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7e7065b9 | 1 | @c Copyright (C) 2004-2020 Free Software Foundation, Inc. |
7fc15ba5 | 2 | @c This is part of the GNU Fortran manual. |
6de9cd9a DN |
3 | @c For copying conditions, see the file gfortran.texi. |
4 | ||
5 | @ignore | |
6 | @c man begin COPYRIGHT | |
7e7065b9 | 7 | Copyright @copyright{} 2004-2020 Free Software Foundation, Inc. |
6de9cd9a DN |
8 | |
9 | Permission is granted to copy, distribute and/or modify this document | |
07a67d6a | 10 | under the terms of the GNU Free Documentation License, Version 1.3 or |
6de9cd9a | 11 | any later version published by the Free Software Foundation; with the |
70b1e376 RW |
12 | Invariant Sections being ``Funding Free Software'', the Front-Cover |
13 | Texts being (a) (see below), and with the Back-Cover Texts being (b) | |
14 | (see below). A copy of the license is included in the gfdl(7) man page. | |
6ccde948 | 15 | |
6de9cd9a DN |
16 | (a) The FSF's Front-Cover Text is: |
17 | ||
18 | A GNU Manual | |
19 | ||
20 | (b) The FSF's Back-Cover Text is: | |
21 | ||
22 | You have freedom to copy and modify this GNU Manual, like GNU | |
23 | software. Copies published by the Free Software Foundation raise | |
24 | funds for GNU development. | |
25 | @c man end | |
26 | @c Set file name and title for the man page. | |
27 | @setfilename gfortran | |
7fc15ba5 | 28 | @settitle GNU Fortran compiler. |
6de9cd9a DN |
29 | @c man begin SYNOPSIS |
30 | gfortran [@option{-c}|@option{-S}|@option{-E}] | |
31 | [@option{-g}] [@option{-pg}] [@option{-O}@var{level}] | |
32 | [@option{-W}@var{warn}@dots{}] [@option{-pedantic}] | |
33 | [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}] | |
34 | [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}] | |
35 | [@option{-f}@var{option}@dots{}] | |
6ccde948 | 36 | [@option{-m}@var{machine-option}@dots{}] |
6de9cd9a DN |
37 | [@option{-o} @var{outfile}] @var{infile}@dots{} |
38 | ||
39 | Only the most useful options are listed here; see below for the | |
40 | remainder. | |
41 | @c man end | |
42 | @c man begin SEEALSO | |
43 | gpl(7), gfdl(7), fsf-funding(7), | |
180295ed | 44 | cpp(1), gcov(1), gcc(1), as(1), ld(1), gdb(1), dbx(1) |
6de9cd9a DN |
45 | and the Info entries for @file{gcc}, @file{cpp}, @file{gfortran}, @file{as}, |
46 | @file{ld}, @file{binutils} and @file{gdb}. | |
47 | @c man end | |
48 | @c man begin BUGS | |
49 | For instructions on reporting bugs, see | |
2f41c1d6 | 50 | @w{@value{BUGURL}}. |
6de9cd9a DN |
51 | @c man end |
52 | @c man begin AUTHOR | |
53 | See the Info entry for @command{gfortran} for contributors to GCC and | |
7fc15ba5 | 54 | GNU Fortran. |
6de9cd9a DN |
55 | @c man end |
56 | @end ignore | |
57 | ||
7fc15ba5 BM |
58 | @node Invoking GNU Fortran |
59 | @chapter GNU Fortran Command Options | |
60 | @cindex GNU Fortran command options | |
6de9cd9a | 61 | @cindex command options |
7fc15ba5 | 62 | @cindex options, @command{gfortran} command |
6de9cd9a DN |
63 | |
64 | @c man begin DESCRIPTION | |
65 | ||
66 | The @command{gfortran} command supports all the options supported by the | |
f4347334 ZG |
67 | @command{gcc} command. Only options specific to GNU Fortran are documented |
68 | here. | |
6de9cd9a DN |
69 | |
70 | @xref{Invoking GCC,,GCC Command Options,gcc,Using the GNU Compiler | |
71 | Collection (GCC)}, for information | |
72 | on the non-Fortran-specific aspects of the @command{gcc} command (and, | |
73 | therefore, the @command{gfortran} command). | |
74 | ||
75 | @cindex options, negative forms | |
7fc15ba5 | 76 | All GCC and GNU Fortran options |
6de9cd9a DN |
77 | are accepted both by @command{gfortran} and by @command{gcc} |
78 | (as well as any other drivers built at the same time, | |
79 | such as @command{g++}), | |
7fc15ba5 BM |
80 | since adding GNU Fortran to the GCC distribution |
81 | enables acceptance of GNU Fortran options | |
6de9cd9a DN |
82 | by all of the relevant drivers. |
83 | ||
84 | In some cases, options have positive and negative forms; | |
85 | the negative form of @option{-ffoo} would be @option{-fno-foo}. | |
86 | This manual documents only one of these two forms, whichever | |
87 | one is not the default. | |
88 | @c man end | |
89 | ||
90 | @menu | |
91 | * Option Summary:: Brief list of all @command{gfortran} options, | |
92 | without explanations. | |
93 | * Fortran Dialect Options:: Controlling the variant of Fortran language | |
94 | compiled. | |
670637ee | 95 | * Preprocessing Options:: Enable and customize preprocessing. |
592600ce | 96 | * Error and Warning Options:: How picky should the compiler be? |
6de9cd9a DN |
97 | * Debugging Options:: Symbol tables, measurements, and debugging dumps. |
98 | * Directory Options:: Where to find module files | |
70263321 | 99 | * Link Options :: Influencing the linking step |
eaa90d25 | 100 | * Runtime Options:: Influencing runtime behavior |
6de9cd9a DN |
101 | * Code Gen Options:: Specifying conventions for function calls, data layout |
102 | and register usage. | |
e655a6cc TK |
103 | * Interoperability Options:: Options for interoperability with other |
104 | languages. | |
a2bef74c | 105 | * Environment Variables:: Environment variables that affect @command{gfortran}. |
6de9cd9a DN |
106 | @end menu |
107 | ||
108 | @node Option Summary | |
a2bef74c | 109 | @section Option summary |
6de9cd9a DN |
110 | |
111 | @c man begin OPTIONS | |
112 | ||
113 | Here is a summary of all the options specific to GNU Fortran, grouped | |
114 | by type. Explanations are in the following sections. | |
115 | ||
116 | @table @emph | |
117 | @item Fortran Language Options | |
a2bef74c | 118 | @xref{Fortran Dialect Options,,Options controlling Fortran dialect}. |
7a56096c | 119 | @gccoptlist{-fall-intrinsics -fallow-argument-mismatch -fallow-invalid-boz @gol |
32bef8ff ME |
120 | -fbackslash -fcray-pointer -fd-lines-as-code -fd-lines-as-comments @gol |
121 | -fdec -fdec-char-conversions -fdec-structure -fdec-intrinsic-ints @gol | |
122 | -fdec-static -fdec-math -fdec-include -fdec-format-defaults @gol | |
123 | -fdec-blank-format-item -fdefault-double-8 -fdefault-integer-8 @gol | |
124 | -fdefault-real-8 -fdefault-real-10 -fdefault-real-16 -fdollar-ok @gol | |
125 | -ffixed-line-length-@var{n} -ffixed-line-length-none -fpad-source @gol | |
126 | -ffree-form -ffree-line-length-@var{n} -ffree-line-length-none @gol | |
127 | -fimplicit-none -finteger-4-integer-8 -fmax-identifier-length @gol | |
128 | -fmodule-private -ffixed-form -fno-range-check -fopenacc -fopenmp @gol | |
129 | -freal-4-real-10 -freal-4-real-16 -freal-4-real-8 -freal-8-real-10 @gol | |
130 | -freal-8-real-16 -freal-8-real-4 -std=@var{std} -ftest-forall-temp | |
f4347334 | 131 | } |
6de9cd9a | 132 | |
670637ee DF |
133 | @item Preprocessing Options |
134 | @xref{Preprocessing Options,,Enable and customize preprocessing}. | |
f4347334 ZG |
135 | @gccoptlist{-A-@var{question}@r{[}=@var{answer}@r{]} |
136 | -A@var{question}=@var{answer} -C -CC -D@var{macro}@r{[}=@var{defn}@r{]} | |
137 | -H -P @gol | |
138 | -U@var{macro} -cpp -dD -dI -dM -dN -dU -fworking-directory | |
139 | -imultilib @var{dir} @gol | |
140 | -iprefix @var{file} -iquote -isysroot @var{dir} -isystem @var{dir} -nocpp | |
141 | -nostdinc @gol | |
142 | -undef | |
143 | } | |
670637ee | 144 | |
592600ce | 145 | @item Error and Warning Options |
a2bef74c DF |
146 | @xref{Error and Warning Options,,Options to request or suppress errors |
147 | and warnings}. | |
e0b9e5f9 | 148 | @gccoptlist{-Waliasing -Wall -Wampersand -Warray-bounds @gol |
15e23330 TK |
149 | -Wc-binding-type -Wcharacter-truncation -Wconversion @gol |
150 | -Wdo-subscript -Wfunction-elimination -Wimplicit-interface @gol | |
f4436343 | 151 | -Wimplicit-procedure -Wintrinsic-shadow -Wuse-without-only @gol |
91c4891a ME |
152 | -Wintrinsics-std -Wline-truncation -Wno-align-commons @gol |
153 | -Wno-overwrite-recursive -Wno-tabs -Wreal-q-constant -Wsurprising @gol | |
154 | -Wunderflow -Wunused-parameter -Wrealloc-lhs -Wrealloc-lhs-all @gol | |
155 | -Wfrontend-loop-interchange -Wtarget-lifetime -fmax-errors=@var{n} @gol | |
156 | -fsyntax-only -pedantic @gol | |
f4436343 | 157 | -pedantic-errors @gol |
f4347334 | 158 | } |
6de9cd9a DN |
159 | |
160 | @item Debugging Options | |
a2bef74c | 161 | @xref{Debugging Options,,Options for debugging your program or GNU Fortran}. |
f4347334 | 162 | @gccoptlist{-fbacktrace -fdump-fortran-optimized -fdump-fortran-original @gol |
5c6aa9a8 TK |
163 | -fdump-fortran-global -fdump-parse-tree -ffpe-trap=@var{list} @gol |
164 | -ffpe-summary=@var{list} | |
f4347334 | 165 | } |
6de9cd9a DN |
166 | |
167 | @item Directory Options | |
a2bef74c | 168 | @xref{Directory Options,,Options for directory search}. |
d8ddea40 | 169 | @gccoptlist{-I@var{dir} -J@var{dir} -fintrinsic-modules-path @var{dir}} |
6de9cd9a | 170 | |
70263321 DF |
171 | @item Link Options |
172 | @xref{Link Options,,Options for influencing the linking step}. | |
173 | @gccoptlist{-static-libgfortran} | |
174 | ||
eaa90d25 TK |
175 | @item Runtime Options |
176 | @xref{Runtime Options,,Options for influencing runtime behavior}. | |
80b91c0b | 177 | @gccoptlist{-fconvert=@var{conversion} -fmax-subrecord-length=@var{length} @gol |
f4347334 ZG |
178 | -frecord-marker=@var{length} -fsign-zero |
179 | } | |
eaa90d25 | 180 | |
e655a6cc TK |
181 | @item Interoperability Options |
182 | @xref{Interoperability Options,,Options for interoperability}. | |
6328ce1f | 183 | @gccoptlist{-fc-prototypes -fc-prototypes-external} |
e655a6cc | 184 | |
6de9cd9a | 185 | @item Code Generation Options |
a2bef74c | 186 | @xref{Code Gen Options,,Options for code generation conventions}. |
f4347334 | 187 | @gccoptlist{-faggressive-function-elimination -fblas-matmul-limit=@var{n} @gol |
ffeebc4f JJ |
188 | -fbounds-check -ftail-call-workaround -ftail-call-workaround=@var{n} @gol |
189 | -fcheck-array-temporaries @gol | |
df1afcca | 190 | -fcheck=@var{<all|array-temps|bits|bounds|do|mem|pointer|recursion>} @gol |
f4436343 ME |
191 | -fcoarray=@var{<none|single|lib>} -fexternal-blas -ff2c @gol |
192 | -ffrontend-loop-interchange -ffrontend-optimize @gol | |
f4347334 | 193 | -finit-character=@var{n} -finit-integer=@var{n} -finit-local-zero @gol |
f4436343 | 194 | -finit-derived -finit-logical=@var{<true|false>} @gol |
95d27703 TK |
195 | -finit-real=@var{<zero|inf|-inf|nan|snan>} |
196 | -finline-matmul-limit=@var{n} @gol | |
197 | -finline-arg-packing -fmax-array-constructor=@var{n} @gol | |
f4436343 ME |
198 | -fmax-stack-var-size=@var{n} -fno-align-commons -fno-automatic @gol |
199 | -fno-protect-parens -fno-underscoring -fsecond-underscore @gol | |
200 | -fpack-derived -frealloc-lhs -frecursive -frepack-arrays @gol | |
201 | -fshort-enums -fstack-arrays | |
f4347334 | 202 | } |
6de9cd9a DN |
203 | @end table |
204 | ||
6de9cd9a | 205 | @node Fortran Dialect Options |
a2bef74c | 206 | @section Options controlling Fortran dialect |
6de9cd9a DN |
207 | @cindex dialect options |
208 | @cindex language, dialect options | |
209 | @cindex options, dialect | |
210 | ||
3397327c BM |
211 | The following options control the details of the Fortran dialect |
212 | accepted by the compiler: | |
6de9cd9a DN |
213 | |
214 | @table @gcctabopt | |
4ba96c02 | 215 | @item -ffree-form |
4d04d67a | 216 | @itemx -ffixed-form |
32864778 | 217 | @opindex @code{ffree-form} |
3435c26f | 218 | @opindex @code{ffixed-form} |
8578f640 | 219 | @cindex options, Fortran dialect |
e739dfac DF |
220 | @cindex file format, free |
221 | @cindex file format, fixed | |
49de9e73 | 222 | Specify the layout used by the source file. The free form layout |
6de9cd9a | 223 | was introduced in Fortran 90. Fixed form was traditionally used in |
3397327c BM |
224 | older Fortran programs. When neither option is specified, the source |
225 | form is determined by the file extension. | |
6de9cd9a | 226 | |
a23eec13 | 227 | @item -fall-intrinsics |
32864778 | 228 | @opindex @code{fall-intrinsics} |
aad9c4f4 AM |
229 | This option causes all intrinsic procedures (including the GNU-specific |
230 | extensions) to be accepted. This can be useful with @option{-std=f95} to | |
231 | force standard-compliance but get access to the full range of intrinsics | |
232 | available with @command{gfortran}. As a consequence, @option{-Wintrinsics-std} | |
233 | will be ignored and no user-defined procedure with the same name as any | |
234 | intrinsic will be called except when it is explicitly declared @code{EXTERNAL}. | |
a23eec13 | 235 | |
7a56096c TK |
236 | @item -fallow-argument-mismatch |
237 | @opindex @code{fallow-argument-mismatch} | |
238 | Some code contains calls to external procedures whith mismatches | |
239 | between the calls and the procedure definition, or with mismatches | |
240 | between different calls. Such code is non-conforming, and will usually | |
e0b9e5f9 TK |
241 | be flagged wi1th an error. This options degrades the error to a |
242 | warning, which can only be disabled by disabling all warnings vial | |
243 | @option{-w}. Only a single occurrence per argument is flagged by this | |
244 | warning. @option{-fallow-argument-mismatch} is implied by | |
245 | @option{-std=legacy}. | |
246 | ||
247 | Using this option is @emph{strongly} discouraged. It is possible to | |
248 | provide standard-conforming code which allows different types of | |
249 | arguments by using an explicit interface and @code{TYPE(*)}. | |
7a56096c | 250 | |
8dc63166 SK |
251 | @item -fallow-invalid-boz |
252 | @opindex @code{allow-invalid-boz} | |
f8e36f0a | 253 | A BOZ literal constant can occur in a limited number of contexts in |
8dc63166 SK |
254 | standard conforming Fortran. This option degrades an error condition |
255 | to a warning, and allows a BOZ literal constant to appear where the | |
f8e36f0a | 256 | Fortran standard would otherwise prohibit its use. |
8dc63166 | 257 | |
e0bcf78c | 258 | @item -fd-lines-as-code |
4d04d67a | 259 | @itemx -fd-lines-as-comments |
32864778 DF |
260 | @opindex @code{fd-lines-as-code} |
261 | @opindex @code{fd-lines-as-comments} | |
4ba96c02 | 262 | Enable special treatment for lines beginning with @code{d} or @code{D} |
3397327c BM |
263 | in fixed form sources. If the @option{-fd-lines-as-code} option is |
264 | given they are treated as if the first column contained a blank. If the | |
e0bcf78c TS |
265 | @option{-fd-lines-as-comments} option is given, they are treated as |
266 | comment lines. | |
267 | ||
f6288c24 FR |
268 | @item -fdec |
269 | @opindex @code{fdec} | |
270 | DEC compatibility mode. Enables extensions and other features that mimic | |
271 | the default behavior of older compilers (such as DEC). | |
272 | These features are non-standard and should be avoided at all costs. | |
f6d17ecd | 273 | For details on GNU Fortran's implementation of these extensions see the |
f6288c24 FR |
274 | full documentation. |
275 | ||
276 | Other flags enabled by this switch are: | |
2afeb1ca ME |
277 | @option{-fdollar-ok} @option{-fcray-pointer} @option{-fdec-char-conversions} |
278 | @option{-fdec-structure} @option{-fdec-intrinsic-ints} @option{-fdec-static} | |
279 | @option{-fdec-math} @option{-fdec-include} @option{-fdec-blank-format-item} | |
f4436343 | 280 | @option{-fdec-format-defaults} |
f6d17ecd FR |
281 | |
282 | If @option{-fd-lines-as-code}/@option{-fd-lines-as-comments} are unset, then | |
283 | @option{-fdec} also sets @option{-fd-lines-as-comments}. | |
f6288c24 | 284 | |
2afeb1ca ME |
285 | @item -fdec-char-conversions |
286 | @opindex @code{fdec-char-conversions} | |
32bef8ff | 287 | Enable the use of character literals in assignments and @code{DATA} statements |
2afeb1ca ME |
288 | for non-character variables. |
289 | ||
f6288c24 FR |
290 | @item -fdec-structure |
291 | @opindex @code{fdec-structure} | |
292 | Enable DEC @code{STRUCTURE} and @code{RECORD} as well as @code{UNION}, | |
293 | @code{MAP}, and dot ('.') as a member separator (in addition to '%'). This is | |
294 | provided for compatibility only; Fortran 90 derived types should be used | |
295 | instead where possible. | |
296 | ||
c98583e9 FR |
297 | @item -fdec-intrinsic-ints |
298 | @opindex @code{fdec-intrinsic-ints} | |
299 | Enable B/I/J/K kind variants of existing integer functions (e.g. BIAND, IIAND, | |
300 | JIAND, etc...). For a complete list of intrinsics see the full documentation. | |
301 | ||
8e8c2744 FR |
302 | @item -fdec-math |
303 | @opindex @code{fdec-math} | |
304 | Enable legacy math intrinsics such as COTAN and degree-valued trigonometric | |
305 | functions (e.g. TAND, ATAND, etc...) for compatability with older code. | |
306 | ||
34d567d1 FR |
307 | @item -fdec-static |
308 | @opindex @code{fdec-static} | |
309 | Enable DEC-style STATIC and AUTOMATIC attributes to explicitly specify | |
310 | the storage of variables and other objects. | |
311 | ||
99b5ace4 JJ |
312 | @item -fdec-include |
313 | @opindex @code{fdec-include} | |
314 | Enable parsing of INCLUDE as a statement in addition to parsing it as | |
315 | INCLUDE line. When parsed as INCLUDE statement, INCLUDE does not have to | |
316 | be on a single line and can use line continuations. | |
317 | ||
88a8126a JB |
318 | @item -fdec-format-defaults |
319 | @opindex @code{fdec-format-defaults} | |
320 | Enable format specifiers F, G and I to be used without width specifiers, | |
321 | default widths will be used instead. | |
322 | ||
17f62b7e JM |
323 | @item -fdec-blank-format-item |
324 | @opindex @code{fdec-blank-format-item} | |
325 | Enable a blank format item at the end of a format specification i.e. nothing | |
326 | following the final comma. | |
327 | ||
6de9cd9a | 328 | @item -fdollar-ok |
32864778 | 329 | @opindex @code{fdollar-ok} |
ab940b73 | 330 | @cindex @code{$} |
6de9cd9a DN |
331 | @cindex symbol names |
332 | @cindex character set | |
f4a55802 DF |
333 | Allow @samp{$} as a valid non-first character in a symbol name. Symbols |
334 | that start with @samp{$} are rejected since it is unclear which rules to | |
cba2a54e | 335 | apply to implicit typing as different vendors implement different rules. |
6e8cb9be | 336 | Using @samp{$} in @code{IMPLICIT} statements is also rejected. |
6de9cd9a | 337 | |
4e6bf178 TB |
338 | @item -fbackslash |
339 | @opindex @code{backslash} | |
131c66cd FXC |
340 | @cindex backslash |
341 | @cindex escape characters | |
8fc541d3 FXC |
342 | Change the interpretation of backslashes in string literals from a single |
343 | backslash character to ``C-style'' escape characters. The following | |
344 | combinations are expanded @code{\a}, @code{\b}, @code{\f}, @code{\n}, | |
345 | @code{\r}, @code{\t}, @code{\v}, @code{\\}, and @code{\0} to the ASCII | |
346 | characters alert, backspace, form feed, newline, carriage return, | |
347 | horizontal tab, vertical tab, backslash, and NUL, respectively. | |
348 | Additionally, @code{\x}@var{nn}, @code{\u}@var{nnnn} and | |
349 | @code{\U}@var{nnnnnnnn} (where each @var{n} is a hexadecimal digit) are | |
350 | translated into the Unicode characters corresponding to the specified code | |
351 | points. All other combinations of a character preceded by \ are | |
352 | unexpanded. | |
131c66cd | 353 | |
654b6073 FXC |
354 | @item -fmodule-private |
355 | @opindex @code{fmodule-private} | |
356 | @cindex module entities | |
357 | @cindex private | |
358 | Set the default accessibility of module entities to @code{PRIVATE}. | |
359 | Use-associated entities will not be accessible unless they are explicitly | |
360 | declared as @code{PUBLIC}. | |
361 | ||
6de9cd9a | 362 | @item -ffixed-line-length-@var{n} |
32864778 | 363 | @opindex @code{ffixed-line-length-}@var{n} |
e739dfac | 364 | @cindex file format, fixed |
6de9cd9a | 365 | Set column after which characters are ignored in typical fixed-form |
f03d260a JJ |
366 | lines in the source file, and, unless @code{-fno-pad-source}, through which |
367 | spaces are assumed (as if padded to that length) after the ends of short | |
368 | fixed-form lines. | |
6de9cd9a | 369 | |
6de9cd9a | 370 | Popular values for @var{n} include 72 (the |
3397327c | 371 | standard and the default), 80 (card image), and 132 (corresponding |
6de9cd9a | 372 | to ``extended-source'' options in some popular compilers). |
3397327c | 373 | @var{n} may also be @samp{none}, meaning that the entire line is meaningful |
6de9cd9a DN |
374 | and that continued character constants never have implicit spaces appended |
375 | to them to fill out the line. | |
376 | @option{-ffixed-line-length-0} means the same thing as | |
377 | @option{-ffixed-line-length-none}. | |
378 | ||
f03d260a JJ |
379 | @item -fno-pad-source |
380 | @opindex @code{fpad-source} | |
381 | By default fixed-form lines have spaces assumed (as if padded to that length) | |
382 | after the ends of short fixed-form lines. This is not done either if | |
383 | @option{-ffixed-line-length-0}, @option{-ffixed-line-length-none} or | |
384 | if @option{-fno-pad-source} option is used. With any of those options | |
385 | continued character constants never have implicit spaces appended | |
386 | to them to fill out the line. | |
387 | ||
16ab8e74 | 388 | @item -ffree-line-length-@var{n} |
32864778 | 389 | @opindex @code{ffree-line-length-}@var{n} |
e739dfac | 390 | @cindex file format, free |
16ab8e74 | 391 | Set column after which characters are ignored in typical free-form |
3397327c | 392 | lines in the source file. The default value is 132. |
16ab8e74 BF |
393 | @var{n} may be @samp{none}, meaning that the entire line is meaningful. |
394 | @option{-ffree-line-length-0} means the same thing as | |
395 | @option{-ffree-line-length-none}. | |
396 | ||
6de9cd9a | 397 | @item -fmax-identifier-length=@var{n} |
32864778 | 398 | @opindex @code{fmax-identifier-length=}@var{n} |
6de9cd9a | 399 | Specify the maximum allowed identifier length. Typical values are |
f489fba1 | 400 | 31 (Fortran 95) and 63 (Fortran 2003 and Fortran 2008). |
6de9cd9a | 401 | |
6de9cd9a | 402 | @item -fimplicit-none |
32864778 | 403 | @opindex @code{fimplicit-none} |
6de9cd9a | 404 | Specify that no implicit typing is allowed, unless overridden by explicit |
40746dcc BM |
405 | @code{IMPLICIT} statements. This is the equivalent of adding |
406 | @code{implicit none} to the start of every procedure. | |
6de9cd9a | 407 | |
83d890b9 | 408 | @item -fcray-pointer |
32864778 | 409 | @opindex @code{fcray-pointer} |
3397327c BM |
410 | Enable the Cray pointer extension, which provides C-like pointer |
411 | functionality. | |
83d890b9 | 412 | |
41dbbb37 TS |
413 | @item -fopenacc |
414 | @opindex @code{fopenacc} | |
415 | @cindex OpenACC | |
416 | Enable the OpenACC extensions. This includes OpenACC @code{!$acc} | |
417 | directives in free form and @code{c$acc}, @code{*$acc} and | |
418 | @code{!$acc} directives in fixed form, @code{!$} conditional | |
419 | compilation sentinels in free form and @code{c$}, @code{*$} and | |
420 | @code{!$} sentinels in fixed form, and when linking arranges for the | |
421 | OpenACC runtime library to be linked in. | |
422 | ||
423 | Note that this is an experimental feature, incomplete, and subject to | |
424 | change in future versions of GCC. See | |
425 | @w{@uref{https://gcc.gnu.org/wiki/OpenACC}} for more information. | |
426 | ||
6c7a4dfd | 427 | @item -fopenmp |
32864778 | 428 | @opindex @code{fopenmp} |
4e8b3590 | 429 | @cindex OpenMP |
3397327c BM |
430 | Enable the OpenMP extensions. This includes OpenMP @code{!$omp} directives |
431 | in free form | |
6c7a4dfd | 432 | and @code{c$omp}, @code{*$omp} and @code{!$omp} directives in fixed form, |
3397327c BM |
433 | @code{!$} conditional compilation sentinels in free form |
434 | and @code{c$}, @code{*$} and @code{!$} sentinels in fixed form, | |
6c7a4dfd | 435 | and when linking arranges for the OpenMP runtime library to be linked |
1e7de83b | 436 | in. The option @option{-fopenmp} implies @option{-frecursive}. |
6c7a4dfd | 437 | |
200c5036 | 438 | @item -fno-range-check |
32864778 | 439 | @opindex @code{frange-check} |
200c5036 | 440 | Disable range checking on results of simplification of constant |
a84b9ee8 SK |
441 | expressions during compilation. For example, GNU Fortran will give |
442 | an error at compile time when simplifying @code{a = 1. / 0}. | |
443 | With this option, no error will be given and @code{a} will be assigned | |
444 | the value @code{+Infinity}. If an expression evaluates to a value | |
445 | outside of the relevant range of [@code{-HUGE()}:@code{HUGE()}], | |
446 | then the expression will be replaced by @code{-Inf} or @code{+Inf} | |
447 | as appropriate. | |
40746dcc BM |
448 | Similarly, @code{DATA i/Z'FFFFFFFF'/} will result in an integer overflow |
449 | on most systems, but with @option{-fno-range-check} the value will | |
450 | ``wrap around'' and @code{i} will be initialized to @math{-1} instead. | |
54554825 | 451 | |
9803c5f0 JW |
452 | @item -fdefault-integer-8 |
453 | @opindex @code{fdefault-integer-8} | |
8f606521 JW |
454 | Set the default integer and logical types to an 8 byte wide type. This option |
455 | also affects the kind of integer constants like @code{42}. Unlike | |
a4cf752c JW |
456 | @option{-finteger-4-integer-8}, it does not promote variables with explicit |
457 | kind declaration. | |
9803c5f0 JW |
458 | |
459 | @item -fdefault-real-8 | |
460 | @opindex @code{fdefault-real-8} | |
8ff7780c DH |
461 | Set the default real type to an 8 byte wide type. This option also affects |
462 | the kind of non-double real constants like @code{1.0}. This option promotes | |
463 | the default width of @code{DOUBLE PRECISION} and double real constants | |
464 | like @code{1.d0} to 16 bytes if possible. If @code{-fdefault-double-8} | |
465 | is given along with @code{fdefault-real-8}, @code{DOUBLE PRECISION} | |
466 | and double real constants are not promoted. Unlike @option{-freal-4-real-8}, | |
467 | @code{fdefault-real-8} does not promote variables with explicit kind | |
468 | declarations. | |
9803c5f0 | 469 | |
d16d81b5 JW |
470 | @item -fdefault-real-10 |
471 | @opindex @code{fdefault-real-10} | |
8ff7780c DH |
472 | Set the default real type to an 10 byte wide type. This option also affects |
473 | the kind of non-double real constants like @code{1.0}. This option promotes | |
474 | the default width of @code{DOUBLE PRECISION} and double real constants | |
475 | like @code{1.d0} to 16 bytes if possible. If @code{-fdefault-double-8} | |
476 | is given along with @code{fdefault-real-10}, @code{DOUBLE PRECISION} | |
477 | and double real constants are not promoted. Unlike @option{-freal-4-real-10}, | |
478 | @code{fdefault-real-10} does not promote variables with explicit kind | |
479 | declarations. | |
d16d81b5 JW |
480 | |
481 | @item -fdefault-real-16 | |
482 | @opindex @code{fdefault-real-16} | |
8ff7780c DH |
483 | Set the default real type to an 16 byte wide type. This option also affects |
484 | the kind of non-double real constants like @code{1.0}. This option promotes | |
485 | the default width of @code{DOUBLE PRECISION} and double real constants | |
486 | like @code{1.d0} to 16 bytes if possible. If @code{-fdefault-double-8} | |
487 | is given along with @code{fdefault-real-16}, @code{DOUBLE PRECISION} | |
488 | and double real constants are not promoted. Unlike @option{-freal-4-real-16}, | |
489 | @code{fdefault-real-16} does not promote variables with explicit kind | |
490 | declarations. | |
d16d81b5 | 491 | |
9803c5f0 JW |
492 | @item -fdefault-double-8 |
493 | @opindex @code{fdefault-double-8} | |
8ff7780c DH |
494 | Set the @code{DOUBLE PRECISION} type and double real constants |
495 | like @code{1.d0} to an 8 byte wide type. Do nothing if this | |
496 | is already the default. This option prevents @option{-fdefault-real-8}, | |
497 | @option{-fdefault-real-10}, and @option{-fdefault-real-16}, | |
498 | from promoting @code{DOUBLE PRECISION} and double real constants like | |
499 | @code{1.d0} to 16 bytes. | |
9803c5f0 JW |
500 | |
501 | @item -finteger-4-integer-8 | |
502 | @opindex @code{finteger-4-integer-8} | |
503 | Promote all @code{INTEGER(KIND=4)} entities to an @code{INTEGER(KIND=8)} | |
504 | entities. If @code{KIND=8} is unavailable, then an error will be issued. | |
505 | This option should be used with care and may not be suitable for your codes. | |
506 | Areas of possible concern include calls to external procedures, | |
507 | alignment in @code{EQUIVALENCE} and/or @code{COMMON}, generic interfaces, | |
508 | BOZ literal constant conversion, and I/O. Inspection of the intermediate | |
509 | representation of the translated Fortran code, produced by | |
510 | @option{-fdump-tree-original}, is suggested. | |
511 | ||
f4347334 ZG |
512 | @item -freal-4-real-8 |
513 | @itemx -freal-4-real-10 | |
9803c5f0 | 514 | @itemx -freal-4-real-16 |
f4347334 ZG |
515 | @itemx -freal-8-real-4 |
516 | @itemx -freal-8-real-10 | |
517 | @itemx -freal-8-real-16 | |
518 | @opindex @code{freal-4-real-8} | |
519 | @opindex @code{freal-4-real-10} | |
520 | @opindex @code{freal-4-real-16} | |
521 | @opindex @code{freal-8-real-4} | |
522 | @opindex @code{freal-8-real-10} | |
523 | @opindex @code{freal-8-real-16} | |
524 | @cindex options, real kind type promotion | |
525 | Promote all @code{REAL(KIND=M)} entities to @code{REAL(KIND=N)} entities. | |
526 | If @code{REAL(KIND=N)} is unavailable, then an error will be issued. | |
527 | All other real kind types are unaffected by this option. | |
528 | These options should be used with care and may not be suitable for your | |
529 | codes. Areas of possible concern include calls to external procedures, | |
530 | alignment in @code{EQUIVALENCE} and/or @code{COMMON}, generic interfaces, | |
531 | BOZ literal constant conversion, and I/O. Inspection of the intermediate | |
532 | representation of the translated Fortran code, produced by | |
533 | @option{-fdump-tree-original}, is suggested. | |
534 | ||
6de9cd9a | 535 | @item -std=@var{std} |
32864778 | 536 | @opindex @code{std=}@var{std} option |
8179b067 JB |
537 | Specify the standard to which the program is expected to conform, |
538 | which may be one of @samp{f95}, @samp{f2003}, @samp{f2008}, | |
539 | @samp{f2018}, @samp{gnu}, or @samp{legacy}. The default value for | |
540 | @var{std} is @samp{gnu}, which specifies a superset of the latest | |
541 | Fortran standard that includes all of the extensions supported by GNU | |
542 | Fortran, although warnings will be given for obsolete extensions not | |
543 | recommended for use in new code. The @samp{legacy} value is | |
544 | equivalent but without the warnings for obsolete extensions, and may | |
545 | be useful for old non-standard programs. The @samp{f95}, | |
546 | @samp{f2003}, @samp{f2008}, and @samp{f2018} values specify strict | |
547 | conformance to the Fortran 95, Fortran 2003, Fortran 2008 and Fortran | |
548 | 2018 standards, respectively; errors are given for all extensions | |
549 | beyond the relevant language standard, and warnings are given for the | |
550 | Fortran 77 features that are permitted but obsolescent in later | |
286f737c JW |
551 | standards. The deprecated option @samp{-std=f2008ts} acts as an alias for |
552 | @samp{-std=f2018}. It is only present for backwards compatibility with | |
553 | earlier gfortran versions and should not be used any more. | |
6de9cd9a | 554 | |
7bd5dad2 LK |
555 | @item -ftest-forall-temp |
556 | @opindex @code{ftest-forall-temp} | |
557 | Enhance test coverage by forcing most forall assignments to use temporary. | |
558 | ||
6de9cd9a DN |
559 | @end table |
560 | ||
670637ee DF |
561 | @node Preprocessing Options |
562 | @section Enable and customize preprocessing | |
563 | @cindex preprocessor | |
564 | @cindex options, preprocessor | |
565 | @cindex CPP | |
566 | ||
567 | Preprocessor related options. See section | |
568 | @ref{Preprocessing and conditional compilation} for more detailed | |
569 | information on preprocessing in @command{gfortran}. | |
570 | ||
571 | @table @gcctabopt | |
572 | @item -cpp | |
4d04d67a | 573 | @itemx -nocpp |
670637ee DF |
574 | @opindex @code{cpp} |
575 | @opindex @code{fpp} | |
576 | @cindex preprocessor, enable | |
577 | @cindex preprocessor, disable | |
578 | Enable preprocessing. The preprocessor is automatically invoked if | |
579 | the file extension is @file{.fpp}, @file{.FPP}, @file{.F}, @file{.FOR}, | |
580 | @file{.FTN}, @file{.F90}, @file{.F95}, @file{.F03} or @file{.F08}. Use | |
581 | this option to manually enable preprocessing of any kind of Fortran file. | |
582 | ||
583 | To disable preprocessing of files with any of the above listed extensions, | |
584 | use the negative form: @option{-nocpp}. | |
585 | ||
f90b55a6 TK |
586 | The preprocessor is run in traditional mode. Any restrictions of the |
587 | file-format, especially the limits on line length, apply for | |
588 | preprocessed output as well, so it might be advisable to use the | |
589 | @option{-ffree-line-length-none} or @option{-ffixed-line-length-none} | |
590 | options. | |
670637ee DF |
591 | |
592 | @item -dM | |
593 | @opindex @code{dM} | |
594 | @cindex preprocessor, debugging | |
595 | @cindex debugging, preprocessor | |
596 | Instead of the normal output, generate a list of @code{'#define'} | |
597 | directives for all the macros defined during the execution of the | |
598 | preprocessor, including predefined macros. This gives you a way | |
599 | of finding out what is predefined in your version of the preprocessor. | |
600 | Assuming you have no file @file{foo.f90}, the command | |
601 | @smallexample | |
fc1e05d2 | 602 | touch foo.f90; gfortran -cpp -E -dM foo.f90 |
670637ee DF |
603 | @end smallexample |
604 | will show all the predefined macros. | |
605 | ||
606 | @item -dD | |
607 | @opindex @code{dD} | |
608 | @cindex preprocessor, debugging | |
609 | @cindex debugging, preprocessor | |
610 | Like @option{-dM} except in two respects: it does not include the | |
611 | predefined macros, and it outputs both the @code{#define} directives | |
612 | and the result of preprocessing. Both kinds of output go to the | |
613 | standard output file. | |
614 | ||
615 | @item -dN | |
616 | @opindex @code{dN} | |
617 | @cindex preprocessor, debugging | |
618 | @cindex debugging, preprocessor | |
619 | Like @option{-dD}, but emit only the macro names, not their expansions. | |
620 | ||
621 | @item -dU | |
622 | @opindex @code{dU} | |
623 | @cindex preprocessor, debugging | |
624 | @cindex debugging, preprocessor | |
625 | Like @option{dD} except that only macros that are expanded, or whose | |
626 | definedness is tested in preprocessor directives, are output; the | |
627 | output is delayed until the use or test of the macro; and @code{'#undef'} | |
628 | directives are also output for macros tested but undefined at the time. | |
629 | ||
630 | @item -dI | |
631 | @opindex @code{dI} | |
632 | @cindex preprocessor, debugging | |
633 | @cindex debugging, preprocessor | |
634 | Output @code{'#include'} directives in addition to the result | |
635 | of preprocessing. | |
636 | ||
637 | @item -fworking-directory | |
638 | @opindex @code{fworking-directory} | |
639 | @cindex preprocessor, working directory | |
640 | Enable generation of linemarkers in the preprocessor output that will | |
641 | let the compiler know the current working directory at the time of | |
642 | preprocessing. When this option is enabled, the preprocessor will emit, | |
643 | after the initial linemarker, a second linemarker with the current | |
644 | working directory followed by two slashes. GCC will use this directory, | |
c5a0818e | 645 | when it is present in the preprocessed input, as the directory emitted |
670637ee DF |
646 | as the current working directory in some debugging information formats. |
647 | This option is implicitly enabled if debugging information is enabled, | |
648 | but this can be inhibited with the negated form | |
649 | @option{-fno-working-directory}. If the @option{-P} flag is present | |
650 | in the command line, this option has no effect, since no @code{#line} | |
651 | directives are emitted whatsoever. | |
652 | ||
c3280643 DF |
653 | @item -idirafter @var{dir} |
654 | @opindex @code{idirafter @var{dir}} | |
655 | @cindex preprocessing, include path | |
656 | Search @var{dir} for include files, but do it after all directories | |
657 | specified with @option{-I} and the standard system directories have | |
658 | been exhausted. @var{dir} is treated as a system include directory. | |
659 | If dir begins with @code{=}, then the @code{=} will be replaced by | |
660 | the sysroot prefix; see @option{--sysroot} and @option{-isysroot}. | |
661 | ||
670637ee DF |
662 | @item -imultilib @var{dir} |
663 | @opindex @code{imultilib @var{dir}} | |
664 | @cindex preprocessing, include path | |
665 | Use @var{dir} as a subdirectory of the directory containing target-specific | |
666 | C++ headers. | |
667 | ||
668 | @item -iprefix @var{prefix} | |
669 | @opindex @code{iprefix @var{prefix}} | |
670 | @cindex preprocessing, include path | |
671 | Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix} | |
672 | options. If the @var{prefix} represents a directory, you should include | |
673 | the final @code{'/'}. | |
674 | ||
675 | @item -isysroot @var{dir} | |
676 | @opindex @code{isysroot @var{dir}} | |
677 | @cindex preprocessing, include path | |
678 | This option is like the @option{--sysroot} option, but applies only to | |
679 | header files. See the @option{--sysroot} option for more information. | |
680 | ||
681 | @item -iquote @var{dir} | |
682 | @opindex @code{iquote @var{dir}} | |
683 | @cindex preprocessing, include path | |
684 | Search @var{dir} only for header files requested with @code{#include "file"}; | |
685 | they are not searched for @code{#include <file>}, before all directories | |
686 | specified by @option{-I} and before the standard system directories. If | |
687 | @var{dir} begins with @code{=}, then the @code{=} will be replaced by the | |
688 | sysroot prefix; see @option{--sysroot} and @option{-isysroot}. | |
689 | ||
690 | @item -isystem @var{dir} | |
691 | @opindex @code{isystem @var{dir}} | |
692 | @cindex preprocessing, include path | |
693 | Search @var{dir} for header files, after all directories specified by | |
694 | @option{-I} but before the standard system directories. Mark it as a | |
695 | system directory, so that it gets the same special treatment as is | |
696 | applied to the standard system directories. If @var{dir} begins with | |
697 | @code{=}, then the @code{=} will be replaced by the sysroot prefix; | |
698 | see @option{--sysroot} and @option{-isysroot}. | |
699 | ||
700 | @item -nostdinc | |
701 | @opindex @code{nostdinc} | |
702 | Do not search the standard system directories for header files. Only | |
703 | the directories you have specified with @option{-I} options (and the | |
704 | directory of the current file, if appropriate) are searched. | |
705 | ||
706 | @item -undef | |
707 | @opindex @code{undef} | |
708 | Do not predefine any system-specific or GCC-specific macros. | |
709 | The standard predefined macros remain defined. | |
710 | ||
711 | @item -A@var{predicate}=@var{answer} | |
712 | @opindex @code{A@var{predicate}=@var{answer}} | |
4d04d67a | 713 | @cindex preprocessing, assertion |
670637ee DF |
714 | Make an assertion with the predicate @var{predicate} and answer @var{answer}. |
715 | This form is preferred to the older form -A predicate(answer), which is still | |
716 | supported, because it does not use shell special characters. | |
717 | ||
718 | @item -A-@var{predicate}=@var{answer} | |
719 | @opindex @code{A-@var{predicate}=@var{answer}} | |
4d04d67a | 720 | @cindex preprocessing, assertion |
670637ee DF |
721 | Cancel an assertion with the predicate @var{predicate} and answer @var{answer}. |
722 | ||
723 | @item -C | |
724 | @opindex @code{C} | |
725 | @cindex preprocessing, keep comments | |
726 | Do not discard comments. All comments are passed through to the output | |
727 | file, except for comments in processed directives, which are deleted | |
728 | along with the directive. | |
729 | ||
730 | You should be prepared for side effects when using @option{-C}; it causes | |
731 | the preprocessor to treat comments as tokens in their own right. For example, | |
732 | comments appearing at the start of what would be a directive line have the | |
733 | effect of turning that line into an ordinary source line, since the first | |
734 | token on the line is no longer a @code{'#'}. | |
735 | ||
736 | Warning: this currently handles C-Style comments only. The preprocessor | |
737 | does not yet recognize Fortran-style comments. | |
738 | ||
739 | @item -CC | |
740 | @opindex @code{CC} | |
741 | @cindex preprocessing, keep comments | |
742 | Do not discard comments, including during macro expansion. This is like | |
743 | @option{-C}, except that comments contained within macros are also passed | |
744 | through to the output file where the macro is expanded. | |
745 | ||
746 | In addition to the side-effects of the @option{-C} option, the @option{-CC} | |
747 | option causes all C++-style comments inside a macro to be converted to C-style | |
748 | comments. This is to prevent later use of that macro from inadvertently | |
749 | commenting out the remainder of the source line. The @option{-CC} option | |
750 | is generally used to support lint comments. | |
751 | ||
752 | Warning: this currently handles C- and C++-Style comments only. The | |
753 | preprocessor does not yet recognize Fortran-style comments. | |
754 | ||
755 | @item -D@var{name} | |
756 | @opindex @code{D@var{name}} | |
757 | @cindex preprocessing, define macros | |
758 | Predefine name as a macro, with definition @code{1}. | |
759 | ||
760 | @item -D@var{name}=@var{definition} | |
761 | @opindex @code{D@var{name}=@var{definition}} | |
762 | @cindex preprocessing, define macros | |
763 | The contents of @var{definition} are tokenized and processed as if they | |
764 | appeared during translation phase three in a @code{'#define'} directive. | |
765 | In particular, the definition will be truncated by embedded newline | |
766 | characters. | |
767 | ||
768 | If you are invoking the preprocessor from a shell or shell-like program | |
769 | you may need to use the shell's quoting syntax to protect characters such | |
770 | as spaces that have a meaning in the shell syntax. | |
771 | ||
772 | If you wish to define a function-like macro on the command line, write | |
773 | its argument list with surrounding parentheses before the equals sign | |
774 | (if any). Parentheses are meaningful to most shells, so you will need | |
775 | to quote the option. With sh and csh, @code{-D'name(args...)=definition'} | |
776 | works. | |
777 | ||
778 | @option{-D} and @option{-U} options are processed in the order they are | |
779 | given on the command line. All -imacros file and -include file options | |
780 | are processed after all -D and -U options. | |
781 | ||
782 | @item -H | |
783 | @opindex @code{H} | |
784 | Print the name of each header file used, in addition to other normal | |
785 | activities. Each name is indented to show how deep in the @code{'#include'} | |
786 | stack it is. | |
787 | ||
788 | @item -P | |
789 | @opindex @code{P} | |
790 | @cindex preprocessing, no linemarkers | |
791 | Inhibit generation of linemarkers in the output from the preprocessor. | |
792 | This might be useful when running the preprocessor on something that | |
793 | is not C code, and will be sent to a program which might be confused | |
794 | by the linemarkers. | |
795 | ||
796 | @item -U@var{name} | |
797 | @opindex @code{U@var{name}} | |
798 | @cindex preprocessing, undefine macros | |
799 | Cancel any previous definition of @var{name}, either built in or provided | |
800 | with a @option{-D} option. | |
801 | @end table | |
802 | ||
803 | ||
592600ce | 804 | @node Error and Warning Options |
a2bef74c | 805 | @section Options to request or suppress errors and warnings |
6de9cd9a | 806 | @cindex options, warnings |
592600ce | 807 | @cindex options, errors |
6de9cd9a | 808 | @cindex warnings, suppressing |
592600ce | 809 | @cindex messages, error |
6de9cd9a DN |
810 | @cindex messages, warning |
811 | @cindex suppressing warnings | |
812 | ||
592600ce BM |
813 | Errors are diagnostic messages that report that the GNU Fortran compiler |
814 | cannot compile the relevant piece of source code. The compiler will | |
815 | continue to process the program in an attempt to report further errors | |
816 | to aid in debugging, but will not produce any compiled output. | |
817 | ||
6de9cd9a | 818 | Warnings are diagnostic messages that report constructions which |
592600ce | 819 | are not inherently erroneous but which are risky or suggest there is |
4ba96c02 | 820 | likely to be a bug in the program. Unless @option{-Werror} is specified, |
592600ce | 821 | they do not prevent compilation of the program. |
6de9cd9a DN |
822 | |
823 | You can request many specific warnings with options beginning @option{-W}, | |
824 | for example @option{-Wimplicit} to request warnings on implicit | |
825 | declarations. Each of these specific warning options also has a | |
826 | negative form beginning @option{-Wno-} to turn off warnings; | |
827 | for example, @option{-Wno-implicit}. This manual lists only one of the | |
828 | two forms, whichever is not the default. | |
829 | ||
592600ce BM |
830 | These options control the amount and kinds of errors and warnings produced |
831 | by GNU Fortran: | |
6de9cd9a DN |
832 | |
833 | @table @gcctabopt | |
efb66586 JD |
834 | @item -fmax-errors=@var{n} |
835 | @opindex @code{fmax-errors=}@var{n} | |
4ba96c02 | 836 | @cindex errors, limiting |
592600ce BM |
837 | Limits the maximum number of error messages to @var{n}, at which point |
838 | GNU Fortran bails out rather than attempting to continue processing the | |
839 | source code. If @var{n} is 0, there is no limit on the number of error | |
840 | messages produced. | |
841 | ||
6de9cd9a | 842 | @item -fsyntax-only |
32864778 | 843 | @opindex @code{fsyntax-only} |
4ba96c02 | 844 | @cindex syntax checking |
c5a0818e | 845 | Check the code for syntax errors, but do not actually compile it. This |
adeb22c4 FXC |
846 | will generate module files for each module present in the code, but no |
847 | other output file. | |
6de9cd9a | 848 | |
28ce22e6 JW |
849 | @item -Wpedantic |
850 | @itemx -pedantic | |
32864778 | 851 | @opindex @code{pedantic} |
28ce22e6 | 852 | @opindex @code{Wpedantic} |
8179b067 | 853 | Issue warnings for uses of extensions to Fortran. |
6de9cd9a DN |
854 | @option{-pedantic} also applies to C-language constructs where they |
855 | occur in GNU Fortran source files, such as use of @samp{\e} in a | |
40746dcc | 856 | character constant within a directive like @code{#include}. |
6de9cd9a | 857 | |
8179b067 | 858 | Valid Fortran programs should compile properly with or without |
6de9cd9a DN |
859 | this option. |
860 | However, without this option, certain GNU extensions and traditional | |
861 | Fortran features are supported as well. | |
862 | With this option, many of them are rejected. | |
863 | ||
864 | Some users try to use @option{-pedantic} to check programs for conformance. | |
865 | They soon find that it does not do quite what they want---it finds some | |
866 | nonstandard practices, but not all. | |
7fc15ba5 | 867 | However, improvements to GNU Fortran in this area are welcome. |
6de9cd9a | 868 | |
f489fba1 | 869 | This should be used in conjunction with @option{-std=f95}, |
8179b067 | 870 | @option{-std=f2003}, @option{-std=f2008} or @option{-std=f2018}. |
6de9cd9a | 871 | |
6de9cd9a | 872 | @item -pedantic-errors |
32864778 | 873 | @opindex @code{pedantic-errors} |
6de9cd9a DN |
874 | Like @option{-pedantic}, except that errors are produced rather than |
875 | warnings. | |
876 | ||
6de9cd9a | 877 | @item -Wall |
32864778 | 878 | @opindex @code{Wall} |
6de9cd9a DN |
879 | @cindex all warnings |
880 | @cindex warnings, all | |
3fbab549 JD |
881 | Enables commonly used warning options pertaining to usage that |
882 | we recommend avoiding and that we believe are easy to avoid. | |
cf21551e | 883 | This currently includes @option{-Waliasing}, @option{-Wampersand}, |
72ac1c07 | 884 | @option{-Wconversion}, @option{-Wsurprising}, @option{-Wc-binding-type}, |
124bdd23 | 885 | @option{-Wintrinsics-std}, @option{-Wtabs}, @option{-Wintrinsic-shadow}, |
f657024b | 886 | @option{-Wline-truncation}, @option{-Wtarget-lifetime}, |
1c122092 ML |
887 | @option{-Winteger-division}, @option{-Wreal-q-constant}, @option{-Wunused} |
888 | and @option{-Wundefined-do-loop}. | |
6de9cd9a | 889 | |
6de9cd9a | 890 | @item -Waliasing |
32864778 | 891 | @opindex @code{Waliasing} |
6de9cd9a | 892 | @cindex aliasing |
32864778 | 893 | @cindex warnings, aliasing |
3010be13 AD |
894 | Warn about possible aliasing of dummy arguments. Specifically, it warns |
895 | if the same actual argument is associated with a dummy argument with | |
40746dcc | 896 | @code{INTENT(IN)} and a dummy argument with @code{INTENT(OUT)} in a call |
3010be13 AD |
897 | with an explicit interface. |
898 | ||
899 | The following example will trigger the warning. | |
6de9cd9a | 900 | @smallexample |
3010be13 AD |
901 | interface |
902 | subroutine bar(a,b) | |
903 | integer, intent(in) :: a | |
904 | integer, intent(out) :: b | |
905 | end subroutine | |
906 | end interface | |
907 | integer :: a | |
908 | ||
909 | call bar(a,a) | |
6de9cd9a DN |
910 | @end smallexample |
911 | ||
3fbab549 | 912 | @item -Wampersand |
32864778 DF |
913 | @opindex @code{Wampersand} |
914 | @cindex warnings, ampersand | |
ab940b73 | 915 | @cindex @code{&} |
8179b067 JB |
916 | Warn about missing ampersand in continued character constants. The |
917 | warning is given with @option{-Wampersand}, @option{-pedantic}, | |
918 | @option{-std=f95}, @option{-std=f2003}, @option{-std=f2008} and | |
919 | @option{-std=f2018}. Note: With no ampersand given in a continued | |
920 | character constant, GNU Fortran assumes continuation at the first | |
921 | non-comment, non-whitespace character after the ampersand that | |
922 | initiated the continuation. | |
3fbab549 | 923 | |
bdfd2ff0 TK |
924 | @item -Warray-temporaries |
925 | @opindex @code{Warray-temporaries} | |
926 | @cindex warnings, array temporaries | |
927 | Warn about array temporaries generated by the compiler. The information | |
928 | generated by this warning is sometimes useful in optimization, in order to | |
929 | avoid such temporaries. | |
930 | ||
0e193637 TB |
931 | @item -Wc-binding-type |
932 | @opindex @code{Wc-binding-type} | |
933 | @cindex warning, C binding type | |
934 | Warn if the a variable might not be C interoperable. In particular, warn if | |
935 | the variable has been declared using an intrinsic type with default kind | |
936 | instead of using a kind parameter defined for C interoperability in the | |
72ac1c07 TK |
937 | intrinsic @code{ISO_C_Binding} module. This option is implied by |
938 | @option{-Wall}. | |
0e193637 | 939 | |
276419d0 | 940 | @item -Wcharacter-truncation |
32864778 DF |
941 | @opindex @code{Wcharacter-truncation} |
942 | @cindex warnings, character truncation | |
276419d0 BM |
943 | Warn when a character assignment will truncate the assigned string. |
944 | ||
802e3f8c RW |
945 | @item -Wline-truncation |
946 | @opindex @code{Wline-truncation} | |
947 | @cindex warnings, line truncation | |
72ac1c07 | 948 | Warn when a source code line will be truncated. This option is |
aecfd035 TB |
949 | implied by @option{-Wall}. For free-form source code, the default is |
950 | @option{-Werror=line-truncation} such that truncations are reported as | |
951 | error. | |
802e3f8c | 952 | |
6de9cd9a | 953 | @item -Wconversion |
32864778 DF |
954 | @opindex @code{Wconversion} |
955 | @cindex warnings, conversion | |
6de9cd9a | 956 | @cindex conversion |
daf8c6f0 DF |
957 | Warn about implicit conversions that are likely to change the value of |
958 | the expression after conversion. Implied by @option{-Wall}. | |
959 | ||
960 | @item -Wconversion-extra | |
961 | @opindex @code{Wconversion-extra} | |
962 | @cindex warnings, conversion | |
963 | @cindex conversion | |
4daa149b TB |
964 | Warn about implicit conversions between different types and kinds. This |
965 | option does @emph{not} imply @option{-Wconversion}. | |
6de9cd9a | 966 | |
72ac1c07 TK |
967 | @item -Wextra |
968 | @opindex @code{Wextra} | |
969 | @cindex extra warnings | |
970 | @cindex warnings, extra | |
971 | Enables some warning options for usages of language features which | |
15e23330 TK |
972 | may be problematic. This currently includes @option{-Wcompare-reals}, |
973 | @option{-Wunused-parameter} and @option{-Wdo-subscript}. | |
72ac1c07 | 974 | |
d88412fc TK |
975 | @item -Wfrontend-loop-interchange |
976 | @opindex @code{Wfrontend-loop-interchange} | |
977 | @cindex warnings, loop interchange | |
978 | @cindex loop interchange, warning | |
f4436343 ME |
979 | Warn when using @option{-ffrontend-loop-interchange} for performing loop |
980 | interchanges. | |
d88412fc | 981 | |
6de9cd9a | 982 | @item -Wimplicit-interface |
32864778 DF |
983 | @opindex @code{Wimplicit-interface} |
984 | @cindex warnings, implicit interface | |
02712c16 | 985 | Warn if a procedure is called without an explicit interface. |
6de9cd9a DN |
986 | Note this only checks that an explicit interface is present. It does not |
987 | check that the declared interfaces are consistent across program units. | |
988 | ||
ca071303 FXC |
989 | @item -Wimplicit-procedure |
990 | @opindex @code{Wimplicit-procedure} | |
991 | @cindex warnings, implicit procedure | |
992 | Warn if a procedure is called that has neither an explicit interface | |
993 | nor has been declared as @code{EXTERNAL}. | |
994 | ||
c219aeb7 TK |
995 | @item -Winteger-division |
996 | @opindex @code{Winteger-division} | |
997 | @cindex warnings, integer division | |
998 | @cindex warnings, division of integers | |
91c4891a | 999 | Warn if a constant integer division truncates its result. |
c219aeb7 TK |
1000 | As an example, 3/5 evaluates to 0. |
1001 | ||
c3005b0f DK |
1002 | @item -Wintrinsics-std |
1003 | @opindex @code{Wintrinsics-std} | |
1207ac67 | 1004 | @cindex warnings, non-standard intrinsics |
c3005b0f DK |
1005 | @cindex warnings, intrinsics of other standards |
1006 | Warn if @command{gfortran} finds a procedure named like an intrinsic not | |
1007 | available in the currently selected standard (with @option{-std}) and treats | |
1008 | it as @code{EXTERNAL} procedure because of this. @option{-fall-intrinsics} can | |
c7d9f803 | 1009 | be used to never trigger this behavior and always link to the intrinsic |
c3005b0f | 1010 | regardless of the selected standard. |
b7892582 | 1011 | |
91c4891a ME |
1012 | @item -Wno-overwrite-recursive |
1013 | @opindex @code{Woverwrite-recursive} | |
1014 | @cindex warnings, overwrite recursive | |
1015 | Do not warn when @option{-fno-automatic} is used with @option{-frecursive}. Recursion | |
1016 | will be broken if the relevant local variables do not have the attribute | |
1017 | @code{AUTOMATIC} explicitly declared. This option can be used to suppress the warning | |
1018 | when it is known that recursion is not broken. Useful for build environments that use | |
1019 | @option{-Werror}. | |
1020 | ||
5a17346a SK |
1021 | @item -Wreal-q-constant |
1022 | @opindex @code{Wreal-q-constant} | |
1023 | @cindex warnings, @code{q} exponent-letter | |
1024 | Produce a warning if a real-literal-constant contains a @code{q} | |
1025 | exponent-letter. | |
1026 | ||
6de9cd9a | 1027 | @item -Wsurprising |
32864778 DF |
1028 | @opindex @code{Wsurprising} |
1029 | @cindex warnings, suspicious code | |
2d8b59df SK |
1030 | Produce a warning when ``suspicious'' code constructs are encountered. |
1031 | While technically legal these usually indicate that an error has been made. | |
6de9cd9a DN |
1032 | |
1033 | This currently produces a warning under the following circumstances: | |
1034 | ||
1035 | @itemize @bullet | |
1036 | @item | |
ffd1953e FXC |
1037 | An INTEGER SELECT construct has a CASE that can never be matched as its |
1038 | lower value is greater than its upper value. | |
6de9cd9a DN |
1039 | |
1040 | @item | |
1041 | A LOGICAL SELECT construct has three CASE statements. | |
39a184ce JD |
1042 | |
1043 | @item | |
1044 | A TRANSFER specifies a source that is shorter than the destination. | |
fee3292b DK |
1045 | |
1046 | @item | |
1047 | The type of a function result is declared more than once with the same type. If | |
1048 | @option{-pedantic} or standard-conforming mode is enabled, this is an error. | |
5e1d6b4c DK |
1049 | |
1050 | @item | |
1051 | A @code{CHARACTER} variable is declared with negative length. | |
6de9cd9a DN |
1052 | @end itemize |
1053 | ||
840bd9f7 | 1054 | @item -Wtabs |
32864778 DF |
1055 | @opindex @code{Wtabs} |
1056 | @cindex warnings, tabs | |
e739dfac | 1057 | @cindex tabulators |
840bd9f7 | 1058 | By default, tabs are accepted as whitespace, but tabs are not members |
fd1935d5 | 1059 | of the Fortran Character Set. For continuation lines, a tab followed |
8179b067 JB |
1060 | by a digit between 1 and 9 is supported. @option{-Wtabs} will cause a |
1061 | warning to be issued if a tab is encountered. Note, @option{-Wtabs} is | |
1062 | active for @option{-pedantic}, @option{-std=f95}, @option{-std=f2003}, | |
286f737c | 1063 | @option{-std=f2008}, @option{-std=f2018} and |
8179b067 | 1064 | @option{-Wall}. |
840bd9f7 | 1065 | |
1c122092 ML |
1066 | @item -Wundefined-do-loop |
1067 | @opindex @code{Wundefined-do-loop} | |
1068 | @cindex warnings, undefined do loop | |
1069 | Warn if a DO loop with step either 1 or -1 yields an underflow or an overflow | |
03e6ca48 ML |
1070 | during iteration of an induction variable of the loop. |
1071 | This option is implied by @option{-Wall}. | |
1c122092 | 1072 | |
2d8b59df | 1073 | @item -Wunderflow |
32864778 DF |
1074 | @opindex @code{Wunderflow} |
1075 | @cindex warnings, underflow | |
1076 | @cindex underflow | |
2d8b59df | 1077 | Produce a warning when numerical constant expressions are |
73e42eef | 1078 | encountered, which yield an UNDERFLOW during compilation. Enabled by default. |
2d8b59df | 1079 | |
c3005b0f DK |
1080 | @item -Wintrinsic-shadow |
1081 | @opindex @code{Wintrinsic-shadow} | |
1082 | @cindex warnings, intrinsic | |
1083 | @cindex intrinsic | |
1084 | Warn if a user-defined procedure or module procedure has the same name as an | |
1085 | intrinsic; in this case, an explicit interface or @code{EXTERNAL} or | |
1086 | @code{INTRINSIC} declaration might be needed to get calls later resolved to | |
72ac1c07 | 1087 | the desired intrinsic/procedure. This option is implied by @option{-Wall}. |
c3005b0f | 1088 | |
7e114fad JV |
1089 | @item -Wuse-without-only |
1090 | @opindex @code{Wuse-without-only} | |
1091 | @cindex warnings, use statements | |
1092 | @cindex intrinsic | |
1093 | Warn if a @code{USE} statement has no @code{ONLY} qualifier and | |
1094 | thus implicitly imports all public entities of the used module. | |
1095 | ||
4ed44ccc DF |
1096 | @item -Wunused-dummy-argument |
1097 | @opindex @code{Wunused-dummy-argument} | |
1098 | @cindex warnings, unused dummy argument | |
1099 | @cindex unused dummy argument | |
1100 | @cindex dummy argument, unused | |
1101 | Warn about unused dummy arguments. This option is implied by @option{-Wall}. | |
1102 | ||
d92693b4 DF |
1103 | @item -Wunused-parameter |
1104 | @opindex @code{Wunused-parameter} | |
1105 | @cindex warnings, unused parameter | |
1106 | @cindex unused parameter | |
1107 | Contrary to @command{gcc}'s meaning of @option{-Wunused-parameter}, | |
1108 | @command{gfortran}'s implementation of this option does not warn | |
4ed44ccc DF |
1109 | about unused dummy arguments (see @option{-Wunused-dummy-argument}), |
1110 | but about unused @code{PARAMETER} values. @option{-Wunused-parameter} | |
3e9c4087 TB |
1111 | is implied by @option{-Wextra} if also @option{-Wunused} or |
1112 | @option{-Wall} is used. | |
d92693b4 | 1113 | |
f613cea7 JW |
1114 | @item -Walign-commons |
1115 | @opindex @code{Walign-commons} | |
ab940b73 RW |
1116 | @cindex warnings, alignment of @code{COMMON} blocks |
1117 | @cindex alignment of @code{COMMON} blocks | |
f613cea7 | 1118 | By default, @command{gfortran} warns about any occasion of variables being |
ab940b73 | 1119 | padded for proper alignment inside a @code{COMMON} block. This warning can be turned |
f613cea7 JW |
1120 | off via @option{-Wno-align-commons}. See also @option{-falign-commons}. |
1121 | ||
51a30b32 TK |
1122 | @item -Wfunction-elimination |
1123 | @opindex @code{Wfunction-elimination} | |
1124 | @cindex function elimination | |
1125 | @cindex warnings, function elimination | |
6457b1f0 | 1126 | Warn if any calls to impure functions are eliminated by the optimizations |
51a30b32 | 1127 | enabled by the @option{-ffrontend-optimize} option. |
6457b1f0 | 1128 | This option is implied by @option{-Wextra}. |
51a30b32 | 1129 | |
f1fb11f1 TB |
1130 | @item -Wrealloc-lhs |
1131 | @opindex @code{Wrealloc-lhs} | |
1132 | @cindex Reallocate the LHS in assignments, notification | |
1133 | Warn when the compiler might insert code to for allocation or reallocation of | |
1134 | an allocatable array variable of intrinsic type in intrinsic assignments. In | |
1135 | hot loops, the Fortran 2003 reallocation feature may reduce the performance. | |
1136 | If the array is already allocated with the correct shape, consider using a | |
1137 | whole-array array-spec (e.g. @code{(:,:,:)}) for the variable on the left-hand | |
1138 | side to prevent the reallocation check. Note that in some cases the warning | |
1139 | is shown, even if the compiler will optimize reallocation checks away. For | |
1140 | instance, when the right-hand side contains the same variable multiplied by | |
1141 | a scalar. See also @option{-frealloc-lhs}. | |
1142 | ||
1143 | @item -Wrealloc-lhs-all | |
1144 | @opindex @code{Wrealloc-lhs-all} | |
1145 | Warn when the compiler inserts code to for allocation or reallocation of an | |
1146 | allocatable variable; this includes scalars and derived types. | |
51a30b32 | 1147 | |
cf21551e TK |
1148 | @item -Wcompare-reals |
1149 | @opindex @code{Wcompare-reals} | |
1150 | Warn when comparing real or complex types for equality or inequality. | |
72ac1c07 | 1151 | This option is implied by @option{-Wextra}. |
cf21551e | 1152 | |
f657024b TB |
1153 | @item -Wtarget-lifetime |
1154 | @opindex @code{Wtargt-lifetime} | |
1155 | Warn if the pointer in a pointer assignment might be longer than the its | |
1156 | target. This option is implied by @option{-Wall}. | |
1157 | ||
0e533e50 TK |
1158 | @item -Wzerotrip |
1159 | @opindex @code{Wzerotrip} | |
1160 | Warn if a @code{DO} loop is known to execute zero times at compile | |
1161 | time. This option is implied by @option{-Wall}. | |
1162 | ||
15e23330 TK |
1163 | @item -Wdo-subscript |
1164 | @opindex @code{Wdo-subscript} | |
1165 | Warn if an array subscript inside a DO loop could lead to an | |
67914693 | 1166 | out-of-bounds access even if the compiler cannot prove that the |
15e23330 TK |
1167 | statement is actually executed, in cases like |
1168 | @smallexample | |
1169 | real a(3) | |
1170 | do i=1,4 | |
1171 | if (condition(i)) then | |
1172 | a(i) = 1.2 | |
1173 | end if | |
1174 | end do | |
1175 | @end smallexample | |
1176 | This option is implied by @option{-Wextra}. | |
1177 | ||
6de9cd9a | 1178 | @item -Werror |
32864778 DF |
1179 | @opindex @code{Werror} |
1180 | @cindex warnings, to errors | |
6de9cd9a | 1181 | Turns all warnings into errors. |
6de9cd9a DN |
1182 | @end table |
1183 | ||
4f7d9db8 | 1184 | @xref{Warning Options,,Options to Request or Suppress Errors and |
592600ce BM |
1185 | Warnings, gcc,Using the GNU Compiler Collection (GCC)}, for information on |
1186 | more options offered by the GBE shared by @command{gfortran}, @command{gcc} | |
1187 | and other GNU compilers. | |
6de9cd9a DN |
1188 | |
1189 | Some of these have no effect when compiling programs written in Fortran. | |
1190 | ||
1191 | @node Debugging Options | |
a2bef74c | 1192 | @section Options for debugging your program or GNU Fortran |
6de9cd9a DN |
1193 | @cindex options, debugging |
1194 | @cindex debugging information options | |
1195 | ||
1196 | GNU Fortran has various special options that are used for debugging | |
7fc15ba5 | 1197 | either your program or the GNU Fortran compiler. |
6de9cd9a DN |
1198 | |
1199 | @table @gcctabopt | |
1607a827 TK |
1200 | @item -fdump-fortran-original |
1201 | @opindex @code{fdump-fortran-original} | |
1202 | Output the internal parse tree after translating the source program | |
cebb1919 TK |
1203 | into internal representation. This option is mostly useful for |
1204 | debugging the GNU Fortran compiler itself. The output generated by | |
1205 | this option might change between releases. This option may also | |
1206 | generate internal compiler errors for features which have only | |
1207 | recently been added. | |
1607a827 | 1208 | |
85dabaed | 1209 | @item -fdump-fortran-optimized |
1607a827 | 1210 | @opindex @code{fdump-fortran-optimized} |
cebb1919 TK |
1211 | Output the parse tree after front-end optimization. Mostly useful for |
1212 | debugging the GNU Fortran compiler itself. The output generated by | |
1213 | this option might change between releases. This option may also | |
1214 | generate internal compiler errors for features which have only | |
1215 | recently been added. | |
1607a827 | 1216 | |
85dabaed | 1217 | @item -fdump-parse-tree |
32864778 | 1218 | @opindex @code{fdump-parse-tree} |
1607a827 | 1219 | Output the internal parse tree after translating the source program |
cebb1919 TK |
1220 | into internal representation. Mostly useful for debugging the GNU |
1221 | Fortran compiler itself. The output generated by this option might | |
1222 | change between releases. This option may also generate internal | |
1223 | compiler errors for features which have only recently been added. This | |
1224 | option is deprecated; use @code{-fdump-fortran-original} instead. | |
6de9cd9a | 1225 | |
5c6aa9a8 TK |
1226 | @item -fdump-fortran-global |
1227 | @opindex @code{fdump-fortran-global} | |
1228 | Output a list of the global identifiers after translating into | |
1229 | middle-end representation. Mostly useful for debugging the GNU Fortran | |
1230 | compiler itself. The output generated by this option might change | |
1231 | between releases. This option may also generate internal compiler | |
1232 | errors for features which have only recently been added. | |
1233 | ||
944b8b35 | 1234 | @item -ffpe-trap=@var{list} |
32864778 | 1235 | @opindex @code{ffpe-trap=}@var{list} |
57b4d355 JB |
1236 | Specify a list of floating point exception traps to enable. On most |
1237 | systems, if a floating point exception occurs and the trap for that | |
1238 | exception is enabled, a SIGFPE signal will be sent and the program | |
1239 | being aborted, producing a core file useful for debugging. @var{list} | |
1240 | is a (possibly empty) comma-separated list of the following | |
1241 | exceptions: @samp{invalid} (invalid floating point operation, such as | |
1242 | @code{SQRT(-1.0)}), @samp{zero} (division by zero), @samp{overflow} | |
1243 | (overflow in a floating point operation), @samp{underflow} (underflow | |
1244 | in a floating point operation), @samp{inexact} (loss of precision | |
1245 | during operation), and @samp{denormal} (operation performed on a | |
1246 | denormal value). The first five exceptions correspond to the five | |
1247 | IEEE 754 exceptions, whereas the last one (@samp{denormal}) is not | |
1248 | part of the IEEE 754 standard but is available on some common | |
1249 | architectures such as x86. | |
1250 | ||
1251 | The first three exceptions (@samp{invalid}, @samp{zero}, and | |
1252 | @samp{overflow}) often indicate serious errors, and unless the program | |
1253 | has provisions for dealing with these exceptions, enabling traps for | |
1254 | these three exceptions is probably a good idea. | |
1255 | ||
1bdfc7aa DH |
1256 | If the option is used more than once in the command line, the lists will |
1257 | be joined: '@code{ffpe-trap=}@var{list1} @code{ffpe-trap=}@var{list2}' | |
06293766 | 1258 | is equivalent to @code{ffpe-trap=}@var{list1},@var{list2}. |
1bdfc7aa DH |
1259 | |
1260 | Note that once enabled an exception cannot be disabled (no negative form). | |
1261 | ||
57b4d355 JB |
1262 | Many, if not most, floating point operations incur loss of precision |
1263 | due to rounding, and hence the @code{ffpe-trap=inexact} is likely to | |
1264 | be uninteresting in practice. | |
1265 | ||
1266 | By default no exception traps are enabled. | |
8307c61b | 1267 | |
fa86f4f9 TB |
1268 | @item -ffpe-summary=@var{list} |
1269 | @opindex @code{ffpe-summary=}@var{list} | |
1270 | Specify a list of floating-point exceptions, whose flag status is printed | |
1271 | to @code{ERROR_UNIT} when invoking @code{STOP} and @code{ERROR STOP}. | |
1272 | @var{list} can be either @samp{none}, @samp{all} or a comma-separated list | |
1273 | of the following exceptions: @samp{invalid}, @samp{zero}, @samp{overflow}, | |
1274 | @samp{underflow}, @samp{inexact} and @samp{denormal}. (See | |
1275 | @option{-ffpe-trap} for a description of the exceptions.) | |
1276 | ||
1bdfc7aa DH |
1277 | If the option is used more than once in the command line, only the |
1278 | last one will be used. | |
1279 | ||
fa86f4f9 TB |
1280 | By default, a summary for all exceptions but @samp{inexact} is shown. |
1281 | ||
de8bd142 JB |
1282 | @item -fno-backtrace |
1283 | @opindex @code{fno-backtrace} | |
868d75db FXC |
1284 | @cindex backtrace |
1285 | @cindex trace | |
de8bd142 JB |
1286 | When a serious runtime error is encountered or a deadly signal is |
1287 | emitted (segmentation fault, illegal instruction, bus error, | |
1288 | floating-point exception, and the other POSIX signals that have the | |
1289 | action @samp{core}), the Fortran runtime library tries to output a | |
1290 | backtrace of the error. @code{-fno-backtrace} disables the backtrace | |
1291 | generation. This option only has influence for compilation of the | |
1292 | Fortran main program. | |
1293 | ||
944b8b35 FXC |
1294 | @end table |
1295 | ||
6de9cd9a DN |
1296 | @xref{Debugging Options,,Options for Debugging Your Program or GCC, |
1297 | gcc,Using the GNU Compiler Collection (GCC)}, for more information on | |
1298 | debugging options. | |
1299 | ||
1300 | @node Directory Options | |
a2bef74c | 1301 | @section Options for directory search |
6de9cd9a DN |
1302 | @cindex directory, options |
1303 | @cindex options, directory search | |
1304 | @cindex search path | |
ab940b73 RW |
1305 | @cindex @code{INCLUDE} directive |
1306 | @cindex directive, @code{INCLUDE} | |
7fc15ba5 | 1307 | These options affect how GNU Fortran searches |
5724da63 | 1308 | for files specified by the @code{INCLUDE} directive and where it searches |
6de9cd9a DN |
1309 | for previously compiled modules. |
1310 | ||
1311 | It also affects the search paths used by @command{cpp} when used to preprocess | |
2d8b59df | 1312 | Fortran source. |
6de9cd9a DN |
1313 | |
1314 | @table @gcctabopt | |
6de9cd9a | 1315 | @item -I@var{dir} |
32864778 | 1316 | @opindex @code{I}@var{dir} |
6de9cd9a DN |
1317 | @cindex directory, search paths for inclusion |
1318 | @cindex inclusion, directory search paths for | |
1319 | @cindex search paths, for included files | |
1320 | @cindex paths, search | |
1321 | @cindex module search path | |
1322 | These affect interpretation of the @code{INCLUDE} directive | |
1323 | (as well as of the @code{#include} directive of the @command{cpp} | |
1324 | preprocessor). | |
1325 | ||
1326 | Also note that the general behavior of @option{-I} and | |
1327 | @code{INCLUDE} is pretty much the same as of @option{-I} with | |
1328 | @code{#include} in the @command{cpp} preprocessor, with regard to | |
1329 | looking for @file{header.gcc} files and other such things. | |
1330 | ||
40746dcc | 1331 | This path is also used to search for @file{.mod} files when previously |
6de9cd9a DN |
1332 | compiled modules are required by a @code{USE} statement. |
1333 | ||
1334 | @xref{Directory Options,,Options for Directory Search, | |
1335 | gcc,Using the GNU Compiler Collection (GCC)}, for information on the | |
1336 | @option{-I} option. | |
1337 | ||
6de9cd9a | 1338 | @item -J@var{dir} |
32864778 | 1339 | @opindex @code{J}@var{dir} |
ccc2ed87 | 1340 | @opindex @code{M}@var{dir} |
276419d0 BM |
1341 | @cindex paths, search |
1342 | @cindex module search path | |
40746dcc | 1343 | This option specifies where to put @file{.mod} files for compiled modules. |
2d8b59df | 1344 | It is also added to the list of directories to searched by an @code{USE} |
6de9cd9a DN |
1345 | statement. |
1346 | ||
1347 | The default is the current directory. | |
1348 | ||
276419d0 | 1349 | @item -fintrinsic-modules-path @var{dir} |
32864778 | 1350 | @opindex @code{fintrinsic-modules-path} @var{dir} |
276419d0 BM |
1351 | @cindex paths, search |
1352 | @cindex module search path | |
1353 | This option specifies the location of pre-compiled intrinsic modules, if | |
1354 | they are not in the default location expected by the compiler. | |
6de9cd9a DN |
1355 | @end table |
1356 | ||
70263321 | 1357 | @node Link Options |
a2bef74c | 1358 | @section Influencing the linking step |
70263321 DF |
1359 | @cindex options, linking |
1360 | @cindex linking, static | |
1361 | ||
1362 | These options come into play when the compiler links object files into an | |
1363 | executable output file. They are meaningless if the compiler is not doing | |
1364 | a link step. | |
1365 | ||
1366 | @table @gcctabopt | |
1367 | @item -static-libgfortran | |
1368 | @opindex @code{static-libgfortran} | |
1369 | On systems that provide @file{libgfortran} as a shared and a static | |
1370 | library, this option forces the use of the static version. If no | |
1371 | shared version of @file{libgfortran} was built when the compiler was | |
1372 | configured, this option has no effect. | |
1373 | @end table | |
1374 | ||
1375 | ||
eaa90d25 | 1376 | @node Runtime Options |
a2bef74c | 1377 | @section Influencing runtime behavior |
e739dfac | 1378 | @cindex options, runtime |
eaa90d25 | 1379 | |
7fc15ba5 | 1380 | These options affect the runtime behavior of programs compiled with GNU Fortran. |
4d04d67a | 1381 | |
eaa90d25 | 1382 | @table @gcctabopt |
eaa90d25 | 1383 | @item -fconvert=@var{conversion} |
32864778 | 1384 | @opindex @code{fconvert=}@var{conversion} |
eaa90d25 TK |
1385 | Specify the representation of data for unformatted files. Valid |
1386 | values for conversion are: @samp{native}, the default; @samp{swap}, | |
1387 | swap between big- and little-endian; @samp{big-endian}, use big-endian | |
1388 | representation for unformatted files; @samp{little-endian}, use little-endian | |
1389 | representation for unformatted files. | |
1390 | ||
1391 | @emph{This option has an effect only when used in the main program. | |
1392 | The @code{CONVERT} specifier and the GFORTRAN_CONVERT_UNIT environment | |
40746dcc | 1393 | variable override the default specified by @option{-fconvert}.} |
d67ab5ee | 1394 | |
d67ab5ee | 1395 | @item -frecord-marker=@var{length} |
32864778 | 1396 | @opindex @code{frecord-marker=}@var{length} |
d67ab5ee | 1397 | Specify the length of record markers for unformatted files. |
07b3bbf2 | 1398 | Valid values for @var{length} are 4 and 8. Default is 4. |
a2bef74c | 1399 | @emph{This is different from previous versions of @command{gfortran}}, |
07b3bbf2 TK |
1400 | which specified a default record marker length of 8 on most |
1401 | systems. If you want to read or write files compatible | |
a2bef74c | 1402 | with earlier versions of @command{gfortran}, use @option{-frecord-marker=8}. |
07b3bbf2 | 1403 | |
07b3bbf2 | 1404 | @item -fmax-subrecord-length=@var{length} |
32864778 | 1405 | @opindex @code{fmax-subrecord-length=}@var{length} |
07b3bbf2 TK |
1406 | Specify the maximum length for a subrecord. The maximum permitted |
1407 | value for length is 2147483639, which is also the default. Only | |
1408 | really useful for use by the gfortran testsuite. | |
0483c79f JD |
1409 | |
1410 | @item -fsign-zero | |
1411 | @opindex @code{fsign-zero} | |
60d340ef TB |
1412 | When enabled, floating point numbers of value zero with the sign bit set |
1413 | are written as negative number in formatted output and treated as | |
c5a0818e FXC |
1414 | negative in the @code{SIGN} intrinsic. @option{-fno-sign-zero} does not |
1415 | print the negative sign of zero values (or values rounded to zero for I/O) | |
1416 | and regards zero as positive number in the @code{SIGN} intrinsic for | |
1417 | compatibility with Fortran 77. The default is @option{-fsign-zero}. | |
eaa90d25 TK |
1418 | @end table |
1419 | ||
6de9cd9a | 1420 | @node Code Gen Options |
a2bef74c | 1421 | @section Options for code generation conventions |
6de9cd9a DN |
1422 | @cindex code generation, conventions |
1423 | @cindex options, code generation | |
e739dfac | 1424 | @cindex options, run-time |
6de9cd9a DN |
1425 | |
1426 | These machine-independent options control the interface conventions | |
1427 | used in code generation. | |
1428 | ||
1429 | Most of them have both positive and negative forms; the negative form | |
1430 | of @option{-ffoo} would be @option{-fno-foo}. In the table below, only | |
1431 | one of the forms is listed---the one which is not the default. You | |
1432 | can figure out the other form by either removing @option{no-} or adding | |
1433 | it. | |
1434 | ||
6de9cd9a | 1435 | @table @gcctabopt |
ee5426a4 | 1436 | @item -fno-automatic |
32864778 | 1437 | @opindex @code{fno-automatic} |
e739dfac DF |
1438 | @cindex @code{SAVE} statement |
1439 | @cindex statement, @code{SAVE} | |
1e7de83b AL |
1440 | Treat each program unit (except those marked as RECURSIVE) as if the |
1441 | @code{SAVE} statement were specified for every local variable and array | |
1442 | referenced in it. Does not affect common blocks. (Some Fortran compilers | |
1443 | provide this option under the name @option{-static} or @option{-save}.) | |
1444 | The default, which is @option{-fautomatic}, uses the stack for local | |
1445 | variables smaller than the value given by @option{-fmax-stack-var-size}. | |
1446 | Use the option @option{-frecursive} to use no static memory. | |
ee5426a4 | 1447 | |
b4e17cad DH |
1448 | Local variables or arrays having an explicit @code{SAVE} attribute are |
1449 | silently ignored unless the @option{-pedantic} option is added. | |
1450 | ||
973ff4c0 | 1451 | @item -ff2c |
e739dfac | 1452 | @opindex ff2c |
973ff4c0 TS |
1453 | @cindex calling convention |
1454 | @cindex @command{f2c} calling convention | |
1455 | @cindex @command{g77} calling convention | |
1456 | @cindex libf2c calling convention | |
1457 | Generate code designed to be compatible with code generated | |
1458 | by @command{g77} and @command{f2c}. | |
1459 | ||
1460 | The calling conventions used by @command{g77} (originally implemented | |
1461 | in @command{f2c}) require functions that return type | |
1462 | default @code{REAL} to actually return the C type @code{double}, and | |
1463 | functions that return type @code{COMPLEX} to return the values via an | |
1464 | extra argument in the calling sequence that points to where to | |
1465 | store the return value. Under the default GNU calling conventions, such | |
1466 | functions simply return their results as they would in GNU | |
8556236b | 1467 | C---default @code{REAL} functions return the C type @code{float}, and |
973ff4c0 | 1468 | @code{COMPLEX} functions return the GNU C type @code{complex}. |
a226fc2b TS |
1469 | Additionally, this option implies the @option{-fsecond-underscore} |
1470 | option, unless @option{-fno-second-underscore} is explicitly requested. | |
973ff4c0 TS |
1471 | |
1472 | This does not affect the generation of code that interfaces with | |
1473 | the @command{libgfortran} library. | |
1474 | ||
40746dcc BM |
1475 | @emph{Caution:} It is not a good idea to mix Fortran code compiled with |
1476 | @option{-ff2c} with code compiled with the default @option{-fno-f2c} | |
973ff4c0 TS |
1477 | calling conventions as, calling @code{COMPLEX} or default @code{REAL} |
1478 | functions between program parts which were compiled with different | |
1479 | calling conventions will break at execution time. | |
1480 | ||
1481 | @emph{Caution:} This will break code which passes intrinsic functions | |
1482 | of type default @code{REAL} or @code{COMPLEX} as actual arguments, as | |
40746dcc | 1483 | the library implementations use the @option{-fno-f2c} calling conventions. |
973ff4c0 | 1484 | |
6de9cd9a | 1485 | @item -fno-underscoring |
32864778 | 1486 | @opindex @code{fno-underscoring} |
6de9cd9a DN |
1487 | @cindex underscore |
1488 | @cindex symbol names, underscores | |
1489 | @cindex transforming symbol names | |
1490 | @cindex symbol names, transforming | |
1491 | Do not transform names of entities specified in the Fortran | |
1492 | source file by appending underscores to them. | |
1493 | ||
7fc15ba5 | 1494 | With @option{-funderscoring} in effect, GNU Fortran appends one |
5724da63 JD |
1495 | underscore to external names with no underscores. This is done to ensure |
1496 | compatibility with code produced by many UNIX Fortran compilers. | |
973ff4c0 | 1497 | |
7fc15ba5 | 1498 | @emph{Caution}: The default behavior of GNU Fortran is |
973ff4c0 | 1499 | incompatible with @command{f2c} and @command{g77}, please use the |
b4cbcd1a | 1500 | @option{-ff2c} option if you want object files compiled with |
7fc15ba5 | 1501 | GNU Fortran to be compatible with object code created with these |
b4cbcd1a | 1502 | tools. |
6de9cd9a DN |
1503 | |
1504 | Use of @option{-fno-underscoring} is not recommended unless you are | |
7fc15ba5 | 1505 | experimenting with issues such as integration of GNU Fortran into |
8307c61b FXC |
1506 | existing system environments (vis-@`{a}-vis existing libraries, tools, |
1507 | and so on). | |
6de9cd9a | 1508 | |
87681fb5 FXC |
1509 | For example, with @option{-funderscoring}, and assuming that @code{j()} and |
1510 | @code{max_count()} are external functions while @code{my_var} and | |
1511 | @code{lvar} are local variables, a statement like | |
6de9cd9a DN |
1512 | @smallexample |
1513 | I = J() + MAX_COUNT (MY_VAR, LVAR) | |
1514 | @end smallexample | |
6de9cd9a DN |
1515 | @noindent |
1516 | is implemented as something akin to: | |
6de9cd9a DN |
1517 | @smallexample |
1518 | i = j_() + max_count__(&my_var__, &lvar); | |
1519 | @end smallexample | |
1520 | ||
1521 | With @option{-fno-underscoring}, the same statement is implemented as: | |
1522 | ||
1523 | @smallexample | |
1524 | i = j() + max_count(&my_var, &lvar); | |
1525 | @end smallexample | |
1526 | ||
1527 | Use of @option{-fno-underscoring} allows direct specification of | |
7fc15ba5 | 1528 | user-defined names while debugging and when interfacing GNU Fortran |
6de9cd9a DN |
1529 | code with other languages. |
1530 | ||
1531 | Note that just because the names match does @emph{not} mean that the | |
7fc15ba5 | 1532 | interface implemented by GNU Fortran for an external name matches the |
6de9cd9a | 1533 | interface implemented by some other language for that same name. |
7fc15ba5 | 1534 | That is, getting code produced by GNU Fortran to link to code produced |
6de9cd9a DN |
1535 | by some other compiler using this or any other method can be only a |
1536 | small part of the overall solution---getting the code generated by | |
1537 | both compilers to agree on issues other than naming can require | |
1538 | significant effort, and, unlike naming disagreements, linkers normally | |
1539 | cannot detect disagreements in these other areas. | |
1540 | ||
1541 | Also, note that with @option{-fno-underscoring}, the lack of appended | |
1542 | underscores introduces the very real possibility that a user-defined | |
1543 | external name will conflict with a name in a system library, which | |
1544 | could make finding unresolved-reference bugs quite difficult in some | |
1545 | cases---they might occur at program run time, and show up only as | |
1546 | buggy behavior at run time. | |
1547 | ||
7fc15ba5 | 1548 | In future versions of GNU Fortran we hope to improve naming and linking |
6de9cd9a DN |
1549 | issues so that debugging always involves using the names as they appear |
1550 | in the source, even if the names as seen by the linker are mangled to | |
1551 | prevent accidental linking between procedures with incompatible | |
1552 | interfaces. | |
1553 | ||
973ff4c0 | 1554 | @item -fsecond-underscore |
32864778 | 1555 | @opindex @code{fsecond-underscore} |
6de9cd9a DN |
1556 | @cindex underscore |
1557 | @cindex symbol names, underscores | |
1558 | @cindex transforming symbol names | |
1559 | @cindex symbol names, transforming | |
973ff4c0 TS |
1560 | @cindex @command{f2c} calling convention |
1561 | @cindex @command{g77} calling convention | |
1562 | @cindex libf2c calling convention | |
7fc15ba5 BM |
1563 | By default, GNU Fortran appends an underscore to external |
1564 | names. If this option is used GNU Fortran appends two | |
973ff4c0 | 1565 | underscores to names with underscores and one underscore to external names |
7fc15ba5 | 1566 | with no underscores. GNU Fortran also appends two underscores to |
973ff4c0 TS |
1567 | internal names with underscores to avoid naming collisions with external |
1568 | names. | |
6de9cd9a DN |
1569 | |
1570 | This option has no effect if @option{-fno-underscoring} is | |
973ff4c0 | 1571 | in effect. It is implied by the @option{-ff2c} option. |
6de9cd9a | 1572 | |
40746dcc | 1573 | Otherwise, with this option, an external name such as @code{MAX_COUNT} |
6de9cd9a | 1574 | is implemented as a reference to the link-time external symbol |
40746dcc | 1575 | @code{max_count__}, instead of @code{max_count_}. This is required |
973ff4c0 TS |
1576 | for compatibility with @command{g77} and @command{f2c}, and is implied |
1577 | by use of the @option{-ff2c} option. | |
6de9cd9a | 1578 | |
f4d1d50a TB |
1579 | @item -fcoarray=@var{<keyword>} |
1580 | @opindex @code{fcoarray} | |
1581 | @cindex coarrays | |
1582 | ||
1583 | @table @asis | |
1584 | @item @samp{none} | |
1585 | Disable coarray support; using coarray declarations and image-control | |
1586 | statements will produce a compile-time error. (Default) | |
1587 | ||
1588 | @item @samp{single} | |
1589 | Single-image mode, i.e. @code{num_images()} is always one. | |
60386f50 TB |
1590 | |
1591 | @item @samp{lib} | |
1592 | Library-based coarray parallelization; a suitable GNU Fortran coarray | |
1593 | library needs to be linked. | |
f4d1d50a TB |
1594 | @end table |
1595 | ||
1596 | ||
d3d3011f FXC |
1597 | @item -fcheck=@var{<keyword>} |
1598 | @opindex @code{fcheck} | |
e739dfac | 1599 | @cindex array, bounds checking |
df1afcca | 1600 | @cindex bit intrinsics checking |
6de9cd9a | 1601 | @cindex bounds checking |
20460eb9 | 1602 | @cindex pointer checking |
22bdbb0f | 1603 | @cindex memory checking |
6de9cd9a | 1604 | @cindex range checking |
6de9cd9a DN |
1605 | @cindex subscript checking |
1606 | @cindex checking subscripts | |
d3d3011f FXC |
1607 | @cindex run-time checking |
1608 | @cindex checking array temporaries | |
1609 | ||
1610 | Enable the generation of run-time checks; the argument shall be | |
a4c54bf2 JD |
1611 | a comma-delimited list of the following keywords. Prefixing a check with |
1612 | @option{no-} disables it if it was activated by a previous specification. | |
d3d3011f FXC |
1613 | |
1614 | @table @asis | |
1615 | @item @samp{all} | |
1616 | Enable all run-time test of @option{-fcheck}. | |
1617 | ||
1618 | @item @samp{array-temps} | |
1619 | Warns at run time when for passing an actual argument a temporary array | |
1620 | had to be generated. The information generated by this warning is | |
1621 | sometimes useful in optimization, in order to avoid such temporaries. | |
1622 | ||
1623 | Note: The warning is only printed once per location. | |
1624 | ||
df1afcca HA |
1625 | @item @samp{bits} |
1626 | Enable generation of run-time checks for invalid arguments to the bit | |
1627 | manipulation intrinsics. | |
1628 | ||
d3d3011f | 1629 | @item @samp{bounds} |
6de9cd9a DN |
1630 | Enable generation of run-time checks for array subscripts |
1631 | and against the declared minimum and maximum values. It also | |
1632 | checks array indices for assumed and deferred | |
aad9c4f4 AM |
1633 | shape arrays against the actual allocated bounds and ensures that all string |
1634 | lengths are equal for character array constructors without an explicit | |
1635 | typespec. | |
6de9cd9a | 1636 | |
d3d3011f | 1637 | Some checks require that @option{-fcheck=bounds} is set for |
8307c61b | 1638 | the compilation of the main program. |
18fe404f | 1639 | |
aad9c4f4 AM |
1640 | Note: In the future this may also include other forms of checking, e.g., |
1641 | checking substring references. | |
43998ed9 | 1642 | |
33abc845 TB |
1643 | @item @samp{do} |
1644 | Enable generation of run-time checks for invalid modification of loop | |
1645 | iteration variables. | |
1646 | ||
22bdbb0f TB |
1647 | @item @samp{mem} |
1648 | Enable generation of run-time checks for memory allocation. | |
1649 | Note: This option does not affect explicit allocations using the | |
1650 | @code{ALLOCATE} statement, which will be always checked. | |
1651 | ||
20460eb9 TB |
1652 | @item @samp{pointer} |
1653 | Enable generation of run-time checks for pointers and allocatables. | |
1654 | ||
43998ed9 TB |
1655 | @item @samp{recursion} |
1656 | Enable generation of run-time checks for recursively called subroutines and | |
1657 | functions which are not marked as recursive. See also @option{-frecursive}. | |
8b5f6dd8 | 1658 | Note: This check does not work for OpenMP programs and is disabled if used |
5b130807 | 1659 | together with @option{-frecursive} and @option{-fopenmp}. |
d3d3011f | 1660 | @end table |
6de9cd9a | 1661 | |
a4c54bf2 JD |
1662 | Example: Assuming you have a file @file{foo.f90}, the command |
1663 | @smallexample | |
1664 | gfortran -fcheck=all,no-array-temps foo.f90 | |
1665 | @end smallexample | |
1666 | will compile the file with all checks enabled as specified above except | |
1667 | warnings for generated array temporaries. | |
1668 | ||
0d52899f | 1669 | |
d3d3011f FXC |
1670 | @item -fbounds-check |
1671 | @opindex @code{fbounds-check} | |
1672 | @c Note: This option is also referred in gcc's manpage | |
1673 | Deprecated alias for @option{-fcheck=bounds}. | |
0d52899f | 1674 | |
ffeebc4f JJ |
1675 | @item -ftail-call-workaround |
1676 | @itemx -ftail-call-workaround=@var{n} | |
1677 | @opindex @code{tail-call-workaround} | |
14688b8d TK |
1678 | Some C interfaces to Fortran codes violate the gfortran ABI by |
1679 | omitting the hidden character length arguments as described in | |
1680 | @xref{Argument passing conventions}. This can lead to crashes | |
1681 | because pushing arguments for tail calls can overflow the stack. | |
1682 | ||
1683 | To provide a workaround for existing binary packages, this option | |
1684 | disables tail call optimization for gfortran procedures with character | |
ffeebc4f JJ |
1685 | arguments. With @option{-ftail-call-workaround=2} tail call optimization |
1686 | is disabled in all gfortran procedures with character arguments, | |
1687 | with @option{-ftail-call-workaround=1} or equivalent | |
1688 | @option{-ftail-call-workaround} only in gfortran procedures with character | |
1689 | arguments that call implicitly prototyped procedures. | |
14688b8d TK |
1690 | |
1691 | Using this option can lead to problems including crashes due to | |
1692 | insufficient stack space. | |
1693 | ||
1694 | It is @emph{very strongly} recommended to fix the code in question. | |
1695 | The @option{-fc-prototypes-external} option can be used to generate | |
1696 | prototypes which conform to gfortran's ABI, for inclusion in the | |
1697 | source code. | |
1698 | ||
1699 | Support for this option will likely be withdrawn in a future release | |
1700 | of gfortran. | |
1701 | ||
ffeebc4f JJ |
1702 | The negative form, @option{-fno-tail-call-workaround} or equivalent |
1703 | @option{-ftail-call-workaround=0}, can be used to disable this option. | |
14688b8d | 1704 | |
ffeebc4f | 1705 | Default is currently @option{-ftail-call-workaround}, this will change |
14688b8d TK |
1706 | in future releases. |
1707 | ||
d3d3011f FXC |
1708 | @item -fcheck-array-temporaries |
1709 | @opindex @code{fcheck-array-temporaries} | |
1710 | Deprecated alias for @option{-fcheck=array-temps}. | |
0d52899f | 1711 | |
63346ddb SK |
1712 | @item -fmax-array-constructor=@var{n} |
1713 | @opindex @code{fmax-array-constructor} | |
1714 | This option can be used to increase the upper limit permitted in | |
1715 | array constructors. The code below requires this option to expand | |
1716 | the array at compile time. | |
1717 | ||
1718 | @smallexample | |
ab940b73 RW |
1719 | program test |
1720 | implicit none | |
1721 | integer j | |
1722 | integer, parameter :: n = 100000 | |
1723 | integer, parameter :: i(n) = (/ (2*j, j = 1, n) /) | |
1724 | print '(10(I0,1X))', i | |
1725 | end program test | |
63346ddb SK |
1726 | @end smallexample |
1727 | ||
1728 | @emph{Caution: This option can lead to long compile times and excessively | |
1729 | large object files.} | |
1730 | ||
1731 | The default value for @var{n} is 65535. | |
1732 | ||
1733 | ||
6de9cd9a | 1734 | @item -fmax-stack-var-size=@var{n} |
32864778 | 1735 | @opindex @code{fmax-stack-var-size} |
6de9cd9a | 1736 | This option specifies the size in bytes of the largest array that will be put |
1e7de83b AL |
1737 | on the stack; if the size is exceeded static memory is used (except in |
1738 | procedures marked as RECURSIVE). Use the option @option{-frecursive} to | |
1739 | allow for recursive procedures which do not have a RECURSIVE attribute or | |
1740 | for parallel programs. Use @option{-fno-automatic} to never use the stack. | |
6de9cd9a DN |
1741 | |
1742 | This option currently only affects local arrays declared with constant | |
1743 | bounds, and may not apply to all character variables. | |
7fc15ba5 | 1744 | Future versions of GNU Fortran may improve this behavior. |
6de9cd9a | 1745 | |
54320207 | 1746 | The default value for @var{n} is 65536. |
6de9cd9a | 1747 | |
c76f8d52 MM |
1748 | @item -fstack-arrays |
1749 | @opindex @code{fstack-arrays} | |
27c33b8f TK |
1750 | Adding this option will make the Fortran compiler put all arrays of |
1751 | unknown size and array temporaries onto stack memory. If your program uses very | |
c5a0818e | 1752 | large local arrays it is possible that you will have to extend your runtime |
2d8c9ad5 | 1753 | limits for stack memory on some operating systems. This flag is enabled |
27c33b8f TK |
1754 | by default at optimization level @option{-Ofast} unless |
1755 | @option{-fmax-stack-var-size} is specified. | |
c76f8d52 | 1756 | |
5139e1e9 | 1757 | @item -fpack-derived |
32864778 DF |
1758 | @opindex @code{fpack-derived} |
1759 | @cindex structure packing | |
7fc15ba5 | 1760 | This option tells GNU Fortran to pack derived type members as closely as |
2d8b59df | 1761 | possible. Code compiled with this option is likely to be incompatible |
6de9cd9a DN |
1762 | with code compiled without this option, and may execute slower. |
1763 | ||
6de9cd9a | 1764 | @item -frepack-arrays |
32864778 DF |
1765 | @opindex @code{frepack-arrays} |
1766 | @cindex repacking arrays | |
7fc15ba5 | 1767 | In some circumstances GNU Fortran may pass assumed shape array |
02712c16 | 1768 | sections via a descriptor describing a noncontiguous area of memory. |
6de9cd9a DN |
1769 | This option adds code to the function prologue to repack the data into |
1770 | a contiguous block at runtime. | |
1771 | ||
1772 | This should result in faster accesses to the array. However it can introduce | |
1773 | significant overhead to the function call, especially when the passed data | |
02712c16 | 1774 | is noncontiguous. |
a63dad5b | 1775 | |
a63dad5b | 1776 | @item -fshort-enums |
32864778 | 1777 | @opindex @code{fshort-enums} |
a63dad5b | 1778 | This option is provided for interoperability with C code that was |
4ba96c02 | 1779 | compiled with the @option{-fshort-enums} option. It will make |
7fc15ba5 | 1780 | GNU Fortran choose the smallest @code{INTEGER} kind a given |
a63dad5b | 1781 | enumerator set will fit in, and give all its enumerators this kind. |
5a0aad31 | 1782 | |
95d27703 TK |
1783 | @item -finline-arg-packing |
1784 | @opindex @code{finline-arg-packing} | |
1785 | When passing an assumed-shape argument of a procedure as actual | |
1786 | argument to an assumed-size or explicit size or as argument to a | |
1787 | procedure that does not have an explicit interface, the argument may | |
1788 | have to be packed, that is put into contiguous memory. An example is | |
1789 | the call to @code{foo} in | |
1790 | @smallexample | |
1791 | subroutine foo(a) | |
1792 | real, dimension(*) :: a | |
1793 | end subroutine foo | |
1794 | subroutine bar(b) | |
1795 | real, dimension(:) :: b | |
1796 | call foo(b) | |
1797 | end subroutine bar | |
1798 | @end smallexample | |
1799 | ||
1800 | When @option{-finline-arg-packing} is in effect, this packing will be | |
1801 | performed by inline code. This allows for more optimization while | |
1802 | increasing code size. | |
1803 | ||
1804 | @option{-finline-arg-packing} is implied by any of the @option{-O} options | |
1805 | except when optimizing for size via @option{-Os}. If the code | |
1806 | contains a very large number of argument that have to be packed, code | |
1807 | size and also compilation time may become excessive. If that is the | |
1808 | case, it may be better to disable this option. Instances of packing | |
1809 | can be found by using by using @option{-Warray-temporaries}. | |
1810 | ||
5a0aad31 | 1811 | @item -fexternal-blas |
32864778 | 1812 | @opindex @code{fexternal-blas} |
a2bef74c DF |
1813 | This option will make @command{gfortran} generate calls to BLAS functions |
1814 | for some matrix operations like @code{MATMUL}, instead of using our own | |
5a0aad31 | 1815 | algorithms, if the size of the matrices involved is larger than a given |
4ba96c02 | 1816 | limit (see @option{-fblas-matmul-limit}). This may be profitable if an |
5a0aad31 FXC |
1817 | optimized vendor BLAS library is available. The BLAS library will have |
1818 | to be specified at link time. | |
1819 | ||
5a0aad31 | 1820 | @item -fblas-matmul-limit=@var{n} |
32864778 | 1821 | @opindex @code{fblas-matmul-limit} |
4ba96c02 | 1822 | Only significant when @option{-fexternal-blas} is in effect. |
5a0aad31 FXC |
1823 | Matrix multiplication of matrices with size larger than (or equal to) @var{n} |
1824 | will be performed by calls to BLAS functions, while others will be | |
1825 | handled by @command{gfortran} internal algorithms. If the matrices | |
1826 | involved are not square, the size comparison is performed using the | |
1827 | geometric mean of the dimensions of the argument and result matrices. | |
1828 | ||
1829 | The default value for @var{n} is 30. | |
1830 | ||
f1abbf69 TK |
1831 | @item -finline-matmul-limit=@var{n} |
1832 | @opindex @code{finline-matmul-limit} | |
1833 | When front-end optimiztion is active, some calls to the @code{MATMUL} | |
1834 | intrinsic function will be inlined. This may result in code size | |
1835 | increase if the size of the matrix cannot be determined at compile | |
1836 | time, as code for both cases is generated. Setting | |
1837 | @code{-finline-matmul-limit=0} will disable inlining in all cases. | |
1838 | Setting this option with a value of @var{n} will produce inline code | |
1839 | for matrices with size up to @var{n}. If the matrices involved are not | |
1840 | square, the size comparison is performed using the geometric mean of | |
1841 | the dimensions of the argument and result matrices. | |
1842 | ||
c7b608a9 TK |
1843 | The default value for @var{n} is 30. The @code{-fblas-matmul-limit} |
1844 | can be used to change this value. | |
f1abbf69 | 1845 | |
1e7de83b AL |
1846 | @item -frecursive |
1847 | @opindex @code{frecursive} | |
1848 | Allow indirect recursion by forcing all local arrays to be allocated | |
1849 | on the stack. This flag cannot be used together with | |
1850 | @option{-fmax-stack-var-size=} or @option{-fno-automatic}. | |
1851 | ||
51b09ce3 | 1852 | @item -finit-local-zero |
7fc61626 | 1853 | @itemx -finit-derived |
4d04d67a RW |
1854 | @itemx -finit-integer=@var{n} |
1855 | @itemx -finit-real=@var{<zero|inf|-inf|nan|snan>} | |
1856 | @itemx -finit-logical=@var{<true|false>} | |
1857 | @itemx -finit-character=@var{n} | |
51b09ce3 | 1858 | @opindex @code{finit-local-zero} |
7fc61626 | 1859 | @opindex @code{finit-derived} |
51b09ce3 AL |
1860 | @opindex @code{finit-integer} |
1861 | @opindex @code{finit-real} | |
1862 | @opindex @code{finit-logical} | |
1863 | @opindex @code{finit-character} | |
1864 | The @option{-finit-local-zero} option instructs the compiler to | |
1865 | initialize local @code{INTEGER}, @code{REAL}, and @code{COMPLEX} | |
1866 | variables to zero, @code{LOGICAL} variables to false, and | |
1867 | @code{CHARACTER} variables to a string of null bytes. Finer-grained | |
1868 | initialization options are provided by the | |
1869 | @option{-finit-integer=@var{n}}, | |
346a77d1 | 1870 | @option{-finit-real=@var{<zero|inf|-inf|nan|snan>}} (which also initializes |
51b09ce3 AL |
1871 | the real and imaginary parts of local @code{COMPLEX} variables), |
1872 | @option{-finit-logical=@var{<true|false>}}, and | |
1873 | @option{-finit-character=@var{n}} (where @var{n} is an ASCII character | |
13051352 FR |
1874 | value) options. |
1875 | ||
1876 | With @option{-finit-derived}, components of derived type variables will be | |
1877 | initialized according to these flags. Components whose type is not covered by | |
1878 | an explicit @option{-finit-*} flag will be treated as described above with | |
1879 | @option{-finit-local-zero}. | |
1880 | ||
1881 | These options do not initialize | |
d6202322 TM |
1882 | @itemize @bullet |
1883 | @item | |
e5b1f5a1 FR |
1884 | objects with the POINTER attribute |
1885 | @item | |
d6202322 TM |
1886 | allocatable arrays |
1887 | @item | |
d6202322 TM |
1888 | variables that appear in an @code{EQUIVALENCE} statement. |
1889 | @end itemize | |
1890 | (These limitations may be removed in future releases). | |
51b09ce3 AL |
1891 | |
1892 | Note that the @option{-finit-real=nan} option initializes @code{REAL} | |
346a77d1 TB |
1893 | and @code{COMPLEX} variables with a quiet NaN. For a signalling NaN |
1894 | use @option{-finit-real=snan}; note, however, that compile-time | |
1895 | optimizations may convert them into quiet NaN and that trapping | |
1896 | needs to be enabled (e.g. via @option{-ffpe-trap}). | |
f613cea7 | 1897 | |
66086032 JB |
1898 | The @option{-finit-integer} option will parse the value into an |
1899 | integer of type @code{INTEGER(kind=C_LONG)} on the host. Said value | |
1900 | is then assigned to the integer variables in the Fortran code, which | |
1901 | might result in wraparound if the value is too large for the kind. | |
1902 | ||
29525822 FXC |
1903 | Finally, note that enabling any of the @option{-finit-*} options will |
1904 | silence warnings that would have been emitted by @option{-Wuninitialized} | |
1905 | for the affected local variables. | |
1906 | ||
f613cea7 JW |
1907 | @item -falign-commons |
1908 | @opindex @code{falign-commons} | |
ab940b73 | 1909 | @cindex alignment of @code{COMMON} blocks |
f613cea7 | 1910 | By default, @command{gfortran} enforces proper alignment of all variables in a |
ab940b73 RW |
1911 | @code{COMMON} block by padding them as needed. On certain platforms this is mandatory, |
1912 | on others it increases performance. If a @code{COMMON} block is not declared with | |
f613cea7 | 1913 | consistent data types everywhere, this padding can cause trouble, and |
ab940b73 RW |
1914 | @option{-fno-align-commons} can be used to disable automatic alignment. The |
1915 | same form of this option should be used for all files that share a @code{COMMON} block. | |
1916 | To avoid potential alignment issues in @code{COMMON} blocks, it is recommended to order | |
4d04d67a | 1917 | objects from largest to smallest. |
72bd130e TB |
1918 | |
1919 | @item -fno-protect-parens | |
1920 | @opindex @code{fno-protect-parens} | |
4d04d67a | 1921 | @cindex re-association of parenthesized expressions |
72bd130e TB |
1922 | By default the parentheses in expression are honored for all optimization |
1923 | levels such that the compiler does not do any re-association. Using | |
ab940b73 RW |
1924 | @option{-fno-protect-parens} allows the compiler to reorder @code{REAL} and |
1925 | @code{COMPLEX} expressions to produce faster code. Note that for the re-association | |
72bd130e | 1926 | optimization @option{-fno-signed-zeros} and @option{-fno-trapping-math} |
7a994646 TB |
1927 | need to be in effect. The parentheses protection is enabled by default, unless |
1928 | @option{-Ofast} is given. | |
597553ab PT |
1929 | |
1930 | @item -frealloc-lhs | |
1931 | @opindex @code{frealloc-lhs} | |
1932 | @cindex Reallocate the LHS in assignments | |
1933 | An allocatable left-hand side of an intrinsic assignment is automatically | |
1934 | (re)allocated if it is either unallocated or has a different shape. The | |
f1fb11f1 TB |
1935 | option is enabled by default except when @option{-std=f95} is given. See |
1936 | also @option{-Wrealloc-lhs}. | |
2757d5ec TK |
1937 | |
1938 | @item -faggressive-function-elimination | |
1939 | @opindex @code{faggressive-function-elimination} | |
1940 | @cindex Elimination of functions with identical argument lists | |
1941 | Functions with identical argument lists are eliminated within | |
1942 | statements, regardless of whether these functions are marked | |
1943 | @code{PURE} or not. For example, in | |
1944 | @smallexample | |
1945 | a = f(b,c) + f(b,c) | |
1946 | @end smallexample | |
51a30b32 TK |
1947 | there will only be a single call to @code{f}. This option only works |
1948 | if @option{-ffrontend-optimize} is in effect. | |
1949 | ||
1950 | @item -ffrontend-optimize | |
1951 | @opindex @code{frontend-optimize} | |
1952 | @cindex Front-end optimization | |
1953 | This option performs front-end optimization, based on manipulating | |
bf9197df JW |
1954 | parts the Fortran parse tree. Enabled by default by any @option{-O} option |
1955 | except @option{-O0} and @option{-Og}. Optimizations enabled by this option | |
1956 | include: | |
1957 | @itemize @bullet | |
1958 | @item inlining calls to @code{MATMUL}, | |
1959 | @item elimination of identical function calls within expressions, | |
1960 | @item removing unnecessary calls to @code{TRIM} in comparisons and assignments, | |
1961 | @item replacing @code{TRIM(a)} with @code{a(1:LEN_TRIM(a))} and | |
1962 | @item short-circuiting of logical operators (@code{.AND.} and @code{.OR.}). | |
1963 | @end itemize | |
1964 | It can be deselected by specifying @option{-fno-frontend-optimize}. | |
d88412fc TK |
1965 | |
1966 | @item -ffrontend-loop-interchange | |
1967 | @opindex @code{frontend-loop-interchange} | |
1968 | @cindex loop interchange, Fortran | |
1969 | Attempt to interchange loops in the Fortran front end where | |
1970 | profitable. Enabled by default by any @option{-O} option. | |
1971 | At the moment, this option only affects @code{FORALL} and | |
1972 | @code{DO CONCURRENT} statements with several forall triplets. | |
6de9cd9a DN |
1973 | @end table |
1974 | ||
1975 | @xref{Code Gen Options,,Options for Code Generation Conventions, | |
1976 | gcc,Using the GNU Compiler Collection (GCC)}, for information on more options | |
1977 | offered by the GBE | |
7fc15ba5 | 1978 | shared by @command{gfortran}, @command{gcc}, and other GNU compilers. |
6de9cd9a | 1979 | |
6de9cd9a DN |
1980 | @c man end |
1981 | ||
e655a6cc TK |
1982 | @node Interoperability Options |
1983 | @section Options for interoperability with other languages | |
1984 | ||
1985 | @table @asis | |
1986 | ||
1987 | @item -fc-prototypes | |
1988 | @opindex @code{c-prototypes} | |
6328ce1f | 1989 | @cindex Generating C prototypes from Fortran BIND(C) enteties |
e655a6cc TK |
1990 | This option will generate C prototypes from @code{BIND(C)} variable |
1991 | declarations, types and procedure interfaces and writes them to | |
1992 | standard output. @code{ENUM} is not yet supported. | |
1993 | ||
1994 | The generated prototypes may need inclusion of an appropriate header, | |
1995 | such as @code{<stdint.h>} or @code{<stdlib.h>}. For types which are | |
1996 | not specified using the appropriate kind from the @code{iso_c_binding} | |
1997 | module, a warning is added as a comment to the code. | |
1998 | ||
1999 | For function pointers, a pointer to a function returning @code{int} | |
2000 | without an explicit argument list is generated. | |
2001 | ||
2002 | Example of use: | |
2003 | @smallexample | |
2004 | $ gfortran -fc-prototypes -fsyntax-only foo.f90 > foo.h | |
2005 | @end smallexample | |
2006 | where the C code intended for interoperating with the Fortran code | |
2007 | then uses @code{#include "foo.h"}. | |
6328ce1f TK |
2008 | |
2009 | @item -fc-prototypes-external | |
2010 | @opindex @code{c-prototypes-external} | |
2011 | @cindex Generating C prototypes from external procedures | |
2012 | This option will generate C prototypes from external functions and | |
2013 | subroutines and write them to standard output. This may be useful for | |
2014 | making sure that C bindings to Fortran code are correct. This option | |
2015 | does not generate prototypes for @code{BIND(C)} procedures, use | |
2016 | @option{-fc-prototypes} for that. | |
2017 | ||
2018 | The generated prototypes may need inclusion of an appropriate | |
2019 | header, such as as @code{<stdint.h>} or @code{<stdlib.h>}. | |
2020 | ||
2021 | This is primarily meant for legacy code to ensure that existing C | |
2022 | bindings match what @command{gfortran} emits. The generated C | |
2023 | prototypes should be correct for the current version of the compiler, | |
2024 | but may not match what other compilers or earlier versions of | |
2025 | @command{gfortran} need. For new developments, use of the | |
2026 | @code{BIND(C)} features is recommended. | |
2027 | ||
2028 | Example of use: | |
2029 | @smallexample | |
2030 | $ gfortran -fc-prototypes-external -fsyntax-only foo.f > foo.h | |
2031 | @end smallexample | |
2032 | where the C code intended for interoperating with the Fortran code | |
2033 | then uses @code{#include "foo.h"}. | |
e655a6cc TK |
2034 | @end table |
2035 | ||
6de9cd9a | 2036 | @node Environment Variables |
a2bef74c | 2037 | @section Environment variables affecting @command{gfortran} |
e739dfac | 2038 | @cindex environment variable |
6de9cd9a DN |
2039 | |
2040 | @c man begin ENVIRONMENT | |
2041 | ||
7fc15ba5 | 2042 | The @command{gfortran} compiler currently does not make use of any environment |
6de9cd9a DN |
2043 | variables to control its operation above and beyond those |
2044 | that affect the operation of @command{gcc}. | |
2045 | ||
2046 | @xref{Environment Variables,,Environment Variables Affecting GCC, | |
2047 | gcc,Using the GNU Compiler Collection (GCC)}, for information on environment | |
2048 | variables. | |
2049 | ||
eaa90d25 | 2050 | @xref{Runtime}, for environment variables that affect the |
7fc15ba5 | 2051 | run-time behavior of programs compiled with GNU Fortran. |
6de9cd9a | 2052 | @c man end |