1 @c Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009
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, 2008, 2009
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 ``Funding Free Software'', the Front-Cover
15 Texts being (a) (see below), and with the Back-Cover Texts being (b)
16 (see below). A copy of the license is included in the gfdl(7) man page.
18 (a) The FSF's Front-Cover Text is:
22 (b) The FSF's Back-Cover Text is:
24 You have freedom to copy and modify this GNU Manual, like GNU
25 software. Copies published by the Free Software Foundation raise
26 funds for GNU development.
28 @c Set file name and title for the man page.
30 @settitle GNU Fortran compiler.
32 gfortran [@option{-c}|@option{-S}|@option{-E}]
33 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
34 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
35 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
36 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
37 [@option{-f}@var{option}@dots{}]
38 [@option{-m}@var{machine-option}@dots{}]
39 [@option{-o} @var{outfile}] @var{infile}@dots{}
41 Only the most useful options are listed here; see below for the
45 gpl(7), gfdl(7), fsf-funding(7),
46 cpp(1), gcov(1), gcc(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
47 and the Info entries for @file{gcc}, @file{cpp}, @file{gfortran}, @file{as},
48 @file{ld}, @file{binutils} and @file{gdb}.
51 For instructions on reporting bugs, see
55 See the Info entry for @command{gfortran} for contributors to GCC and
60 @node Invoking GNU Fortran
61 @chapter GNU Fortran Command Options
62 @cindex GNU Fortran command options
63 @cindex command options
64 @cindex options, @command{gfortran} command
66 @c man begin DESCRIPTION
68 The @command{gfortran} command supports all the options supported by the
69 @command{gcc} command. Only options specific to GNU Fortran are documented here.
71 @xref{Invoking GCC,,GCC Command Options,gcc,Using the GNU Compiler
72 Collection (GCC)}, for information
73 on the non-Fortran-specific aspects of the @command{gcc} command (and,
74 therefore, the @command{gfortran} command).
76 @cindex options, negative forms
77 All GCC and GNU Fortran options
78 are accepted both by @command{gfortran} and by @command{gcc}
79 (as well as any other drivers built at the same time,
80 such as @command{g++}),
81 since adding GNU Fortran to the GCC distribution
82 enables acceptance of GNU Fortran options
83 by all of the relevant drivers.
85 In some cases, options have positive and negative forms;
86 the negative form of @option{-ffoo} would be @option{-fno-foo}.
87 This manual documents only one of these two forms, whichever
88 one is not the default.
92 * Option Summary:: Brief list of all @command{gfortran} options,
94 * Fortran Dialect Options:: Controlling the variant of Fortran language
96 * Preprocessing Options:: Enable and customize preprocessing.
97 * Error and Warning Options:: How picky should the compiler be?
98 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
99 * Directory Options:: Where to find module files
100 * Link Options :: Influencing the linking step
101 * Runtime Options:: Influencing runtime behavior
102 * Code Gen Options:: Specifying conventions for function calls, data layout
104 * Environment Variables:: Environment variables that affect @command{gfortran}.
108 @section Option summary
112 Here is a summary of all the options specific to GNU Fortran, grouped
113 by type. Explanations are in the following sections.
116 @item Fortran Language Options
117 @xref{Fortran Dialect Options,,Options controlling Fortran dialect}.
118 @gccoptlist{-fall-intrinsics -ffree-form -fno-fixed-form @gol
119 -fdollar-ok -fimplicit-none -fmax-identifier-length @gol
120 -std=@var{std} -fd-lines-as-code -fd-lines-as-comments @gol
121 -ffixed-line-length-@var{n} -ffixed-line-length-none @gol
122 -ffree-line-length-@var{n} -ffree-line-length-none @gol
123 -fdefault-double-8 -fdefault-integer-8 -fdefault-real-8 @gol
124 -fcray-pointer -fopenmp -fno-range-check -fbackslash -fmodule-private}
126 @item Preprocessing Options
127 @xref{Preprocessing Options,,Enable and customize preprocessing}.
128 @gccoptlist{-cpp -dD -dI -dM -dN -dU -fworking-directory @gol
129 -imultilib @var{dir} -iprefix @var{file} -isysroot @var{dir} @gol
130 -iquote -isystem @var{dir} -nocpp -nostdinc -undef @gol
131 -A@var{question}=@var{answer} -A-@var{question}@r{[}=@var{answer}@r{]} @gol
132 -C -CC -D@var{macro}@r{[}=@var{defn}@r{]} -U@var{macro} -H -P}
134 @item Error and Warning Options
135 @xref{Error and Warning Options,,Options to request or suppress errors
137 @gccoptlist{-fmax-errors=@var{n} @gol
138 -fsyntax-only -pedantic -pedantic-errors @gol
139 -Wall -Waliasing -Wampersand -Warray-bounds -Wcharacter-truncation @gol
140 -Wconversion -Wimplicit-interface -Wline-truncation -Wintrinsics-std @gol
141 -Wsurprising -Wno-tabs -Wunderflow -Wunused-parameter -Wintrinsics-shadow @gol
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} @gol
152 -fintrinsic-modules-path @var{dir}}
155 @xref{Link Options,,Options for influencing the linking step}.
156 @gccoptlist{-static-libgfortran}
158 @item Runtime Options
159 @xref{Runtime Options,,Options for influencing runtime behavior}.
160 @gccoptlist{-fconvert=@var{conversion} -fno-range-check
161 -frecord-marker=@var{length} @gol -fmax-subrecord-length=@var{length}
164 @item Code Generation Options
165 @xref{Code Gen Options,,Options for code generation conventions}.
166 @gccoptlist{-fno-automatic -ff2c -fno-underscoring @gol
167 -fwhole-file -fsecond-underscore @gol
168 -fbounds-check -fcheck-array-temporaries -fmax-array-constructor =@var{n} @gol
169 -fcheck=@var{<all|bounds|array-temps>}
170 -fmax-stack-var-size=@var{n} @gol
171 -fpack-derived -frepack-arrays -fshort-enums -fexternal-blas @gol
172 -fblas-matmul-limit=@var{n} -frecursive -finit-local-zero @gol
173 -finit-integer=@var{n} -finit-real=@var{<zero|inf|-inf|nan|snan>} @gol
174 -finit-logical=@var{<true|false>} -finit-character=@var{n} -fno-align-commons}
178 * Fortran Dialect Options:: Controlling the variant of Fortran language
180 * Preprocessing Options:: Enable and customize preprocessing.
181 * Error and Warning Options:: How picky should the compiler be?
182 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
183 * Directory Options:: Where to find module files
184 * Link Options :: Influencing the linking step
185 * Runtime Options:: Influencing runtime behavior
186 * Code Gen Options:: Specifying conventions for function calls, data layout
190 @node Fortran Dialect Options
191 @section Options controlling Fortran dialect
192 @cindex dialect options
193 @cindex language, dialect options
194 @cindex options, dialect
196 The following options control the details of the Fortran dialect
197 accepted by the compiler:
202 @opindex @code{ffree-form}
203 @opindex @code{fno-fixed-form}
204 @cindex options, fortran dialect
205 @cindex file format, free
206 @cindex file format, fixed
207 Specify the layout used by the source file. The free form layout
208 was introduced in Fortran 90. Fixed form was traditionally used in
209 older Fortran programs. When neither option is specified, the source
210 form is determined by the file extension.
212 @item -fall-intrinsics
213 @opindex @code{fall-intrinsics}
214 This option causes all intrinsic procedures (including the GNU-specific
215 extensions) to be accepted. This can be useful with @option{-std=f95} to
216 force standard-compliance but get access to the full range of intrinsics
217 available with @command{gfortran}. As a consequence, @option{-Wintrinsics-std}
218 will be ignored and no user-defined procedure with the same name as any
219 intrinsic will be called except when it is explicitly declared @code{EXTERNAL}.
221 @item -fd-lines-as-code
222 @item -fd-lines-as-comments
223 @opindex @code{fd-lines-as-code}
224 @opindex @code{fd-lines-as-comments}
225 Enable special treatment for lines beginning with @code{d} or @code{D}
226 in fixed form sources. If the @option{-fd-lines-as-code} option is
227 given they are treated as if the first column contained a blank. If the
228 @option{-fd-lines-as-comments} option is given, they are treated as
231 @item -fdefault-double-8
232 @opindex @code{fdefault-double-8}
233 Set the @code{DOUBLE PRECISION} type to an 8 byte wide type. If
234 @option{-fdefault-real-8} is given, @code{DOUBLE PRECISION} would
235 instead be promoted to 16 bytes if possible, and @option{-fdefault-double-8}
236 can be used to prevent this. The kind of real constants like @code{1.d0} will
237 not be changed by @option{-fdefault-real-8} though, so also
238 @option{-fdefault-double-8} does not affect it.
240 @item -fdefault-integer-8
241 @opindex @code{fdefault-integer-8}
242 Set the default integer and logical types to an 8 byte wide type.
243 Do nothing if this is already the default. This option also affects
244 the kind of integer constants like @code{42}.
246 @item -fdefault-real-8
247 @opindex @code{fdefault-real-8}
248 Set the default real type to an 8 byte wide type.
249 Do nothing if this is already the default. This option also affects
250 the kind of non-double real constants like @code{1.0}, and does promote
251 the default width of @code{DOUBLE PRECISION} to 16 bytes if possible, unless
252 @code{-fdefault-double-8} is given, too.
255 @opindex @code{fdollar-ok}
258 @cindex character set
259 Allow @samp{$} as a valid non-first character in a symbol name. Symbols
260 that start with @samp{$} are rejected since it is unclear which rules to
261 apply to implicit typing as different vedors implement different rules.
264 @opindex @code{backslash}
266 @cindex escape characters
267 Change the interpretation of backslashes in string literals from a single
268 backslash character to ``C-style'' escape characters. The following
269 combinations are expanded @code{\a}, @code{\b}, @code{\f}, @code{\n},
270 @code{\r}, @code{\t}, @code{\v}, @code{\\}, and @code{\0} to the ASCII
271 characters alert, backspace, form feed, newline, carriage return,
272 horizontal tab, vertical tab, backslash, and NUL, respectively.
273 Additionally, @code{\x}@var{nn}, @code{\u}@var{nnnn} and
274 @code{\U}@var{nnnnnnnn} (where each @var{n} is a hexadecimal digit) are
275 translated into the Unicode characters corresponding to the specified code
276 points. All other combinations of a character preceded by \ are
279 @item -fmodule-private
280 @opindex @code{fmodule-private}
281 @cindex module entities
283 Set the default accessibility of module entities to @code{PRIVATE}.
284 Use-associated entities will not be accessible unless they are explicitly
285 declared as @code{PUBLIC}.
287 @item -ffixed-line-length-@var{n}
288 @opindex @code{ffixed-line-length-}@var{n}
289 @cindex file format, fixed
290 Set column after which characters are ignored in typical fixed-form
291 lines in the source file, and through which spaces are assumed (as
292 if padded to that length) after the ends of short fixed-form lines.
294 Popular values for @var{n} include 72 (the
295 standard and the default), 80 (card image), and 132 (corresponding
296 to ``extended-source'' options in some popular compilers).
297 @var{n} may also be @samp{none}, meaning that the entire line is meaningful
298 and that continued character constants never have implicit spaces appended
299 to them to fill out the line.
300 @option{-ffixed-line-length-0} means the same thing as
301 @option{-ffixed-line-length-none}.
303 @item -ffree-line-length-@var{n}
304 @opindex @code{ffree-line-length-}@var{n}
305 @cindex file format, free
306 Set column after which characters are ignored in typical free-form
307 lines in the source file. The default value is 132.
308 @var{n} may be @samp{none}, meaning that the entire line is meaningful.
309 @option{-ffree-line-length-0} means the same thing as
310 @option{-ffree-line-length-none}.
312 @item -fmax-identifier-length=@var{n}
313 @opindex @code{fmax-identifier-length=}@var{n}
314 Specify the maximum allowed identifier length. Typical values are
315 31 (Fortran 95) and 63 (Fortran 2003 and Fortran 2008).
317 @item -fimplicit-none
318 @opindex @code{fimplicit-none}
319 Specify that no implicit typing is allowed, unless overridden by explicit
320 @code{IMPLICIT} statements. This is the equivalent of adding
321 @code{implicit none} to the start of every procedure.
324 @opindex @code{fcray-pointer}
325 Enable the Cray pointer extension, which provides C-like pointer
329 @opindex @code{fopenmp}
331 Enable the OpenMP extensions. This includes OpenMP @code{!$omp} directives
333 and @code{c$omp}, @code{*$omp} and @code{!$omp} directives in fixed form,
334 @code{!$} conditional compilation sentinels in free form
335 and @code{c$}, @code{*$} and @code{!$} sentinels in fixed form,
336 and when linking arranges for the OpenMP runtime library to be linked
337 in. The option @option{-fopenmp} implies @option{-frecursive}.
339 @item -fno-range-check
340 @opindex @code{frange-check}
341 Disable range checking on results of simplification of constant
342 expressions during compilation. For example, GNU Fortran will give
343 an error at compile time when simplifying @code{a = 1. / 0}.
344 With this option, no error will be given and @code{a} will be assigned
345 the value @code{+Infinity}. If an expression evaluates to a value
346 outside of the relevant range of [@code{-HUGE()}:@code{HUGE()}],
347 then the expression will be replaced by @code{-Inf} or @code{+Inf}
349 Similarly, @code{DATA i/Z'FFFFFFFF'/} will result in an integer overflow
350 on most systems, but with @option{-fno-range-check} the value will
351 ``wrap around'' and @code{i} will be initialized to @math{-1} instead.
354 @opindex @code{std=}@var{std} option
355 Specify the standard to which the program is expected to conform, which
356 may be one of @samp{f95}, @samp{f2003}, @samp{f2008}, @samp{gnu}, or
357 @samp{legacy}. The default value for @var{std} is @samp{gnu}, which
358 specifies a superset of the Fortran 95 standard that includes all of the
359 extensions supported by GNU Fortran, although warnings will be given for
360 obsolete extensions not recommended for use in new code. The
361 @samp{legacy} value is equivalent but without the warnings for obsolete
362 extensions, and may be useful for old non-standard programs. The
363 @samp{f95}, @samp{f2003} and @samp{f2008} values specify strict
364 conformance to the Fortran 95, Fortran 2003 and Fortran 2008 standards,
365 respectively; errors are given for all extensions beyond the relevant
366 language standard, and warnings are given for the Fortran 77 features
367 that are permitted but obsolescent in later standards.
371 @node Preprocessing Options
372 @section Enable and customize preprocessing
374 @cindex options, preprocessor
377 Preprocessor related options. See section
378 @ref{Preprocessing and conditional compilation} for more detailed
379 information on preprocessing in @command{gfortran}.
386 @cindex preprocessor, enable
387 @cindex preprocessor, disable
388 Enable preprocessing. The preprocessor is automatically invoked if
389 the file extension is @file{.fpp}, @file{.FPP}, @file{.F}, @file{.FOR},
390 @file{.FTN}, @file{.F90}, @file{.F95}, @file{.F03} or @file{.F08}. Use
391 this option to manually enable preprocessing of any kind of Fortran file.
393 To disable preprocessing of files with any of the above listed extensions,
394 use the negative form: @option{-nocpp}.
396 The preprocessor is run in traditional mode, be aware that any
397 restrictions of the file-format, e.g. fixed-form line width,
398 apply for preprocessed output as well.
402 @cindex preprocessor, debugging
403 @cindex debugging, preprocessor
404 Instead of the normal output, generate a list of @code{'#define'}
405 directives for all the macros defined during the execution of the
406 preprocessor, including predefined macros. This gives you a way
407 of finding out what is predefined in your version of the preprocessor.
408 Assuming you have no file @file{foo.f90}, the command
410 touch foo.f90; gfortran -cpp -dM foo.f90
412 will show all the predefined macros.
416 @cindex preprocessor, debugging
417 @cindex debugging, preprocessor
418 Like @option{-dM} except in two respects: it does not include the
419 predefined macros, and it outputs both the @code{#define} directives
420 and the result of preprocessing. Both kinds of output go to the
421 standard output file.
425 @cindex preprocessor, debugging
426 @cindex debugging, preprocessor
427 Like @option{-dD}, but emit only the macro names, not their expansions.
431 @cindex preprocessor, debugging
432 @cindex debugging, preprocessor
433 Like @option{dD} except that only macros that are expanded, or whose
434 definedness is tested in preprocessor directives, are output; the
435 output is delayed until the use or test of the macro; and @code{'#undef'}
436 directives are also output for macros tested but undefined at the time.
440 @cindex preprocessor, debugging
441 @cindex debugging, preprocessor
442 Output @code{'#include'} directives in addition to the result
445 @item -fworking-directory
446 @opindex @code{fworking-directory}
447 @cindex preprocessor, working directory
448 Enable generation of linemarkers in the preprocessor output that will
449 let the compiler know the current working directory at the time of
450 preprocessing. When this option is enabled, the preprocessor will emit,
451 after the initial linemarker, a second linemarker with the current
452 working directory followed by two slashes. GCC will use this directory,
453 when it's present in the preprocessed input, as the directory emitted
454 as the current working directory in some debugging information formats.
455 This option is implicitly enabled if debugging information is enabled,
456 but this can be inhibited with the negated form
457 @option{-fno-working-directory}. If the @option{-P} flag is present
458 in the command line, this option has no effect, since no @code{#line}
459 directives are emitted whatsoever.
461 @item -idirafter @var{dir}
462 @opindex @code{idirafter @var{dir}}
463 @cindex preprocessing, include path
464 Search @var{dir} for include files, but do it after all directories
465 specified with @option{-I} and the standard system directories have
466 been exhausted. @var{dir} is treated as a system include directory.
467 If dir begins with @code{=}, then the @code{=} will be replaced by
468 the sysroot prefix; see @option{--sysroot} and @option{-isysroot}.
470 @item -imultilib @var{dir}
471 @opindex @code{imultilib @var{dir}}
472 @cindex preprocessing, include path
473 Use @var{dir} as a subdirectory of the directory containing target-specific
476 @item -iprefix @var{prefix}
477 @opindex @code{iprefix @var{prefix}}
478 @cindex preprocessing, include path
479 Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix}
480 options. If the @var{prefix} represents a directory, you should include
481 the final @code{'/'}.
483 @item -isysroot @var{dir}
484 @opindex @code{isysroot @var{dir}}
485 @cindex preprocessing, include path
486 This option is like the @option{--sysroot} option, but applies only to
487 header files. See the @option{--sysroot} option for more information.
489 @item -iquote @var{dir}
490 @opindex @code{iquote @var{dir}}
491 @cindex preprocessing, include path
492 Search @var{dir} only for header files requested with @code{#include "file"};
493 they are not searched for @code{#include <file>}, before all directories
494 specified by @option{-I} and before the standard system directories. If
495 @var{dir} begins with @code{=}, then the @code{=} will be replaced by the
496 sysroot prefix; see @option{--sysroot} and @option{-isysroot}.
498 @item -isystem @var{dir}
499 @opindex @code{isystem @var{dir}}
500 @cindex preprocessing, include path
501 Search @var{dir} for header files, after all directories specified by
502 @option{-I} but before the standard system directories. Mark it as a
503 system directory, so that it gets the same special treatment as is
504 applied to the standard system directories. If @var{dir} begins with
505 @code{=}, then the @code{=} will be replaced by the sysroot prefix;
506 see @option{--sysroot} and @option{-isysroot}.
509 @opindex @code{nostdinc}
510 Do not search the standard system directories for header files. Only
511 the directories you have specified with @option{-I} options (and the
512 directory of the current file, if appropriate) are searched.
515 @opindex @code{undef}
516 Do not predefine any system-specific or GCC-specific macros.
517 The standard predefined macros remain defined.
519 @item -A@var{predicate}=@var{answer}
520 @opindex @code{A@var{predicate}=@var{answer}}
521 @cindex preprocessing, assertation
522 Make an assertion with the predicate @var{predicate} and answer @var{answer}.
523 This form is preferred to the older form -A predicate(answer), which is still
524 supported, because it does not use shell special characters.
526 @item -A-@var{predicate}=@var{answer}
527 @opindex @code{A-@var{predicate}=@var{answer}}
528 @cindex preprocessing, assertation
529 Cancel an assertion with the predicate @var{predicate} and answer @var{answer}.
533 @cindex preprocessing, keep comments
534 Do not discard comments. All comments are passed through to the output
535 file, except for comments in processed directives, which are deleted
536 along with the directive.
538 You should be prepared for side effects when using @option{-C}; it causes
539 the preprocessor to treat comments as tokens in their own right. For example,
540 comments appearing at the start of what would be a directive line have the
541 effect of turning that line into an ordinary source line, since the first
542 token on the line is no longer a @code{'#'}.
544 Warning: this currently handles C-Style comments only. The preprocessor
545 does not yet recognize Fortran-style comments.
549 @cindex preprocessing, keep comments
550 Do not discard comments, including during macro expansion. This is like
551 @option{-C}, except that comments contained within macros are also passed
552 through to the output file where the macro is expanded.
554 In addition to the side-effects of the @option{-C} option, the @option{-CC}
555 option causes all C++-style comments inside a macro to be converted to C-style
556 comments. This is to prevent later use of that macro from inadvertently
557 commenting out the remainder of the source line. The @option{-CC} option
558 is generally used to support lint comments.
560 Warning: this currently handles C- and C++-Style comments only. The
561 preprocessor does not yet recognize Fortran-style comments.
564 @opindex @code{D@var{name}}
565 @cindex preprocessing, define macros
566 Predefine name as a macro, with definition @code{1}.
568 @item -D@var{name}=@var{definition}
569 @opindex @code{D@var{name}=@var{definition}}
570 @cindex preprocessing, define macros
571 The contents of @var{definition} are tokenized and processed as if they
572 appeared during translation phase three in a @code{'#define'} directive.
573 In particular, the definition will be truncated by embedded newline
576 If you are invoking the preprocessor from a shell or shell-like program
577 you may need to use the shell's quoting syntax to protect characters such
578 as spaces that have a meaning in the shell syntax.
580 If you wish to define a function-like macro on the command line, write
581 its argument list with surrounding parentheses before the equals sign
582 (if any). Parentheses are meaningful to most shells, so you will need
583 to quote the option. With sh and csh, @code{-D'name(args...)=definition'}
586 @option{-D} and @option{-U} options are processed in the order they are
587 given on the command line. All -imacros file and -include file options
588 are processed after all -D and -U options.
592 Print the name of each header file used, in addition to other normal
593 activities. Each name is indented to show how deep in the @code{'#include'}
598 @cindex preprocessing, no linemarkers
599 Inhibit generation of linemarkers in the output from the preprocessor.
600 This might be useful when running the preprocessor on something that
601 is not C code, and will be sent to a program which might be confused
605 @opindex @code{U@var{name}}
606 @cindex preprocessing, undefine macros
607 Cancel any previous definition of @var{name}, either built in or provided
608 with a @option{-D} option.
612 @node Error and Warning Options
613 @section Options to request or suppress errors and warnings
614 @cindex options, warnings
615 @cindex options, errors
616 @cindex warnings, suppressing
617 @cindex messages, error
618 @cindex messages, warning
619 @cindex suppressing warnings
621 Errors are diagnostic messages that report that the GNU Fortran compiler
622 cannot compile the relevant piece of source code. The compiler will
623 continue to process the program in an attempt to report further errors
624 to aid in debugging, but will not produce any compiled output.
626 Warnings are diagnostic messages that report constructions which
627 are not inherently erroneous but which are risky or suggest there is
628 likely to be a bug in the program. Unless @option{-Werror} is specified,
629 they do not prevent compilation of the program.
631 You can request many specific warnings with options beginning @option{-W},
632 for example @option{-Wimplicit} to request warnings on implicit
633 declarations. Each of these specific warning options also has a
634 negative form beginning @option{-Wno-} to turn off warnings;
635 for example, @option{-Wno-implicit}. This manual lists only one of the
636 two forms, whichever is not the default.
638 These options control the amount and kinds of errors and warnings produced
642 @item -fmax-errors=@var{n}
643 @opindex @code{fmax-errors=}@var{n}
644 @cindex errors, limiting
645 Limits the maximum number of error messages to @var{n}, at which point
646 GNU Fortran bails out rather than attempting to continue processing the
647 source code. If @var{n} is 0, there is no limit on the number of error
651 @opindex @code{fsyntax-only}
652 @cindex syntax checking
653 Check the code for syntax errors, but don't actually compile it. This
654 will generate module files for each module present in the code, but no
658 @opindex @code{pedantic}
659 Issue warnings for uses of extensions to Fortran 95.
660 @option{-pedantic} also applies to C-language constructs where they
661 occur in GNU Fortran source files, such as use of @samp{\e} in a
662 character constant within a directive like @code{#include}.
664 Valid Fortran 95 programs should compile properly with or without
666 However, without this option, certain GNU extensions and traditional
667 Fortran features are supported as well.
668 With this option, many of them are rejected.
670 Some users try to use @option{-pedantic} to check programs for conformance.
671 They soon find that it does not do quite what they want---it finds some
672 nonstandard practices, but not all.
673 However, improvements to GNU Fortran in this area are welcome.
675 This should be used in conjunction with @option{-std=f95},
676 @option{-std=f2003} or @option{-std=f2008}.
678 @item -pedantic-errors
679 @opindex @code{pedantic-errors}
680 Like @option{-pedantic}, except that errors are produced rather than
686 @cindex warnings, all
687 Enables commonly used warning options pertaining to usage that
688 we recommend avoiding and that we believe are easy to avoid.
689 This currently includes @option{-Waliasing},
690 @option{-Wampersand}, @option{-Wsurprising}, @option{-Wintrinsics-std},
691 @option{-Wno-tabs}, @option{-Wintrinsic-shadow} and @option{-Wline-truncation}.
694 @opindex @code{Waliasing}
696 @cindex warnings, aliasing
697 Warn about possible aliasing of dummy arguments. Specifically, it warns
698 if the same actual argument is associated with a dummy argument with
699 @code{INTENT(IN)} and a dummy argument with @code{INTENT(OUT)} in a call
700 with an explicit interface.
702 The following example will trigger the warning.
706 integer, intent(in) :: a
707 integer, intent(out) :: b
716 @opindex @code{Wampersand}
717 @cindex warnings, ampersand
719 Warn about missing ampersand in continued character constants. The warning is
720 given with @option{-Wampersand}, @option{-pedantic}, @option{-std=f95},
721 @option{-std=f2003} and @option{-std=f2008}. Note: With no ampersand
722 given in a continued character constant, GNU Fortran assumes continuation
723 at the first non-comment, non-whitespace character after the ampersand
724 that initiated the continuation.
726 @item -Warray-temporaries
727 @opindex @code{Warray-temporaries}
728 @cindex warnings, array temporaries
729 Warn about array temporaries generated by the compiler. The information
730 generated by this warning is sometimes useful in optimization, in order to
731 avoid such temporaries.
733 @item -Wcharacter-truncation
734 @opindex @code{Wcharacter-truncation}
735 @cindex warnings, character truncation
736 Warn when a character assignment will truncate the assigned string.
738 @item -Wline-truncation
739 @opindex @code{Wline-truncation}
740 @cindex warnings, line truncation
741 Warn when a source code line will be truncated.
744 @opindex @code{Wconversion}
745 @cindex warnings, conversion
747 Warn about implicit conversions between different types.
749 @item -Wimplicit-interface
750 @opindex @code{Wimplicit-interface}
751 @cindex warnings, implicit interface
752 Warn if a procedure is called without an explicit interface.
753 Note this only checks that an explicit interface is present. It does not
754 check that the declared interfaces are consistent across program units.
756 @item -Wintrinsics-std
757 @opindex @code{Wintrinsics-std}
758 @cindex warnings, non-standard intrinsics
759 @cindex warnings, intrinsics of other standards
760 Warn if @command{gfortran} finds a procedure named like an intrinsic not
761 available in the currently selected standard (with @option{-std}) and treats
762 it as @code{EXTERNAL} procedure because of this. @option{-fall-intrinsics} can
763 be used to never trigger this behaviour and always link to the intrinsic
764 regardless of the selected standard.
767 @opindex @code{Wsurprising}
768 @cindex warnings, suspicious code
769 Produce a warning when ``suspicious'' code constructs are encountered.
770 While technically legal these usually indicate that an error has been made.
772 This currently produces a warning under the following circumstances:
776 An INTEGER SELECT construct has a CASE that can never be matched as its
777 lower value is greater than its upper value.
780 A LOGICAL SELECT construct has three CASE statements.
783 A TRANSFER specifies a source that is shorter than the destination.
786 The type of a function result is declared more than once with the same type. If
787 @option{-pedantic} or standard-conforming mode is enabled, this is an error.
791 @opindex @code{Wtabs}
792 @cindex warnings, tabs
794 By default, tabs are accepted as whitespace, but tabs are not members
795 of the Fortran Character Set. For continuation lines, a tab followed
796 by a digit between 1 and 9 is supported. @option{-Wno-tabs} will cause
797 a warning to be issued if a tab is encountered. Note, @option{-Wno-tabs}
798 is active for @option{-pedantic}, @option{-std=f95}, @option{-std=f2003},
799 @option{-std=f2008} and @option{-Wall}.
802 @opindex @code{Wunderflow}
803 @cindex warnings, underflow
805 Produce a warning when numerical constant expressions are
806 encountered, which yield an UNDERFLOW during compilation.
808 @item -Wintrinsic-shadow
809 @opindex @code{Wintrinsic-shadow}
810 @cindex warnings, intrinsic
812 Warn if a user-defined procedure or module procedure has the same name as an
813 intrinsic; in this case, an explicit interface or @code{EXTERNAL} or
814 @code{INTRINSIC} declaration might be needed to get calls later resolved to
815 the desired intrinsic/procedure.
817 @item -Wunused-parameter
818 @opindex @code{Wunused-parameter}
819 @cindex warnings, unused parameter
820 @cindex unused parameter
821 Contrary to @command{gcc}'s meaning of @option{-Wunused-parameter},
822 @command{gfortran}'s implementation of this option does not warn
823 about unused dummy arguments, but about unused @code{PARAMETER} values.
824 @option{-Wunused-parameter} is not included in @option{-Wall} but is
825 implied by @option{-Wall -Wextra}.
827 @item -Walign-commons
828 @opindex @code{Walign-commons}
829 @cindex warnings, alignment of COMMON blocks
830 @cindex alignment of COMMON blocks
831 By default, @command{gfortran} warns about any occasion of variables being
832 padded for proper alignment inside a COMMON block. This warning can be turned
833 off via @option{-Wno-align-commons}. See also @option{-falign-commons}.
836 @opindex @code{Werror}
837 @cindex warnings, to errors
838 Turns all warnings into errors.
841 @xref{Error and Warning Options,,Options to Request or Suppress Errors and
842 Warnings, gcc,Using the GNU Compiler Collection (GCC)}, for information on
843 more options offered by the GBE shared by @command{gfortran}, @command{gcc}
844 and other GNU compilers.
846 Some of these have no effect when compiling programs written in Fortran.
848 @node Debugging Options
849 @section Options for debugging your program or GNU Fortran
850 @cindex options, debugging
851 @cindex debugging information options
853 GNU Fortran has various special options that are used for debugging
854 either your program or the GNU Fortran compiler.
857 @item -fdump-parse-tree
858 @opindex @code{fdump-parse-tree}
859 Output the internal parse tree before starting code generation. Only
860 really useful for debugging the GNU Fortran compiler itself.
862 @item -ffpe-trap=@var{list}
863 @opindex @code{ffpe-trap=}@var{list}
864 Specify a list of IEEE exceptions when a Floating Point Exception
865 (FPE) should be raised. On most systems, this will result in a SIGFPE
866 signal being sent and the program being interrupted, producing a core
867 file useful for debugging. @var{list} is a (possibly empty) comma-separated
868 list of the following IEEE exceptions: @samp{invalid} (invalid floating
869 point operation, such as @code{SQRT(-1.0)}), @samp{zero} (division by
870 zero), @samp{overflow} (overflow in a floating point operation),
871 @samp{underflow} (underflow in a floating point operation),
872 @samp{precision} (loss of precision during operation) and @samp{denormal}
873 (operation produced a denormal value).
875 Some of the routines in the Fortran runtime library, like
876 @samp{CPU_TIME}, are likely to trigger floating point exceptions when
877 @code{ffpe-trap=precision} is used. For this reason, the use of
878 @code{ffpe-trap=precision} is not recommended.
881 @opindex @code{fbacktrace}
884 Specify that, when a runtime error is encountered or a deadly signal is
885 emitted (segmentation fault, illegal instruction, bus error or
886 floating-point exception), the Fortran runtime
887 library should output a backtrace of the error. This option
888 only has influence for compilation of the Fortran main program.
892 @opindex @code{fdump-core}
893 Request that a core-dump file is written to disk when a runtime error
894 is encountered on systems that support core dumps. This option is
895 only effective for the compilation of the Fortran main program.
898 @xref{Debugging Options,,Options for Debugging Your Program or GCC,
899 gcc,Using the GNU Compiler Collection (GCC)}, for more information on
902 @node Directory Options
903 @section Options for directory search
904 @cindex directory, options
905 @cindex options, directory search
907 @cindex INCLUDE directive
908 @cindex directive, INCLUDE
909 These options affect how GNU Fortran searches
910 for files specified by the @code{INCLUDE} directive and where it searches
911 for previously compiled modules.
913 It also affects the search paths used by @command{cpp} when used to preprocess
918 @opindex @code{I}@var{dir}
919 @cindex directory, search paths for inclusion
920 @cindex inclusion, directory search paths for
921 @cindex search paths, for included files
922 @cindex paths, search
923 @cindex module search path
924 These affect interpretation of the @code{INCLUDE} directive
925 (as well as of the @code{#include} directive of the @command{cpp}
928 Also note that the general behavior of @option{-I} and
929 @code{INCLUDE} is pretty much the same as of @option{-I} with
930 @code{#include} in the @command{cpp} preprocessor, with regard to
931 looking for @file{header.gcc} files and other such things.
933 This path is also used to search for @file{.mod} files when previously
934 compiled modules are required by a @code{USE} statement.
936 @xref{Directory Options,,Options for Directory Search,
937 gcc,Using the GNU Compiler Collection (GCC)}, for information on the
942 @opindex @code{J}@var{dir}
943 @opindex @code{M}@var{dir}
944 @cindex paths, search
945 @cindex module search path
946 This option specifies where to put @file{.mod} files for compiled modules.
947 It is also added to the list of directories to searched by an @code{USE}
950 The default is the current directory.
952 @option{-M} is deprecated to avoid conflicts with existing GCC options.
954 @item -fintrinsic-modules-path @var{dir}
955 @opindex @code{fintrinsic-modules-path} @var{dir}
956 @cindex paths, search
957 @cindex module search path
958 This option specifies the location of pre-compiled intrinsic modules, if
959 they are not in the default location expected by the compiler.
963 @section Influencing the linking step
964 @cindex options, linking
965 @cindex linking, static
967 These options come into play when the compiler links object files into an
968 executable output file. They are meaningless if the compiler is not doing
972 @item -static-libgfortran
973 @opindex @code{static-libgfortran}
974 On systems that provide @file{libgfortran} as a shared and a static
975 library, this option forces the use of the static version. If no
976 shared version of @file{libgfortran} was built when the compiler was
977 configured, this option has no effect.
981 @node Runtime Options
982 @section Influencing runtime behavior
983 @cindex options, runtime
985 These options affect the runtime behavior of programs compiled with GNU Fortran.
987 @item -fconvert=@var{conversion}
988 @opindex @code{fconvert=}@var{conversion}
989 Specify the representation of data for unformatted files. Valid
990 values for conversion are: @samp{native}, the default; @samp{swap},
991 swap between big- and little-endian; @samp{big-endian}, use big-endian
992 representation for unformatted files; @samp{little-endian}, use little-endian
993 representation for unformatted files.
995 @emph{This option has an effect only when used in the main program.
996 The @code{CONVERT} specifier and the GFORTRAN_CONVERT_UNIT environment
997 variable override the default specified by @option{-fconvert}.}
1000 @item -fno-range-check
1001 @opindex @code{fno-range-check}
1002 Disable range checking of input values during integer @code{READ} operations.
1003 For example, GNU Fortran will give an error if an input value is
1004 outside of the relevant range of [@code{-HUGE()}:@code{HUGE()}]. In other words,
1005 with @code{INTEGER (kind=4) :: i} , attempting to read @math{-2147483648} will
1006 give an error unless @option{-fno-range-check} is given.
1009 @item -frecord-marker=@var{length}
1010 @opindex @code{frecord-marker=}@var{length}
1011 Specify the length of record markers for unformatted files.
1012 Valid values for @var{length} are 4 and 8. Default is 4.
1013 @emph{This is different from previous versions of @command{gfortran}},
1014 which specified a default record marker length of 8 on most
1015 systems. If you want to read or write files compatible
1016 with earlier versions of @command{gfortran}, use @option{-frecord-marker=8}.
1018 @item -fmax-subrecord-length=@var{length}
1019 @opindex @code{fmax-subrecord-length=}@var{length}
1020 Specify the maximum length for a subrecord. The maximum permitted
1021 value for length is 2147483639, which is also the default. Only
1022 really useful for use by the gfortran testsuite.
1025 @opindex @code{fsign-zero}
1026 When writing zero values, show the negative sign if the sign bit is set.
1027 @code{fno-sign-zero} does not print the negative sign of zero values for
1028 compatibility with F77. Default behavior is to show the negative sign.
1031 @node Code Gen Options
1032 @section Options for code generation conventions
1033 @cindex code generation, conventions
1034 @cindex options, code generation
1035 @cindex options, run-time
1037 These machine-independent options control the interface conventions
1038 used in code generation.
1040 Most of them have both positive and negative forms; the negative form
1041 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
1042 one of the forms is listed---the one which is not the default. You
1043 can figure out the other form by either removing @option{no-} or adding
1047 @item -fno-automatic
1048 @opindex @code{fno-automatic}
1049 @cindex @code{SAVE} statement
1050 @cindex statement, @code{SAVE}
1051 Treat each program unit (except those marked as RECURSIVE) as if the
1052 @code{SAVE} statement were specified for every local variable and array
1053 referenced in it. Does not affect common blocks. (Some Fortran compilers
1054 provide this option under the name @option{-static} or @option{-save}.)
1055 The default, which is @option{-fautomatic}, uses the stack for local
1056 variables smaller than the value given by @option{-fmax-stack-var-size}.
1057 Use the option @option{-frecursive} to use no static memory.
1061 @cindex calling convention
1062 @cindex @command{f2c} calling convention
1063 @cindex @command{g77} calling convention
1064 @cindex libf2c calling convention
1065 Generate code designed to be compatible with code generated
1066 by @command{g77} and @command{f2c}.
1068 The calling conventions used by @command{g77} (originally implemented
1069 in @command{f2c}) require functions that return type
1070 default @code{REAL} to actually return the C type @code{double}, and
1071 functions that return type @code{COMPLEX} to return the values via an
1072 extra argument in the calling sequence that points to where to
1073 store the return value. Under the default GNU calling conventions, such
1074 functions simply return their results as they would in GNU
1075 C---default @code{REAL} functions return the C type @code{float}, and
1076 @code{COMPLEX} functions return the GNU C type @code{complex}.
1077 Additionally, this option implies the @option{-fsecond-underscore}
1078 option, unless @option{-fno-second-underscore} is explicitly requested.
1080 This does not affect the generation of code that interfaces with
1081 the @command{libgfortran} library.
1083 @emph{Caution:} It is not a good idea to mix Fortran code compiled with
1084 @option{-ff2c} with code compiled with the default @option{-fno-f2c}
1085 calling conventions as, calling @code{COMPLEX} or default @code{REAL}
1086 functions between program parts which were compiled with different
1087 calling conventions will break at execution time.
1089 @emph{Caution:} This will break code which passes intrinsic functions
1090 of type default @code{REAL} or @code{COMPLEX} as actual arguments, as
1091 the library implementations use the @option{-fno-f2c} calling conventions.
1093 @item -fno-underscoring
1094 @opindex @code{fno-underscoring}
1096 @cindex symbol names, underscores
1097 @cindex transforming symbol names
1098 @cindex symbol names, transforming
1099 Do not transform names of entities specified in the Fortran
1100 source file by appending underscores to them.
1102 With @option{-funderscoring} in effect, GNU Fortran appends one
1103 underscore to external names with no underscores. This is done to ensure
1104 compatibility with code produced by many UNIX Fortran compilers.
1106 @emph{Caution}: The default behavior of GNU Fortran is
1107 incompatible with @command{f2c} and @command{g77}, please use the
1108 @option{-ff2c} option if you want object files compiled with
1109 GNU Fortran to be compatible with object code created with these
1112 Use of @option{-fno-underscoring} is not recommended unless you are
1113 experimenting with issues such as integration of GNU Fortran into
1114 existing system environments (vis-@`{a}-vis existing libraries, tools,
1117 For example, with @option{-funderscoring}, and assuming other defaults like
1118 @option{-fcase-lower} and that @code{j()} and @code{max_count()} are
1119 external functions while @code{my_var} and @code{lvar} are local variables,
1122 I = J() + MAX_COUNT (MY_VAR, LVAR)
1125 is implemented as something akin to:
1127 i = j_() + max_count__(&my_var__, &lvar);
1130 With @option{-fno-underscoring}, the same statement is implemented as:
1133 i = j() + max_count(&my_var, &lvar);
1136 Use of @option{-fno-underscoring} allows direct specification of
1137 user-defined names while debugging and when interfacing GNU Fortran
1138 code with other languages.
1140 Note that just because the names match does @emph{not} mean that the
1141 interface implemented by GNU Fortran for an external name matches the
1142 interface implemented by some other language for that same name.
1143 That is, getting code produced by GNU Fortran to link to code produced
1144 by some other compiler using this or any other method can be only a
1145 small part of the overall solution---getting the code generated by
1146 both compilers to agree on issues other than naming can require
1147 significant effort, and, unlike naming disagreements, linkers normally
1148 cannot detect disagreements in these other areas.
1150 Also, note that with @option{-fno-underscoring}, the lack of appended
1151 underscores introduces the very real possibility that a user-defined
1152 external name will conflict with a name in a system library, which
1153 could make finding unresolved-reference bugs quite difficult in some
1154 cases---they might occur at program run time, and show up only as
1155 buggy behavior at run time.
1157 In future versions of GNU Fortran we hope to improve naming and linking
1158 issues so that debugging always involves using the names as they appear
1159 in the source, even if the names as seen by the linker are mangled to
1160 prevent accidental linking between procedures with incompatible
1164 @opindex @code{fwhole-file}
1165 By default, GNU Fortran parses, resolves and translates each procedure
1166 in a file separately. Using this option modifies this such that the
1167 whole file is parsed and placed in a single front-end tree. During
1168 resolution, in addition to all the usual checks and fixups, references
1169 to external procedures that are in the same file effect resolution of
1170 that procedure, if not already done, and a check of the interfaces. The
1171 dependences are resolved by changing the order in which the file is
1172 translated into the backend tree. Thus, a procedure that is referenced
1173 is translated before the reference and the duplication of backend tree
1174 declarations eliminated.
1176 @item -fsecond-underscore
1177 @opindex @code{fsecond-underscore}
1179 @cindex symbol names, underscores
1180 @cindex transforming symbol names
1181 @cindex symbol names, transforming
1182 @cindex @command{f2c} calling convention
1183 @cindex @command{g77} calling convention
1184 @cindex libf2c calling convention
1185 By default, GNU Fortran appends an underscore to external
1186 names. If this option is used GNU Fortran appends two
1187 underscores to names with underscores and one underscore to external names
1188 with no underscores. GNU Fortran also appends two underscores to
1189 internal names with underscores to avoid naming collisions with external
1192 This option has no effect if @option{-fno-underscoring} is
1193 in effect. It is implied by the @option{-ff2c} option.
1195 Otherwise, with this option, an external name such as @code{MAX_COUNT}
1196 is implemented as a reference to the link-time external symbol
1197 @code{max_count__}, instead of @code{max_count_}. This is required
1198 for compatibility with @command{g77} and @command{f2c}, and is implied
1199 by use of the @option{-ff2c} option.
1201 @item -fcheck=@var{<keyword>}
1202 @opindex @code{fcheck}
1203 @cindex array, bounds checking
1204 @cindex bounds checking
1205 @cindex range checking
1206 @cindex subscript checking
1207 @cindex checking subscripts
1208 @cindex run-time checking
1209 @cindex checking array temporaries
1211 Enable the generation of run-time checks; the argument shall be
1212 a comma-delimited list of the following keywords.
1216 Enable all run-time test of @option{-fcheck}.
1218 @item @samp{array-temps}
1219 Warns at run time when for passing an actual argument a temporary array
1220 had to be generated. The information generated by this warning is
1221 sometimes useful in optimization, in order to avoid such temporaries.
1223 Note: The warning is only printed once per location.
1226 Enable generation of run-time checks for array subscripts
1227 and against the declared minimum and maximum values. It also
1228 checks array indices for assumed and deferred
1229 shape arrays against the actual allocated bounds and ensures that all string
1230 lengths are equal for character array constructors without an explicit
1233 Some checks require that @option{-fcheck=bounds} is set for
1234 the compilation of the main program.
1236 Note: In the future this may also include other forms of checking, e.g.,
1237 checking substring references.
1240 Enable generation of run-time checks for invalid modification of loop
1241 iteration variables.
1243 @item @samp{recursion}
1244 Enable generation of run-time checks for recursively called subroutines and
1245 functions which are not marked as recursive. See also @option{-frecursive}.
1249 @item -fbounds-check
1250 @opindex @code{fbounds-check}
1251 @c Note: This option is also referred in gcc's manpage
1252 Deprecated alias for @option{-fcheck=bounds}.
1254 @item -fcheck-array-temporaries
1255 @opindex @code{fcheck-array-temporaries}
1256 Deprecated alias for @option{-fcheck=array-temps}.
1258 @item -fmax-array-constructor=@var{n}
1259 @opindex @code{fmax-array-constructor}
1260 This option can be used to increase the upper limit permitted in
1261 array constructors. The code below requires this option to expand
1262 the array at compile time.
1266 @code{implicit none}
1268 @code{integer, parameter :: n = 100000}
1269 @code{integer, parameter :: i(n) = (/ (2*j, j = 1, n) /)}
1270 @code{print '(10(I0,1X))', i}
1271 @code{end program test}
1274 @emph{Caution: This option can lead to long compile times and excessively
1275 large object files.}
1277 The default value for @var{n} is 65535.
1280 @item -fmax-stack-var-size=@var{n}
1281 @opindex @code{fmax-stack-var-size}
1282 This option specifies the size in bytes of the largest array that will be put
1283 on the stack; if the size is exceeded static memory is used (except in
1284 procedures marked as RECURSIVE). Use the option @option{-frecursive} to
1285 allow for recursive procedures which do not have a RECURSIVE attribute or
1286 for parallel programs. Use @option{-fno-automatic} to never use the stack.
1288 This option currently only affects local arrays declared with constant
1289 bounds, and may not apply to all character variables.
1290 Future versions of GNU Fortran may improve this behavior.
1292 The default value for @var{n} is 32768.
1294 @item -fpack-derived
1295 @opindex @code{fpack-derived}
1296 @cindex structure packing
1297 This option tells GNU Fortran to pack derived type members as closely as
1298 possible. Code compiled with this option is likely to be incompatible
1299 with code compiled without this option, and may execute slower.
1301 @item -frepack-arrays
1302 @opindex @code{frepack-arrays}
1303 @cindex repacking arrays
1304 In some circumstances GNU Fortran may pass assumed shape array
1305 sections via a descriptor describing a noncontiguous area of memory.
1306 This option adds code to the function prologue to repack the data into
1307 a contiguous block at runtime.
1309 This should result in faster accesses to the array. However it can introduce
1310 significant overhead to the function call, especially when the passed data
1314 @opindex @code{fshort-enums}
1315 This option is provided for interoperability with C code that was
1316 compiled with the @option{-fshort-enums} option. It will make
1317 GNU Fortran choose the smallest @code{INTEGER} kind a given
1318 enumerator set will fit in, and give all its enumerators this kind.
1320 @item -fexternal-blas
1321 @opindex @code{fexternal-blas}
1322 This option will make @command{gfortran} generate calls to BLAS functions
1323 for some matrix operations like @code{MATMUL}, instead of using our own
1324 algorithms, if the size of the matrices involved is larger than a given
1325 limit (see @option{-fblas-matmul-limit}). This may be profitable if an
1326 optimized vendor BLAS library is available. The BLAS library will have
1327 to be specified at link time.
1329 @item -fblas-matmul-limit=@var{n}
1330 @opindex @code{fblas-matmul-limit}
1331 Only significant when @option{-fexternal-blas} is in effect.
1332 Matrix multiplication of matrices with size larger than (or equal to) @var{n}
1333 will be performed by calls to BLAS functions, while others will be
1334 handled by @command{gfortran} internal algorithms. If the matrices
1335 involved are not square, the size comparison is performed using the
1336 geometric mean of the dimensions of the argument and result matrices.
1338 The default value for @var{n} is 30.
1341 @opindex @code{frecursive}
1342 Allow indirect recursion by forcing all local arrays to be allocated
1343 on the stack. This flag cannot be used together with
1344 @option{-fmax-stack-var-size=} or @option{-fno-automatic}.
1346 @item -finit-local-zero
1347 @item -finit-integer=@var{n}
1348 @item -finit-real=@var{<zero|inf|-inf|nan|snan>}
1349 @item -finit-logical=@var{<true|false>}
1350 @item -finit-character=@var{n}
1351 @opindex @code{finit-local-zero}
1352 @opindex @code{finit-integer}
1353 @opindex @code{finit-real}
1354 @opindex @code{finit-logical}
1355 @opindex @code{finit-character}
1356 The @option{-finit-local-zero} option instructs the compiler to
1357 initialize local @code{INTEGER}, @code{REAL}, and @code{COMPLEX}
1358 variables to zero, @code{LOGICAL} variables to false, and
1359 @code{CHARACTER} variables to a string of null bytes. Finer-grained
1360 initialization options are provided by the
1361 @option{-finit-integer=@var{n}},
1362 @option{-finit-real=@var{<zero|inf|-inf|nan|snan>}} (which also initializes
1363 the real and imaginary parts of local @code{COMPLEX} variables),
1364 @option{-finit-logical=@var{<true|false>}}, and
1365 @option{-finit-character=@var{n}} (where @var{n} is an ASCII character
1366 value) options. These options do not initialize components of derived
1367 type variables, nor do they initialize variables that appear in an
1368 @code{EQUIVALENCE} statement. (This limitation may be removed in
1371 Note that the @option{-finit-real=nan} option initializes @code{REAL}
1372 and @code{COMPLEX} variables with a quiet NaN. For a signalling NaN
1373 use @option{-finit-real=snan}; note, however, that compile-time
1374 optimizations may convert them into quiet NaN and that trapping
1375 needs to be enabled (e.g. via @option{-ffpe-trap}).
1377 @item -falign-commons
1378 @opindex @code{falign-commons}
1379 @cindex alignment of COMMON blocks
1380 By default, @command{gfortran} enforces proper alignment of all variables in a
1381 COMMON block by padding them as needed. On certain platforms this is mandatory,
1382 on others it increases performance. If a COMMON block is not declared with
1383 consistent data types everywhere, this padding can cause trouble, and
1384 @option{-fno-align-commons } can be used to disable automatic alignment. The
1385 same form of this option should be used for all files that share a COMMON block.
1386 To avoid potential alignment issues in COMMON blocks, it is recommended to order
1387 objects from largests to smallest.
1390 @xref{Code Gen Options,,Options for Code Generation Conventions,
1391 gcc,Using the GNU Compiler Collection (GCC)}, for information on more options
1393 shared by @command{gfortran}, @command{gcc}, and other GNU compilers.
1398 @node Environment Variables
1399 @section Environment variables affecting @command{gfortran}
1400 @cindex environment variable
1402 @c man begin ENVIRONMENT
1404 The @command{gfortran} compiler currently does not make use of any environment
1405 variables to control its operation above and beyond those
1406 that affect the operation of @command{gcc}.
1408 @xref{Environment Variables,,Environment Variables Affecting GCC,
1409 gcc,Using the GNU Compiler Collection (GCC)}, for information on environment
1412 @xref{Runtime}, for environment variables that affect the
1413 run-time behavior of programs compiled with GNU Fortran.