHAPE((/0.,0.,0.,1./),SHAPE(x))
952 DATA i/1/, j/2/, x/3*0.,1./
955 Note that variables which are explicitly initialized in declarations
956 or in @code{DATA} statements automatically acquire the @code{SAVE}
959 @node Extensions to namelist
960 @section Extensions to namelist
963 GNU Fortran fully supports the Fortran 95 standard for namelist I/O
964 including array qualifiers, substrings and fully qualified derived types.
965 The output from a namelist write is compatible with namelist read. The
966 output has all names in upper case and indentation to column 1 after the
967 namelist name. Two extensions are permitted:
969 Old-style use of @samp{$} instead of @samp{&}
972 X(:)%Y(2) = 1.0 2.0 3.0
977 It should be noted that the default terminator is @samp{/} rather than
980 Querying of the namelist when inputting from stdin. After at least
981 one space, entering @samp{?} sends to stdout the namelist name and the names of
982 the variables in the namelist:
993 Entering @samp{=?} outputs the namelist to stdout, as if
994 @code{WRITE(*,NML = mynml)} had been called:
999 X(1)%Y= 0.000000 , 1.000000 , 0.000000 ,
1000 X(2)%Y= 0.000000 , 2.000000 , 0.000000 ,
1001 X(3)%Y= 0.000000 , 3.000000 , 0.000000 ,
1005 To aid this dialog, when input is from stdin, errors send their
1006 messages to stderr and execution continues, even if @code{IOSTAT} is set.
1008 @code{PRINT} namelist is permitted. This causes an error if
1009 @option{-std=f95} is used.
1012 REAL, dimension (4) :: x = (/1.0, 2.0, 3.0, 4.0/)
1015 END PROGRAM test_print
1018 Expanded namelist reads are permitted. This causes an error if
1019 @option{-std=f95} is used. In the following example, the first element
1020 of the array will be given the value 0.00 and the two succeeding
1021 elements will be given the values 1.00 and 2.00.
1024 X(1,1) = 0.00 , 1.00 , 2.00
1028 @node X format descriptor without count field
1029 @section @code{X} format descriptor without count field
1031 To support legacy codes, GNU Fortran permits the count field of the
1032 @code{X} edit descriptor in @code{FORMAT} statements to be omitted.
1033 When omitted, the count is implicitly assumed to be one.
1037 10 FORMAT (I1, X, I1)
1040 @node Commas in FORMAT specifications
1041 @section Commas in @code{FORMAT} specifications
1043 To support legacy codes, GNU Fortran allows the comma separator
1044 to be omitted immediately before and after character string edit
1045 descriptors in @code{FORMAT} statements.
1049 10 FORMAT ('FOO='I1' BAR='I2)
1053 @node Missing period in FORMAT specifications
1054 @section Missing period in @code{FORMAT} specifications
1056 To support legacy codes, GNU Fortran allows missing periods in format
1057 specifications if and only if @option{-std=legacy} is given on the
1058 command line. This is considered non-conforming code and is
1067 @node I/O item lists
1068 @section I/O item lists
1069 @cindex I/O item lists
1071 To support legacy codes, GNU Fortran allows the input item list
1072 of the @code{READ} statement, and the output item lists of the
1073 @code{WRITE} and @code{PRINT} statements, to start with a comma.
1075 @node BOZ literal constants
1076 @section BOZ literal constants
1077 @cindex BOZ literal constants
1079 As an extension, GNU Fortran allows hexadecimal BOZ literal constants to
1080 be specified using the X prefix, in addition to the standard Z prefix.
1081 BOZ literal constants can also be specified by adding a suffix to the
1082 string. For example, @code{Z'ABC'} and @code{'ABC'Z} are equivalent.
1084 The Fortran standard restricts the appearance of a BOZ literal constant
1085 to the @code{DATA} statement, and it is expected to be assigned to an
1086 @code{INTEGER} variable. GNU Fortran permits a BOZ literal to appear in
1087 any initialization expression as well as assignment statements.
1089 Attempts to use a BOZ literal constant to do a bitwise initialization of
1090 a variable can lead to confusion. A BOZ literal constant is converted
1091 to an @code{INTEGER} value with the kind type with the largest decimal
1092 representation, and this value is then converted numerically to the type
1093 and kind of the variable in question. Thus, one should not expect a
1094 bitwise copy of the BOZ literal constant to be assigned to a @code{REAL}
1097 Similarly, initializing an @code{INTEGER} variable with a statement such
1098 as @code{DATA i/Z'FFFFFFFF'/} will produce an integer overflow rather
1099 than the desired result of @math{-1} when @code{i} is a 32-bit integer
1100 on a system that supports 64-bit integers. The @samp{-fno-range-check}
1101 option can be used as a workaround for legacy code that initializes
1102 integers in this manner.
1104 @node Real array indices
1105 @section Real array indices
1106 @cindex array, indices of type real
1108 As an extension, GNU Fortran allows the use of @code{REAL} expressions
1109 or variables as array indices.
1111 @node Unary operators
1112 @section Unary operators
1113 @cindex operators, unary
1115 As an extension, GNU Fortran allows unary plus and unary minus operators
1116 to appear as the second operand of binary arithmetic operators without
1117 the need for parenthesis.
1123 @node Implicitly convert LOGICAL and INTEGER values
1124 @section Implicitly convert @code{LOGICAL} and @code{INTEGER} values
1125 @cindex conversion, to integer
1126 @cindex conversion, to logical
1128 As an extension for backwards compatibility with other compilers, GNU
1129 Fortran allows the implicit conversion of @code{LOGICAL} values to
1130 @code{INTEGER} values and vice versa. When converting from a
1131 @code{LOGICAL} to an @code{INTEGER}, @code{.FALSE.} is interpreted as
1132 zero, and @code{.TRUE.} is interpreted as one. When converting from
1133 @code{INTEGER} to @code{LOGICAL}, the value zero is interpreted as
1134 @code{.FALSE.} and any nonzero value is interpreted as @code{.TRUE.}.
1138 IF (i) PRINT *, 'True'
1141 However, there is no implicit conversion of @code{LOGICAL} and
1142 @code{INTEGER} values performed during I/O operations.
1144 @node Hollerith constants support
1145 @section Hollerith constants support
1146 @cindex Hollerith constants
1148 GNU Fortran supports Hollerith constants in assignments, function
1149 arguments, and @code{DATA} and @code{ASSIGN} statements. A Hollerith
1150 constant is written as a string of characters preceded by an integer
1151 constant indicating the character count, and the letter @code{H} or
1152 @code{h}, and stored in bytewise fashion in a numeric (@code{INTEGER},
1153 @code{REAL}, or @code{complex}) or @code{LOGICAL} variable. The
1154 constant will be padded or truncated to fit the size of the variable in
1157 Examples of valid uses of Hollerith constants:
1160 data x /16Habcdefghijklmnop, 16Hqrstuvwxyz012345/
1161 x(1) = 16HABCDEFGHIJKLMNOP
1165 Invalid Hollerith constants examples:
1168 a = 8H12345678 ! Valid, but the Hollerith constant will be truncated.
1169 a = 0H ! At least one character is needed.
1172 In general, Hollerith constants were used to provide a rudimentary
1173 facility for handling character strings in early Fortran compilers,
1174 prior to the introduction of @code{CHARACTER} variables in Fortran 77;
1175 in those cases, the standard-compliant equivalent is to convert the
1176 program to use proper character strings. On occasion, there may be a
1177 case where the intent is specifically to initialize a numeric variable
1178 with a given byte sequence. In these cases, the same result can be
1179 obtained by using the @code{TRANSFER} statement, as in this example.
1181 INTEGER(KIND=4) :: a
1182 a = TRANSFER ("abcd", a) ! equivalent to: a = 4Habcd
1187 @section Cray pointers
1188 @cindex pointer, cray
1190 Cray pointers are part of a non-standard extension that provides a
1191 C-like pointer in Fortran. This is accomplished through a pair of
1192 variables: an integer "pointer" that holds a memory address, and a
1193 "pointee" that is used to dereference the pointer.
1195 Pointer/pointee pairs are declared in statements of the form:
1197 pointer ( <pointer> , <pointee> )
1201 pointer ( <pointer1> , <pointee1> ), ( <pointer2> , <pointee2> ), ...
1203 The pointer is an integer that is intended to hold a memory address.
1204 The pointee may be an array or scalar. A pointee can be an assumed
1205 size array---that is, the last dimension may be left unspecified by
1206 using a @code{*} in place of a value---but a pointee cannot be an
1207 assumed shape array. No space is allocated for the pointee.
1209 The pointee may have its type declared before or after the pointer
1210 statement, and its array specification (if any) may be declared
1211 before, during, or after the pointer statement. The pointer may be
1212 declared as an integer prior to the pointer statement. However, some
1213 machines have default integer sizes that are different than the size
1214 of a pointer, and so the following code is not portable:
1219 If a pointer is declared with a kind that is too small, the compiler
1220 will issue a warning; the resulting binary will probably not work
1221 correctly, because the memory addresses stored in the pointers may be
1222 truncated. It is safer to omit the first line of the above example;
1223 if explicit declaration of ipt's type is omitted, then the compiler
1224 will ensure that ipt is an integer variable large enough to hold a
1227 Pointer arithmetic is valid with Cray pointers, but it is not the same
1228 as C pointer arithmetic. Cray pointers are just ordinary integers, so
1229 the user is responsible for determining how many bytes to add to a
1230 pointer in order to increment it. Consider the following example:
1234 pointer (ipt, pointee)
1238 The last statement does not set @code{ipt} to the address of
1239 @code{target(1)}, as it would in C pointer arithmetic. Adding @code{1}
1240 to @code{ipt} just adds one byte to the address stored in @code{ipt}.
1242 Any expression involving the pointee will be translated to use the
1243 value stored in the pointer as the base address.
1245 To get the address of elements, this extension provides an intrinsic
1246 function @code{LOC()}. The @code{LOC()} function is equivalent to the
1247 @code{&} operator in C, except the address is cast to an integer type:
1250 pointer(ipt, arpte(10))
1252 ipt = loc(ar) ! Makes arpte is an alias for ar
1253 arpte(1) = 1.0 ! Sets ar(1) to 1.0
1255 The pointer can also be set by a call to the @code{MALLOC} intrinsic
1258 Cray pointees often are used to alias an existing variable. For
1266 As long as @code{ipt} remains unchanged, @code{iarr} is now an alias for
1267 @code{target}. The optimizer, however, will not detect this aliasing, so
1268 it is unsafe to use @code{iarr} and @code{target} simultaneously. Using
1269 a pointee in any way that violates the Fortran aliasing rules or
1270 assumptions is illegal. It is the user's responsibility to avoid doing
1271 this; the compiler works under the assumption that no such aliasing
1274 Cray pointers will work correctly when there is no aliasing (i.e., when
1275 they are used to access a dynamically allocated block of memory), and
1276 also in any routine where a pointee is used, but any variable with which
1277 it shares storage is not used. Code that violates these rules may not
1278 run as the user intends. This is not a bug in the optimizer; any code
1279 that violates the aliasing rules is illegal. (Note that this is not
1280 unique to GNU Fortran; any Fortran compiler that supports Cray pointers
1281 will ``incorrectly'' optimize code with illegal aliasing.)
1283 There are a number of restrictions on the attributes that can be applied
1284 to Cray pointers and pointees. Pointees may not have the
1285 @code{ALLOCATABLE}, @code{INTENT}, @code{OPTIONAL}, @code{DUMMY},
1286 @code{TARGET}, @code{INTRINSIC}, or @code{POINTER} attributes. Pointers
1287 may not have the @code{DIMENSION}, @code{POINTER}, @code{TARGET},
1288 @code{ALLOCATABLE}, @code{EXTERNAL}, or @code{INTRINSIC} attributes.
1289 Pointees may not occur in more than one pointer statement. A pointee
1290 cannot be a pointer. Pointees cannot occur in equivalence, common, or
1293 A Cray pointer may also point to a function or a subroutine. For
1294 example, the following excerpt is valid:
1298 pointer (subptr,subpte)
1308 A pointer may be modified during the course of a program, and this
1309 will change the location to which the pointee refers. However, when
1310 pointees are passed as arguments, they are treated as ordinary
1311 variables in the invoked function. Subsequent changes to the pointer
1312 will not change the base address of the array that was passed.
1314 @node CONVERT specifier
1315 @section CONVERT specifier
1316 @cindex CONVERT specifier
1318 GNU Fortran allows the conversion of unformatted data between little-
1319 and big-endian representation to facilitate moving of data
1320 between different systems. The conversion can be indicated with
1321 the @code{CONVERT} specifier on the @code{OPEN} statement.
1322 @xref{GFORTRAN_CONVERT_UNIT}, for an alternative way of specifying
1323 the data format via an environment variable.
1325 Valid values for @code{CONVERT} are:
1327 @item @code{CONVERT='NATIVE'} Use the native format. This is the default.
1328 @item @code{CONVERT='SWAP'} Swap between little- and big-endian.
1329 @item @code{CONVERT='LITTLE_ENDIAN'} Use the little-endian representation
1330 for unformatted files.
1331 @item @code{CONVERT='BIG_ENDIAN'} Use the big-endian representation for
1335 Using the option could look like this:
1337 open(file='big.dat',form='unformatted',access='sequential', &
1338 convert='big_endian')
1341 The value of the conversion can be queried by using
1342 @code{INQUIRE(CONVERT=ch)}. The values returned are
1343 @code{'BIG_ENDIAN'} and @code{'LITTLE_ENDIAN'}.
1345 @code{CONVERT} works between big- and little-endian for
1346 @code{INTEGER} values of all supported kinds and for @code{REAL}
1347 on IEEE systems of kinds 4 and 8. Conversion between different
1348 ``extended double'' types on different architectures such as
1349 m68k and x86_64, which GNU Fortran
1350 supports as @code{REAL(KIND=10)} and @code{REAL(KIND=16)}, will
1353 @emph{Note that the values specified via the GFORTRAN_CONVERT_UNIT
1354 environment variable will override the CONVERT specifier in the
1355 open statement}. This is to give control over data formats to
1356 users who do not have the source code of their program available.
1358 Using anything but the native representation for unformatted data
1359 carries a significant speed overhead. If speed in this area matters
1360 to you, it is best if you use this only for data that needs to be
1367 GNU Fortran attempts to be OpenMP Application Program Interface v2.5
1368 compatible when invoked with the @option{-fopenmp} option. GNU Fortran
1369 then generates parallelized code according to the OpenMP directives
1370 used in the source. The OpenMP Fortran runtime library
1371 routines are provided both in a form of a Fortran 90 module named
1372 @code{omp_lib} and in a form of a Fortran @code{include} file named
1375 For details refer to the actual
1376 @uref{http://www.openmp.org/drupal/mp-documents/spec25.pdf,
1377 OpenMP Application Program Interface v2.5} specification and to the
1378 @ref{Top,,Introduction,libgomp,GNU OpenMP runtime library}.
1380 @node Argument list functions
1381 @section Argument list functions %VAL, %REF and %LOC
1382 @cindex argument list functions
1387 GNU Fortran supports argument list functions @code{%VAL}, @code{%REF}
1388 and @code{%LOC} statements, for backward compatibility with g77.
1389 It is recommended that these should be used only for code that is
1390 accessing facilities outside of GNU Fortran, such as operating system
1391 or windowing facilities. It is best to constrain such uses to isolated
1392 portions of a program--portions that deal specifically and exclusively
1393 with low-level, system-dependent facilities. Such portions might well
1394 provide a portable interface for use by the program as a whole, but are
1395 themselves not portable, and should be thoroughly tested each time they
1396 are rebuilt using a new compiler or version of a compiler.
1398 @code{%VAL} passes a scalar argument by value, @code{%REF} passes it by
1399 reference and @code{%LOC} passes its memory location. Since gfortran
1400 already passes scalar arguments by reference, @code{%REF} is in effect
1401 a do-nothing. @code{%LOC} has the same effect as a fortran pointer.
1403 An example of passing an argument by value to a C subroutine foo.:
1406 C prototype void foo_ (float x);
1415 For details refer to the g77 manual
1416 @uref{http://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/index.html#Top}.
1418 Also, the gfortran testsuite c_by_val.f and its partner c_by_val.c are
1421 @c ---------------------------------------------------------------------
1422 @c Intrinsic Procedures
1423 @c ---------------------------------------------------------------------
1425 @include intrinsic.texi
1432 @c ---------------------------------------------------------------------
1434 @c ---------------------------------------------------------------------
1437 @unnumbered Contributing
1438 @cindex Contributing
1440 Free software is only possible if people contribute to efforts
1442 We're always in need of more people helping out with ideas
1443 and comments, writing documentation and contributing code.
1445 If you want to contribute to GNU Fortran,
1446 have a look at the long lists of projects you can take on.
1447 Some of these projects are small,
1448 some of them are large;
1449 some are completely orthogonal to the rest of what is
1450 happening on GNU Fortran,
1451 but others are ``mainstream'' projects in need of enthusiastic hackers.
1452 All of these projects are important!
1453 We'll eventually get around to the things here,
1454 but they are also things doable by someone who is willing and able.
1459 * Proposed Extensions::
1464 @section Contributors to GNU Fortran
1465 @cindex Contributors
1469 Most of the parser was hand-crafted by @emph{Andy Vaught}, who is
1470 also the initiator of the whole project. Thanks Andy!
1471 Most of the interface with GCC was written by @emph{Paul Brook}.
1473 The following individuals have contributed code and/or
1474 ideas and significant help to the GNU Fortran project
1475 (in no particular order):
1479 @item Katherine Holcomb
1480 @item Tobias Schl@"uter
1481 @item Steven Bosscher
1484 @item Niels Kristian Bech Jensen
1485 @item Steven Johnson
1490 @item Fran@,{c}ois-Xavier Coudert
1491 @item Steven G. Kargl
1493 @item Janne Blomqvist
1500 @item Richard Henderson
1501 @item Richard Sandiford
1502 @item Richard Guenther
1503 @item Bernhard Fischer
1506 The following people have contributed bug reports,
1507 smaller or larger patches,
1508 and much needed feedback and encouragement for the
1509 GNU Fortran project:
1512 @item Erik Schnetter
1517 Many other individuals have helped debug,
1518 test and improve the GNU Fortran compiler over the past few years,
1519 and we welcome you to do the same!
1520 If you already have done so,
1521 and you would like to see your name listed in the
1522 list above, please contact us.
1530 @item Help build the test suite
1531 Solicit more code for donation to the test suite.
1532 We can keep code private on request.
1534 @item Bug hunting/squishing
1535 Find bugs and write more test cases!
1536 Test cases are especially very welcome,
1537 because it allows us to concentrate on fixing bugs
1538 instead of isolating them.
1540 @item Smaller projects (``bug'' fixes):
1542 @item Allow init exprs to be numbers raised to integer powers.
1543 @item Implement correct rounding.
1544 @item Implement F restrictions on Fortran 95 syntax.
1545 @item See about making Emacs-parsable error messages.
1549 If you wish to work on the runtime libraries,
1550 please contact a project maintainer.
1554 @node Proposed Extensions
1555 @section Proposed Extensions
1557 Here's a list of proposed extensions for the GNU Fortran compiler, in no particular
1558 order. Most of these are necessary to be fully compatible with
1559 existing Fortran compilers, but they are not part of the official
1560 J3 Fortran 95 standard.
1562 @subsection Compiler extensions:
1565 User-specified alignment rules for structures.
1568 Flag to generate @code{Makefile} info.
1571 Automatically extend single precision constants to double.
1574 Compile code that conserves memory by dynamically allocating common and
1575 module storage either on stack or heap.
1578 Compile flag to generate code for array conformance checking (suggest -CC).
1581 User control of symbol names (underscores, etc).
1584 Compile setting for maximum size of stack frame size before spilling
1585 parts to static or heap.
1588 Flag to force local variables into static space.
1591 Flag to force local variables onto stack.
1594 Flag for maximum errors before ending compile.
1597 Option to initialize otherwise uninitialized integer and floating
1602 @subsection Environment Options
1605 Pluggable library modules for random numbers, linear algebra.
1606 LA should use BLAS calling conventions.
1609 Environment variables controlling actions on arithmetic exceptions like
1610 overflow, underflow, precision loss---Generate NaN, abort, default.
1614 Set precision for fp units that support it (i387).
1617 Variable for setting fp rounding mode.
1620 Variable to fill uninitialized variables with a user-defined bit
1624 Environment variable controlling filename that is opened for that unit
1628 Environment variable to clear/trash memory being freed.
1631 Environment variable to control tracing of allocations and frees.
1634 Environment variable to display allocated memory at normal program end.
1637 Environment variable for filename for * IO-unit.
1640 Environment variable for temporary file directory.
1643 Environment variable forcing standard output to be line buffered (unix).
1648 @c ---------------------------------------------------------------------
1649 @c GNU General Public License
1650 @c ---------------------------------------------------------------------
1656 @c ---------------------------------------------------------------------
1657 @c GNU Free Documentation License
1658 @c ---------------------------------------------------------------------
1664 @c ---------------------------------------------------------------------
1665 @c Funding Free Software
1666 @c ---------------------------------------------------------------------
1668 @include funding.texi
1670 @c ---------------------------------------------------------------------
1672 @c ---------------------------------------------------------------------
1675 @unnumbered Option Index
1676 @command{gfortran}'s command line options are indexed here without any
1677 initial @samp{-} or @samp{--}. Where an option has both positive and
1678 negative forms (such as -foption and -fno-option), relevant entries in
1679 the manual are indexed under the most appropriate form; it may sometimes
1680 be useful to look up both forms.
1684 @unnumbered Keyword Index