1 @c Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012
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, 2010, 2011
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 1.3 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
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 -fbackslash -fcray-pointer -fd-lines-as-code @gol
120 -fd-lines-as-comments -fdefault-double-8 -fdefault-integer-8 @gol
121 -fdefault-real-8 -fdollar-ok -ffixed-line-length-@var{n} @gol
122 -ffixed-line-length-none -ffree-form -ffree-line-length-@var{n} @gol
123 -ffree-line-length-none -fimplicit-none -finteger-4-integer-8 @gol
124 -fmax-identifier-length -fmodule-private -fno-fixed-form -fno-range-check @gol
125 -fopenmp -freal-4-real-10 -freal-4-real-16 -freal-4-real-8 @gol
126 -freal-8-real-10 -freal-8-real-16 -freal-8-real-4 -std=@var{std}
129 @item Preprocessing Options
130 @xref{Preprocessing Options,,Enable and customize preprocessing}.
131 @gccoptlist{-A-@var{question}@r{[}=@var{answer}@r{]}
132 -A@var{question}=@var{answer} -C -CC -D@var{macro}@r{[}=@var{defn}@r{]}
134 -U@var{macro} -cpp -dD -dI -dM -dN -dU -fworking-directory
135 -imultilib @var{dir} @gol
136 -iprefix @var{file} -iquote -isysroot @var{dir} -isystem @var{dir} -nocpp
141 @item Error and Warning Options
142 @xref{Error and Warning Options,,Options to request or suppress errors
144 @gccoptlist{-Waliasing -Wall -Wampersand -Warray-bounds
145 -Wcharacter-truncation @gol
146 -Wconversion -Wfunction-elimination -Wimplicit-interface @gol
147 -Wimplicit-procedure -Wintrinsic-shadow -Wintrinsics-std @gol
148 -Wline-truncation -Wno-align-commons -Wno-tabs -Wreal-q-constant @gol
149 -Wsurprising -Wunderflow -Wunused-parameter -fmax-errors=@var{n}
151 -pedantic -pedantic-errors
154 @item Debugging Options
155 @xref{Debugging Options,,Options for debugging your program or GNU Fortran}.
156 @gccoptlist{-fbacktrace -fdump-fortran-optimized -fdump-fortran-original @gol
157 -fdump-parse-tree -ffpe-trap=@var{list}
160 @item Directory Options
161 @xref{Directory Options,,Options for directory search}.
162 @gccoptlist{-I@var{dir} -J@var{dir} -fintrinsic-modules-path @var{dir}}
165 @xref{Link Options,,Options for influencing the linking step}.
166 @gccoptlist{-static-libgfortran}
168 @item Runtime Options
169 @xref{Runtime Options,,Options for influencing runtime behavior}.
170 @gccoptlist{-fconvert=@var{conversion} -fmax-subrecord-length=@var{length}
171 -fno-range-check @gol
172 -frecord-marker=@var{length} -fsign-zero
175 @item Code Generation Options
176 @xref{Code Gen Options,,Options for code generation conventions}.
177 @gccoptlist{-faggressive-function-elimination -fblas-matmul-limit=@var{n} @gol
178 -fbounds-check -fcheck-array-temporaries @gol
179 -fcheck=@var{<all|array-temps|bounds|do|mem|pointer|recursion>} @gol
180 -fcoarray=@var{<none|single|lib>} -fexternal-blas -ff2c
181 -ffrontend-optimize @gol
182 -finit-character=@var{n} -finit-integer=@var{n} -finit-local-zero @gol
183 -finit-logical=@var{<true|false>}
184 -finit-real=@var{<zero|inf|-inf|nan|snan>} @gol
185 -fmax-array-constructor=@var{n} -fmax-stack-var-size=@var{n}
186 -fno-align-commons @gol
187 -fno-automatic -fno-protect-parens -fno-underscoring -fno-whole-file @gol
188 -fsecond-underscore -fpack-derived -frealloc-lhs -frecursive @gol
189 -frepack-arrays -fshort-enums -fstack-arrays
193 @node Fortran Dialect Options
194 @section Options controlling Fortran dialect
195 @cindex dialect options
196 @cindex language, dialect options
197 @cindex options, dialect
199 The following options control the details of the Fortran dialect
200 accepted by the compiler:
205 @opindex @code{ffree-form}
206 @opindex @code{fno-fixed-form}
207 @cindex options, fortran dialect
208 @cindex file format, free
209 @cindex file format, fixed
210 Specify the layout used by the source file. The free form layout
211 was introduced in Fortran 90. Fixed form was traditionally used in
212 older Fortran programs. When neither option is specified, the source
213 form is determined by the file extension.
215 @item -fall-intrinsics
216 @opindex @code{fall-intrinsics}
217 This option causes all intrinsic procedures (including the GNU-specific
218 extensions) to be accepted. This can be useful with @option{-std=f95} to
219 force standard-compliance but get access to the full range of intrinsics
220 available with @command{gfortran}. As a consequence, @option{-Wintrinsics-std}
221 will be ignored and no user-defined procedure with the same name as any
222 intrinsic will be called except when it is explicitly declared @code{EXTERNAL}.
224 @item -fd-lines-as-code
225 @itemx -fd-lines-as-comments
226 @opindex @code{fd-lines-as-code}
227 @opindex @code{fd-lines-as-comments}
228 Enable special treatment for lines beginning with @code{d} or @code{D}
229 in fixed form sources. If the @option{-fd-lines-as-code} option is
230 given they are treated as if the first column contained a blank. If the
231 @option{-fd-lines-as-comments} option is given, they are treated as
234 @item -fdefault-double-8
235 @opindex @code{fdefault-double-8}
236 Set the @code{DOUBLE PRECISION} type to an 8 byte wide type. If
237 @option{-fdefault-real-8} is given, @code{DOUBLE PRECISION} would
238 instead be promoted to 16 bytes if possible, and @option{-fdefault-double-8}
239 can be used to prevent this. The kind of real constants like @code{1.d0} will
240 not be changed by @option{-fdefault-real-8} though, so also
241 @option{-fdefault-double-8} does not affect it.
243 @item -fdefault-integer-8
244 @opindex @code{fdefault-integer-8}
245 Set the default integer and logical types to an 8 byte wide type.
246 Do nothing if this is already the default. This option also affects
247 the kind of integer constants like @code{42}.
249 @item -fdefault-real-8
250 @opindex @code{fdefault-real-8}
251 Set the default real type to an 8 byte wide type.
252 Do nothing if this is already the default. This option also affects
253 the kind of non-double real constants like @code{1.0}, and does promote
254 the default width of @code{DOUBLE PRECISION} to 16 bytes if possible, unless
255 @code{-fdefault-double-8} is given, too.
258 @opindex @code{fdollar-ok}
261 @cindex character set
262 Allow @samp{$} as a valid non-first character in a symbol name. Symbols
263 that start with @samp{$} are rejected since it is unclear which rules to
264 apply to implicit typing as different vendors implement different rules.
265 Using @samp{$} in @code{IMPLICIT} statements is also rejected.
268 @opindex @code{backslash}
270 @cindex escape characters
271 Change the interpretation of backslashes in string literals from a single
272 backslash character to ``C-style'' escape characters. The following
273 combinations are expanded @code{\a}, @code{\b}, @code{\f}, @code{\n},
274 @code{\r}, @code{\t}, @code{\v}, @code{\\}, and @code{\0} to the ASCII
275 characters alert, backspace, form feed, newline, carriage return,
276 horizontal tab, vertical tab, backslash, and NUL, respectively.
277 Additionally, @code{\x}@var{nn}, @code{\u}@var{nnnn} and
278 @code{\U}@var{nnnnnnnn} (where each @var{n} is a hexadecimal digit) are
279 translated into the Unicode characters corresponding to the specified code
280 points. All other combinations of a character preceded by \ are
283 @item -fmodule-private
284 @opindex @code{fmodule-private}
285 @cindex module entities
287 Set the default accessibility of module entities to @code{PRIVATE}.
288 Use-associated entities will not be accessible unless they are explicitly
289 declared as @code{PUBLIC}.
291 @item -ffixed-line-length-@var{n}
292 @opindex @code{ffixed-line-length-}@var{n}
293 @cindex file format, fixed
294 Set column after which characters are ignored in typical fixed-form
295 lines in the source file, and through which spaces are assumed (as
296 if padded to that length) after the ends of short fixed-form lines.
298 Popular values for @var{n} include 72 (the
299 standard and the default), 80 (card image), and 132 (corresponding
300 to ``extended-source'' options in some popular compilers).
301 @var{n} may also be @samp{none}, meaning that the entire line is meaningful
302 and that continued character constants never have implicit spaces appended
303 to them to fill out the line.
304 @option{-ffixed-line-length-0} means the same thing as
305 @option{-ffixed-line-length-none}.
307 @item -ffree-line-length-@var{n}
308 @opindex @code{ffree-line-length-}@var{n}
309 @cindex file format, free
310 Set column after which characters are ignored in typical free-form
311 lines in the source file. The default value is 132.
312 @var{n} may be @samp{none}, meaning that the entire line is meaningful.
313 @option{-ffree-line-length-0} means the same thing as
314 @option{-ffree-line-length-none}.
316 @item -fmax-identifier-length=@var{n}
317 @opindex @code{fmax-identifier-length=}@var{n}
318 Specify the maximum allowed identifier length. Typical values are
319 31 (Fortran 95) and 63 (Fortran 2003 and Fortran 2008).
321 @item -fimplicit-none
322 @opindex @code{fimplicit-none}
323 Specify that no implicit typing is allowed, unless overridden by explicit
324 @code{IMPLICIT} statements. This is the equivalent of adding
325 @code{implicit none} to the start of every procedure.
327 @item -finteger-4-integer-8
328 @opindex @code{finteger-4-integer-8}
329 Promote all @code{INTEGER(KIND=4)} entities to an @code{INTEGER(KIND=8)}
330 entities. If @code{KIND=8} is unavailable, then an error will be issued.
331 This option should be used with care and may not be suitable for your codes.
332 Areas of possible concern include calls to external procedures,
333 alignment in @code{EQUIVALENCE} and/or @code{COMMON}, generic interfaces,
334 BOZ literal constant conversion, and I/O. Inspection of the intermediate
335 representation of the translated Fortran code, produced by
336 @option{-fdump-tree-original}, is suggested.
339 @opindex @code{fcray-pointer}
340 Enable the Cray pointer extension, which provides C-like pointer
344 @opindex @code{fopenmp}
346 Enable the OpenMP extensions. This includes OpenMP @code{!$omp} directives
348 and @code{c$omp}, @code{*$omp} and @code{!$omp} directives in fixed form,
349 @code{!$} conditional compilation sentinels in free form
350 and @code{c$}, @code{*$} and @code{!$} sentinels in fixed form,
351 and when linking arranges for the OpenMP runtime library to be linked
352 in. The option @option{-fopenmp} implies @option{-frecursive}.
354 @item -fno-range-check
355 @opindex @code{frange-check}
356 Disable range checking on results of simplification of constant
357 expressions during compilation. For example, GNU Fortran will give
358 an error at compile time when simplifying @code{a = 1. / 0}.
359 With this option, no error will be given and @code{a} will be assigned
360 the value @code{+Infinity}. If an expression evaluates to a value
361 outside of the relevant range of [@code{-HUGE()}:@code{HUGE()}],
362 then the expression will be replaced by @code{-Inf} or @code{+Inf}
364 Similarly, @code{DATA i/Z'FFFFFFFF'/} will result in an integer overflow
365 on most systems, but with @option{-fno-range-check} the value will
366 ``wrap around'' and @code{i} will be initialized to @math{-1} instead.
368 @item -freal-4-real-8
369 @itemx -freal-4-real-10
370 @itemx -freal-8-real-4
371 @itemx -freal-8-real-10
372 @itemx -freal-8-real-16
373 @opindex @code{freal-4-real-8}
374 @opindex @code{freal-4-real-10}
375 @opindex @code{freal-4-real-16}
376 @opindex @code{freal-8-real-4}
377 @opindex @code{freal-8-real-10}
378 @opindex @code{freal-8-real-16}
379 @cindex options, real kind type promotion
380 Promote all @code{REAL(KIND=M)} entities to @code{REAL(KIND=N)} entities.
381 If @code{REAL(KIND=N)} is unavailable, then an error will be issued.
382 All other real kind types are unaffected by this option.
383 These options should be used with care and may not be suitable for your
384 codes. Areas of possible concern include calls to external procedures,
385 alignment in @code{EQUIVALENCE} and/or @code{COMMON}, generic interfaces,
386 BOZ literal constant conversion, and I/O. Inspection of the intermediate
387 representation of the translated Fortran code, produced by
388 @option{-fdump-tree-original}, is suggested.
391 @opindex @code{std=}@var{std} option
392 Specify the standard to which the program is expected to conform, which
393 may be one of @samp{f95}, @samp{f2003}, @samp{f2008}, @samp{gnu}, or
394 @samp{legacy}. The default value for @var{std} is @samp{gnu}, which
395 specifies a superset of the Fortran 95 standard that includes all of the
396 extensions supported by GNU Fortran, although warnings will be given for
397 obsolete extensions not recommended for use in new code. The
398 @samp{legacy} value is equivalent but without the warnings for obsolete
399 extensions, and may be useful for old non-standard programs. The
400 @samp{f95}, @samp{f2003} and @samp{f2008} values specify strict
401 conformance to the Fortran 95, Fortran 2003 and Fortran 2008 standards,
402 respectively; errors are given for all extensions beyond the relevant
403 language standard, and warnings are given for the Fortran 77 features
404 that are permitted but obsolescent in later standards. @samp{-std=f2008ts}
405 allows the Fortran 2008 standard including the additions of the
406 Technical Specification (TS) 29113 on Further Interoperability of Fortran
411 @node Preprocessing Options
412 @section Enable and customize preprocessing
414 @cindex options, preprocessor
417 Preprocessor related options. See section
418 @ref{Preprocessing and conditional compilation} for more detailed
419 information on preprocessing in @command{gfortran}.
426 @cindex preprocessor, enable
427 @cindex preprocessor, disable
428 Enable preprocessing. The preprocessor is automatically invoked if
429 the file extension is @file{.fpp}, @file{.FPP}, @file{.F}, @file{.FOR},
430 @file{.FTN}, @file{.F90}, @file{.F95}, @file{.F03} or @file{.F08}. Use
431 this option to manually enable preprocessing of any kind of Fortran file.
433 To disable preprocessing of files with any of the above listed extensions,
434 use the negative form: @option{-nocpp}.
436 The preprocessor is run in traditional mode. Any restrictions of the
437 file-format, especially the limits on line length, apply for
438 preprocessed output as well, so it might be advisable to use the
439 @option{-ffree-line-length-none} or @option{-ffixed-line-length-none}
444 @cindex preprocessor, debugging
445 @cindex debugging, preprocessor
446 Instead of the normal output, generate a list of @code{'#define'}
447 directives for all the macros defined during the execution of the
448 preprocessor, including predefined macros. This gives you a way
449 of finding out what is predefined in your version of the preprocessor.
450 Assuming you have no file @file{foo.f90}, the command
452 touch foo.f90; gfortran -cpp -E -dM foo.f90
454 will show all the predefined macros.
458 @cindex preprocessor, debugging
459 @cindex debugging, preprocessor
460 Like @option{-dM} except in two respects: it does not include the
461 predefined macros, and it outputs both the @code{#define} directives
462 and the result of preprocessing. Both kinds of output go to the
463 standard output file.
467 @cindex preprocessor, debugging
468 @cindex debugging, preprocessor
469 Like @option{-dD}, but emit only the macro names, not their expansions.
473 @cindex preprocessor, debugging
474 @cindex debugging, preprocessor
475 Like @option{dD} except that only macros that are expanded, or whose
476 definedness is tested in preprocessor directives, are output; the
477 output is delayed until the use or test of the macro; and @code{'#undef'}
478 directives are also output for macros tested but undefined at the time.
482 @cindex preprocessor, debugging
483 @cindex debugging, preprocessor
484 Output @code{'#include'} directives in addition to the result
487 @item -fworking-directory
488 @opindex @code{fworking-directory}
489 @cindex preprocessor, working directory
490 Enable generation of linemarkers in the preprocessor output that will
491 let the compiler know the current working directory at the time of
492 preprocessing. When this option is enabled, the preprocessor will emit,
493 after the initial linemarker, a second linemarker with the current
494 working directory followed by two slashes. GCC will use this directory,
495 when it is present in the preprocessed input, as the directory emitted
496 as the current working directory in some debugging information formats.
497 This option is implicitly enabled if debugging information is enabled,
498 but this can be inhibited with the negated form
499 @option{-fno-working-directory}. If the @option{-P} flag is present
500 in the command line, this option has no effect, since no @code{#line}
501 directives are emitted whatsoever.
503 @item -idirafter @var{dir}
504 @opindex @code{idirafter @var{dir}}
505 @cindex preprocessing, include path
506 Search @var{dir} for include files, but do it after all directories
507 specified with @option{-I} and the standard system directories have
508 been exhausted. @var{dir} is treated as a system include directory.
509 If dir begins with @code{=}, then the @code{=} will be replaced by
510 the sysroot prefix; see @option{--sysroot} and @option{-isysroot}.
512 @item -imultilib @var{dir}
513 @opindex @code{imultilib @var{dir}}
514 @cindex preprocessing, include path
515 Use @var{dir} as a subdirectory of the directory containing target-specific
518 @item -iprefix @var{prefix}
519 @opindex @code{iprefix @var{prefix}}
520 @cindex preprocessing, include path
521 Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix}
522 options. If the @var{prefix} represents a directory, you should include
523 the final @code{'/'}.
525 @item -isysroot @var{dir}
526 @opindex @code{isysroot @var{dir}}
527 @cindex preprocessing, include path
528 This option is like the @option{--sysroot} option, but applies only to
529 header files. See the @option{--sysroot} option for more information.
531 @item -iquote @var{dir}
532 @opindex @code{iquote @var{dir}}
533 @cindex preprocessing, include path
534 Search @var{dir} only for header files requested with @code{#include "file"};
535 they are not searched for @code{#include <file>}, before all directories
536 specified by @option{-I} and before the standard system directories. If
537 @var{dir} begins with @code{=}, then the @code{=} will be replaced by the
538 sysroot prefix; see @option{--sysroot} and @option{-isysroot}.
540 @item -isystem @var{dir}
541 @opindex @code{isystem @var{dir}}
542 @cindex preprocessing, include path
543 Search @var{dir} for header files, after all directories specified by
544 @option{-I} but before the standard system directories. Mark it as a
545 system directory, so that it gets the same special treatment as is
546 applied to the standard system directories. If @var{dir} begins with
547 @code{=}, then the @code{=} will be replaced by the sysroot prefix;
548 see @option{--sysroot} and @option{-isysroot}.
551 @opindex @code{nostdinc}
552 Do not search the standard system directories for header files. Only
553 the directories you have specified with @option{-I} options (and the
554 directory of the current file, if appropriate) are searched.
557 @opindex @code{undef}
558 Do not predefine any system-specific or GCC-specific macros.
559 The standard predefined macros remain defined.
561 @item -A@var{predicate}=@var{answer}
562 @opindex @code{A@var{predicate}=@var{answer}}
563 @cindex preprocessing, assertion
564 Make an assertion with the predicate @var{predicate} and answer @var{answer}.
565 This form is preferred to the older form -A predicate(answer), which is still
566 supported, because it does not use shell special characters.
568 @item -A-@var{predicate}=@var{answer}
569 @opindex @code{A-@var{predicate}=@var{answer}}
570 @cindex preprocessing, assertion
571 Cancel an assertion with the predicate @var{predicate} and answer @var{answer}.
575 @cindex preprocessing, keep comments
576 Do not discard comments. All comments are passed through to the output
577 file, except for comments in processed directives, which are deleted
578 along with the directive.
580 You should be prepared for side effects when using @option{-C}; it causes
581 the preprocessor to treat comments as tokens in their own right. For example,
582 comments appearing at the start of what would be a directive line have the
583 effect of turning that line into an ordinary source line, since the first
584 token on the line is no longer a @code{'#'}.
586 Warning: this currently handles C-Style comments only. The preprocessor
587 does not yet recognize Fortran-style comments.
591 @cindex preprocessing, keep comments
592 Do not discard comments, including during macro expansion. This is like
593 @option{-C}, except that comments contained within macros are also passed
594 through to the output file where the macro is expanded.
596 In addition to the side-effects of the @option{-C} option, the @option{-CC}
597 option causes all C++-style comments inside a macro to be converted to C-style
598 comments. This is to prevent later use of that macro from inadvertently
599 commenting out the remainder of the source line. The @option{-CC} option
600 is generally used to support lint comments.
602 Warning: this currently handles C- and C++-Style comments only. The
603 preprocessor does not yet recognize Fortran-style comments.
606 @opindex @code{D@var{name}}
607 @cindex preprocessing, define macros
608 Predefine name as a macro, with definition @code{1}.
610 @item -D@var{name}=@var{definition}
611 @opindex @code{D@var{name}=@var{definition}}
612 @cindex preprocessing, define macros
613 The contents of @var{definition} are tokenized and processed as if they
614 appeared during translation phase three in a @code{'#define'} directive.
615 In particular, the definition will be truncated by embedded newline
618 If you are invoking the preprocessor from a shell or shell-like program
619 you may need to use the shell's quoting syntax to protect characters such
620 as spaces that have a meaning in the shell syntax.
622 If you wish to define a function-like macro on the command line, write
623 its argument list with surrounding parentheses before the equals sign
624 (if any). Parentheses are meaningful to most shells, so you will need
625 to quote the option. With sh and csh, @code{-D'name(args...)=definition'}
628 @option{-D} and @option{-U} options are processed in the order they are
629 given on the command line. All -imacros file and -include file options
630 are processed after all -D and -U options.
634 Print the name of each header file used, in addition to other normal
635 activities. Each name is indented to show how deep in the @code{'#include'}
640 @cindex preprocessing, no linemarkers
641 Inhibit generation of linemarkers in the output from the preprocessor.
642 This might be useful when running the preprocessor on something that
643 is not C code, and will be sent to a program which might be confused
647 @opindex @code{U@var{name}}
648 @cindex preprocessing, undefine macros
649 Cancel any previous definition of @var{name}, either built in or provided
650 with a @option{-D} option.
654 @node Error and Warning Options
655 @section Options to request or suppress errors and warnings
656 @cindex options, warnings
657 @cindex options, errors
658 @cindex warnings, suppressing
659 @cindex messages, error
660 @cindex messages, warning
661 @cindex suppressing warnings
663 Errors are diagnostic messages that report that the GNU Fortran compiler
664 cannot compile the relevant piece of source code. The compiler will
665 continue to process the program in an attempt to report further errors
666 to aid in debugging, but will not produce any compiled output.
668 Warnings are diagnostic messages that report constructions which
669 are not inherently erroneous but which are risky or suggest there is
670 likely to be a bug in the program. Unless @option{-Werror} is specified,
671 they do not prevent compilation of the program.
673 You can request many specific warnings with options beginning @option{-W},
674 for example @option{-Wimplicit} to request warnings on implicit
675 declarations. Each of these specific warning options also has a
676 negative form beginning @option{-Wno-} to turn off warnings;
677 for example, @option{-Wno-implicit}. This manual lists only one of the
678 two forms, whichever is not the default.
680 These options control the amount and kinds of errors and warnings produced
684 @item -fmax-errors=@var{n}
685 @opindex @code{fmax-errors=}@var{n}
686 @cindex errors, limiting
687 Limits the maximum number of error messages to @var{n}, at which point
688 GNU Fortran bails out rather than attempting to continue processing the
689 source code. If @var{n} is 0, there is no limit on the number of error
693 @opindex @code{fsyntax-only}
694 @cindex syntax checking
695 Check the code for syntax errors, but do not actually compile it. This
696 will generate module files for each module present in the code, but no
700 @opindex @code{pedantic}
701 Issue warnings for uses of extensions to Fortran 95.
702 @option{-pedantic} also applies to C-language constructs where they
703 occur in GNU Fortran source files, such as use of @samp{\e} in a
704 character constant within a directive like @code{#include}.
706 Valid Fortran 95 programs should compile properly with or without
708 However, without this option, certain GNU extensions and traditional
709 Fortran features are supported as well.
710 With this option, many of them are rejected.
712 Some users try to use @option{-pedantic} to check programs for conformance.
713 They soon find that it does not do quite what they want---it finds some
714 nonstandard practices, but not all.
715 However, improvements to GNU Fortran in this area are welcome.
717 This should be used in conjunction with @option{-std=f95},
718 @option{-std=f2003} or @option{-std=f2008}.
720 @item -pedantic-errors
721 @opindex @code{pedantic-errors}
722 Like @option{-pedantic}, except that errors are produced rather than
728 @cindex warnings, all
729 Enables commonly used warning options pertaining to usage that
730 we recommend avoiding and that we believe are easy to avoid.
731 This currently includes @option{-Waliasing}, @option{-Wampersand},
732 @option{-Wconversion}, @option{-Wsurprising}, @option{-Wintrinsics-std},
733 @option{-Wno-tabs}, @option{-Wintrinsic-shadow}, @option{-Wline-truncation},
734 @option{-Wreal-q-constant} and @option{-Wunused}.
737 @opindex @code{Waliasing}
739 @cindex warnings, aliasing
740 Warn about possible aliasing of dummy arguments. Specifically, it warns
741 if the same actual argument is associated with a dummy argument with
742 @code{INTENT(IN)} and a dummy argument with @code{INTENT(OUT)} in a call
743 with an explicit interface.
745 The following example will trigger the warning.
749 integer, intent(in) :: a
750 integer, intent(out) :: b
759 @opindex @code{Wampersand}
760 @cindex warnings, ampersand
762 Warn about missing ampersand in continued character constants. The warning is
763 given with @option{-Wampersand}, @option{-pedantic}, @option{-std=f95},
764 @option{-std=f2003} and @option{-std=f2008}. Note: With no ampersand
765 given in a continued character constant, GNU Fortran assumes continuation
766 at the first non-comment, non-whitespace character after the ampersand
767 that initiated the continuation.
769 @item -Warray-temporaries
770 @opindex @code{Warray-temporaries}
771 @cindex warnings, array temporaries
772 Warn about array temporaries generated by the compiler. The information
773 generated by this warning is sometimes useful in optimization, in order to
774 avoid such temporaries.
776 @item -Wcharacter-truncation
777 @opindex @code{Wcharacter-truncation}
778 @cindex warnings, character truncation
779 Warn when a character assignment will truncate the assigned string.
781 @item -Wline-truncation
782 @opindex @code{Wline-truncation}
783 @cindex warnings, line truncation
784 Warn when a source code line will be truncated.
787 @opindex @code{Wconversion}
788 @cindex warnings, conversion
790 Warn about implicit conversions that are likely to change the value of
791 the expression after conversion. Implied by @option{-Wall}.
793 @item -Wconversion-extra
794 @opindex @code{Wconversion-extra}
795 @cindex warnings, conversion
797 Warn about implicit conversions between different types and kinds.
799 @item -Wimplicit-interface
800 @opindex @code{Wimplicit-interface}
801 @cindex warnings, implicit interface
802 Warn if a procedure is called without an explicit interface.
803 Note this only checks that an explicit interface is present. It does not
804 check that the declared interfaces are consistent across program units.
806 @item -Wimplicit-procedure
807 @opindex @code{Wimplicit-procedure}
808 @cindex warnings, implicit procedure
809 Warn if a procedure is called that has neither an explicit interface
810 nor has been declared as @code{EXTERNAL}.
812 @item -Wintrinsics-std
813 @opindex @code{Wintrinsics-std}
814 @cindex warnings, non-standard intrinsics
815 @cindex warnings, intrinsics of other standards
816 Warn if @command{gfortran} finds a procedure named like an intrinsic not
817 available in the currently selected standard (with @option{-std}) and treats
818 it as @code{EXTERNAL} procedure because of this. @option{-fall-intrinsics} can
819 be used to never trigger this behavior and always link to the intrinsic
820 regardless of the selected standard.
822 @item -Wreal-q-constant
823 @opindex @code{Wreal-q-constant}
824 @cindex warnings, @code{q} exponent-letter
825 Produce a warning if a real-literal-constant contains a @code{q}
829 @opindex @code{Wsurprising}
830 @cindex warnings, suspicious code
831 Produce a warning when ``suspicious'' code constructs are encountered.
832 While technically legal these usually indicate that an error has been made.
834 This currently produces a warning under the following circumstances:
838 An INTEGER SELECT construct has a CASE that can never be matched as its
839 lower value is greater than its upper value.
842 A LOGICAL SELECT construct has three CASE statements.
845 A TRANSFER specifies a source that is shorter than the destination.
848 The type of a function result is declared more than once with the same type. If
849 @option{-pedantic} or standard-conforming mode is enabled, this is an error.
852 A @code{CHARACTER} variable is declared with negative length.
856 @opindex @code{Wtabs}
857 @cindex warnings, tabs
859 By default, tabs are accepted as whitespace, but tabs are not members
860 of the Fortran Character Set. For continuation lines, a tab followed
861 by a digit between 1 and 9 is supported. @option{-Wno-tabs} will cause
862 a warning to be issued if a tab is encountered. Note, @option{-Wno-tabs}
863 is active for @option{-pedantic}, @option{-std=f95}, @option{-std=f2003},
864 @option{-std=f2008} and @option{-Wall}.
867 @opindex @code{Wunderflow}
868 @cindex warnings, underflow
870 Produce a warning when numerical constant expressions are
871 encountered, which yield an UNDERFLOW during compilation.
873 @item -Wintrinsic-shadow
874 @opindex @code{Wintrinsic-shadow}
875 @cindex warnings, intrinsic
877 Warn if a user-defined procedure or module procedure has the same name as an
878 intrinsic; in this case, an explicit interface or @code{EXTERNAL} or
879 @code{INTRINSIC} declaration might be needed to get calls later resolved to
880 the desired intrinsic/procedure.
882 @item -Wunused-dummy-argument
883 @opindex @code{Wunused-dummy-argument}
884 @cindex warnings, unused dummy argument
885 @cindex unused dummy argument
886 @cindex dummy argument, unused
887 Warn about unused dummy arguments. This option is implied by @option{-Wall}.
889 @item -Wunused-parameter
890 @opindex @code{Wunused-parameter}
891 @cindex warnings, unused parameter
892 @cindex unused parameter
893 Contrary to @command{gcc}'s meaning of @option{-Wunused-parameter},
894 @command{gfortran}'s implementation of this option does not warn
895 about unused dummy arguments (see @option{-Wunused-dummy-argument}),
896 but about unused @code{PARAMETER} values. @option{-Wunused-parameter}
897 is not included in @option{-Wall} but is implied by @option{-Wall -Wextra}.
899 @item -Walign-commons
900 @opindex @code{Walign-commons}
901 @cindex warnings, alignment of @code{COMMON} blocks
902 @cindex alignment of @code{COMMON} blocks
903 By default, @command{gfortran} warns about any occasion of variables being
904 padded for proper alignment inside a @code{COMMON} block. This warning can be turned
905 off via @option{-Wno-align-commons}. See also @option{-falign-commons}.
907 @item -Wfunction-elimination
908 @opindex @code{Wfunction-elimination}
909 @cindex function elimination
910 @cindex warnings, function elimination
911 Warn if any calls to functions are eliminated by the optimizations
912 enabled by the @option{-ffrontend-optimize} option.
916 @opindex @code{Werror}
917 @cindex warnings, to errors
918 Turns all warnings into errors.
921 @xref{Warning Options,,Options to Request or Suppress Errors and
922 Warnings, gcc,Using the GNU Compiler Collection (GCC)}, for information on
923 more options offered by the GBE shared by @command{gfortran}, @command{gcc}
924 and other GNU compilers.
926 Some of these have no effect when compiling programs written in Fortran.
928 @node Debugging Options
929 @section Options for debugging your program or GNU Fortran
930 @cindex options, debugging
931 @cindex debugging information options
933 GNU Fortran has various special options that are used for debugging
934 either your program or the GNU Fortran compiler.
937 @item -fdump-fortran-original
938 @opindex @code{fdump-fortran-original}
939 Output the internal parse tree after translating the source program
940 into internal representation. Only really useful for debugging the
941 GNU Fortran compiler itself.
943 @item -fdump-optimized-tree
944 @opindex @code{fdump-fortran-optimized}
945 Output the parse tree after front-end optimization. Only really
946 useful for debugging the GNU Fortran compiler itself.
948 @opindex @code{fdump-parse-tree}
949 Output the internal parse tree after translating the source program
950 into internal representation. Only really useful for debugging the
951 GNU Fortran compiler itself. This option is deprecated; use
952 @code{-fdump-fortran-original} instead.
954 @item -ffpe-trap=@var{list}
955 @opindex @code{ffpe-trap=}@var{list}
956 Specify a list of floating point exception traps to enable. On most
957 systems, if a floating point exception occurs and the trap for that
958 exception is enabled, a SIGFPE signal will be sent and the program
959 being aborted, producing a core file useful for debugging. @var{list}
960 is a (possibly empty) comma-separated list of the following
961 exceptions: @samp{invalid} (invalid floating point operation, such as
962 @code{SQRT(-1.0)}), @samp{zero} (division by zero), @samp{overflow}
963 (overflow in a floating point operation), @samp{underflow} (underflow
964 in a floating point operation), @samp{inexact} (loss of precision
965 during operation), and @samp{denormal} (operation performed on a
966 denormal value). The first five exceptions correspond to the five
967 IEEE 754 exceptions, whereas the last one (@samp{denormal}) is not
968 part of the IEEE 754 standard but is available on some common
969 architectures such as x86.
971 The first three exceptions (@samp{invalid}, @samp{zero}, and
972 @samp{overflow}) often indicate serious errors, and unless the program
973 has provisions for dealing with these exceptions, enabling traps for
974 these three exceptions is probably a good idea.
976 Many, if not most, floating point operations incur loss of precision
977 due to rounding, and hence the @code{ffpe-trap=inexact} is likely to
978 be uninteresting in practice.
980 By default no exception traps are enabled.
983 @opindex @code{fno-backtrace}
986 When a serious runtime error is encountered or a deadly signal is
987 emitted (segmentation fault, illegal instruction, bus error,
988 floating-point exception, and the other POSIX signals that have the
989 action @samp{core}), the Fortran runtime library tries to output a
990 backtrace of the error. @code{-fno-backtrace} disables the backtrace
991 generation. This option only has influence for compilation of the
992 Fortran main program.
996 @xref{Debugging Options,,Options for Debugging Your Program or GCC,
997 gcc,Using the GNU Compiler Collection (GCC)}, for more information on
1000 @node Directory Options
1001 @section Options for directory search
1002 @cindex directory, options
1003 @cindex options, directory search
1005 @cindex @code{INCLUDE} directive
1006 @cindex directive, @code{INCLUDE}
1007 These options affect how GNU Fortran searches
1008 for files specified by the @code{INCLUDE} directive and where it searches
1009 for previously compiled modules.
1011 It also affects the search paths used by @command{cpp} when used to preprocess
1016 @opindex @code{I}@var{dir}
1017 @cindex directory, search paths for inclusion
1018 @cindex inclusion, directory search paths for
1019 @cindex search paths, for included files
1020 @cindex paths, search
1021 @cindex module search path
1022 These affect interpretation of the @code{INCLUDE} directive
1023 (as well as of the @code{#include} directive of the @command{cpp}
1026 Also note that the general behavior of @option{-I} and
1027 @code{INCLUDE} is pretty much the same as of @option{-I} with
1028 @code{#include} in the @command{cpp} preprocessor, with regard to
1029 looking for @file{header.gcc} files and other such things.
1031 This path is also used to search for @file{.mod} files when previously
1032 compiled modules are required by a @code{USE} statement.
1034 @xref{Directory Options,,Options for Directory Search,
1035 gcc,Using the GNU Compiler Collection (GCC)}, for information on the
1039 @opindex @code{J}@var{dir}
1040 @opindex @code{M}@var{dir}
1041 @cindex paths, search
1042 @cindex module search path
1043 This option specifies where to put @file{.mod} files for compiled modules.
1044 It is also added to the list of directories to searched by an @code{USE}
1047 The default is the current directory.
1049 @item -fintrinsic-modules-path @var{dir}
1050 @opindex @code{fintrinsic-modules-path} @var{dir}
1051 @cindex paths, search
1052 @cindex module search path
1053 This option specifies the location of pre-compiled intrinsic modules, if
1054 they are not in the default location expected by the compiler.
1058 @section Influencing the linking step
1059 @cindex options, linking
1060 @cindex linking, static
1062 These options come into play when the compiler links object files into an
1063 executable output file. They are meaningless if the compiler is not doing
1067 @item -static-libgfortran
1068 @opindex @code{static-libgfortran}
1069 On systems that provide @file{libgfortran} as a shared and a static
1070 library, this option forces the use of the static version. If no
1071 shared version of @file{libgfortran} was built when the compiler was
1072 configured, this option has no effect.
1076 @node Runtime Options
1077 @section Influencing runtime behavior
1078 @cindex options, runtime
1080 These options affect the runtime behavior of programs compiled with GNU Fortran.
1083 @item -fconvert=@var{conversion}
1084 @opindex @code{fconvert=}@var{conversion}
1085 Specify the representation of data for unformatted files. Valid
1086 values for conversion are: @samp{native}, the default; @samp{swap},
1087 swap between big- and little-endian; @samp{big-endian}, use big-endian
1088 representation for unformatted files; @samp{little-endian}, use little-endian
1089 representation for unformatted files.
1091 @emph{This option has an effect only when used in the main program.
1092 The @code{CONVERT} specifier and the GFORTRAN_CONVERT_UNIT environment
1093 variable override the default specified by @option{-fconvert}.}
1096 @item -fno-range-check
1097 @opindex @code{fno-range-check}
1098 Disable range checking of input values during integer @code{READ} operations.
1099 For example, GNU Fortran will give an error if an input value is
1100 outside of the relevant range of [@code{-HUGE()}:@code{HUGE()}]. In other words,
1101 with @code{INTEGER (kind=4) :: i} , attempting to read @math{-2147483648} will
1102 give an error unless @option{-fno-range-check} is given.
1105 @item -frecord-marker=@var{length}
1106 @opindex @code{frecord-marker=}@var{length}
1107 Specify the length of record markers for unformatted files.
1108 Valid values for @var{length} are 4 and 8. Default is 4.
1109 @emph{This is different from previous versions of @command{gfortran}},
1110 which specified a default record marker length of 8 on most
1111 systems. If you want to read or write files compatible
1112 with earlier versions of @command{gfortran}, use @option{-frecord-marker=8}.
1114 @item -fmax-subrecord-length=@var{length}
1115 @opindex @code{fmax-subrecord-length=}@var{length}
1116 Specify the maximum length for a subrecord. The maximum permitted
1117 value for length is 2147483639, which is also the default. Only
1118 really useful for use by the gfortran testsuite.
1121 @opindex @code{fsign-zero}
1122 When enabled, floating point numbers of value zero with the sign bit set
1123 are written as negative number in formatted output and treated as
1124 negative in the @code{SIGN} intrinsic. @option{-fno-sign-zero} does not
1125 print the negative sign of zero values (or values rounded to zero for I/O)
1126 and regards zero as positive number in the @code{SIGN} intrinsic for
1127 compatibility with Fortran 77. The default is @option{-fsign-zero}.
1130 @node Code Gen Options
1131 @section Options for code generation conventions
1132 @cindex code generation, conventions
1133 @cindex options, code generation
1134 @cindex options, run-time
1136 These machine-independent options control the interface conventions
1137 used in code generation.
1139 Most of them have both positive and negative forms; the negative form
1140 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
1141 one of the forms is listed---the one which is not the default. You
1142 can figure out the other form by either removing @option{no-} or adding
1146 @item -fno-automatic
1147 @opindex @code{fno-automatic}
1148 @cindex @code{SAVE} statement
1149 @cindex statement, @code{SAVE}
1150 Treat each program unit (except those marked as RECURSIVE) as if the
1151 @code{SAVE} statement were specified for every local variable and array
1152 referenced in it. Does not affect common blocks. (Some Fortran compilers
1153 provide this option under the name @option{-static} or @option{-save}.)
1154 The default, which is @option{-fautomatic}, uses the stack for local
1155 variables smaller than the value given by @option{-fmax-stack-var-size}.
1156 Use the option @option{-frecursive} to use no static memory.
1160 @cindex calling convention
1161 @cindex @command{f2c} calling convention
1162 @cindex @command{g77} calling convention
1163 @cindex libf2c calling convention
1164 Generate code designed to be compatible with code generated
1165 by @command{g77} and @command{f2c}.
1167 The calling conventions used by @command{g77} (originally implemented
1168 in @command{f2c}) require functions that return type
1169 default @code{REAL} to actually return the C type @code{double}, and
1170 functions that return type @code{COMPLEX} to return the values via an
1171 extra argument in the calling sequence that points to where to
1172 store the return value. Under the default GNU calling conventions, such
1173 functions simply return their results as they would in GNU
1174 C---default @code{REAL} functions return the C type @code{float}, and
1175 @code{COMPLEX} functions return the GNU C type @code{complex}.
1176 Additionally, this option implies the @option{-fsecond-underscore}
1177 option, unless @option{-fno-second-underscore} is explicitly requested.
1179 This does not affect the generation of code that interfaces with
1180 the @command{libgfortran} library.
1182 @emph{Caution:} It is not a good idea to mix Fortran code compiled with
1183 @option{-ff2c} with code compiled with the default @option{-fno-f2c}
1184 calling conventions as, calling @code{COMPLEX} or default @code{REAL}
1185 functions between program parts which were compiled with different
1186 calling conventions will break at execution time.
1188 @emph{Caution:} This will break code which passes intrinsic functions
1189 of type default @code{REAL} or @code{COMPLEX} as actual arguments, as
1190 the library implementations use the @option{-fno-f2c} calling conventions.
1192 @item -fno-underscoring
1193 @opindex @code{fno-underscoring}
1195 @cindex symbol names, underscores
1196 @cindex transforming symbol names
1197 @cindex symbol names, transforming
1198 Do not transform names of entities specified in the Fortran
1199 source file by appending underscores to them.
1201 With @option{-funderscoring} in effect, GNU Fortran appends one
1202 underscore to external names with no underscores. This is done to ensure
1203 compatibility with code produced by many UNIX Fortran compilers.
1205 @emph{Caution}: The default behavior of GNU Fortran is
1206 incompatible with @command{f2c} and @command{g77}, please use the
1207 @option{-ff2c} option if you want object files compiled with
1208 GNU Fortran to be compatible with object code created with these
1211 Use of @option{-fno-underscoring} is not recommended unless you are
1212 experimenting with issues such as integration of GNU Fortran into
1213 existing system environments (vis-@`{a}-vis existing libraries, tools,
1216 For example, with @option{-funderscoring}, and assuming other defaults like
1217 @option{-fcase-lower} and that @code{j()} and @code{max_count()} are
1218 external functions while @code{my_var} and @code{lvar} are local variables,
1221 I = J() + MAX_COUNT (MY_VAR, LVAR)
1224 is implemented as something akin to:
1226 i = j_() + max_count__(&my_var__, &lvar);
1229 With @option{-fno-underscoring}, the same statement is implemented as:
1232 i = j() + max_count(&my_var, &lvar);
1235 Use of @option{-fno-underscoring} allows direct specification of
1236 user-defined names while debugging and when interfacing GNU Fortran
1237 code with other languages.
1239 Note that just because the names match does @emph{not} mean that the
1240 interface implemented by GNU Fortran for an external name matches the
1241 interface implemented by some other language for that same name.
1242 That is, getting code produced by GNU Fortran to link to code produced
1243 by some other compiler using this or any other method can be only a
1244 small part of the overall solution---getting the code generated by
1245 both compilers to agree on issues other than naming can require
1246 significant effort, and, unlike naming disagreements, linkers normally
1247 cannot detect disagreements in these other areas.
1249 Also, note that with @option{-fno-underscoring}, the lack of appended
1250 underscores introduces the very real possibility that a user-defined
1251 external name will conflict with a name in a system library, which
1252 could make finding unresolved-reference bugs quite difficult in some
1253 cases---they might occur at program run time, and show up only as
1254 buggy behavior at run time.
1256 In future versions of GNU Fortran we hope to improve naming and linking
1257 issues so that debugging always involves using the names as they appear
1258 in the source, even if the names as seen by the linker are mangled to
1259 prevent accidental linking between procedures with incompatible
1262 @item -fno-whole-file
1263 @opindex @code{fno-whole-file}
1264 This flag causes the compiler to resolve and translate each procedure in
1267 By default, the whole file is parsed and placed in a single front-end tree.
1268 During resolution, in addition to all the usual checks and fixups, references
1269 to external procedures that are in the same file effect resolution of
1270 that procedure, if not already done, and a check of the interfaces. The
1271 dependences are resolved by changing the order in which the file is
1272 translated into the backend tree. Thus, a procedure that is referenced
1273 is translated before the reference and the duplication of backend tree
1274 declarations eliminated.
1276 The @option{-fno-whole-file} option is deprecated and may lead to wrong code.
1278 @item -fsecond-underscore
1279 @opindex @code{fsecond-underscore}
1281 @cindex symbol names, underscores
1282 @cindex transforming symbol names
1283 @cindex symbol names, transforming
1284 @cindex @command{f2c} calling convention
1285 @cindex @command{g77} calling convention
1286 @cindex libf2c calling convention
1287 By default, GNU Fortran appends an underscore to external
1288 names. If this option is used GNU Fortran appends two
1289 underscores to names with underscores and one underscore to external names
1290 with no underscores. GNU Fortran also appends two underscores to
1291 internal names with underscores to avoid naming collisions with external
1294 This option has no effect if @option{-fno-underscoring} is
1295 in effect. It is implied by the @option{-ff2c} option.
1297 Otherwise, with this option, an external name such as @code{MAX_COUNT}
1298 is implemented as a reference to the link-time external symbol
1299 @code{max_count__}, instead of @code{max_count_}. This is required
1300 for compatibility with @command{g77} and @command{f2c}, and is implied
1301 by use of the @option{-ff2c} option.
1303 @item -fcoarray=@var{<keyword>}
1304 @opindex @code{fcoarray}
1309 Disable coarray support; using coarray declarations and image-control
1310 statements will produce a compile-time error. (Default)
1313 Single-image mode, i.e. @code{num_images()} is always one.
1316 Library-based coarray parallelization; a suitable GNU Fortran coarray
1317 library needs to be linked.
1321 @item -fcheck=@var{<keyword>}
1322 @opindex @code{fcheck}
1323 @cindex array, bounds checking
1324 @cindex bounds checking
1325 @cindex pointer checking
1326 @cindex memory checking
1327 @cindex range checking
1328 @cindex subscript checking
1329 @cindex checking subscripts
1330 @cindex run-time checking
1331 @cindex checking array temporaries
1333 Enable the generation of run-time checks; the argument shall be
1334 a comma-delimited list of the following keywords.
1338 Enable all run-time test of @option{-fcheck}.
1340 @item @samp{array-temps}
1341 Warns at run time when for passing an actual argument a temporary array
1342 had to be generated. The information generated by this warning is
1343 sometimes useful in optimization, in order to avoid such temporaries.
1345 Note: The warning is only printed once per location.
1348 Enable generation of run-time checks for array subscripts
1349 and against the declared minimum and maximum values. It also
1350 checks array indices for assumed and deferred
1351 shape arrays against the actual allocated bounds and ensures that all string
1352 lengths are equal for character array constructors without an explicit
1355 Some checks require that @option{-fcheck=bounds} is set for
1356 the compilation of the main program.
1358 Note: In the future this may also include other forms of checking, e.g.,
1359 checking substring references.
1362 Enable generation of run-time checks for invalid modification of loop
1363 iteration variables.
1366 Enable generation of run-time checks for memory allocation.
1367 Note: This option does not affect explicit allocations using the
1368 @code{ALLOCATE} statement, which will be always checked.
1370 @item @samp{pointer}
1371 Enable generation of run-time checks for pointers and allocatables.
1373 @item @samp{recursion}
1374 Enable generation of run-time checks for recursively called subroutines and
1375 functions which are not marked as recursive. See also @option{-frecursive}.
1376 Note: This check does not work for OpenMP programs and is disabled if used
1377 together with @option{-frecursive} and @option{-fopenmp}.
1381 @item -fbounds-check
1382 @opindex @code{fbounds-check}
1383 @c Note: This option is also referred in gcc's manpage
1384 Deprecated alias for @option{-fcheck=bounds}.
1386 @item -fcheck-array-temporaries
1387 @opindex @code{fcheck-array-temporaries}
1388 Deprecated alias for @option{-fcheck=array-temps}.
1390 @item -fmax-array-constructor=@var{n}
1391 @opindex @code{fmax-array-constructor}
1392 This option can be used to increase the upper limit permitted in
1393 array constructors. The code below requires this option to expand
1394 the array at compile time.
1400 integer, parameter :: n = 100000
1401 integer, parameter :: i(n) = (/ (2*j, j = 1, n) /)
1402 print '(10(I0,1X))', i
1406 @emph{Caution: This option can lead to long compile times and excessively
1407 large object files.}
1409 The default value for @var{n} is 65535.
1412 @item -fmax-stack-var-size=@var{n}
1413 @opindex @code{fmax-stack-var-size}
1414 This option specifies the size in bytes of the largest array that will be put
1415 on the stack; if the size is exceeded static memory is used (except in
1416 procedures marked as RECURSIVE). Use the option @option{-frecursive} to
1417 allow for recursive procedures which do not have a RECURSIVE attribute or
1418 for parallel programs. Use @option{-fno-automatic} to never use the stack.
1420 This option currently only affects local arrays declared with constant
1421 bounds, and may not apply to all character variables.
1422 Future versions of GNU Fortran may improve this behavior.
1424 The default value for @var{n} is 32768.
1426 @item -fstack-arrays
1427 @opindex @code{fstack-arrays}
1428 Adding this option will make the fortran compiler put all local arrays,
1429 even those of unknown size onto stack memory. If your program uses very
1430 large local arrays it is possible that you will have to extend your runtime
1431 limits for stack memory on some operating systems. This flag is enabled
1432 by default at optimization level @option{-Ofast}.
1435 @item -fpack-derived
1436 @opindex @code{fpack-derived}
1437 @cindex structure packing
1438 This option tells GNU Fortran to pack derived type members as closely as
1439 possible. Code compiled with this option is likely to be incompatible
1440 with code compiled without this option, and may execute slower.
1442 @item -frepack-arrays
1443 @opindex @code{frepack-arrays}
1444 @cindex repacking arrays
1445 In some circumstances GNU Fortran may pass assumed shape array
1446 sections via a descriptor describing a noncontiguous area of memory.
1447 This option adds code to the function prologue to repack the data into
1448 a contiguous block at runtime.
1450 This should result in faster accesses to the array. However it can introduce
1451 significant overhead to the function call, especially when the passed data
1455 @opindex @code{fshort-enums}
1456 This option is provided for interoperability with C code that was
1457 compiled with the @option{-fshort-enums} option. It will make
1458 GNU Fortran choose the smallest @code{INTEGER} kind a given
1459 enumerator set will fit in, and give all its enumerators this kind.
1461 @item -fexternal-blas
1462 @opindex @code{fexternal-blas}
1463 This option will make @command{gfortran} generate calls to BLAS functions
1464 for some matrix operations like @code{MATMUL}, instead of using our own
1465 algorithms, if the size of the matrices involved is larger than a given
1466 limit (see @option{-fblas-matmul-limit}). This may be profitable if an
1467 optimized vendor BLAS library is available. The BLAS library will have
1468 to be specified at link time.
1470 @item -fblas-matmul-limit=@var{n}
1471 @opindex @code{fblas-matmul-limit}
1472 Only significant when @option{-fexternal-blas} is in effect.
1473 Matrix multiplication of matrices with size larger than (or equal to) @var{n}
1474 will be performed by calls to BLAS functions, while others will be
1475 handled by @command{gfortran} internal algorithms. If the matrices
1476 involved are not square, the size comparison is performed using the
1477 geometric mean of the dimensions of the argument and result matrices.
1479 The default value for @var{n} is 30.
1482 @opindex @code{frecursive}
1483 Allow indirect recursion by forcing all local arrays to be allocated
1484 on the stack. This flag cannot be used together with
1485 @option{-fmax-stack-var-size=} or @option{-fno-automatic}.
1487 @item -finit-local-zero
1488 @itemx -finit-integer=@var{n}
1489 @itemx -finit-real=@var{<zero|inf|-inf|nan|snan>}
1490 @itemx -finit-logical=@var{<true|false>}
1491 @itemx -finit-character=@var{n}
1492 @opindex @code{finit-local-zero}
1493 @opindex @code{finit-integer}
1494 @opindex @code{finit-real}
1495 @opindex @code{finit-logical}
1496 @opindex @code{finit-character}
1497 The @option{-finit-local-zero} option instructs the compiler to
1498 initialize local @code{INTEGER}, @code{REAL}, and @code{COMPLEX}
1499 variables to zero, @code{LOGICAL} variables to false, and
1500 @code{CHARACTER} variables to a string of null bytes. Finer-grained
1501 initialization options are provided by the
1502 @option{-finit-integer=@var{n}},
1503 @option{-finit-real=@var{<zero|inf|-inf|nan|snan>}} (which also initializes
1504 the real and imaginary parts of local @code{COMPLEX} variables),
1505 @option{-finit-logical=@var{<true|false>}}, and
1506 @option{-finit-character=@var{n}} (where @var{n} is an ASCII character
1507 value) options. These options do not initialize
1512 components of derived type variables
1514 variables that appear in an @code{EQUIVALENCE} statement.
1516 (These limitations may be removed in future releases).
1518 Note that the @option{-finit-real=nan} option initializes @code{REAL}
1519 and @code{COMPLEX} variables with a quiet NaN. For a signalling NaN
1520 use @option{-finit-real=snan}; note, however, that compile-time
1521 optimizations may convert them into quiet NaN and that trapping
1522 needs to be enabled (e.g. via @option{-ffpe-trap}).
1524 Finally, note that enabling any of the @option{-finit-*} options will
1525 silence warnings that would have been emitted by @option{-Wuninitialized}
1526 for the affected local variables.
1528 @item -falign-commons
1529 @opindex @code{falign-commons}
1530 @cindex alignment of @code{COMMON} blocks
1531 By default, @command{gfortran} enforces proper alignment of all variables in a
1532 @code{COMMON} block by padding them as needed. On certain platforms this is mandatory,
1533 on others it increases performance. If a @code{COMMON} block is not declared with
1534 consistent data types everywhere, this padding can cause trouble, and
1535 @option{-fno-align-commons} can be used to disable automatic alignment. The
1536 same form of this option should be used for all files that share a @code{COMMON} block.
1537 To avoid potential alignment issues in @code{COMMON} blocks, it is recommended to order
1538 objects from largest to smallest.
1540 @item -fno-protect-parens
1541 @opindex @code{fno-protect-parens}
1542 @cindex re-association of parenthesized expressions
1543 By default the parentheses in expression are honored for all optimization
1544 levels such that the compiler does not do any re-association. Using
1545 @option{-fno-protect-parens} allows the compiler to reorder @code{REAL} and
1546 @code{COMPLEX} expressions to produce faster code. Note that for the re-association
1547 optimization @option{-fno-signed-zeros} and @option{-fno-trapping-math}
1548 need to be in effect. The parentheses protection is enabled by default, unless
1549 @option{-Ofast} is given.
1552 @opindex @code{frealloc-lhs}
1553 @cindex Reallocate the LHS in assignments
1554 An allocatable left-hand side of an intrinsic assignment is automatically
1555 (re)allocated if it is either unallocated or has a different shape. The
1556 option is enabled by default except when @option{-std=f95} is given.
1558 @item -faggressive-function-elimination
1559 @opindex @code{faggressive-function-elimination}
1560 @cindex Elimination of functions with identical argument lists
1561 Functions with identical argument lists are eliminated within
1562 statements, regardless of whether these functions are marked
1563 @code{PURE} or not. For example, in
1567 there will only be a single call to @code{f}. This option only works
1568 if @option{-ffrontend-optimize} is in effect.
1570 @item -ffrontend-optimize
1571 @opindex @code{frontend-optimize}
1572 @cindex Front-end optimization
1573 This option performs front-end optimization, based on manipulating
1574 parts the Fortran parse tree. Enabled by default by any @option{-O}
1575 option. Optimizations enabled by this option include elimination of
1576 identical function calls within expressions, removing unnecessary
1577 calls to @code{TRIM} in comparisons and assignments and replacing
1578 @code{TRIM(a)} with @code{a(1:LEN_TRIM(a))}.
1579 It can be deselected by specifying @option{-fno-frontend-optimize}.
1582 @xref{Code Gen Options,,Options for Code Generation Conventions,
1583 gcc,Using the GNU Compiler Collection (GCC)}, for information on more options
1585 shared by @command{gfortran}, @command{gcc}, and other GNU compilers.
1589 @node Environment Variables
1590 @section Environment variables affecting @command{gfortran}
1591 @cindex environment variable
1593 @c man begin ENVIRONMENT
1595 The @command{gfortran} compiler currently does not make use of any environment
1596 variables to control its operation above and beyond those
1597 that affect the operation of @command{gcc}.
1599 @xref{Environment Variables,,Environment Variables Affecting GCC,
1600 gcc,Using the GNU Compiler Collection (GCC)}, for information on environment
1603 @xref{Runtime}, for environment variables that affect the
1604 run-time behavior of programs compiled with GNU Fortran.