1GFORTRAN(1)                           GNU                          GFORTRAN(1)
2
3
4

NAME

6       gfortran - GNU Fortran compiler
7

SYNOPSIS

9       gfortran [-c|-S|-E]
10                [-g] [-pg] [-Olevel]
11                [-Wwarn...] [-pedantic]
12                [-Idir...] [-Ldir...]
13                [-Dmacro[=defn]...] [-Umacro]
14                [-foption...]
15                [-mmachine-option...]
16                [-o outfile] infile...
17
18       Only the most useful options are listed here; see below for the
19       remainder.
20

DESCRIPTION

22       The gfortran command supports all the options supported by the gcc
23       command.  Only options specific to GNU Fortran are documented here.
24
25       All GCC and GNU Fortran options are accepted both by gfortran and by
26       gcc (as well as any other drivers built at the same time, such as g++),
27       since adding GNU Fortran to the GCC distribution enables acceptance of
28       GNU Fortran options by all of the relevant drivers.
29
30       In some cases, options have positive and negative forms; the negative
31       form of -ffoo would be -fno-foo.  This manual documents only one of
32       these two forms, whichever one is not the default.
33

OPTIONS

35       Here is a summary of all the options specific to GNU Fortran, grouped
36       by type.  Explanations are in the following sections.
37
38       Fortran Language Options
39           -fall-intrinsics -fallow-argument-mismatch -fallow-invalid-boz
40           -fbackslash -fcray-pointer -fd-lines-as-code -fd-lines-as-comments
41           -fdec -fdec-char-conversions -fdec-structure -fdec-intrinsic-ints
42           -fdec-static -fdec-math -fdec-include -fdec-format-defaults
43           -fdec-blank-format-item -fdefault-double-8 -fdefault-integer-8
44           -fdefault-real-8 -fdefault-real-10 -fdefault-real-16 -fdollar-ok
45           -ffixed-line-length-n -ffixed-line-length-none -fpad-source
46           -ffree-form -ffree-line-length-n -ffree-line-length-none
47           -fimplicit-none -finteger-4-integer-8 -fmax-identifier-length
48           -fmodule-private -ffixed-form -fno-range-check -fopenacc -fopenmp
49           -freal-4-real-10 -freal-4-real-16 -freal-4-real-8 -freal-8-real-10
50           -freal-8-real-16 -freal-8-real-4 -std=std -ftest-forall-temp
51
52       Preprocessing Options
53           -A-question[=answer] -Aquestion=answer -C -CC -Dmacro[=defn] -H -P
54           -Umacro -cpp -dD -dI -dM -dN -dU -fworking-directory -imultilib dir
55           -iprefix file -iquote -isysroot dir -isystem dir -nocpp -nostdinc
56           -undef
57
58       Error and Warning Options
59           -Waliasing -Wall -Wampersand -Warray-bounds -Wc-binding-type
60           -Wcharacter-truncation -Wconversion -Wdo-subscript
61           -Wfunction-elimination -Wimplicit-interface -Wimplicit-procedure
62           -Wintrinsic-shadow -Wuse-without-only -Wintrinsics-std
63           -Wline-truncation -Wno-align-commons -Wno-overwrite-recursive
64           -Wno-tabs -Wreal-q-constant -Wsurprising -Wunderflow
65           -Wunused-parameter -Wrealloc-lhs -Wrealloc-lhs-all
66           -Wfrontend-loop-interchange -Wtarget-lifetime -fmax-errors=n
67           -fsyntax-only -pedantic -pedantic-errors
68
69       Debugging Options
70           -fbacktrace -fdump-fortran-optimized -fdump-fortran-original
71           -fdebug-aux-vars -fdump-fortran-global -fdump-parse-tree
72           -ffpe-trap=list -ffpe-summary=list
73
74       Directory Options
75           -Idir  -Jdir -fintrinsic-modules-path dir
76
77       Link Options
78           -static-libgfortran
79
80       Runtime Options
81           -fconvert=conversion -fmax-subrecord-length=length
82           -frecord-marker=length -fsign-zero
83
84       Interoperability Options
85           -fc-prototypes -fc-prototypes-external
86
87       Code Generation Options
88           -faggressive-function-elimination -fblas-matmul-limit=n
89           -fbounds-check -ftail-call-workaround -ftail-call-workaround=n
90           -fcheck-array-temporaries
91           -fcheck=<all|array-temps|bits|bounds|do|mem|pointer|recursion>
92           -fcoarray=<none|single|lib> -fexternal-blas -ff2c
93           -ffrontend-loop-interchange -ffrontend-optimize -finit-character=n
94           -finit-integer=n -finit-local-zero -finit-derived
95           -finit-logical=<true|false> -finit-real=<zero|inf|-inf|nan|snan>
96           -finline-matmul-limit=n -finline-arg-packing
97           -fmax-array-constructor=n -fmax-stack-var-size=n -fno-align-commons
98           -fno-automatic -fno-protect-parens -fno-underscoring
99           -fsecond-underscore -fpack-derived -frealloc-lhs -frecursive
100           -frepack-arrays -fshort-enums -fstack-arrays
101
102   Options controlling Fortran dialect
103       The following options control the details of the Fortran dialect
104       accepted by the compiler:
105
106       -ffree-form
107       -ffixed-form
108           Specify the layout used by the source file.  The free form layout
109           was introduced in Fortran 90.  Fixed form was traditionally used in
110           older Fortran programs.  When neither option is specified, the
111           source form is determined by the file extension.
112
113       -fall-intrinsics
114           This option causes all intrinsic procedures (including the GNU-
115           specific extensions) to be accepted.  This can be useful with
116           -std=f95 to force standard-compliance but get access to the full
117           range of intrinsics available with gfortran.  As a consequence,
118           -Wintrinsics-std will be ignored and no user-defined procedure with
119           the same name as any intrinsic will be called except when it is
120           explicitly declared "EXTERNAL".
121
122       -fallow-argument-mismatch
123           Some code contains calls to external procedures with mismatches
124           between the calls and the procedure definition, or with mismatches
125           between different calls. Such code is non-conforming, and will
126           usually be flagged with an error.  This options degrades the error
127           to a warning, which can only be disabled by disabling all warnings
128           via -w.  Only a single occurrence per argument is flagged by this
129           warning.  -fallow-argument-mismatch is implied by -std=legacy.
130
131           Using this option is strongly discouraged.  It is possible to
132           provide standard-conforming code which allows different types of
133           arguments by using an explicit interface and TYPE(*).
134
135       -fallow-invalid-boz
136           A BOZ literal constant can occur in a limited number of contexts in
137           standard conforming Fortran.  This option degrades an error
138           condition to a warning, and allows a BOZ literal constant to appear
139           where the Fortran standard would otherwise prohibit its use.
140
141       -fd-lines-as-code
142       -fd-lines-as-comments
143           Enable special treatment for lines beginning with "d" or "D" in
144           fixed form sources.  If the -fd-lines-as-code option is given they
145           are treated as if the first column contained a blank.  If the
146           -fd-lines-as-comments option is given, they are treated as comment
147           lines.
148
149       -fdec
150           DEC compatibility mode. Enables extensions and other features that
151           mimic the default behavior of older compilers (such as DEC).  These
152           features are non-standard and should be avoided at all costs.  For
153           details on GNU Fortran's implementation of these extensions see the
154           full documentation.
155
156           Other flags enabled by this switch are: -fdollar-ok -fcray-pointer
157           -fdec-char-conversions -fdec-structure -fdec-intrinsic-ints
158           -fdec-static -fdec-math -fdec-include -fdec-blank-format-item
159           -fdec-format-defaults
160
161           If -fd-lines-as-code/-fd-lines-as-comments are unset, then -fdec
162           also sets -fd-lines-as-comments.
163
164       -fdec-char-conversions
165           Enable the use of character literals in assignments and "DATA"
166           statements for non-character variables.
167
168       -fdec-structure
169           Enable DEC "STRUCTURE" and "RECORD" as well as "UNION", "MAP", and
170           dot ('.') as a member separator (in addition to '%'). This is
171           provided for compatibility only; Fortran 90 derived types should be
172           used instead where possible.
173
174       -fdec-intrinsic-ints
175           Enable B/I/J/K kind variants of existing integer functions (e.g.
176           BIAND, IIAND, JIAND, etc...). For a complete list of intrinsics see
177           the full documentation.
178
179       -fdec-math
180           Enable legacy math intrinsics such as COTAN and degree-valued
181           trigonometric functions (e.g. TAND, ATAND, etc...) for
182           compatability with older code.
183
184       -fdec-static
185           Enable DEC-style STATIC and AUTOMATIC attributes to explicitly
186           specify the storage of variables and other objects.
187
188       -fdec-include
189           Enable parsing of INCLUDE as a statement in addition to parsing it
190           as INCLUDE line.  When parsed as INCLUDE statement, INCLUDE does
191           not have to be on a single line and can use line continuations.
192
193       -fdec-format-defaults
194           Enable format specifiers F, G and I to be used without width
195           specifiers, default widths will be used instead.
196
197       -fdec-blank-format-item
198           Enable a blank format item at the end of a format specification
199           i.e. nothing following the final comma.
200
201       -fdollar-ok
202           Allow $ as a valid non-first character in a symbol name. Symbols
203           that start with $ are rejected since it is unclear which rules to
204           apply to implicit typing as different vendors implement different
205           rules.  Using $ in "IMPLICIT" statements is also rejected.
206
207       -fbackslash
208           Change the interpretation of backslashes in string literals from a
209           single backslash character to "C-style" escape characters. The
210           following combinations are expanded "\a", "\b", "\f", "\n", "\r",
211           "\t", "\v", "\\", and "\0" to the ASCII characters alert,
212           backspace, form feed, newline, carriage return, horizontal tab,
213           vertical tab, backslash, and NUL, respectively.  Additionally,
214           "\x"nn, "\u"nnnn and "\U"nnnnnnnn (where each n is a hexadecimal
215           digit) are translated into the Unicode characters corresponding to
216           the specified code points. All other combinations of a character
217           preceded by \ are unexpanded.
218
219       -fmodule-private
220           Set the default accessibility of module entities to "PRIVATE".
221           Use-associated entities will not be accessible unless they are
222           explicitly declared as "PUBLIC".
223
224       -ffixed-line-length-n
225           Set column after which characters are ignored in typical fixed-form
226           lines in the source file, and, unless "-fno-pad-source", through
227           which spaces are assumed (as if padded to that length) after the
228           ends of short fixed-form lines.
229
230           Popular values for n include 72 (the standard and the default), 80
231           (card image), and 132 (corresponding to "extended-source" options
232           in some popular compilers).  n may also be none, meaning that the
233           entire line is meaningful and that continued character constants
234           never have implicit spaces appended to them to fill out the line.
235           -ffixed-line-length-0 means the same thing as
236           -ffixed-line-length-none.
237
238       -fno-pad-source
239           By default fixed-form lines have spaces assumed (as if padded to
240           that length) after the ends of short fixed-form lines.  This is not
241           done either if -ffixed-line-length-0, -ffixed-line-length-none or
242           if -fno-pad-source option is used.  With any of those options
243           continued character constants never have implicit spaces appended
244           to them to fill out the line.
245
246       -ffree-line-length-n
247           Set column after which characters are ignored in typical free-form
248           lines in the source file. The default value is 132.  n may be none,
249           meaning that the entire line is meaningful.  -ffree-line-length-0
250           means the same thing as -ffree-line-length-none.
251
252       -fmax-identifier-length=n
253           Specify the maximum allowed identifier length. Typical values are
254           31 (Fortran 95) and 63 (Fortran 2003 and Fortran 2008).
255
256       -fimplicit-none
257           Specify that no implicit typing is allowed, unless overridden by
258           explicit "IMPLICIT" statements.  This is the equivalent of adding
259           "implicit none" to the start of every procedure.
260
261       -fcray-pointer
262           Enable the Cray pointer extension, which provides C-like pointer
263           functionality.
264
265       -fopenacc
266           Enable the OpenACC extensions.  This includes OpenACC "!$acc"
267           directives in free form and "c$acc", *$acc and "!$acc" directives
268           in fixed form, "!$" conditional compilation sentinels in free form
269           and "c$", "*$" and "!$" sentinels in fixed form, and when linking
270           arranges for the OpenACC runtime library to be linked in.
271
272       -fopenmp
273           Enable the OpenMP extensions.  This includes OpenMP "!$omp"
274           directives in free form and "c$omp", *$omp and "!$omp" directives
275           in fixed form, "!$" conditional compilation sentinels in free form
276           and "c$", "*$" and "!$" sentinels in fixed form, and when linking
277           arranges for the OpenMP runtime library to be linked in.  The
278           option -fopenmp implies -frecursive.
279
280       -fno-range-check
281           Disable range checking on results of simplification of constant
282           expressions during compilation.  For example, GNU Fortran will give
283           an error at compile time when simplifying "a = 1. / 0".  With this
284           option, no error will be given and "a" will be assigned the value
285           "+Infinity".  If an expression evaluates to a value outside of the
286           relevant range of ["-HUGE()":"HUGE()"], then the expression will be
287           replaced by "-Inf" or "+Inf" as appropriate.  Similarly, "DATA
288           i/Z'FFFFFFFF'/" will result in an integer overflow on most systems,
289           but with -fno-range-check the value will "wrap around" and "i" will
290           be initialized to -1 instead.
291
292       -fdefault-integer-8
293           Set the default integer and logical types to an 8 byte wide type.
294           This option also affects the kind of integer constants like 42.
295           Unlike -finteger-4-integer-8, it does not promote variables with
296           explicit kind declaration.
297
298       -fdefault-real-8
299           Set the default real type to an 8 byte wide type.  This option also
300           affects the kind of non-double real constants like 1.0.  This
301           option promotes the default width of "DOUBLE PRECISION" and double
302           real constants like "1.d0" to 16 bytes if possible.  If
303           "-fdefault-double-8" is given along with "fdefault-real-8", "DOUBLE
304           PRECISION" and double real constants are not promoted.  Unlike
305           -freal-4-real-8, "fdefault-real-8" does not promote variables with
306           explicit kind declarations.
307
308       -fdefault-real-10
309           Set the default real type to an 10 byte wide type.  This option
310           also affects the kind of non-double real constants like 1.0.  This
311           option promotes the default width of "DOUBLE PRECISION" and double
312           real constants like "1.d0" to 16 bytes if possible.  If
313           "-fdefault-double-8" is given along with "fdefault-real-10",
314           "DOUBLE PRECISION" and double real constants are not promoted.
315           Unlike -freal-4-real-10, "fdefault-real-10" does not promote
316           variables with explicit kind declarations.
317
318       -fdefault-real-16
319           Set the default real type to an 16 byte wide type.  This option
320           also affects the kind of non-double real constants like 1.0.  This
321           option promotes the default width of "DOUBLE PRECISION" and double
322           real constants like "1.d0" to 16 bytes if possible.  If
323           "-fdefault-double-8" is given along with "fdefault-real-16",
324           "DOUBLE PRECISION" and double real constants are not promoted.
325           Unlike -freal-4-real-16, "fdefault-real-16" does not promote
326           variables with explicit kind declarations.
327
328       -fdefault-double-8
329           Set the "DOUBLE PRECISION" type and double real constants like
330           "1.d0" to an 8 byte wide type.  Do nothing if this is already the
331           default.  This option prevents -fdefault-real-8, -fdefault-real-10,
332           and -fdefault-real-16, from promoting "DOUBLE PRECISION" and double
333           real constants like "1.d0" to 16 bytes.
334
335       -finteger-4-integer-8
336           Promote all "INTEGER(KIND=4)" entities to an "INTEGER(KIND=8)"
337           entities.  If "KIND=8" is unavailable, then an error will be
338           issued.  This option should be used with care and may not be
339           suitable for your codes.  Areas of possible concern include calls
340           to external procedures, alignment in "EQUIVALENCE" and/or "COMMON",
341           generic interfaces, BOZ literal constant conversion, and I/O.
342           Inspection of the intermediate representation of the translated
343           Fortran code, produced by -fdump-tree-original, is suggested.
344
345       -freal-4-real-8
346       -freal-4-real-10
347       -freal-4-real-16
348       -freal-8-real-4
349       -freal-8-real-10
350       -freal-8-real-16
351           Promote all "REAL(KIND=M)" entities to "REAL(KIND=N)" entities.  If
352           "REAL(KIND=N)" is unavailable, then an error will be issued.  The
353           "-freal-4-" flags also affect the default real kind and the
354           "-freal-8-" flags also the double-precision real kind.  All other
355           real-kind types are unaffected by this option.  The promotion is
356           also applied to real literal constants of default and double-
357           precision kind and a specified kind number of 4 or 8, respectively.
358           However, "-fdefault-real-8", "-fdefault-real-10",
359           "-fdefault-real-10", and "-fdefault-double-8" take precedence for
360           the default and double-precision real kinds, both for real literal
361           constants and for declarations without a kind number.  Note that
362           for "REAL(KIND=KIND(1.0))" the literal may get promoted and then
363           the result may get promoted again.  These options should be used
364           with care and may not be suitable for your codes.  Areas of
365           possible concern include calls to external procedures, alignment in
366           "EQUIVALENCE" and/or "COMMON", generic interfaces, BOZ literal
367           constant conversion, and I/O and calls to intrinsic procedures when
368           passing a value to the "kind=" dummy argument.  Inspection of the
369           intermediate representation of the translated Fortran code,
370           produced by -fdump-fortran-original or -fdump-tree-original, is
371           suggested.
372
373       -std=std
374           Specify the standard to which the program is expected to conform,
375           which may be one of f95, f2003, f2008, f2018, gnu, or legacy.  The
376           default value for std is gnu, which specifies a superset of the
377           latest Fortran standard that includes all of the extensions
378           supported by GNU Fortran, although warnings will be given for
379           obsolete extensions not recommended for use in new code.  The
380           legacy value is equivalent but without the warnings for obsolete
381           extensions, and may be useful for old non-standard programs.  The
382           f95, f2003, f2008, and f2018 values specify strict conformance to
383           the Fortran 95, Fortran 2003, Fortran 2008 and Fortran 2018
384           standards, respectively; errors are given for all extensions beyond
385           the relevant language standard, and warnings are given for the
386           Fortran 77 features that are permitted but obsolescent in later
387           standards. The deprecated option -std=f2008ts acts as an alias for
388           -std=f2018. It is only present for backwards compatibility with
389           earlier gfortran versions and should not be used any more.
390
391       -ftest-forall-temp
392           Enhance test coverage by forcing most forall assignments to use
393           temporary.
394
395   Enable and customize preprocessing
396       Preprocessor related options. See section Preprocessing and conditional
397       compilation for more detailed information on preprocessing in gfortran.
398
399       -cpp
400       -nocpp
401           Enable preprocessing. The preprocessor is automatically invoked if
402           the file extension is .fpp, .FPP,  .F, .FOR, .FTN, .F90, .F95, .F03
403           or .F08. Use this option to manually enable preprocessing of any
404           kind of Fortran file.
405
406           To disable preprocessing of files with any of the above listed
407           extensions, use the negative form: -nocpp.
408
409           The preprocessor is run in traditional mode. Any restrictions of
410           the file-format, especially the limits on line length, apply for
411           preprocessed output as well, so it might be advisable to use the
412           -ffree-line-length-none or -ffixed-line-length-none options.
413
414       -dM Instead of the normal output, generate a list of '#define'
415           directives for all the macros defined during the execution of the
416           preprocessor, including predefined macros. This gives you a way of
417           finding out what is predefined in your version of the preprocessor.
418           Assuming you have no file foo.f90, the command
419
420                     touch foo.f90; gfortran -cpp -E -dM foo.f90
421
422           will show all the predefined macros.
423
424       -dD Like -dM except in two respects: it does not include the predefined
425           macros, and it outputs both the "#define" directives and the result
426           of preprocessing. Both kinds of output go to the standard output
427           file.
428
429       -dN Like -dD, but emit only the macro names, not their expansions.
430
431       -dU Like dD except that only macros that are expanded, or whose
432           definedness is tested in preprocessor directives, are output; the
433           output is delayed until the use or test of the macro; and '#undef'
434           directives are also output for macros tested but undefined at the
435           time.
436
437       -dI Output '#include' directives in addition to the result of
438           preprocessing.
439
440       -fworking-directory
441           Enable generation of linemarkers in the preprocessor output that
442           will let the compiler know the current working directory at the
443           time of preprocessing. When this option is enabled, the
444           preprocessor will emit, after the initial linemarker, a second
445           linemarker with the current working directory followed by two
446           slashes. GCC will use this directory, when it is present in the
447           preprocessed input, as the directory emitted as the current working
448           directory in some debugging information formats.  This option is
449           implicitly enabled if debugging information is enabled, but this
450           can be inhibited with the negated form -fno-working-directory. If
451           the -P flag is present in the command line, this option has no
452           effect, since no "#line" directives are emitted whatsoever.
453
454       -idirafter dir
455           Search dir for include files, but do it after all directories
456           specified with -I and the standard system directories have been
457           exhausted. dir is treated as a system include directory.  If dir
458           begins with "=", then the "=" will be replaced by the sysroot
459           prefix; see --sysroot and -isysroot.
460
461       -imultilib dir
462           Use dir as a subdirectory of the directory containing target-
463           specific C++ headers.
464
465       -iprefix prefix
466           Specify prefix as the prefix for subsequent -iwithprefix options.
467           If the prefix represents a directory, you should include the final
468           '/'.
469
470       -isysroot dir
471           This option is like the --sysroot option, but applies only to
472           header files. See the --sysroot option for more information.
473
474       -iquote dir
475           Search dir only for header files requested with "#include "file"";
476           they are not searched for "#include <file>", before all directories
477           specified by -I and before the standard system directories. If dir
478           begins with "=", then the "=" will be replaced by the sysroot
479           prefix; see --sysroot and -isysroot.
480
481       -isystem dir
482           Search dir for header files, after all directories specified by -I
483           but before the standard system directories. Mark it as a system
484           directory, so that it gets the same special treatment as is applied
485           to the standard system directories. If dir begins with "=", then
486           the "=" will be replaced by the sysroot prefix; see --sysroot and
487           -isysroot.
488
489       -nostdinc
490           Do not search the standard system directories for header files.
491           Only the directories you have specified with -I options (and the
492           directory of the current file, if appropriate) are searched.
493
494       -undef
495           Do not predefine any system-specific or GCC-specific macros.  The
496           standard predefined macros remain defined.
497
498       -Apredicate=answer
499           Make an assertion with the predicate predicate and answer answer.
500           This form is preferred to the older form -A predicate(answer),
501           which is still supported, because it does not use shell special
502           characters.
503
504       -A-predicate=answer
505           Cancel an assertion with the predicate predicate and answer answer.
506
507       -C  Do not discard comments. All comments are passed through to the
508           output file, except for comments in processed directives, which are
509           deleted along with the directive.
510
511           You should be prepared for side effects when using -C; it causes
512           the preprocessor to treat comments as tokens in their own right.
513           For example, comments appearing at the start of what would be a
514           directive line have the effect of turning that line into an
515           ordinary source line, since the first token on the line is no
516           longer a '#'.
517
518           Warning: this currently handles C-Style comments only. The
519           preprocessor does not yet recognize Fortran-style comments.
520
521       -CC Do not discard comments, including during macro expansion. This is
522           like -C, except that comments contained within macros are also
523           passed through to the output file where the macro is expanded.
524
525           In addition to the side-effects of the -C option, the -CC option
526           causes all C++-style comments inside a macro to be converted to
527           C-style comments. This is to prevent later use of that macro from
528           inadvertently commenting out the remainder of the source line. The
529           -CC option is generally used to support lint comments.
530
531           Warning: this currently handles C- and C++-Style comments only. The
532           preprocessor does not yet recognize Fortran-style comments.
533
534       -Dname
535           Predefine name as a macro, with definition 1.
536
537       -Dname=definition
538           The contents of definition are tokenized and processed as if they
539           appeared during translation phase three in a '#define' directive.
540           In particular, the definition will be truncated by embedded newline
541           characters.
542
543           If you are invoking the preprocessor from a shell or shell-like
544           program you may need to use the shell's quoting syntax to protect
545           characters such as spaces that have a meaning in the shell syntax.
546
547           If you wish to define a function-like macro on the command line,
548           write its argument list with surrounding parentheses before the
549           equals sign (if any). Parentheses are meaningful to most shells, so
550           you will need to quote the option. With sh and csh,
551           "-D'name(args...)=definition'" works.
552
553           -D and -U options are processed in the order they are given on the
554           command line. All -imacros file and -include file options are
555           processed after all -D and -U options.
556
557       -H  Print the name of each header file used, in addition to other
558           normal activities. Each name is indented to show how deep in the
559           '#include' stack it is.
560
561       -P  Inhibit generation of linemarkers in the output from the
562           preprocessor.  This might be useful when running the preprocessor
563           on something that is not C code, and will be sent to a program
564           which might be confused by the linemarkers.
565
566       -Uname
567           Cancel any previous definition of name, either built in or provided
568           with a -D option.
569
570   Options to request or suppress errors and warnings
571       Errors are diagnostic messages that report that the GNU Fortran
572       compiler cannot compile the relevant piece of source code.  The
573       compiler will continue to process the program in an attempt to report
574       further errors to aid in debugging, but will not produce any compiled
575       output.
576
577       Warnings are diagnostic messages that report constructions which are
578       not inherently erroneous but which are risky or suggest there is likely
579       to be a bug in the program.  Unless -Werror is specified, they do not
580       prevent compilation of the program.
581
582       You can request many specific warnings with options beginning -W, for
583       example -Wimplicit to request warnings on implicit declarations.  Each
584       of these specific warning options also has a negative form beginning
585       -Wno- to turn off warnings; for example, -Wno-implicit.  This manual
586       lists only one of the two forms, whichever is not the default.
587
588       These options control the amount and kinds of errors and warnings
589       produced by GNU Fortran:
590
591       -fmax-errors=n
592           Limits the maximum number of error messages to n, at which point
593           GNU Fortran bails out rather than attempting to continue processing
594           the source code.  If n is 0, there is no limit on the number of
595           error messages produced.
596
597       -fsyntax-only
598           Check the code for syntax errors, but do not actually compile it.
599           This will generate module files for each module present in the
600           code, but no other output file.
601
602       -Wpedantic
603       -pedantic
604           Issue warnings for uses of extensions to Fortran.  -pedantic also
605           applies to C-language constructs where they occur in GNU Fortran
606           source files, such as use of \e in a character constant within a
607           directive like "#include".
608
609           Valid Fortran programs should compile properly with or without this
610           option.  However, without this option, certain GNU extensions and
611           traditional Fortran features are supported as well.  With this
612           option, many of them are rejected.
613
614           Some users try to use -pedantic to check programs for conformance.
615           They soon find that it does not do quite what they want---it finds
616           some nonstandard practices, but not all.  However, improvements to
617           GNU Fortran in this area are welcome.
618
619           This should be used in conjunction with -std=f95, -std=f2003,
620           -std=f2008 or -std=f2018.
621
622       -pedantic-errors
623           Like -pedantic, except that errors are produced rather than
624           warnings.
625
626       -Wall
627           Enables commonly used warning options pertaining to usage that we
628           recommend avoiding and that we believe are easy to avoid.  This
629           currently includes -Waliasing, -Wampersand, -Wconversion,
630           -Wsurprising, -Wc-binding-type, -Wintrinsics-std, -Wtabs,
631           -Wintrinsic-shadow, -Wline-truncation, -Wtarget-lifetime,
632           -Winteger-division, -Wreal-q-constant, -Wunused and
633           -Wundefined-do-loop.
634
635       -Waliasing
636           Warn about possible aliasing of dummy arguments. Specifically, it
637           warns if the same actual argument is associated with a dummy
638           argument with "INTENT(IN)" and a dummy argument with "INTENT(OUT)"
639           in a call with an explicit interface.
640
641           The following example will trigger the warning.
642
643                     interface
644                       subroutine bar(a,b)
645                         integer, intent(in) :: a
646                         integer, intent(out) :: b
647                       end subroutine
648                     end interface
649                     integer :: a
650
651                     call bar(a,a)
652
653       -Wampersand
654           Warn about missing ampersand in continued character constants. The
655           warning is given with -Wampersand, -pedantic, -std=f95, -std=f2003,
656           -std=f2008 and -std=f2018. Note: With no ampersand given in a
657           continued character constant, GNU Fortran assumes continuation at
658           the first non-comment, non-whitespace character after the ampersand
659           that initiated the continuation.
660
661       -Warray-temporaries
662           Warn about array temporaries generated by the compiler.  The
663           information generated by this warning is sometimes useful in
664           optimization, in order to avoid such temporaries.
665
666       -Wc-binding-type
667           Warn if the a variable might not be C interoperable.  In
668           particular, warn if the variable has been declared using an
669           intrinsic type with default kind instead of using a kind parameter
670           defined for C interoperability in the intrinsic "ISO_C_Binding"
671           module.  This option is implied by -Wall.
672
673       -Wcharacter-truncation
674           Warn when a character assignment will truncate the assigned string.
675
676       -Wline-truncation
677           Warn when a source code line will be truncated.  This option is
678           implied by -Wall.  For free-form source code, the default is
679           -Werror=line-truncation such that truncations are reported as
680           error.
681
682       -Wconversion
683           Warn about implicit conversions that are likely to change the value
684           of the expression after conversion. Implied by -Wall.
685
686       -Wconversion-extra
687           Warn about implicit conversions between different types and kinds.
688           This option does not imply -Wconversion.
689
690       -Wextra
691           Enables some warning options for usages of language features which
692           may be problematic. This currently includes -Wcompare-reals,
693           -Wunused-parameter and -Wdo-subscript.
694
695       -Wfrontend-loop-interchange
696           Warn when using -ffrontend-loop-interchange for performing loop
697           interchanges.
698
699       -Wimplicit-interface
700           Warn if a procedure is called without an explicit interface.  Note
701           this only checks that an explicit interface is present.  It does
702           not check that the declared interfaces are consistent across
703           program units.
704
705       -Wimplicit-procedure
706           Warn if a procedure is called that has neither an explicit
707           interface nor has been declared as "EXTERNAL".
708
709       -Winteger-division
710           Warn if a constant integer division truncates its result.  As an
711           example, 3/5 evaluates to 0.
712
713       -Wintrinsics-std
714           Warn if gfortran finds a procedure named like an intrinsic not
715           available in the currently selected standard (with -std) and treats
716           it as "EXTERNAL" procedure because of this.  -fall-intrinsics can
717           be used to never trigger this behavior and always link to the
718           intrinsic regardless of the selected standard.
719
720       -Wno-overwrite-recursive
721           Do not warn when -fno-automatic is used with -frecursive. Recursion
722           will be broken if the relevant local variables do not have the
723           attribute "AUTOMATIC" explicitly declared. This option can be used
724           to suppress the warning when it is known that recursion is not
725           broken. Useful for build environments that use -Werror.
726
727       -Wreal-q-constant
728           Produce a warning if a real-literal-constant contains a "q"
729           exponent-letter.
730
731       -Wsurprising
732           Produce a warning when "suspicious" code constructs are
733           encountered.  While technically legal these usually indicate that
734           an error has been made.
735
736           This currently produces a warning under the following
737           circumstances:
738
739           *   An INTEGER SELECT construct has a CASE that can never be
740               matched as its lower value is greater than its upper value.
741
742           *   A LOGICAL SELECT construct has three CASE statements.
743
744           *   A TRANSFER specifies a source that is shorter than the
745               destination.
746
747           *   The type of a function result is declared more than once with
748               the same type.  If -pedantic or standard-conforming mode is
749               enabled, this is an error.
750
751           *   A "CHARACTER" variable is declared with negative length.
752
753       -Wtabs
754           By default, tabs are accepted as whitespace, but tabs are not
755           members of the Fortran Character Set.  For continuation lines, a
756           tab followed by a digit between 1 and 9 is supported.  -Wtabs will
757           cause a warning to be issued if a tab is encountered. Note, -Wtabs
758           is active for -pedantic, -std=f95, -std=f2003, -std=f2008,
759           -std=f2018 and -Wall.
760
761       -Wundefined-do-loop
762           Warn if a DO loop with step either 1 or -1 yields an underflow or
763           an overflow during iteration of an induction variable of the loop.
764           This option is implied by -Wall.
765
766       -Wunderflow
767           Produce a warning when numerical constant expressions are
768           encountered, which yield an UNDERFLOW during compilation. Enabled
769           by default.
770
771       -Wintrinsic-shadow
772           Warn if a user-defined procedure or module procedure has the same
773           name as an intrinsic; in this case, an explicit interface or
774           "EXTERNAL" or "INTRINSIC" declaration might be needed to get calls
775           later resolved to the desired intrinsic/procedure.  This option is
776           implied by -Wall.
777
778       -Wuse-without-only
779           Warn if a "USE" statement has no "ONLY" qualifier and thus
780           implicitly imports all public entities of the used module.
781
782       -Wunused-dummy-argument
783           Warn about unused dummy arguments. This option is implied by -Wall.
784
785       -Wunused-parameter
786           Contrary to gcc's meaning of -Wunused-parameter, gfortran's
787           implementation of this option does not warn about unused dummy
788           arguments (see -Wunused-dummy-argument), but about unused
789           "PARAMETER" values. -Wunused-parameter is implied by -Wextra if
790           also -Wunused or -Wall is used.
791
792       -Walign-commons
793           By default, gfortran warns about any occasion of variables being
794           padded for proper alignment inside a "COMMON" block. This warning
795           can be turned off via -Wno-align-commons. See also -falign-commons.
796
797       -Wfunction-elimination
798           Warn if any calls to impure functions are eliminated by the
799           optimizations enabled by the -ffrontend-optimize option.  This
800           option is implied by -Wextra.
801
802       -Wrealloc-lhs
803           Warn when the compiler might insert code to for allocation or
804           reallocation of an allocatable array variable of intrinsic type in
805           intrinsic assignments.  In hot loops, the Fortran 2003 reallocation
806           feature may reduce the performance.  If the array is already
807           allocated with the correct shape, consider using a whole-array
808           array-spec (e.g. "(:,:,:)") for the variable on the left-hand side
809           to prevent the reallocation check. Note that in some cases the
810           warning is shown, even if the compiler will optimize reallocation
811           checks away.  For instance, when the right-hand side contains the
812           same variable multiplied by a scalar.  See also -frealloc-lhs.
813
814       -Wrealloc-lhs-all
815           Warn when the compiler inserts code to for allocation or
816           reallocation of an allocatable variable; this includes scalars and
817           derived types.
818
819       -Wcompare-reals
820           Warn when comparing real or complex types for equality or
821           inequality.  This option is implied by -Wextra.
822
823       -Wtarget-lifetime
824           Warn if the pointer in a pointer assignment might be longer than
825           the its target. This option is implied by -Wall.
826
827       -Wzerotrip
828           Warn if a "DO" loop is known to execute zero times at compile time.
829           This option is implied by -Wall.
830
831       -Wdo-subscript
832           Warn if an array subscript inside a DO loop could lead to an out-
833           of-bounds access even if the compiler cannot prove that the
834           statement is actually executed, in cases like
835
836                     real a(3)
837                     do i=1,4
838                       if (condition(i)) then
839                         a(i) = 1.2
840                       end if
841                     end do
842
843           This option is implied by -Wextra.
844
845       -Werror
846           Turns all warnings into errors.
847
848       Some of these have no effect when compiling programs written in
849       Fortran.
850
851   Options for debugging your program or GNU Fortran
852       GNU Fortran has various special options that are used for debugging
853       either your program or the GNU Fortran compiler.
854
855       -fdump-fortran-original
856           Output the internal parse tree after translating the source program
857           into internal representation.  This option is mostly useful for
858           debugging the GNU Fortran compiler itself. The output generated by
859           this option might change between releases. This option may also
860           generate internal compiler errors for features which have only
861           recently been added.
862
863       -fdump-fortran-optimized
864           Output the parse tree after front-end optimization.  Mostly useful
865           for debugging the GNU Fortran compiler itself. The output generated
866           by this option might change between releases.  This option may also
867           generate internal compiler errors for features which have only
868           recently been added.
869
870       -fdump-parse-tree
871           Output the internal parse tree after translating the source program
872           into internal representation.  Mostly useful for debugging the GNU
873           Fortran compiler itself. The output generated by this option might
874           change between releases. This option may also generate internal
875           compiler errors for features which have only recently been added.
876           This option is deprecated; use "-fdump-fortran-original" instead.
877
878       -fdebug-aux-vars
879           Renames internal variables created by the gfortran front end and
880           makes them accessible to a debugger.  The name of the internal
881           variables then start with upper-case letters followed by an
882           underscore.  This option is useful for debugging the compiler's
883           code generation together with "-fdump-tree-original" and enabling
884           debugging of the executable program by using "-g" or "-ggdb3".
885
886       -fdump-fortran-global
887           Output a list of the global identifiers after translating into
888           middle-end representation. Mostly useful for debugging the GNU
889           Fortran compiler itself. The output generated by this option might
890           change between releases.  This option may also generate internal
891           compiler errors for features which have only recently been added.
892
893       -ffpe-trap=list
894           Specify a list of floating point exception traps to enable.  On
895           most systems, if a floating point exception occurs and the trap for
896           that exception is enabled, a SIGFPE signal will be sent and the
897           program being aborted, producing a core file useful for debugging.
898           list is a (possibly empty) comma-separated list of the following
899           exceptions: invalid (invalid floating point operation, such as
900           "SQRT(-1.0)"), zero (division by zero), overflow (overflow in a
901           floating point operation), underflow (underflow in a floating point
902           operation), inexact (loss of precision during operation), and
903           denormal (operation performed on a denormal value).  The first five
904           exceptions correspond to the five IEEE 754 exceptions, whereas the
905           last one (denormal) is not part of the IEEE 754 standard but is
906           available on some common architectures such as x86.
907
908           The first three exceptions (invalid, zero, and overflow) often
909           indicate serious errors, and unless the program has provisions for
910           dealing with these exceptions, enabling traps for these three
911           exceptions is probably a good idea.
912
913           If the option is used more than once in the command line, the lists
914           will be joined: '"ffpe-trap="list1 "ffpe-trap="list2' is equivalent
915           to "ffpe-trap="list1,list2.
916
917           Note that once enabled an exception cannot be disabled (no negative
918           form).
919
920           Many, if not most, floating point operations incur loss of
921           precision due to rounding, and hence the "ffpe-trap=inexact" is
922           likely to be uninteresting in practice.
923
924           By default no exception traps are enabled.
925
926       -ffpe-summary=list
927           Specify a list of floating-point exceptions, whose flag status is
928           printed to "ERROR_UNIT" when invoking "STOP" and "ERROR STOP".
929           list can be either none, all or a comma-separated list of the
930           following exceptions: invalid, zero, overflow, underflow, inexact
931           and denormal. (See -ffpe-trap for a description of the exceptions.)
932
933           If the option is used more than once in the command line, only the
934           last one will be used.
935
936           By default, a summary for all exceptions but inexact is shown.
937
938       -fno-backtrace
939           When a serious runtime error is encountered or a deadly signal is
940           emitted (segmentation fault, illegal instruction, bus error,
941           floating-point exception, and the other POSIX signals that have the
942           action core), the Fortran runtime library tries to output a
943           backtrace of the error. "-fno-backtrace" disables the backtrace
944           generation. This option only has influence for compilation of the
945           Fortran main program.
946
947   Options for directory search
948       These options affect how GNU Fortran searches for files specified by
949       the "INCLUDE" directive and where it searches for previously compiled
950       modules.
951
952       It also affects the search paths used by cpp when used to preprocess
953       Fortran source.
954
955       -Idir
956           These affect interpretation of the "INCLUDE" directive (as well as
957           of the "#include" directive of the cpp preprocessor).
958
959           Also note that the general behavior of -I and "INCLUDE" is pretty
960           much the same as of -I with "#include" in the cpp preprocessor,
961           with regard to looking for header.gcc files and other such things.
962
963           This path is also used to search for .mod files when previously
964           compiled modules are required by a "USE" statement.
965
966       -Jdir
967           This option specifies where to put .mod files for compiled modules.
968           It is also added to the list of directories to searched by an "USE"
969           statement.
970
971           The default is the current directory.
972
973       -fintrinsic-modules-path dir
974           This option specifies the location of pre-compiled intrinsic
975           modules, if they are not in the default location expected by the
976           compiler.
977
978   Influencing the linking step
979       These options come into play when the compiler links object files into
980       an executable output file. They are meaningless if the compiler is not
981       doing a link step.
982
983       -static-libgfortran
984           On systems that provide libgfortran as a shared and a static
985           library, this option forces the use of the static version. If no
986           shared version of libgfortran was built when the compiler was
987           configured, this option has no effect.
988
989   Influencing runtime behavior
990       These options affect the runtime behavior of programs compiled with GNU
991       Fortran.
992
993       -fconvert=conversion
994           Specify the representation of data for unformatted files.  Valid
995           values for conversion are: native, the default; swap, swap between
996           big- and little-endian; big-endian, use big-endian representation
997           for unformatted files; little-endian, use little-endian
998           representation for unformatted files.
999
1000           This option has an effect only when used in the main program.  The
1001           "CONVERT" specifier and the GFORTRAN_CONVERT_UNIT environment
1002           variable override the default specified by -fconvert.
1003
1004       -frecord-marker=length
1005           Specify the length of record markers for unformatted files.  Valid
1006           values for length are 4 and 8.  Default is 4.  This is different
1007           from previous versions of gfortran, which specified a default
1008           record marker length of 8 on most systems.  If you want to read or
1009           write files compatible with earlier versions of gfortran, use
1010           -frecord-marker=8.
1011
1012       -fmax-subrecord-length=length
1013           Specify the maximum length for a subrecord.  The maximum permitted
1014           value for length is 2147483639, which is also the default.  Only
1015           really useful for use by the gfortran testsuite.
1016
1017       -fsign-zero
1018           When enabled, floating point numbers of value zero with the sign
1019           bit set are written as negative number in formatted output and
1020           treated as negative in the "SIGN" intrinsic.  -fno-sign-zero does
1021           not print the negative sign of zero values (or values rounded to
1022           zero for I/O) and regards zero as positive number in the "SIGN"
1023           intrinsic for compatibility with Fortran 77. The default is
1024           -fsign-zero.
1025
1026   Options for code generation conventions
1027       These machine-independent options control the interface conventions
1028       used in code generation.
1029
1030       Most of them have both positive and negative forms; the negative form
1031       of -ffoo would be -fno-foo.  In the table below, only one of the forms
1032       is listed---the one which is not the default.  You can figure out the
1033       other form by either removing no- or adding it.
1034
1035       -fno-automatic
1036           Treat each program unit (except those marked as RECURSIVE) as if
1037           the "SAVE" statement were specified for every local variable and
1038           array referenced in it. Does not affect common blocks. (Some
1039           Fortran compilers provide this option under the name -static or
1040           -save.)  The default, which is -fautomatic, uses the stack for
1041           local variables smaller than the value given by
1042           -fmax-stack-var-size.  Use the option -frecursive to use no static
1043           memory.
1044
1045           Local variables or arrays having an explicit "SAVE" attribute are
1046           silently ignored unless the -pedantic option is added.
1047
1048       -ff2c
1049           Generate code designed to be compatible with code generated by g77
1050           and f2c.
1051
1052           The calling conventions used by g77 (originally implemented in f2c)
1053           require functions that return type default "REAL" to actually
1054           return the C type "double", and functions that return type
1055           "COMPLEX" to return the values via an extra argument in the calling
1056           sequence that points to where to store the return value.  Under the
1057           default GNU calling conventions, such functions simply return their
1058           results as they would in GNU C---default "REAL" functions return
1059           the C type "float", and "COMPLEX" functions return the GNU C type
1060           "complex".  Additionally, this option implies the
1061           -fsecond-underscore option, unless -fno-second-underscore is
1062           explicitly requested.
1063
1064           This does not affect the generation of code that interfaces with
1065           the libgfortran library.
1066
1067           Caution: It is not a good idea to mix Fortran code compiled with
1068           -ff2c with code compiled with the default -fno-f2c calling
1069           conventions as, calling "COMPLEX" or default "REAL" functions
1070           between program parts which were compiled with different calling
1071           conventions will break at execution time.
1072
1073           Caution: This will break code which passes intrinsic functions of
1074           type default "REAL" or "COMPLEX" as actual arguments, as the
1075           library implementations use the -fno-f2c calling conventions.
1076
1077       -fno-underscoring
1078           Do not transform names of entities specified in the Fortran source
1079           file by appending underscores to them.
1080
1081           With -funderscoring in effect, GNU Fortran appends one underscore
1082           to external names with no underscores.  This is done to ensure
1083           compatibility with code produced by many UNIX Fortran compilers.
1084
1085           Caution: The default behavior of GNU Fortran is incompatible with
1086           f2c and g77, please use the -ff2c option if you want object files
1087           compiled with GNU Fortran to be compatible with object code created
1088           with these tools.
1089
1090           Use of -fno-underscoring is not recommended unless you are
1091           experimenting with issues such as integration of GNU Fortran into
1092           existing system environments (vis-a-vis existing libraries, tools,
1093           and so on).
1094
1095           For example, with -funderscoring, and assuming that "j()" and
1096           "max_count()" are external functions while "my_var" and "lvar" are
1097           local variables, a statement like
1098
1099                   I = J() + MAX_COUNT (MY_VAR, LVAR)
1100
1101           is implemented as something akin to:
1102
1103                   i = j_() + max_count__(&my_var__, &lvar);
1104
1105           With -fno-underscoring, the same statement is implemented as:
1106
1107                   i = j() + max_count(&my_var, &lvar);
1108
1109           Use of -fno-underscoring allows direct specification of user-
1110           defined names while debugging and when interfacing GNU Fortran code
1111           with other languages.
1112
1113           Note that just because the names match does not mean that the
1114           interface implemented by GNU Fortran for an external name matches
1115           the interface implemented by some other language for that same
1116           name.  That is, getting code produced by GNU Fortran to link to
1117           code produced by some other compiler using this or any other method
1118           can be only a small part of the overall solution---getting the code
1119           generated by both compilers to agree on issues other than naming
1120           can require significant effort, and, unlike naming disagreements,
1121           linkers normally cannot detect disagreements in these other areas.
1122
1123           Also, note that with -fno-underscoring, the lack of appended
1124           underscores introduces the very real possibility that a user-
1125           defined external name will conflict with a name in a system
1126           library, which could make finding unresolved-reference bugs quite
1127           difficult in some cases---they might occur at program run time, and
1128           show up only as buggy behavior at run time.
1129
1130           In future versions of GNU Fortran we hope to improve naming and
1131           linking issues so that debugging always involves using the names as
1132           they appear in the source, even if the names as seen by the linker
1133           are mangled to prevent accidental linking between procedures with
1134           incompatible interfaces.
1135
1136       -fsecond-underscore
1137           By default, GNU Fortran appends an underscore to external names.
1138           If this option is used GNU Fortran appends two underscores to names
1139           with underscores and one underscore to external names with no
1140           underscores.  GNU Fortran also appends two underscores to internal
1141           names with underscores to avoid naming collisions with external
1142           names.
1143
1144           This option has no effect if -fno-underscoring is in effect.  It is
1145           implied by the -ff2c option.
1146
1147           Otherwise, with this option, an external name such as "MAX_COUNT"
1148           is implemented as a reference to the link-time external symbol
1149           "max_count__", instead of "max_count_".  This is required for
1150           compatibility with g77 and f2c, and is implied by use of the -ff2c
1151           option.
1152
1153       -fcoarray=<keyword>
1154           none
1155               Disable coarray support; using coarray declarations and image-
1156               control statements will produce a compile-time error. (Default)
1157
1158           single
1159               Single-image mode, i.e. "num_images()" is always one.
1160
1161           lib Library-based coarray parallelization; a suitable GNU Fortran
1162               coarray library needs to be linked.
1163
1164       -fcheck=<keyword>
1165           Enable the generation of run-time checks; the argument shall be a
1166           comma-delimited list of the following keywords.  Prefixing a check
1167           with no- disables it if it was activated by a previous
1168           specification.
1169
1170           all Enable all run-time test of -fcheck.
1171
1172           array-temps
1173               Warns at run time when for passing an actual argument a
1174               temporary array had to be generated. The information generated
1175               by this warning is sometimes useful in optimization, in order
1176               to avoid such temporaries.
1177
1178               Note: The warning is only printed once per location.
1179
1180           bits
1181               Enable generation of run-time checks for invalid arguments to
1182               the bit manipulation intrinsics.
1183
1184           bounds
1185               Enable generation of run-time checks for array subscripts and
1186               against the declared minimum and maximum values.  It also
1187               checks array indices for assumed and deferred shape arrays
1188               against the actual allocated bounds and ensures that all string
1189               lengths are equal for character array constructors without an
1190               explicit typespec.
1191
1192               Some checks require that -fcheck=bounds is set for the
1193               compilation of the main program.
1194
1195               Note: In the future this may also include other forms of
1196               checking, e.g., checking substring references.
1197
1198           do  Enable generation of run-time checks for invalid modification
1199               of loop iteration variables.
1200
1201           mem Enable generation of run-time checks for memory allocation.
1202               Note: This option does not affect explicit allocations using
1203               the "ALLOCATE" statement, which will be always checked.
1204
1205           pointer
1206               Enable generation of run-time checks for pointers and
1207               allocatables.
1208
1209           recursion
1210               Enable generation of run-time checks for recursively called
1211               subroutines and functions which are not marked as recursive.
1212               See also -frecursive.  Note: This check does not work for
1213               OpenMP programs and is disabled if used together with
1214               -frecursive and -fopenmp.
1215
1216           Example: Assuming you have a file foo.f90, the command
1217
1218                     gfortran -fcheck=all,no-array-temps foo.f90
1219
1220           will compile the file with all checks enabled as specified above
1221           except warnings for generated array temporaries.
1222
1223       -fbounds-check
1224           Deprecated alias for -fcheck=bounds.
1225
1226       -ftail-call-workaround
1227       -ftail-call-workaround=n
1228           Some C interfaces to Fortran codes violate the gfortran ABI by
1229           omitting the hidden character length arguments as described in
1230             This can lead to crashes because pushing arguments for tail calls
1231           can overflow the stack.
1232
1233           To provide a workaround for existing binary packages, this option
1234           disables tail call optimization for gfortran procedures with
1235           character arguments.  With -ftail-call-workaround=2 tail call
1236           optimization is disabled in all gfortran procedures with character
1237           arguments, with -ftail-call-workaround=1 or equivalent
1238           -ftail-call-workaround only in gfortran procedures with character
1239           arguments that call implicitly prototyped procedures.
1240
1241           Using this option can lead to problems including crashes due to
1242           insufficient stack space.
1243
1244           It is very strongly recommended to fix the code in question.  The
1245           -fc-prototypes-external option can be used to generate prototypes
1246           which conform to gfortran's ABI, for inclusion in the source code.
1247
1248           Support for this option will likely be withdrawn in a future
1249           release of gfortran.
1250
1251           The negative form, -fno-tail-call-workaround or equivalent
1252           -ftail-call-workaround=0, can be used to disable this option.
1253
1254           Default is currently -ftail-call-workaround, this will change in
1255           future releases.
1256
1257       -fcheck-array-temporaries
1258           Deprecated alias for -fcheck=array-temps.
1259
1260       -fmax-array-constructor=n
1261           This option can be used to increase the upper limit permitted in
1262           array constructors.  The code below requires this option to expand
1263           the array at compile time.
1264
1265                   program test
1266                   implicit none
1267                   integer j
1268                   integer, parameter :: n = 100000
1269                   integer, parameter :: i(n) = (/ (2*j, j = 1, n) /)
1270                   print '(10(I0,1X))', i
1271                   end program test
1272
1273           Caution:  This option can lead to long compile times and
1274           excessively large object files.
1275
1276           The default value for n is 65535.
1277
1278       -fmax-stack-var-size=n
1279           This option specifies the size in bytes of the largest array that
1280           will be put on the stack; if the size is exceeded static memory is
1281           used (except in procedures marked as RECURSIVE). Use the option
1282           -frecursive to allow for recursive procedures which do not have a
1283           RECURSIVE attribute or for parallel programs. Use -fno-automatic to
1284           never use the stack.
1285
1286           This option currently only affects local arrays declared with
1287           constant bounds, and may not apply to all character variables.
1288           Future versions of GNU Fortran may improve this behavior.
1289
1290           The default value for n is 65536.
1291
1292       -fstack-arrays
1293           Adding this option will make the Fortran compiler put all arrays of
1294           unknown size and array temporaries onto stack memory.  If your
1295           program uses very large local arrays it is possible that you will
1296           have to extend your runtime limits for stack memory on some
1297           operating systems. This flag is enabled by default at optimization
1298           level -Ofast unless -fmax-stack-var-size is specified.
1299
1300       -fpack-derived
1301           This option tells GNU Fortran to pack derived type members as
1302           closely as possible.  Code compiled with this option is likely to
1303           be incompatible with code compiled without this option, and may
1304           execute slower.
1305
1306       -frepack-arrays
1307           In some circumstances GNU Fortran may pass assumed shape array
1308           sections via a descriptor describing a noncontiguous area of
1309           memory.  This option adds code to the function prologue to repack
1310           the data into a contiguous block at runtime.
1311
1312           This should result in faster accesses to the array.  However it can
1313           introduce significant overhead to the function call, especially
1314           when the passed data is noncontiguous.
1315
1316       -fshort-enums
1317           This option is provided for interoperability with C code that was
1318           compiled with the -fshort-enums option.  It will make GNU Fortran
1319           choose the smallest "INTEGER" kind a given enumerator set will fit
1320           in, and give all its enumerators this kind.
1321
1322       -finline-arg-packing
1323           When passing an assumed-shape argument of a procedure as actual
1324           argument to an assumed-size or explicit size or as argument to a
1325           procedure that does not have an explicit interface, the argument
1326           may have to be packed, that is put into contiguous memory. An
1327           example is the call to "foo" in
1328
1329                     subroutine foo(a)
1330                        real, dimension(*) :: a
1331                     end subroutine foo
1332                     subroutine bar(b)
1333                        real, dimension(:) :: b
1334                        call foo(b)
1335                     end subroutine bar
1336
1337           When -finline-arg-packing is in effect, this packing will be
1338           performed by inline code. This allows for more optimization while
1339           increasing code size.
1340
1341           -finline-arg-packing is implied by any of the -O options except
1342           when optimizing for size via -Os.  If the code contains a very
1343           large number of argument that have to be packed, code size and also
1344           compilation time may become excessive.  If that is the case, it may
1345           be better to disable this option.  Instances of packing can be
1346           found by using by using -Warray-temporaries.
1347
1348       -fexternal-blas
1349           This option will make gfortran generate calls to BLAS functions for
1350           some matrix operations like "MATMUL", instead of using our own
1351           algorithms, if the size of the matrices involved is larger than a
1352           given limit (see -fblas-matmul-limit).  This may be profitable if
1353           an optimized vendor BLAS library is available.  The BLAS library
1354           will have to be specified at link time.
1355
1356       -fblas-matmul-limit=n
1357           Only significant when -fexternal-blas is in effect.  Matrix
1358           multiplication of matrices with size larger than (or equal to) n
1359           will be performed by calls to BLAS functions, while others will be
1360           handled by gfortran internal algorithms. If the matrices involved
1361           are not square, the size comparison is performed using the
1362           geometric mean of the dimensions of the argument and result
1363           matrices.
1364
1365           The default value for n is 30.
1366
1367       -finline-matmul-limit=n
1368           When front-end optimization is active, some calls to the "MATMUL"
1369           intrinsic function will be inlined.  This may result in code size
1370           increase if the size of the matrix cannot be determined at compile
1371           time, as code for both cases is generated.  Setting
1372           "-finline-matmul-limit=0" will disable inlining in all cases.
1373           Setting this option with a value of n will produce inline code for
1374           matrices with size up to n. If the matrices involved are not
1375           square, the size comparison is performed using the geometric mean
1376           of the dimensions of the argument and result matrices.
1377
1378           The default value for n is 30.  The "-fblas-matmul-limit" can be
1379           used to change this value.
1380
1381       -frecursive
1382           Allow indirect recursion by forcing all local arrays to be
1383           allocated on the stack. This flag cannot be used together with
1384           -fmax-stack-var-size= or -fno-automatic.
1385
1386       -finit-local-zero
1387       -finit-derived
1388       -finit-integer=n
1389       -finit-real=<zero|inf|-inf|nan|snan>
1390       -finit-logical=<true|false>
1391       -finit-character=n
1392           The -finit-local-zero option instructs the compiler to initialize
1393           local "INTEGER", "REAL", and "COMPLEX" variables to zero, "LOGICAL"
1394           variables to false, and "CHARACTER" variables to a string of null
1395           bytes.  Finer-grained initialization options are provided by the
1396           -finit-integer=n, -finit-real=<zero|inf|-inf|nan|snan> (which also
1397           initializes the real and imaginary parts of local "COMPLEX"
1398           variables), -finit-logical=<true|false>, and -finit-character=n
1399           (where n is an ASCII character value) options.
1400
1401           With -finit-derived, components of derived type variables will be
1402           initialized according to these flags.  Components whose type is not
1403           covered by an explicit -finit-* flag will be treated as described
1404           above with -finit-local-zero.
1405
1406           These options do not initialize
1407
1408           *   objects with the POINTER attribute
1409
1410           *   allocatable arrays
1411
1412           *   variables that appear in an "EQUIVALENCE" statement.
1413
1414           (These limitations may be removed in future releases).
1415
1416           Note that the -finit-real=nan option initializes "REAL" and
1417           "COMPLEX" variables with a quiet NaN. For a signalling NaN use
1418           -finit-real=snan; note, however, that compile-time optimizations
1419           may convert them into quiet NaN and that trapping needs to be
1420           enabled (e.g. via -ffpe-trap).
1421
1422           The -finit-integer option will parse the value into an integer of
1423           type "INTEGER(kind=C_LONG)" on the host.  Said value is then
1424           assigned to the integer variables in the Fortran code, which might
1425           result in wraparound if the value is too large for the kind.
1426
1427           Finally, note that enabling any of the -finit-* options will
1428           silence warnings that would have been emitted by -Wuninitialized
1429           for the affected local variables.
1430
1431       -falign-commons
1432           By default, gfortran enforces proper alignment of all variables in
1433           a "COMMON" block by padding them as needed. On certain platforms
1434           this is mandatory, on others it increases performance. If a
1435           "COMMON" block is not declared with consistent data types
1436           everywhere, this padding can cause trouble, and -fno-align-commons
1437           can be used to disable automatic alignment. The same form of this
1438           option should be used for all files that share a "COMMON" block.
1439           To avoid potential alignment issues in "COMMON" blocks, it is
1440           recommended to order objects from largest to smallest.
1441
1442       -fno-protect-parens
1443           By default the parentheses in expression are honored for all
1444           optimization levels such that the compiler does not do any re-
1445           association. Using -fno-protect-parens allows the compiler to
1446           reorder "REAL" and "COMPLEX" expressions to produce faster code.
1447           Note that for the re-association optimization -fno-signed-zeros and
1448           -fno-trapping-math need to be in effect. The parentheses protection
1449           is enabled by default, unless -Ofast is given.
1450
1451       -frealloc-lhs
1452           An allocatable left-hand side of an intrinsic assignment is
1453           automatically (re)allocated if it is either unallocated or has a
1454           different shape. The option is enabled by default except when
1455           -std=f95 is given. See also -Wrealloc-lhs.
1456
1457       -faggressive-function-elimination
1458           Functions with identical argument lists are eliminated within
1459           statements, regardless of whether these functions are marked "PURE"
1460           or not. For example, in
1461
1462                     a = f(b,c) + f(b,c)
1463
1464           there will only be a single call to "f".  This option only works if
1465           -ffrontend-optimize is in effect.
1466
1467       -ffrontend-optimize
1468           This option performs front-end optimization, based on manipulating
1469           parts the Fortran parse tree.  Enabled by default by any -O option
1470           except -O0 and -Og.  Optimizations enabled by this option include:
1471
1472           *<inlining calls to "MATMUL",>
1473           *<elimination of identical function calls within expressions,>
1474           *<removing unnecessary calls to "TRIM" in comparisons and
1475           assignments,>
1476           *<replacing TRIM(a) with "a(1:LEN_TRIM(a))" and>
1477           *<short-circuiting of logical operators (".AND." and ".OR.").>
1478
1479           It can be deselected by specifying -fno-frontend-optimize.
1480
1481       -ffrontend-loop-interchange
1482           Attempt to interchange loops in the Fortran front end where
1483           profitable.  Enabled by default by any -O option.  At the moment,
1484           this option only affects "FORALL" and "DO CONCURRENT" statements
1485           with several forall triplets.
1486

ENVIRONMENT

1488       The gfortran compiler currently does not make use of any environment
1489       variables to control its operation above and beyond those that affect
1490       the operation of gcc.
1491

BUGS

1493       For instructions on reporting bugs, see
1494       <http://bugzilla.redhat.com/bugzilla>.
1495

SEE ALSO

1497       gpl(7), gfdl(7), fsf-funding(7), cpp(1), gcov(1), gcc(1), as(1), ld(1),
1498       gdb(1), dbx(1) and the Info entries for gcc, cpp, gfortran, as, ld,
1499       binutils and gdb.
1500

AUTHOR

1502       See the Info entry for gfortran for contributors to GCC and GNU
1503       Fortran.
1504
1506       Copyright (c) 2004-2021 Free Software Foundation, Inc.
1507
1508       Permission is granted to copy, distribute and/or modify this document
1509       under the terms of the GNU Free Documentation License, Version 1.3 or
1510       any later version published by the Free Software Foundation; with the
1511       Invariant Sections being "Funding Free Software", the Front-Cover Texts
1512       being (a) (see below), and with the Back-Cover Texts being (b) (see
1513       below).  A copy of the license is included in the gfdl(7) man page.
1514
1515       (a) The FSF's Front-Cover Text is:
1516
1517            A GNU Manual
1518
1519       (b) The FSF's Back-Cover Text is:
1520
1521            You have freedom to copy and modify this GNU Manual, like GNU
1522            software.  Copies published by the Free Software Foundation raise
1523            funds for GNU development.
1524
1525
1526
1527gcc-11                            2021-07-28                       GFORTRAN(1)
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