1 @c Copyright (C) 2004, 2005, 2006, 2007, 2008
2 @c Free Software Foundation, Inc.
3 @c This is part of the GNU Fortran manual.
4 @c For copying conditions, see the file gfortran.texi.
8 Copyright @copyright{} 2004, 2005, 2006, 2007
9 Free Software Foundation, Inc.
11 Permission is granted to copy, distribute and/or modify this document
12 under the terms of the GNU Free Documentation License, Version 1.2 or
13 any later version published by the Free Software Foundation; with the
14 Invariant Sections being ``GNU General Public License'' and ``Funding
15 Free Software'', the Front-Cover texts being (a) (see below), and with
16 the Back-Cover Texts being (b) (see below). A copy of the license is
17 included in the gfdl(7) man page.
19 (a) The FSF's Front-Cover Text is:
23 (b) The FSF's Back-Cover Text is:
25 You have freedom to copy and modify this GNU Manual, like GNU
26 software. Copies published by the Free Software Foundation raise
27 funds for GNU development.
29 @c Set file name and title for the man page.
31 @settitle GNU Fortran compiler.
33 gfortran [@option{-c}|@option{-S}|@option{-E}]
34 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
35 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
36 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
37 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
38 [@option{-f}@var{option}@dots{}]
39 [@option{-m}@var{machine-option}@dots{}]
40 [@option{-o} @var{outfile}] @var{infile}@dots{}
42 Only the most useful options are listed here; see below for the
46 gpl(7), gfdl(7), fsf-funding(7),
47 cpp(1), gcov(1), gcc(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
48 and the Info entries for @file{gcc}, @file{cpp}, @file{gfortran}, @file{as},
49 @file{ld}, @file{binutils} and @file{gdb}.
52 For instructions on reporting bugs, see
56 See the Info entry for @command{gfortran} for contributors to GCC and
61 @node Invoking GNU Fortran
62 @chapter GNU Fortran Command Options
63 @cindex GNU Fortran command options
64 @cindex command options
65 @cindex options, @command{gfortran} command
67 @c man begin DESCRIPTION
69 The @command{gfortran} command supports all the options supported by the
70 @command{gcc} command. Only options specific to GNU Fortran are documented here.
72 @xref{Invoking GCC,,GCC Command Options,gcc,Using the GNU Compiler
73 Collection (GCC)}, for information
74 on the non-Fortran-specific aspects of the @command{gcc} command (and,
75 therefore, the @command{gfortran} command).
77 @cindex options, negative forms
78 All GCC and GNU Fortran options
79 are accepted both by @command{gfortran} and by @command{gcc}
80 (as well as any other drivers built at the same time,
81 such as @command{g++}),
82 since adding GNU Fortran to the GCC distribution
83 enables acceptance of GNU Fortran options
84 by all of the relevant drivers.
86 In some cases, options have positive and negative forms;
87 the negative form of @option{-ffoo} would be @option{-fno-foo}.
88 This manual documents only one of these two forms, whichever
89 one is not the default.
93 * Option Summary:: Brief list of all @command{gfortran} options,
95 * Fortran Dialect Options:: Controlling the variant of Fortran language
97 * Preprocessing Options:: Enable and customize preprocessing.
98 * Error and Warning Options:: How picky should the compiler be?
99 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
100 * Directory Options:: Where to find module files
101 * Link Options :: Influencing the linking step
102 * Runtime Options:: Influencing runtime behavior
103 * Code Gen Options:: Specifying conventions for function calls, data layout
105 * Environment Variables:: Environment variables that affect @command{gfortran}.
109 @section Option summary
113 Here is a summary of all the options specific to GNU Fortran, grouped
114 by type. Explanations are in the following sections.
117 @item Fortran Language Options
118 @xref{Fortran Dialect Options,,Options controlling Fortran dialect}.
119 @gccoptlist{-fall-intrinsics -ffree-form -fno-fixed-form @gol
120 -fdollar-ok -fimplicit-none -fmax-identifier-length @gol
121 -std=@var{std} -fd-lines-as-code -fd-lines-as-comments @gol
122 -ffixed-line-length-@var{n} -ffixed-line-length-none @gol
123 -ffree-line-length-@var{n} -ffree-line-length-none @gol
124 -fdefault-double-8 -fdefault-integer-8 -fdefault-real-8 @gol
125 -fcray-pointer -fopenmp -fno-range-check -fbackslash -fmodule-private}
127 @item Preprocessing Options
128 @xref{Preprocessing Options,,Enable and customize preprocessing}.
129 @gccoptlist{-cpp -dD -dI -dM -dN -dU -fworking-directory @gol
130 -imultilib @var{dir} -iprefix @var{file} -isysroot @var{dir} @gol
131 -iquote -isystem @var{dir} -nocpp -nostdinc -undef @gol
132 -A@var{question}=@var{answer} -A-@var{question}@r{[}=@var{answer}@r{]} @gol
133 -C -CC -D@var{macro}@r{[}=@var{defn}@r{]} -U@var{macro} -H -P}
135 @item Error and Warning Options
136 @xref{Error and Warning Options,,Options to request or suppress errors
138 @gccoptlist{-fmax-errors=@var{n} @gol
139 -fsyntax-only -pedantic -pedantic-errors @gol
140 -Wall -Waliasing -Wampersand -Warray-bounds -Wcharacter-truncation @gol
141 -Wconversion -Wimplicit-interface -Wline-truncation -Wintrinsics-std @gol
142 -Wsurprising -Wno-tabs -Wunderflow -Wunused-parameter -Wintrinsics-shadow}
144 @item Debugging Options
145 @xref{Debugging Options,,Options for debugging your program or GNU Fortran}.
146 @gccoptlist{-fdump-parse-tree -ffpe-trap=@var{list} @gol
147 -fdump-core -fbacktrace}
149 @item Directory Options
150 @xref{Directory Options,,Options for directory search}.
151 @gccoptlist{-I@var{dir} -J@var{dir} -M@var{dir} -fintrinsic-modules-path @var{dir}}
154 @xref{Link Options,,Options for influencing the linking step}.
155 @gccoptlist{-static-libgfortran}
157 @item Runtime Options
158 @xref{Runtime Options,,Options for influencing runtime behavior}.
159 @gccoptlist{-fconvert=@var{conversion} -fno-range-check
160 -frecord-marker=@var{length} @gol -fmax-subrecord-length=@var{length}
163 @item Code Generation Options
164 @xref{Code Gen Options,,Options for code generation conventions}.
165 @gccoptlist{-fno-automatic -ff2c -fno-underscoring
166 -fsecond-underscore @gol
167 -fbounds-check -fcheck-array-temporaries -fmax-stack-var-size=@var{n} @gol
168 -fpack-derived -frepack-arrays -fshort-enums -fexternal-blas @gol
169 -fblas-matmul-limit=@var{n} -frecursive -finit-local-zero @gol
170 -finit-integer=@var{n} -finit-real=@var{<zero|inf|-inf|nan>} @gol
171 -finit-logical=@var{<true|false>} -finit-character=@var{n}}
175 * Fortran Dialect Options:: Controlling the variant of Fortran language
177 * Preprocessing Options:: Enable and customize preprocessing.
178 * Error and Warning Options:: How picky should the compiler be?
179 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
180 * Directory Options:: Where to find module files
181 * Link Options :: Influencing the linking step
182 * Runtime Options:: Influencing runtime behavior
183 * Code Gen Options:: Specifying conventions for function calls, data layout
187 @node Fortran Dialect Options
188 @section Options controlling Fortran dialect
189 @cindex dialect options
190 @cindex language, dialect options
191 @cindex options, dialect
193 The following options control the details of the Fortran dialect
194 accepted by the compiler:
199 @opindex @code{ffree-form}
200 @opindex @code{fno-fixed-form}
201 @cindex options, fortran dialect
202 @cindex file format, free
203 @cindex file format, fixed
204 Specify the layout used by the source file. The free form layout
205 was introduced in Fortran 90. Fixed form was traditionally used in
206 older Fortran programs. When neither option is specified, the source
207 form is determined by the file extension.
209 @item -fall-intrinsics
210 @opindex @code{fall-intrinsics}
211 Accept all of the intrinsic procedures provided in libgfortran
212 without regard to the setting of @option{-std}. In particular,
213 this option can be quite useful with @option{-std=f95}. Additionally,
214 @command{gfortran} will ignore @option{-Wintrinsics-std} and will never try
215 to link to an @code{EXTERNAL} version if the intrinsic is not included in the
218 @item -fd-lines-as-code
219 @item -fd-lines-as-comments
220 @opindex @code{fd-lines-as-code}
221 @opindex @code{fd-lines-as-comments}
222 Enable special treatment for lines beginning with @code{d} or @code{D}
223 in fixed form sources. If the @option{-fd-lines-as-code} option is
224 given they are treated as if the first column contained a blank. If the
225 @option{-fd-lines-as-comments} option is given, they are treated as
228 @item -fdefault-double-8
229 @opindex @code{fdefault-double-8}
230 Set the @code{DOUBLE PRECISION} type to an 8 byte wide type.
232 @item -fdefault-integer-8
233 @opindex @code{fdefault-integer-8}
234 Set the default integer and logical types to an 8 byte wide type.
235 Do nothing if this is already the default.
237 @item -fdefault-real-8
238 @opindex @code{fdefault-real-8}
239 Set the default real type to an 8 byte wide type.
240 Do nothing if this is already the default.
243 @opindex @code{fdollar-ok}
246 @cindex character set
247 Allow @samp{$} as a valid character in a symbol name.
250 @opindex @code{backslash}
252 @cindex escape characters
253 Change the interpretation of backslashes in string literals from a single
254 backslash character to ``C-style'' escape characters. The following
255 combinations are expanded @code{\a}, @code{\b}, @code{\f}, @code{\n},
256 @code{\r}, @code{\t}, @code{\v}, @code{\\}, and @code{\0} to the ASCII
257 characters alert, backspace, form feed, newline, carriage return,
258 horizontal tab, vertical tab, backslash, and NUL, respectively.
259 Additionally, @code{\x}@var{nn}, @code{\u}@var{nnnn} and
260 @code{\U}@var{nnnnnnnn} (where each @var{n} is a hexadecimal digit) are
261 translated into the Unicode characters corresponding to the specified code
262 points. All other combinations of a character preceded by \ are
265 @item -fmodule-private
266 @opindex @code{fmodule-private}
267 @cindex module entities
269 Set the default accessibility of module entities to @code{PRIVATE}.
270 Use-associated entities will not be accessible unless they are explicitly
271 declared as @code{PUBLIC}.
273 @item -ffixed-line-length-@var{n}
274 @opindex @code{ffixed-line-length-}@var{n}
275 @cindex file format, fixed
276 Set column after which characters are ignored in typical fixed-form
277 lines in the source file, and through which spaces are assumed (as
278 if padded to that length) after the ends of short fixed-form lines.
280 Popular values for @var{n} include 72 (the
281 standard and the default), 80 (card image), and 132 (corresponding
282 to ``extended-source'' options in some popular compilers).
283 @var{n} may also be @samp{none}, meaning that the entire line is meaningful
284 and that continued character constants never have implicit spaces appended
285 to them to fill out the line.
286 @option{-ffixed-line-length-0} means the same thing as
287 @option{-ffixed-line-length-none}.
289 @item -ffree-line-length-@var{n}
290 @opindex @code{ffree-line-length-}@var{n}
291 @cindex file format, free
292 Set column after which characters are ignored in typical free-form
293 lines in the source file. The default value is 132.
294 @var{n} may be @samp{none}, meaning that the entire line is meaningful.
295 @option{-ffree-line-length-0} means the same thing as
296 @option{-ffree-line-length-none}.
298 @item -fmax-identifier-length=@var{n}
299 @opindex @code{fmax-identifier-length=}@var{n}
300 Specify the maximum allowed identifier length. Typical values are
301 31 (Fortran 95) and 63 (Fortran 2003 and Fortran 2008).
303 @item -fimplicit-none
304 @opindex @code{fimplicit-none}
305 Specify that no implicit typing is allowed, unless overridden by explicit
306 @code{IMPLICIT} statements. This is the equivalent of adding
307 @code{implicit none} to the start of every procedure.
310 @opindex @code{fcray-pointer}
311 Enable the Cray pointer extension, which provides C-like pointer
315 @opindex @code{fopenmp}
317 Enable the OpenMP extensions. This includes OpenMP @code{!$omp} directives
319 and @code{c$omp}, @code{*$omp} and @code{!$omp} directives in fixed form,
320 @code{!$} conditional compilation sentinels in free form
321 and @code{c$}, @code{*$} and @code{!$} sentinels in fixed form,
322 and when linking arranges for the OpenMP runtime library to be linked
323 in. The option @option{-fopenmp} implies @option{-frecursive}.
325 @item -fno-range-check
326 @opindex @code{frange-check}
327 Disable range checking on results of simplification of constant
328 expressions during compilation. For example, GNU Fortran will give
329 an error at compile time when simplifying @code{a = 1. / 0}.
330 With this option, no error will be given and @code{a} will be assigned
331 the value @code{+Infinity}. If an expression evaluates to a value
332 outside of the relevant range of [@code{-HUGE()}:@code{HUGE()}],
333 then the expression will be replaced by @code{-Inf} or @code{+Inf}
335 Similarly, @code{DATA i/Z'FFFFFFFF'/} will result in an integer overflow
336 on most systems, but with @option{-fno-range-check} the value will
337 ``wrap around'' and @code{i} will be initialized to @math{-1} instead.
340 @opindex @code{std=}@var{std} option
341 Specify the standard to which the program is expected to conform, which
342 may be one of @samp{f95}, @samp{f2003}, @samp{f2008}, @samp{gnu}, or
343 @samp{legacy}. The default value for @var{std} is @samp{gnu}, which
344 specifies a superset of the Fortran 95 standard that includes all of the
345 extensions supported by GNU Fortran, although warnings will be given for
346 obsolete extensions not recommended for use in new code. The
347 @samp{legacy} value is equivalent but without the warnings for obsolete
348 extensions, and may be useful for old non-standard programs. The
349 @samp{f95}, @samp{f2003} and @samp{f2008} values specify strict
350 conformance to the Fortran 95, Fortran 2003 and Fortran 2008 standards,
351 respectively; errors are given for all extensions beyond the relevant
352 language standard, and warnings are given for the Fortran 77 features
353 that are permitted but obsolescent in later standards.
357 @node Preprocessing Options
358 @section Enable and customize preprocessing
360 @cindex options, preprocessor
363 Preprocessor related options. See section
364 @ref{Preprocessing and conditional compilation} for more detailed
365 information on preprocessing in @command{gfortran}.
372 @cindex preprocessor, enable
373 @cindex preprocessor, disable
374 Enable preprocessing. The preprocessor is automatically invoked if
375 the file extension is @file{.fpp}, @file{.FPP}, @file{.F}, @file{.FOR},
376 @file{.FTN}, @file{.F90}, @file{.F95}, @file{.F03} or @file{.F08}. Use
377 this option to manually enable preprocessing of any kind of Fortran file.
379 To disable preprocessing of files with any of the above listed extensions,
380 use the negative form: @option{-nocpp}.
382 The preprocessor is run in traditional mode, be aware that any
383 restrictions of the file-format, e.g. fixed-form line width,
384 apply for preprocessed output as well.
388 @cindex preprocessor, debugging
389 @cindex debugging, preprocessor
390 Instead of the normal output, generate a list of @code{'#define'}
391 directives for all the macros defined during the execution of the
392 preprocessor, including predefined macros. This gives you a way
393 of finding out what is predefined in your version of the preprocessor.
394 Assuming you have no file @file{foo.f90}, the command
396 touch foo.f90; gfortran -cpp -dM foo.f90
398 will show all the predefined macros.
402 @cindex preprocessor, debugging
403 @cindex debugging, preprocessor
404 Like @option{-dM} except in two respects: it does not include the
405 predefined macros, and it outputs both the @code{#define} directives
406 and the result of preprocessing. Both kinds of output go to the
407 standard output file.
411 @cindex preprocessor, debugging
412 @cindex debugging, preprocessor
413 Like @option{-dD}, but emit only the macro names, not their expansions.
417 @cindex preprocessor, debugging
418 @cindex debugging, preprocessor
419 Like @option{dD} except that only macros that are expanded, or whose
420 definedness is tested in preprocessor directives, are output; the
421 output is delayed until the use or test of the macro; and @code{'#undef'}
422 directives are also output for macros tested but undefined at the time.
426 @cindex preprocessor, debugging
427 @cindex debugging, preprocessor
428 Output @code{'#include'} directives in addition to the result
431 @item -fworking-directory
432 @opindex @code{fworking-directory}
433 @cindex preprocessor, working directory
434 Enable generation of linemarkers in the preprocessor output that will
435 let the compiler know the current working directory at the time of
436 preprocessing. When this option is enabled, the preprocessor will emit,
437 after the initial linemarker, a second linemarker with the current
438 working directory followed by two slashes. GCC will use this directory,
439 when it's present in the preprocessed input, as the directory emitted
440 as the current working directory in some debugging information formats.
441 This option is implicitly enabled if debugging information is enabled,
442 but this can be inhibited with the negated form
443 @option{-fno-working-directory}. If the @option{-P} flag is present
444 in the command line, this option has no effect, since no @code{#line}
445 directives are emitted whatsoever.
447 @item -imultilib @var{dir}
448 @opindex @code{imultilib @var{dir}}
449 @cindex preprocessing, include path
450 Use @var{dir} as a subdirectory of the directory containing target-specific
453 @item -iprefix @var{prefix}
454 @opindex @code{iprefix @var{prefix}}
455 @cindex preprocessing, include path
456 Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix}
457 options. If the @var{prefix} represents a directory, you should include
458 the final @code{'/'}.
460 @item -isysroot @var{dir}
461 @opindex @code{isysroot @var{dir}}
462 @cindex preprocessing, include path
463 This option is like the @option{--sysroot} option, but applies only to
464 header files. See the @option{--sysroot} option for more information.
466 @item -iquote @var{dir}
467 @opindex @code{iquote @var{dir}}
468 @cindex preprocessing, include path
469 Search @var{dir} only for header files requested with @code{#include "file"};
470 they are not searched for @code{#include <file>}, before all directories
471 specified by @option{-I} and before the standard system directories. If
472 @var{dir} begins with @code{=}, then the @code{=} will be replaced by the
473 sysroot prefix; see @option{--sysroot} and @option{-isysroot}.
475 @item -isystem @var{dir}
476 @opindex @code{isystem @var{dir}}
477 @cindex preprocessing, include path
478 Search @var{dir} for header files, after all directories specified by
479 @option{-I} but before the standard system directories. Mark it as a
480 system directory, so that it gets the same special treatment as is
481 applied to the standard system directories. If @var{dir} begins with
482 @code{=}, then the @code{=} will be replaced by the sysroot prefix;
483 see @option{--sysroot} and @option{-isysroot}.
486 @opindex @code{nostdinc}
487 Do not search the standard system directories for header files. Only
488 the directories you have specified with @option{-I} options (and the
489 directory of the current file, if appropriate) are searched.
492 @opindex @code{undef}
493 Do not predefine any system-specific or GCC-specific macros.
494 The standard predefined macros remain defined.
496 @item -A@var{predicate}=@var{answer}
497 @opindex @code{A@var{predicate}=@var{answer}}
498 @cindex preprocessing, assertation
499 Make an assertion with the predicate @var{predicate} and answer @var{answer}.
500 This form is preferred to the older form -A predicate(answer), which is still
501 supported, because it does not use shell special characters.
503 @item -A-@var{predicate}=@var{answer}
504 @opindex @code{A-@var{predicate}=@var{answer}}
505 @cindex preprocessing, assertation
506 Cancel an assertion with the predicate @var{predicate} and answer @var{answer}.
510 @cindex preprocessing, keep comments
511 Do not discard comments. All comments are passed through to the output
512 file, except for comments in processed directives, which are deleted
513 along with the directive.
515 You should be prepared for side effects when using @option{-C}; it causes
516 the preprocessor to treat comments as tokens in their own right. For example,
517 comments appearing at the start of what would be a directive line have the
518 effect of turning that line into an ordinary source line, since the first
519 token on the line is no longer a @code{'#'}.
521 Warning: this currently handles C-Style comments only. The preprocessor
522 does not yet recognize Fortran-style comments.
526 @cindex preprocessing, keep comments
527 Do not discard comments, including during macro expansion. This is like
528 @option{-C}, except that comments contained within macros are also passed
529 through to the output file where the macro is expanded.
531 In addition to the side-effects of the @option{-C} option, the @option{-CC}
532 option causes all C++-style comments inside a macro to be converted to C-style
533 comments. This is to prevent later use of that macro from inadvertently
534 commenting out the remainder of the source line. The @option{-CC} option
535 is generally used to support lint comments.
537 Warning: this currently handles C- and C++-Style comments only. The
538 preprocessor does not yet recognize Fortran-style comments.
541 @opindex @code{D@var{name}}
542 @cindex preprocessing, define macros
543 Predefine name as a macro, with definition @code{1}.
545 @item -D@var{name}=@var{definition}
546 @opindex @code{D@var{name}=@var{definition}}
547 @cindex preprocessing, define macros
548 The contents of @var{definition} are tokenized and processed as if they
549 appeared during translation phase three in a @code{'#define'} directive.
550 In particular, the definition will be truncated by embedded newline
553 If you are invoking the preprocessor from a shell or shell-like program
554 you may need to use the shell's quoting syntax to protect characters such
555 as spaces that have a meaning in the shell syntax.
557 If you wish to define a function-like macro on the command line, write
558 its argument list with surrounding parentheses before the equals sign
559 (if any). Parentheses are meaningful to most shells, so you will need
560 to quote the option. With sh and csh, @code{-D'name(args...)=definition'}
563 @option{-D} and @option{-U} options are processed in the order they are
564 given on the command line. All -imacros file and -include file options
565 are processed after all -D and -U options.
569 Print the name of each header file used, in addition to other normal
570 activities. Each name is indented to show how deep in the @code{'#include'}
575 @cindex preprocessing, no linemarkers
576 Inhibit generation of linemarkers in the output from the preprocessor.
577 This might be useful when running the preprocessor on something that
578 is not C code, and will be sent to a program which might be confused
582 @opindex @code{U@var{name}}
583 @cindex preprocessing, undefine macros
584 Cancel any previous definition of @var{name}, either built in or provided
585 with a @option{-D} option.
589 @node Error and Warning Options
590 @section Options to request or suppress errors and warnings
591 @cindex options, warnings
592 @cindex options, errors
593 @cindex warnings, suppressing
594 @cindex messages, error
595 @cindex messages, warning
596 @cindex suppressing warnings
598 Errors are diagnostic messages that report that the GNU Fortran compiler
599 cannot compile the relevant piece of source code. The compiler will
600 continue to process the program in an attempt to report further errors
601 to aid in debugging, but will not produce any compiled output.
603 Warnings are diagnostic messages that report constructions which
604 are not inherently erroneous but which are risky or suggest there is
605 likely to be a bug in the program. Unless @option{-Werror} is specified,
606 they do not prevent compilation of the program.
608 You can request many specific warnings with options beginning @option{-W},
609 for example @option{-Wimplicit} to request warnings on implicit
610 declarations. Each of these specific warning options also has a
611 negative form beginning @option{-Wno-} to turn off warnings;
612 for example, @option{-Wno-implicit}. This manual lists only one of the
613 two forms, whichever is not the default.
615 These options control the amount and kinds of errors and warnings produced
619 @item -fmax-errors=@var{n}
620 @opindex @code{fmax-errors=}@var{n}
621 @cindex errors, limiting
622 Limits the maximum number of error messages to @var{n}, at which point
623 GNU Fortran bails out rather than attempting to continue processing the
624 source code. If @var{n} is 0, there is no limit on the number of error
628 @opindex @code{fsyntax-only}
629 @cindex syntax checking
630 Check the code for syntax errors, but don't actually compile it. This
631 will generate module files for each module present in the code, but no
635 @opindex @code{pedantic}
636 Issue warnings for uses of extensions to Fortran 95.
637 @option{-pedantic} also applies to C-language constructs where they
638 occur in GNU Fortran source files, such as use of @samp{\e} in a
639 character constant within a directive like @code{#include}.
641 Valid Fortran 95 programs should compile properly with or without
643 However, without this option, certain GNU extensions and traditional
644 Fortran features are supported as well.
645 With this option, many of them are rejected.
647 Some users try to use @option{-pedantic} to check programs for conformance.
648 They soon find that it does not do quite what they want---it finds some
649 nonstandard practices, but not all.
650 However, improvements to GNU Fortran in this area are welcome.
652 This should be used in conjunction with @option{-std=f95},
653 @option{-std=f2003} or @option{-std=f2008}.
655 @item -pedantic-errors
656 @opindex @code{pedantic-errors}
657 Like @option{-pedantic}, except that errors are produced rather than
663 @cindex warnings, all
664 Enables commonly used warning options pertaining to usage that
665 we recommend avoiding and that we believe are easy to avoid.
666 This currently includes @option{-Waliasing},
667 @option{-Wampersand}, @option{-Wsurprising}, @option{-Wintrinsics-std},
668 @option{-Wno-tabs}, @option{-Wintrinsic-shadow} and @option{-Wline-truncation}.
671 @opindex @code{Waliasing}
673 @cindex warnings, aliasing
674 Warn about possible aliasing of dummy arguments. Specifically, it warns
675 if the same actual argument is associated with a dummy argument with
676 @code{INTENT(IN)} and a dummy argument with @code{INTENT(OUT)} in a call
677 with an explicit interface.
679 The following example will trigger the warning.
683 integer, intent(in) :: a
684 integer, intent(out) :: b
693 @opindex @code{Wampersand}
694 @cindex warnings, ampersand
696 Warn about missing ampersand in continued character constants. The warning is
697 given with @option{-Wampersand}, @option{-pedantic}, @option{-std=f95},
698 @option{-std=f2003} and @option{-std=f2008}. Note: With no ampersand
699 given in a continued character constant, GNU Fortran assumes continuation
700 at the first non-comment, non-whitespace character after the ampersand
701 that initiated the continuation.
703 @item -Warray-temporaries
704 @opindex @code{Warray-temporaries}
705 @cindex warnings, array temporaries
706 Warn about array temporaries generated by the compiler. The information
707 generated by this warning is sometimes useful in optimization, in order to
708 avoid such temporaries.
710 @item -Wcharacter-truncation
711 @opindex @code{Wcharacter-truncation}
712 @cindex warnings, character truncation
713 Warn when a character assignment will truncate the assigned string.
715 @item -Wline-truncation
716 @opindex @code{Wline-truncation}
717 @cindex warnings, line truncation
718 Warn when a source code line will be truncated.
721 @opindex @code{Wconversion}
722 @cindex warnings, conversion
724 Warn about implicit conversions between different types.
726 @item -Wimplicit-interface
727 @opindex @code{Wimplicit-interface}
728 @cindex warnings, implicit interface
729 Warn if a procedure is called without an explicit interface.
730 Note this only checks that an explicit interface is present. It does not
731 check that the declared interfaces are consistent across program units.
733 @item -Wintrinsics-std
734 @opindex @code{Wintrinsics-std}
735 @cindex warnings, non-standard intrinsics
736 @cindex warnings, intrinsics of other standards
737 Warn if @command{gfortran} finds a procedure named like an intrinsic not
738 available in the currently selected standard (with @option{-std}) and treats
739 it as @code{EXTERNAL} procedure because of this. @option{-fall-intrinsics} can
740 be used to never trigger this behaviour and always link to the intrinsic
741 regardless of the selected standard.
744 @opindex @code{Wsurprising}
745 @cindex warnings, suspicious code
746 Produce a warning when ``suspicious'' code constructs are encountered.
747 While technically legal these usually indicate that an error has been made.
749 This currently produces a warning under the following circumstances:
753 An INTEGER SELECT construct has a CASE that can never be matched as its
754 lower value is greater than its upper value.
757 A LOGICAL SELECT construct has three CASE statements.
760 A TRANSFER specifies a source that is shorter than the destination.
764 @opindex @code{Wtabs}
765 @cindex warnings, tabs
767 By default, tabs are accepted as whitespace, but tabs are not members
768 of the Fortran Character Set. For continuation lines, a tab followed
769 by a digit between 1 and 9 is supported. @option{-Wno-tabs} will cause
770 a warning to be issued if a tab is encountered. Note, @option{-Wno-tabs}
771 is active for @option{-pedantic}, @option{-std=f95}, @option{-std=f2003},
772 @option{-std=f2008} and @option{-Wall}.
775 @opindex @code{Wunderflow}
776 @cindex warnings, underflow
778 Produce a warning when numerical constant expressions are
779 encountered, which yield an UNDERFLOW during compilation.
781 @item -Wintrinsic-shadow
782 @opindex @code{Wintrinsic-shadow}
783 @cindex warnings, intrinsic
785 Warn if a user-defined procedure or module procedure has the same name as an
786 intrinsic; in this case, an explicit interface or @code{EXTERNAL} or
787 @code{INTRINSIC} declaration might be needed to get calls later resolved to
788 the desired intrinsic/procedure.
790 @item -Wunused-parameter
791 @opindex @code{Wunused-parameter}
792 @cindex warnings, unused parameter
793 @cindex unused parameter
794 Contrary to @command{gcc}'s meaning of @option{-Wunused-parameter},
795 @command{gfortran}'s implementation of this option does not warn
796 about unused dummy arguments, but about unused @code{PARAMETER} values.
797 @option{-Wunused-parameter} is not included in @option{-Wall} but is
798 implied by @option{-Wall -Wextra}.
801 @opindex @code{Werror}
802 @cindex warnings, to errors
803 Turns all warnings into errors.
806 @xref{Error and Warning Options,,Options to Request or Suppress Errors and
807 Warnings, gcc,Using the GNU Compiler Collection (GCC)}, for information on
808 more options offered by the GBE shared by @command{gfortran}, @command{gcc}
809 and other GNU compilers.
811 Some of these have no effect when compiling programs written in Fortran.
813 @node Debugging Options
814 @section Options for debugging your program or GNU Fortran
815 @cindex options, debugging
816 @cindex debugging information options
818 GNU Fortran has various special options that are used for debugging
819 either your program or the GNU Fortran compiler.
822 @item -fdump-parse-tree
823 @opindex @code{fdump-parse-tree}
824 Output the internal parse tree before starting code generation. Only
825 really useful for debugging the GNU Fortran compiler itself.
827 @item -ffpe-trap=@var{list}
828 @opindex @code{ffpe-trap=}@var{list}
829 Specify a list of IEEE exceptions when a Floating Point Exception
830 (FPE) should be raised. On most systems, this will result in a SIGFPE
831 signal being sent and the program being interrupted, producing a core
832 file useful for debugging. @var{list} is a (possibly empty) comma-separated
833 list of the following IEEE exceptions: @samp{invalid} (invalid floating
834 point operation, such as @code{SQRT(-1.0)}), @samp{zero} (division by
835 zero), @samp{overflow} (overflow in a floating point operation),
836 @samp{underflow} (underflow in a floating point operation),
837 @samp{precision} (loss of precision during operation) and @samp{denormal}
838 (operation produced a denormal value).
840 Some of the routines in the Fortran runtime library, like
841 @samp{CPU_TIME}, are likely to to trigger floating point exceptions when
842 @code{ffpe-trap=precision} is used. For this reason, the use of
843 @code{ffpe-trap=precision} is not recommended.
846 @opindex @code{fbacktrace}
849 Specify that, when a runtime error is encountered or a deadly signal is
850 emitted (segmentation fault, illegal instruction, bus error or
851 floating-point exception), the Fortran runtime
852 library should output a backtrace of the error. This option
853 only has influence for compilation of the Fortran main program.
857 @opindex @code{fdump-core}
858 Request that a core-dump file is written to disk when a runtime error
859 is encountered on systems that support core dumps. This option is
860 only effective for the compilation of the Fortran main program.
863 @xref{Debugging Options,,Options for Debugging Your Program or GCC,
864 gcc,Using the GNU Compiler Collection (GCC)}, for more information on
867 @node Directory Options
868 @section Options for directory search
869 @cindex directory, options
870 @cindex options, directory search
872 @cindex INCLUDE directive
873 @cindex directive, INCLUDE
874 These options affect how GNU Fortran searches
875 for files specified by the @code{INCLUDE} directive and where it searches
876 for previously compiled modules.
878 It also affects the search paths used by @command{cpp} when used to preprocess
883 @opindex @code{I}@var{dir}
884 @cindex directory, search paths for inclusion
885 @cindex inclusion, directory search paths for
886 @cindex search paths, for included files
887 @cindex paths, search
888 @cindex module search path
889 These affect interpretation of the @code{INCLUDE} directive
890 (as well as of the @code{#include} directive of the @command{cpp}
893 Also note that the general behavior of @option{-I} and
894 @code{INCLUDE} is pretty much the same as of @option{-I} with
895 @code{#include} in the @command{cpp} preprocessor, with regard to
896 looking for @file{header.gcc} files and other such things.
898 This path is also used to search for @file{.mod} files when previously
899 compiled modules are required by a @code{USE} statement.
901 @xref{Directory Options,,Options for Directory Search,
902 gcc,Using the GNU Compiler Collection (GCC)}, for information on the
907 @opindex @code{J}@var{dir}
908 @opindex @code{M}@var{dir}
909 @cindex paths, search
910 @cindex module search path
911 This option specifies where to put @file{.mod} files for compiled modules.
912 It is also added to the list of directories to searched by an @code{USE}
915 The default is the current directory.
917 @option{-M} is deprecated to avoid conflicts with existing GCC options.
919 @item -fintrinsic-modules-path @var{dir}
920 @opindex @code{fintrinsic-modules-path} @var{dir}
921 @cindex paths, search
922 @cindex module search path
923 This option specifies the location of pre-compiled intrinsic modules, if
924 they are not in the default location expected by the compiler.
928 @section Influencing the linking step
929 @cindex options, linking
930 @cindex linking, static
932 These options come into play when the compiler links object files into an
933 executable output file. They are meaningless if the compiler is not doing
937 @item -static-libgfortran
938 @opindex @code{static-libgfortran}
939 On systems that provide @file{libgfortran} as a shared and a static
940 library, this option forces the use of the static version. If no
941 shared version of @file{libgfortran} was built when the compiler was
942 configured, this option has no effect.
946 @node Runtime Options
947 @section Influencing runtime behavior
948 @cindex options, runtime
950 These options affect the runtime behavior of programs compiled with GNU Fortran.
952 @item -fconvert=@var{conversion}
953 @opindex @code{fconvert=}@var{conversion}
954 Specify the representation of data for unformatted files. Valid
955 values for conversion are: @samp{native}, the default; @samp{swap},
956 swap between big- and little-endian; @samp{big-endian}, use big-endian
957 representation for unformatted files; @samp{little-endian}, use little-endian
958 representation for unformatted files.
960 @emph{This option has an effect only when used in the main program.
961 The @code{CONVERT} specifier and the GFORTRAN_CONVERT_UNIT environment
962 variable override the default specified by @option{-fconvert}.}
965 @item -fno-range-check
966 @opindex @code{-fno-range-check}
967 Disable range checking of input values during integer @code{READ} operations.
968 For example, GNU Fortran will give an error if an input value is
969 outside of the relevant range of [@code{-HUGE()}:@code{HUGE()}]. In other words,
970 with @code{INTEGER (kind=4) :: i} , attempting to read @math{-2147483648} will
971 give an error unless @option{-fno-range-check} is given.
974 @item -frecord-marker=@var{length}
975 @opindex @code{frecord-marker=}@var{length}
976 Specify the length of record markers for unformatted files.
977 Valid values for @var{length} are 4 and 8. Default is 4.
978 @emph{This is different from previous versions of @command{gfortran}},
979 which specified a default record marker length of 8 on most
980 systems. If you want to read or write files compatible
981 with earlier versions of @command{gfortran}, use @option{-frecord-marker=8}.
983 @item -fmax-subrecord-length=@var{length}
984 @opindex @code{fmax-subrecord-length=}@var{length}
985 Specify the maximum length for a subrecord. The maximum permitted
986 value for length is 2147483639, which is also the default. Only
987 really useful for use by the gfortran testsuite.
990 @opindex @code{fsign-zero}
991 When writing zero values, show the negative sign if the sign bit is set.
992 @code{fno-sign-zero} does not print the negative sign of zero values for
993 compatibility with F77. Default behavior is to show the negative sign.
996 @node Code Gen Options
997 @section Options for code generation conventions
998 @cindex code generation, conventions
999 @cindex options, code generation
1000 @cindex options, run-time
1002 These machine-independent options control the interface conventions
1003 used in code generation.
1005 Most of them have both positive and negative forms; the negative form
1006 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
1007 one of the forms is listed---the one which is not the default. You
1008 can figure out the other form by either removing @option{no-} or adding
1012 @item -fno-automatic
1013 @opindex @code{fno-automatic}
1014 @cindex @code{SAVE} statement
1015 @cindex statement, @code{SAVE}
1016 Treat each program unit (except those marked as RECURSIVE) as if the
1017 @code{SAVE} statement were specified for every local variable and array
1018 referenced in it. Does not affect common blocks. (Some Fortran compilers
1019 provide this option under the name @option{-static} or @option{-save}.)
1020 The default, which is @option{-fautomatic}, uses the stack for local
1021 variables smaller than the value given by @option{-fmax-stack-var-size}.
1022 Use the option @option{-frecursive} to use no static memory.
1026 @cindex calling convention
1027 @cindex @command{f2c} calling convention
1028 @cindex @command{g77} calling convention
1029 @cindex libf2c calling convention
1030 Generate code designed to be compatible with code generated
1031 by @command{g77} and @command{f2c}.
1033 The calling conventions used by @command{g77} (originally implemented
1034 in @command{f2c}) require functions that return type
1035 default @code{REAL} to actually return the C type @code{double}, and
1036 functions that return type @code{COMPLEX} to return the values via an
1037 extra argument in the calling sequence that points to where to
1038 store the return value. Under the default GNU calling conventions, such
1039 functions simply return their results as they would in GNU
1040 C---default @code{REAL} functions return the C type @code{float}, and
1041 @code{COMPLEX} functions return the GNU C type @code{complex}.
1042 Additionally, this option implies the @option{-fsecond-underscore}
1043 option, unless @option{-fno-second-underscore} is explicitly requested.
1045 This does not affect the generation of code that interfaces with
1046 the @command{libgfortran} library.
1048 @emph{Caution:} It is not a good idea to mix Fortran code compiled with
1049 @option{-ff2c} with code compiled with the default @option{-fno-f2c}
1050 calling conventions as, calling @code{COMPLEX} or default @code{REAL}
1051 functions between program parts which were compiled with different
1052 calling conventions will break at execution time.
1054 @emph{Caution:} This will break code which passes intrinsic functions
1055 of type default @code{REAL} or @code{COMPLEX} as actual arguments, as
1056 the library implementations use the @option{-fno-f2c} calling conventions.
1058 @item -fno-underscoring
1059 @opindex @code{fno-underscoring}
1061 @cindex symbol names, underscores
1062 @cindex transforming symbol names
1063 @cindex symbol names, transforming
1064 Do not transform names of entities specified in the Fortran
1065 source file by appending underscores to them.
1067 With @option{-funderscoring} in effect, GNU Fortran appends one
1068 underscore to external names with no underscores. This is done to ensure
1069 compatibility with code produced by many UNIX Fortran compilers.
1071 @emph{Caution}: The default behavior of GNU Fortran is
1072 incompatible with @command{f2c} and @command{g77}, please use the
1073 @option{-ff2c} option if you want object files compiled with
1074 GNU Fortran to be compatible with object code created with these
1077 Use of @option{-fno-underscoring} is not recommended unless you are
1078 experimenting with issues such as integration of GNU Fortran into
1079 existing system environments (vis-@`{a}-vis existing libraries, tools,
1082 For example, with @option{-funderscoring}, and assuming other defaults like
1083 @option{-fcase-lower} and that @code{j()} and @code{max_count()} are
1084 external functions while @code{my_var} and @code{lvar} are local variables,
1087 I = J() + MAX_COUNT (MY_VAR, LVAR)
1090 is implemented as something akin to:
1092 i = j_() + max_count__(&my_var__, &lvar);
1095 With @option{-fno-underscoring}, the same statement is implemented as:
1098 i = j() + max_count(&my_var, &lvar);
1101 Use of @option{-fno-underscoring} allows direct specification of
1102 user-defined names while debugging and when interfacing GNU Fortran
1103 code with other languages.
1105 Note that just because the names match does @emph{not} mean that the
1106 interface implemented by GNU Fortran for an external name matches the
1107 interface implemented by some other language for that same name.
1108 That is, getting code produced by GNU Fortran to link to code produced
1109 by some other compiler using this or any other method can be only a
1110 small part of the overall solution---getting the code generated by
1111 both compilers to agree on issues other than naming can require
1112 significant effort, and, unlike naming disagreements, linkers normally
1113 cannot detect disagreements in these other areas.
1115 Also, note that with @option{-fno-underscoring}, the lack of appended
1116 underscores introduces the very real possibility that a user-defined
1117 external name will conflict with a name in a system library, which
1118 could make finding unresolved-reference bugs quite difficult in some
1119 cases---they might occur at program run time, and show up only as
1120 buggy behavior at run time.
1122 In future versions of GNU Fortran we hope to improve naming and linking
1123 issues so that debugging always involves using the names as they appear
1124 in the source, even if the names as seen by the linker are mangled to
1125 prevent accidental linking between procedures with incompatible
1128 @item -fsecond-underscore
1129 @opindex @code{fsecond-underscore}
1131 @cindex symbol names, underscores
1132 @cindex transforming symbol names
1133 @cindex symbol names, transforming
1134 @cindex @command{f2c} calling convention
1135 @cindex @command{g77} calling convention
1136 @cindex libf2c calling convention
1137 By default, GNU Fortran appends an underscore to external
1138 names. If this option is used GNU Fortran appends two
1139 underscores to names with underscores and one underscore to external names
1140 with no underscores. GNU Fortran also appends two underscores to
1141 internal names with underscores to avoid naming collisions with external
1144 This option has no effect if @option{-fno-underscoring} is
1145 in effect. It is implied by the @option{-ff2c} option.
1147 Otherwise, with this option, an external name such as @code{MAX_COUNT}
1148 is implemented as a reference to the link-time external symbol
1149 @code{max_count__}, instead of @code{max_count_}. This is required
1150 for compatibility with @command{g77} and @command{f2c}, and is implied
1151 by use of the @option{-ff2c} option.
1153 @item -fbounds-check
1154 @opindex @code{fbounds-check}
1155 @cindex array, bounds checking
1156 @cindex bounds checking
1157 @cindex range checking
1158 @cindex subscript checking
1159 @cindex checking subscripts
1160 Enable generation of run-time checks for array subscripts
1161 and against the declared minimum and maximum values. It also
1162 checks array indices for assumed and deferred
1163 shape arrays against the actual allocated bounds.
1165 Some checks require that @option{-fbounds-check} is set for
1166 the compilation of the main program.
1168 In the future this may also include other forms of checking, e.g., checking
1169 substring references.
1172 @item fcheck-array-temporaries
1173 @opindex @code{fcheck-array-temporaries}
1174 @cindex checking array temporaries
1175 Warns at run time when for passing an actual argument a temporary array
1176 had to be generated. The information generated by this warning is
1177 sometimes useful in optimization, in order to avoid such temporaries.
1179 Note: The warning is only printed once per location.
1182 @item -fmax-stack-var-size=@var{n}
1183 @opindex @code{fmax-stack-var-size}
1184 This option specifies the size in bytes of the largest array that will be put
1185 on the stack; if the size is exceeded static memory is used (except in
1186 procedures marked as RECURSIVE). Use the option @option{-frecursive} to
1187 allow for recursive procedures which do not have a RECURSIVE attribute or
1188 for parallel programs. Use @option{-fno-automatic} to never use the stack.
1190 This option currently only affects local arrays declared with constant
1191 bounds, and may not apply to all character variables.
1192 Future versions of GNU Fortran may improve this behavior.
1194 The default value for @var{n} is 32768.
1196 @item -fpack-derived
1197 @opindex @code{fpack-derived}
1198 @cindex structure packing
1199 This option tells GNU Fortran to pack derived type members as closely as
1200 possible. Code compiled with this option is likely to be incompatible
1201 with code compiled without this option, and may execute slower.
1203 @item -frepack-arrays
1204 @opindex @code{frepack-arrays}
1205 @cindex repacking arrays
1206 In some circumstances GNU Fortran may pass assumed shape array
1207 sections via a descriptor describing a noncontiguous area of memory.
1208 This option adds code to the function prologue to repack the data into
1209 a contiguous block at runtime.
1211 This should result in faster accesses to the array. However it can introduce
1212 significant overhead to the function call, especially when the passed data
1216 @opindex @code{fshort-enums}
1217 This option is provided for interoperability with C code that was
1218 compiled with the @option{-fshort-enums} option. It will make
1219 GNU Fortran choose the smallest @code{INTEGER} kind a given
1220 enumerator set will fit in, and give all its enumerators this kind.
1222 @item -fexternal-blas
1223 @opindex @code{fexternal-blas}
1224 This option will make @command{gfortran} generate calls to BLAS functions
1225 for some matrix operations like @code{MATMUL}, instead of using our own
1226 algorithms, if the size of the matrices involved is larger than a given
1227 limit (see @option{-fblas-matmul-limit}). This may be profitable if an
1228 optimized vendor BLAS library is available. The BLAS library will have
1229 to be specified at link time.
1231 @item -fblas-matmul-limit=@var{n}
1232 @opindex @code{fblas-matmul-limit}
1233 Only significant when @option{-fexternal-blas} is in effect.
1234 Matrix multiplication of matrices with size larger than (or equal to) @var{n}
1235 will be performed by calls to BLAS functions, while others will be
1236 handled by @command{gfortran} internal algorithms. If the matrices
1237 involved are not square, the size comparison is performed using the
1238 geometric mean of the dimensions of the argument and result matrices.
1240 The default value for @var{n} is 30.
1243 @opindex @code{frecursive}
1244 Allow indirect recursion by forcing all local arrays to be allocated
1245 on the stack. This flag cannot be used together with
1246 @option{-fmax-stack-var-size=} or @option{-fno-automatic}.
1248 @item -finit-local-zero
1249 @item -finit-integer=@var{n}
1250 @item -finit-real=@var{<zero|inf|-inf|nan>}
1251 @item -finit-logical=@var{<true|false>}
1252 @item -finit-character=@var{n}
1253 @opindex @code{finit-local-zero}
1254 @opindex @code{finit-integer}
1255 @opindex @code{finit-real}
1256 @opindex @code{finit-logical}
1257 @opindex @code{finit-character}
1258 The @option{-finit-local-zero} option instructs the compiler to
1259 initialize local @code{INTEGER}, @code{REAL}, and @code{COMPLEX}
1260 variables to zero, @code{LOGICAL} variables to false, and
1261 @code{CHARACTER} variables to a string of null bytes. Finer-grained
1262 initialization options are provided by the
1263 @option{-finit-integer=@var{n}},
1264 @option{-finit-real=@var{<zero|inf|-inf|nan>}} (which also initializes
1265 the real and imaginary parts of local @code{COMPLEX} variables),
1266 @option{-finit-logical=@var{<true|false>}}, and
1267 @option{-finit-character=@var{n}} (where @var{n} is an ASCII character
1268 value) options. These options do not initialize components of derived
1269 type variables, nor do they initialize variables that appear in an
1270 @code{EQUIVALENCE} statement. (This limitation may be removed in
1273 Note that the @option{-finit-real=nan} option initializes @code{REAL}
1274 and @code{COMPLEX} variables with a quiet NaN.
1277 @xref{Code Gen Options,,Options for Code Generation Conventions,
1278 gcc,Using the GNU Compiler Collection (GCC)}, for information on more options
1280 shared by @command{gfortran}, @command{gcc}, and other GNU compilers.
1285 @node Environment Variables
1286 @section Environment variables affecting @command{gfortran}
1287 @cindex environment variable
1289 @c man begin ENVIRONMENT
1291 The @command{gfortran} compiler currently does not make use of any environment
1292 variables to control its operation above and beyond those
1293 that affect the operation of @command{gcc}.
1295 @xref{Environment Variables,,Environment Variables Affecting GCC,
1296 gcc,Using the GNU Compiler Collection (GCC)}, for information on environment
1299 @xref{Runtime}, for environment variables that affect the
1300 run-time behavior of programs compiled with GNU Fortran.