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d1e082c2 | 1 | @c Copyright (C) 2004-2013 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 | |
d1e082c2 | 7 | Copyright @copyright{} 2004-2013 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), | |
44 | cpp(1), gcov(1), gcc(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1) | |
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. | |
a2bef74c | 103 | * Environment Variables:: Environment variables that affect @command{gfortran}. |
6de9cd9a DN |
104 | @end menu |
105 | ||
106 | @node Option Summary | |
a2bef74c | 107 | @section Option summary |
6de9cd9a DN |
108 | |
109 | @c man begin OPTIONS | |
110 | ||
111 | Here is a summary of all the options specific to GNU Fortran, grouped | |
112 | by type. Explanations are in the following sections. | |
113 | ||
114 | @table @emph | |
115 | @item Fortran Language Options | |
a2bef74c | 116 | @xref{Fortran Dialect Options,,Options controlling Fortran dialect}. |
f4347334 ZG |
117 | @gccoptlist{-fall-intrinsics -fbackslash -fcray-pointer -fd-lines-as-code @gol |
118 | -fd-lines-as-comments -fdefault-double-8 -fdefault-integer-8 @gol | |
119 | -fdefault-real-8 -fdollar-ok -ffixed-line-length-@var{n} @gol | |
120 | -ffixed-line-length-none -ffree-form -ffree-line-length-@var{n} @gol | |
121 | -ffree-line-length-none -fimplicit-none -finteger-4-integer-8 @gol | |
122 | -fmax-identifier-length -fmodule-private -fno-fixed-form -fno-range-check @gol | |
123 | -fopenmp -freal-4-real-10 -freal-4-real-16 -freal-4-real-8 @gol | |
124 | -freal-8-real-10 -freal-8-real-16 -freal-8-real-4 -std=@var{std} | |
125 | } | |
6de9cd9a | 126 | |
670637ee DF |
127 | @item Preprocessing Options |
128 | @xref{Preprocessing Options,,Enable and customize preprocessing}. | |
f4347334 ZG |
129 | @gccoptlist{-A-@var{question}@r{[}=@var{answer}@r{]} |
130 | -A@var{question}=@var{answer} -C -CC -D@var{macro}@r{[}=@var{defn}@r{]} | |
131 | -H -P @gol | |
132 | -U@var{macro} -cpp -dD -dI -dM -dN -dU -fworking-directory | |
133 | -imultilib @var{dir} @gol | |
134 | -iprefix @var{file} -iquote -isysroot @var{dir} -isystem @var{dir} -nocpp | |
135 | -nostdinc @gol | |
136 | -undef | |
137 | } | |
670637ee | 138 | |
592600ce | 139 | @item Error and Warning Options |
a2bef74c DF |
140 | @xref{Error and Warning Options,,Options to request or suppress errors |
141 | and warnings}. | |
f4347334 | 142 | @gccoptlist{-Waliasing -Wall -Wampersand -Warray-bounds |
0e193637 | 143 | -Wc-binding-type -Wcharacter-truncation @gol |
f4347334 ZG |
144 | -Wconversion -Wfunction-elimination -Wimplicit-interface @gol |
145 | -Wimplicit-procedure -Wintrinsic-shadow -Wintrinsics-std @gol | |
146 | -Wline-truncation -Wno-align-commons -Wno-tabs -Wreal-q-constant @gol | |
904e9dbb | 147 | -Wsurprising -Wunderflow -Wunused-parameter -Wrealloc-lhs -Wrealloc-lhs-all @gol |
f657024b | 148 | -Wtarget-lifetime -fmax-errors=@var{n} -fsyntax-only -pedantic -pedantic-errors |
f4347334 | 149 | } |
6de9cd9a DN |
150 | |
151 | @item Debugging Options | |
a2bef74c | 152 | @xref{Debugging Options,,Options for debugging your program or GNU Fortran}. |
f4347334 | 153 | @gccoptlist{-fbacktrace -fdump-fortran-optimized -fdump-fortran-original @gol |
fa86f4f9 | 154 | -fdump-parse-tree -ffpe-trap=@var{list} -ffpe-summary=@var{list} |
f4347334 | 155 | } |
6de9cd9a DN |
156 | |
157 | @item Directory Options | |
a2bef74c | 158 | @xref{Directory Options,,Options for directory search}. |
d8ddea40 | 159 | @gccoptlist{-I@var{dir} -J@var{dir} -fintrinsic-modules-path @var{dir}} |
6de9cd9a | 160 | |
70263321 DF |
161 | @item Link Options |
162 | @xref{Link Options,,Options for influencing the linking step}. | |
163 | @gccoptlist{-static-libgfortran} | |
164 | ||
eaa90d25 TK |
165 | @item Runtime Options |
166 | @xref{Runtime Options,,Options for influencing runtime behavior}. | |
80b91c0b | 167 | @gccoptlist{-fconvert=@var{conversion} -fmax-subrecord-length=@var{length} @gol |
f4347334 ZG |
168 | -frecord-marker=@var{length} -fsign-zero |
169 | } | |
eaa90d25 | 170 | |
6de9cd9a | 171 | @item Code Generation Options |
a2bef74c | 172 | @xref{Code Gen Options,,Options for code generation conventions}. |
f4347334 ZG |
173 | @gccoptlist{-faggressive-function-elimination -fblas-matmul-limit=@var{n} @gol |
174 | -fbounds-check -fcheck-array-temporaries @gol | |
f4d1d50a | 175 | -fcheck=@var{<all|array-temps|bounds|do|mem|pointer|recursion>} @gol |
f4347334 ZG |
176 | -fcoarray=@var{<none|single|lib>} -fexternal-blas -ff2c |
177 | -ffrontend-optimize @gol | |
178 | -finit-character=@var{n} -finit-integer=@var{n} -finit-local-zero @gol | |
179 | -finit-logical=@var{<true|false>} | |
180 | -finit-real=@var{<zero|inf|-inf|nan|snan>} @gol | |
181 | -fmax-array-constructor=@var{n} -fmax-stack-var-size=@var{n} | |
182 | -fno-align-commons @gol | |
9fa52231 | 183 | -fno-automatic -fno-protect-parens -fno-underscoring @gol |
f4347334 ZG |
184 | -fsecond-underscore -fpack-derived -frealloc-lhs -frecursive @gol |
185 | -frepack-arrays -fshort-enums -fstack-arrays | |
186 | } | |
6de9cd9a DN |
187 | @end table |
188 | ||
6de9cd9a | 189 | @node Fortran Dialect Options |
a2bef74c | 190 | @section Options controlling Fortran dialect |
6de9cd9a DN |
191 | @cindex dialect options |
192 | @cindex language, dialect options | |
193 | @cindex options, dialect | |
194 | ||
3397327c BM |
195 | The following options control the details of the Fortran dialect |
196 | accepted by the compiler: | |
6de9cd9a DN |
197 | |
198 | @table @gcctabopt | |
4ba96c02 | 199 | @item -ffree-form |
4d04d67a | 200 | @itemx -ffixed-form |
32864778 DF |
201 | @opindex @code{ffree-form} |
202 | @opindex @code{fno-fixed-form} | |
8578f640 | 203 | @cindex options, Fortran dialect |
e739dfac DF |
204 | @cindex file format, free |
205 | @cindex file format, fixed | |
49de9e73 | 206 | Specify the layout used by the source file. The free form layout |
6de9cd9a | 207 | was introduced in Fortran 90. Fixed form was traditionally used in |
3397327c BM |
208 | older Fortran programs. When neither option is specified, the source |
209 | form is determined by the file extension. | |
6de9cd9a | 210 | |
a23eec13 | 211 | @item -fall-intrinsics |
32864778 | 212 | @opindex @code{fall-intrinsics} |
aad9c4f4 AM |
213 | This option causes all intrinsic procedures (including the GNU-specific |
214 | extensions) to be accepted. This can be useful with @option{-std=f95} to | |
215 | force standard-compliance but get access to the full range of intrinsics | |
216 | available with @command{gfortran}. As a consequence, @option{-Wintrinsics-std} | |
217 | will be ignored and no user-defined procedure with the same name as any | |
218 | intrinsic will be called except when it is explicitly declared @code{EXTERNAL}. | |
a23eec13 | 219 | |
e0bcf78c | 220 | @item -fd-lines-as-code |
4d04d67a | 221 | @itemx -fd-lines-as-comments |
32864778 DF |
222 | @opindex @code{fd-lines-as-code} |
223 | @opindex @code{fd-lines-as-comments} | |
4ba96c02 | 224 | Enable special treatment for lines beginning with @code{d} or @code{D} |
3397327c BM |
225 | in fixed form sources. If the @option{-fd-lines-as-code} option is |
226 | given they are treated as if the first column contained a blank. If the | |
e0bcf78c TS |
227 | @option{-fd-lines-as-comments} option is given, they are treated as |
228 | comment lines. | |
229 | ||
6de9cd9a | 230 | @item -fdollar-ok |
32864778 | 231 | @opindex @code{fdollar-ok} |
ab940b73 | 232 | @cindex @code{$} |
6de9cd9a DN |
233 | @cindex symbol names |
234 | @cindex character set | |
f4a55802 DF |
235 | Allow @samp{$} as a valid non-first character in a symbol name. Symbols |
236 | that start with @samp{$} are rejected since it is unclear which rules to | |
cba2a54e | 237 | apply to implicit typing as different vendors implement different rules. |
6e8cb9be | 238 | Using @samp{$} in @code{IMPLICIT} statements is also rejected. |
6de9cd9a | 239 | |
4e6bf178 TB |
240 | @item -fbackslash |
241 | @opindex @code{backslash} | |
131c66cd FXC |
242 | @cindex backslash |
243 | @cindex escape characters | |
8fc541d3 FXC |
244 | Change the interpretation of backslashes in string literals from a single |
245 | backslash character to ``C-style'' escape characters. The following | |
246 | combinations are expanded @code{\a}, @code{\b}, @code{\f}, @code{\n}, | |
247 | @code{\r}, @code{\t}, @code{\v}, @code{\\}, and @code{\0} to the ASCII | |
248 | characters alert, backspace, form feed, newline, carriage return, | |
249 | horizontal tab, vertical tab, backslash, and NUL, respectively. | |
250 | Additionally, @code{\x}@var{nn}, @code{\u}@var{nnnn} and | |
251 | @code{\U}@var{nnnnnnnn} (where each @var{n} is a hexadecimal digit) are | |
252 | translated into the Unicode characters corresponding to the specified code | |
253 | points. All other combinations of a character preceded by \ are | |
254 | unexpanded. | |
131c66cd | 255 | |
654b6073 FXC |
256 | @item -fmodule-private |
257 | @opindex @code{fmodule-private} | |
258 | @cindex module entities | |
259 | @cindex private | |
260 | Set the default accessibility of module entities to @code{PRIVATE}. | |
261 | Use-associated entities will not be accessible unless they are explicitly | |
262 | declared as @code{PUBLIC}. | |
263 | ||
6de9cd9a | 264 | @item -ffixed-line-length-@var{n} |
32864778 | 265 | @opindex @code{ffixed-line-length-}@var{n} |
e739dfac | 266 | @cindex file format, fixed |
6de9cd9a DN |
267 | Set column after which characters are ignored in typical fixed-form |
268 | lines in the source file, and through which spaces are assumed (as | |
269 | if padded to that length) after the ends of short fixed-form lines. | |
270 | ||
6de9cd9a | 271 | Popular values for @var{n} include 72 (the |
3397327c | 272 | standard and the default), 80 (card image), and 132 (corresponding |
6de9cd9a | 273 | to ``extended-source'' options in some popular compilers). |
3397327c | 274 | @var{n} may also be @samp{none}, meaning that the entire line is meaningful |
6de9cd9a DN |
275 | and that continued character constants never have implicit spaces appended |
276 | to them to fill out the line. | |
277 | @option{-ffixed-line-length-0} means the same thing as | |
278 | @option{-ffixed-line-length-none}. | |
279 | ||
16ab8e74 | 280 | @item -ffree-line-length-@var{n} |
32864778 | 281 | @opindex @code{ffree-line-length-}@var{n} |
e739dfac | 282 | @cindex file format, free |
16ab8e74 | 283 | Set column after which characters are ignored in typical free-form |
3397327c | 284 | lines in the source file. The default value is 132. |
16ab8e74 BF |
285 | @var{n} may be @samp{none}, meaning that the entire line is meaningful. |
286 | @option{-ffree-line-length-0} means the same thing as | |
287 | @option{-ffree-line-length-none}. | |
288 | ||
6de9cd9a | 289 | @item -fmax-identifier-length=@var{n} |
32864778 | 290 | @opindex @code{fmax-identifier-length=}@var{n} |
6de9cd9a | 291 | Specify the maximum allowed identifier length. Typical values are |
f489fba1 | 292 | 31 (Fortran 95) and 63 (Fortran 2003 and Fortran 2008). |
6de9cd9a | 293 | |
6de9cd9a | 294 | @item -fimplicit-none |
32864778 | 295 | @opindex @code{fimplicit-none} |
6de9cd9a | 296 | Specify that no implicit typing is allowed, unless overridden by explicit |
40746dcc BM |
297 | @code{IMPLICIT} statements. This is the equivalent of adding |
298 | @code{implicit none} to the start of every procedure. | |
6de9cd9a | 299 | |
83d890b9 | 300 | @item -fcray-pointer |
32864778 | 301 | @opindex @code{fcray-pointer} |
3397327c BM |
302 | Enable the Cray pointer extension, which provides C-like pointer |
303 | functionality. | |
83d890b9 | 304 | |
6c7a4dfd | 305 | @item -fopenmp |
32864778 | 306 | @opindex @code{fopenmp} |
4e8b3590 | 307 | @cindex OpenMP |
3397327c BM |
308 | Enable the OpenMP extensions. This includes OpenMP @code{!$omp} directives |
309 | in free form | |
6c7a4dfd | 310 | and @code{c$omp}, @code{*$omp} and @code{!$omp} directives in fixed form, |
3397327c BM |
311 | @code{!$} conditional compilation sentinels in free form |
312 | and @code{c$}, @code{*$} and @code{!$} sentinels in fixed form, | |
6c7a4dfd | 313 | and when linking arranges for the OpenMP runtime library to be linked |
1e7de83b | 314 | in. The option @option{-fopenmp} implies @option{-frecursive}. |
6c7a4dfd | 315 | |
200c5036 | 316 | @item -fno-range-check |
32864778 | 317 | @opindex @code{frange-check} |
200c5036 | 318 | Disable range checking on results of simplification of constant |
a84b9ee8 SK |
319 | expressions during compilation. For example, GNU Fortran will give |
320 | an error at compile time when simplifying @code{a = 1. / 0}. | |
321 | With this option, no error will be given and @code{a} will be assigned | |
322 | the value @code{+Infinity}. If an expression evaluates to a value | |
323 | outside of the relevant range of [@code{-HUGE()}:@code{HUGE()}], | |
324 | then the expression will be replaced by @code{-Inf} or @code{+Inf} | |
325 | as appropriate. | |
40746dcc BM |
326 | Similarly, @code{DATA i/Z'FFFFFFFF'/} will result in an integer overflow |
327 | on most systems, but with @option{-fno-range-check} the value will | |
328 | ``wrap around'' and @code{i} will be initialized to @math{-1} instead. | |
54554825 | 329 | |
9803c5f0 JW |
330 | @item -fdefault-integer-8 |
331 | @opindex @code{fdefault-integer-8} | |
332 | Set the default integer and logical types to an 8 byte wide type. | |
333 | Do nothing if this is already the default. This option also affects | |
a4cf752c JW |
334 | the kind of integer constants like @code{42}. Unlike |
335 | @option{-finteger-4-integer-8}, it does not promote variables with explicit | |
336 | kind declaration. | |
9803c5f0 JW |
337 | |
338 | @item -fdefault-real-8 | |
339 | @opindex @code{fdefault-real-8} | |
340 | Set the default real type to an 8 byte wide type. | |
341 | Do nothing if this is already the default. This option also affects | |
342 | the kind of non-double real constants like @code{1.0}, and does promote | |
343 | the default width of @code{DOUBLE PRECISION} to 16 bytes if possible, unless | |
a4cf752c JW |
344 | @code{-fdefault-double-8} is given, too. Unlike @option{-freal-4-real-8}, |
345 | it does not promote variables with explicit kind declaration. | |
9803c5f0 JW |
346 | |
347 | @item -fdefault-double-8 | |
348 | @opindex @code{fdefault-double-8} | |
349 | Set the @code{DOUBLE PRECISION} type to an 8 byte wide type. If | |
350 | @option{-fdefault-real-8} is given, @code{DOUBLE PRECISION} would | |
351 | instead be promoted to 16 bytes if possible, and @option{-fdefault-double-8} | |
352 | can be used to prevent this. The kind of real constants like @code{1.d0} will | |
353 | not be changed by @option{-fdefault-real-8} though, so also | |
354 | @option{-fdefault-double-8} does not affect it. | |
355 | ||
356 | @item -finteger-4-integer-8 | |
357 | @opindex @code{finteger-4-integer-8} | |
358 | Promote all @code{INTEGER(KIND=4)} entities to an @code{INTEGER(KIND=8)} | |
359 | entities. If @code{KIND=8} is unavailable, then an error will be issued. | |
360 | This option should be used with care and may not be suitable for your codes. | |
361 | Areas of possible concern include calls to external procedures, | |
362 | alignment in @code{EQUIVALENCE} and/or @code{COMMON}, generic interfaces, | |
363 | BOZ literal constant conversion, and I/O. Inspection of the intermediate | |
364 | representation of the translated Fortran code, produced by | |
365 | @option{-fdump-tree-original}, is suggested. | |
366 | ||
f4347334 ZG |
367 | @item -freal-4-real-8 |
368 | @itemx -freal-4-real-10 | |
9803c5f0 | 369 | @itemx -freal-4-real-16 |
f4347334 ZG |
370 | @itemx -freal-8-real-4 |
371 | @itemx -freal-8-real-10 | |
372 | @itemx -freal-8-real-16 | |
373 | @opindex @code{freal-4-real-8} | |
374 | @opindex @code{freal-4-real-10} | |
375 | @opindex @code{freal-4-real-16} | |
376 | @opindex @code{freal-8-real-4} | |
377 | @opindex @code{freal-8-real-10} | |
378 | @opindex @code{freal-8-real-16} | |
379 | @cindex options, real kind type promotion | |
380 | Promote all @code{REAL(KIND=M)} entities to @code{REAL(KIND=N)} entities. | |
381 | If @code{REAL(KIND=N)} is unavailable, then an error will be issued. | |
382 | All other real kind types are unaffected by this option. | |
383 | These options should be used with care and may not be suitable for your | |
384 | codes. Areas of possible concern include calls to external procedures, | |
385 | alignment in @code{EQUIVALENCE} and/or @code{COMMON}, generic interfaces, | |
386 | BOZ literal constant conversion, and I/O. Inspection of the intermediate | |
387 | representation of the translated Fortran code, produced by | |
388 | @option{-fdump-tree-original}, is suggested. | |
389 | ||
6de9cd9a | 390 | @item -std=@var{std} |
32864778 | 391 | @opindex @code{std=}@var{std} option |
276419d0 | 392 | Specify the standard to which the program is expected to conform, which |
f489fba1 FXC |
393 | may be one of @samp{f95}, @samp{f2003}, @samp{f2008}, @samp{gnu}, or |
394 | @samp{legacy}. The default value for @var{std} is @samp{gnu}, which | |
395 | specifies a superset of the Fortran 95 standard that includes all of the | |
396 | extensions supported by GNU Fortran, although warnings will be given for | |
397 | obsolete extensions not recommended for use in new code. The | |
398 | @samp{legacy} value is equivalent but without the warnings for obsolete | |
399 | extensions, and may be useful for old non-standard programs. The | |
400 | @samp{f95}, @samp{f2003} and @samp{f2008} values specify strict | |
401 | conformance to the Fortran 95, Fortran 2003 and Fortran 2008 standards, | |
402 | respectively; errors are given for all extensions beyond the relevant | |
403 | language standard, and warnings are given for the Fortran 77 features | |
4650947d | 404 | that are permitted but obsolescent in later standards. @samp{-std=f2008ts} |
2e8d9212 | 405 | allows the Fortran 2008 standard including the additions of the |
4650947d TB |
406 | Technical Specification (TS) 29113 on Further Interoperability of Fortran |
407 | with C. | |
6de9cd9a | 408 | |
6de9cd9a DN |
409 | @end table |
410 | ||
670637ee DF |
411 | @node Preprocessing Options |
412 | @section Enable and customize preprocessing | |
413 | @cindex preprocessor | |
414 | @cindex options, preprocessor | |
415 | @cindex CPP | |
416 | ||
417 | Preprocessor related options. See section | |
418 | @ref{Preprocessing and conditional compilation} for more detailed | |
419 | information on preprocessing in @command{gfortran}. | |
420 | ||
421 | @table @gcctabopt | |
422 | @item -cpp | |
4d04d67a | 423 | @itemx -nocpp |
670637ee DF |
424 | @opindex @code{cpp} |
425 | @opindex @code{fpp} | |
426 | @cindex preprocessor, enable | |
427 | @cindex preprocessor, disable | |
428 | Enable preprocessing. The preprocessor is automatically invoked if | |
429 | the file extension is @file{.fpp}, @file{.FPP}, @file{.F}, @file{.FOR}, | |
430 | @file{.FTN}, @file{.F90}, @file{.F95}, @file{.F03} or @file{.F08}. Use | |
431 | this option to manually enable preprocessing of any kind of Fortran file. | |
432 | ||
433 | To disable preprocessing of files with any of the above listed extensions, | |
434 | use the negative form: @option{-nocpp}. | |
435 | ||
f90b55a6 TK |
436 | The preprocessor is run in traditional mode. Any restrictions of the |
437 | file-format, especially the limits on line length, apply for | |
438 | preprocessed output as well, so it might be advisable to use the | |
439 | @option{-ffree-line-length-none} or @option{-ffixed-line-length-none} | |
440 | options. | |
670637ee DF |
441 | |
442 | @item -dM | |
443 | @opindex @code{dM} | |
444 | @cindex preprocessor, debugging | |
445 | @cindex debugging, preprocessor | |
446 | Instead of the normal output, generate a list of @code{'#define'} | |
447 | directives for all the macros defined during the execution of the | |
448 | preprocessor, including predefined macros. This gives you a way | |
449 | of finding out what is predefined in your version of the preprocessor. | |
450 | Assuming you have no file @file{foo.f90}, the command | |
451 | @smallexample | |
fc1e05d2 | 452 | touch foo.f90; gfortran -cpp -E -dM foo.f90 |
670637ee DF |
453 | @end smallexample |
454 | will show all the predefined macros. | |
455 | ||
456 | @item -dD | |
457 | @opindex @code{dD} | |
458 | @cindex preprocessor, debugging | |
459 | @cindex debugging, preprocessor | |
460 | Like @option{-dM} except in two respects: it does not include the | |
461 | predefined macros, and it outputs both the @code{#define} directives | |
462 | and the result of preprocessing. Both kinds of output go to the | |
463 | standard output file. | |
464 | ||
465 | @item -dN | |
466 | @opindex @code{dN} | |
467 | @cindex preprocessor, debugging | |
468 | @cindex debugging, preprocessor | |
469 | Like @option{-dD}, but emit only the macro names, not their expansions. | |
470 | ||
471 | @item -dU | |
472 | @opindex @code{dU} | |
473 | @cindex preprocessor, debugging | |
474 | @cindex debugging, preprocessor | |
475 | Like @option{dD} except that only macros that are expanded, or whose | |
476 | definedness is tested in preprocessor directives, are output; the | |
477 | output is delayed until the use or test of the macro; and @code{'#undef'} | |
478 | directives are also output for macros tested but undefined at the time. | |
479 | ||
480 | @item -dI | |
481 | @opindex @code{dI} | |
482 | @cindex preprocessor, debugging | |
483 | @cindex debugging, preprocessor | |
484 | Output @code{'#include'} directives in addition to the result | |
485 | of preprocessing. | |
486 | ||
487 | @item -fworking-directory | |
488 | @opindex @code{fworking-directory} | |
489 | @cindex preprocessor, working directory | |
490 | Enable generation of linemarkers in the preprocessor output that will | |
491 | let the compiler know the current working directory at the time of | |
492 | preprocessing. When this option is enabled, the preprocessor will emit, | |
493 | after the initial linemarker, a second linemarker with the current | |
494 | working directory followed by two slashes. GCC will use this directory, | |
c5a0818e | 495 | when it is present in the preprocessed input, as the directory emitted |
670637ee DF |
496 | as the current working directory in some debugging information formats. |
497 | This option is implicitly enabled if debugging information is enabled, | |
498 | but this can be inhibited with the negated form | |
499 | @option{-fno-working-directory}. If the @option{-P} flag is present | |
500 | in the command line, this option has no effect, since no @code{#line} | |
501 | directives are emitted whatsoever. | |
502 | ||
c3280643 DF |
503 | @item -idirafter @var{dir} |
504 | @opindex @code{idirafter @var{dir}} | |
505 | @cindex preprocessing, include path | |
506 | Search @var{dir} for include files, but do it after all directories | |
507 | specified with @option{-I} and the standard system directories have | |
508 | been exhausted. @var{dir} is treated as a system include directory. | |
509 | If dir begins with @code{=}, then the @code{=} will be replaced by | |
510 | the sysroot prefix; see @option{--sysroot} and @option{-isysroot}. | |
511 | ||
670637ee DF |
512 | @item -imultilib @var{dir} |
513 | @opindex @code{imultilib @var{dir}} | |
514 | @cindex preprocessing, include path | |
515 | Use @var{dir} as a subdirectory of the directory containing target-specific | |
516 | C++ headers. | |
517 | ||
518 | @item -iprefix @var{prefix} | |
519 | @opindex @code{iprefix @var{prefix}} | |
520 | @cindex preprocessing, include path | |
521 | Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix} | |
522 | options. If the @var{prefix} represents a directory, you should include | |
523 | the final @code{'/'}. | |
524 | ||
525 | @item -isysroot @var{dir} | |
526 | @opindex @code{isysroot @var{dir}} | |
527 | @cindex preprocessing, include path | |
528 | This option is like the @option{--sysroot} option, but applies only to | |
529 | header files. See the @option{--sysroot} option for more information. | |
530 | ||
531 | @item -iquote @var{dir} | |
532 | @opindex @code{iquote @var{dir}} | |
533 | @cindex preprocessing, include path | |
534 | Search @var{dir} only for header files requested with @code{#include "file"}; | |
535 | they are not searched for @code{#include <file>}, before all directories | |
536 | specified by @option{-I} and before the standard system directories. If | |
537 | @var{dir} begins with @code{=}, then the @code{=} will be replaced by the | |
538 | sysroot prefix; see @option{--sysroot} and @option{-isysroot}. | |
539 | ||
540 | @item -isystem @var{dir} | |
541 | @opindex @code{isystem @var{dir}} | |
542 | @cindex preprocessing, include path | |
543 | Search @var{dir} for header files, after all directories specified by | |
544 | @option{-I} but before the standard system directories. Mark it as a | |
545 | system directory, so that it gets the same special treatment as is | |
546 | applied to the standard system directories. If @var{dir} begins with | |
547 | @code{=}, then the @code{=} will be replaced by the sysroot prefix; | |
548 | see @option{--sysroot} and @option{-isysroot}. | |
549 | ||
550 | @item -nostdinc | |
551 | @opindex @code{nostdinc} | |
552 | Do not search the standard system directories for header files. Only | |
553 | the directories you have specified with @option{-I} options (and the | |
554 | directory of the current file, if appropriate) are searched. | |
555 | ||
556 | @item -undef | |
557 | @opindex @code{undef} | |
558 | Do not predefine any system-specific or GCC-specific macros. | |
559 | The standard predefined macros remain defined. | |
560 | ||
561 | @item -A@var{predicate}=@var{answer} | |
562 | @opindex @code{A@var{predicate}=@var{answer}} | |
4d04d67a | 563 | @cindex preprocessing, assertion |
670637ee DF |
564 | Make an assertion with the predicate @var{predicate} and answer @var{answer}. |
565 | This form is preferred to the older form -A predicate(answer), which is still | |
566 | supported, because it does not use shell special characters. | |
567 | ||
568 | @item -A-@var{predicate}=@var{answer} | |
569 | @opindex @code{A-@var{predicate}=@var{answer}} | |
4d04d67a | 570 | @cindex preprocessing, assertion |
670637ee DF |
571 | Cancel an assertion with the predicate @var{predicate} and answer @var{answer}. |
572 | ||
573 | @item -C | |
574 | @opindex @code{C} | |
575 | @cindex preprocessing, keep comments | |
576 | Do not discard comments. All comments are passed through to the output | |
577 | file, except for comments in processed directives, which are deleted | |
578 | along with the directive. | |
579 | ||
580 | You should be prepared for side effects when using @option{-C}; it causes | |
581 | the preprocessor to treat comments as tokens in their own right. For example, | |
582 | comments appearing at the start of what would be a directive line have the | |
583 | effect of turning that line into an ordinary source line, since the first | |
584 | token on the line is no longer a @code{'#'}. | |
585 | ||
586 | Warning: this currently handles C-Style comments only. The preprocessor | |
587 | does not yet recognize Fortran-style comments. | |
588 | ||
589 | @item -CC | |
590 | @opindex @code{CC} | |
591 | @cindex preprocessing, keep comments | |
592 | Do not discard comments, including during macro expansion. This is like | |
593 | @option{-C}, except that comments contained within macros are also passed | |
594 | through to the output file where the macro is expanded. | |
595 | ||
596 | In addition to the side-effects of the @option{-C} option, the @option{-CC} | |
597 | option causes all C++-style comments inside a macro to be converted to C-style | |
598 | comments. This is to prevent later use of that macro from inadvertently | |
599 | commenting out the remainder of the source line. The @option{-CC} option | |
600 | is generally used to support lint comments. | |
601 | ||
602 | Warning: this currently handles C- and C++-Style comments only. The | |
603 | preprocessor does not yet recognize Fortran-style comments. | |
604 | ||
605 | @item -D@var{name} | |
606 | @opindex @code{D@var{name}} | |
607 | @cindex preprocessing, define macros | |
608 | Predefine name as a macro, with definition @code{1}. | |
609 | ||
610 | @item -D@var{name}=@var{definition} | |
611 | @opindex @code{D@var{name}=@var{definition}} | |
612 | @cindex preprocessing, define macros | |
613 | The contents of @var{definition} are tokenized and processed as if they | |
614 | appeared during translation phase three in a @code{'#define'} directive. | |
615 | In particular, the definition will be truncated by embedded newline | |
616 | characters. | |
617 | ||
618 | If you are invoking the preprocessor from a shell or shell-like program | |
619 | you may need to use the shell's quoting syntax to protect characters such | |
620 | as spaces that have a meaning in the shell syntax. | |
621 | ||
622 | If you wish to define a function-like macro on the command line, write | |
623 | its argument list with surrounding parentheses before the equals sign | |
624 | (if any). Parentheses are meaningful to most shells, so you will need | |
625 | to quote the option. With sh and csh, @code{-D'name(args...)=definition'} | |
626 | works. | |
627 | ||
628 | @option{-D} and @option{-U} options are processed in the order they are | |
629 | given on the command line. All -imacros file and -include file options | |
630 | are processed after all -D and -U options. | |
631 | ||
632 | @item -H | |
633 | @opindex @code{H} | |
634 | Print the name of each header file used, in addition to other normal | |
635 | activities. Each name is indented to show how deep in the @code{'#include'} | |
636 | stack it is. | |
637 | ||
638 | @item -P | |
639 | @opindex @code{P} | |
640 | @cindex preprocessing, no linemarkers | |
641 | Inhibit generation of linemarkers in the output from the preprocessor. | |
642 | This might be useful when running the preprocessor on something that | |
643 | is not C code, and will be sent to a program which might be confused | |
644 | by the linemarkers. | |
645 | ||
646 | @item -U@var{name} | |
647 | @opindex @code{U@var{name}} | |
648 | @cindex preprocessing, undefine macros | |
649 | Cancel any previous definition of @var{name}, either built in or provided | |
650 | with a @option{-D} option. | |
651 | @end table | |
652 | ||
653 | ||
592600ce | 654 | @node Error and Warning Options |
a2bef74c | 655 | @section Options to request or suppress errors and warnings |
6de9cd9a | 656 | @cindex options, warnings |
592600ce | 657 | @cindex options, errors |
6de9cd9a | 658 | @cindex warnings, suppressing |
592600ce | 659 | @cindex messages, error |
6de9cd9a DN |
660 | @cindex messages, warning |
661 | @cindex suppressing warnings | |
662 | ||
592600ce BM |
663 | Errors are diagnostic messages that report that the GNU Fortran compiler |
664 | cannot compile the relevant piece of source code. The compiler will | |
665 | continue to process the program in an attempt to report further errors | |
666 | to aid in debugging, but will not produce any compiled output. | |
667 | ||
6de9cd9a | 668 | Warnings are diagnostic messages that report constructions which |
592600ce | 669 | are not inherently erroneous but which are risky or suggest there is |
4ba96c02 | 670 | likely to be a bug in the program. Unless @option{-Werror} is specified, |
592600ce | 671 | they do not prevent compilation of the program. |
6de9cd9a DN |
672 | |
673 | You can request many specific warnings with options beginning @option{-W}, | |
674 | for example @option{-Wimplicit} to request warnings on implicit | |
675 | declarations. Each of these specific warning options also has a | |
676 | negative form beginning @option{-Wno-} to turn off warnings; | |
677 | for example, @option{-Wno-implicit}. This manual lists only one of the | |
678 | two forms, whichever is not the default. | |
679 | ||
592600ce BM |
680 | These options control the amount and kinds of errors and warnings produced |
681 | by GNU Fortran: | |
6de9cd9a DN |
682 | |
683 | @table @gcctabopt | |
efb66586 JD |
684 | @item -fmax-errors=@var{n} |
685 | @opindex @code{fmax-errors=}@var{n} | |
4ba96c02 | 686 | @cindex errors, limiting |
592600ce BM |
687 | Limits the maximum number of error messages to @var{n}, at which point |
688 | GNU Fortran bails out rather than attempting to continue processing the | |
689 | source code. If @var{n} is 0, there is no limit on the number of error | |
690 | messages produced. | |
691 | ||
6de9cd9a | 692 | @item -fsyntax-only |
32864778 | 693 | @opindex @code{fsyntax-only} |
4ba96c02 | 694 | @cindex syntax checking |
c5a0818e | 695 | Check the code for syntax errors, but do not actually compile it. This |
adeb22c4 FXC |
696 | will generate module files for each module present in the code, but no |
697 | other output file. | |
6de9cd9a | 698 | |
6de9cd9a | 699 | @item -pedantic |
32864778 | 700 | @opindex @code{pedantic} |
7fc15ba5 | 701 | Issue warnings for uses of extensions to Fortran 95. |
6de9cd9a DN |
702 | @option{-pedantic} also applies to C-language constructs where they |
703 | occur in GNU Fortran source files, such as use of @samp{\e} in a | |
40746dcc | 704 | character constant within a directive like @code{#include}. |
6de9cd9a | 705 | |
7fc15ba5 | 706 | Valid Fortran 95 programs should compile properly with or without |
6de9cd9a DN |
707 | this option. |
708 | However, without this option, certain GNU extensions and traditional | |
709 | Fortran features are supported as well. | |
710 | With this option, many of them are rejected. | |
711 | ||
712 | Some users try to use @option{-pedantic} to check programs for conformance. | |
713 | They soon find that it does not do quite what they want---it finds some | |
714 | nonstandard practices, but not all. | |
7fc15ba5 | 715 | However, improvements to GNU Fortran in this area are welcome. |
6de9cd9a | 716 | |
f489fba1 FXC |
717 | This should be used in conjunction with @option{-std=f95}, |
718 | @option{-std=f2003} or @option{-std=f2008}. | |
6de9cd9a | 719 | |
6de9cd9a | 720 | @item -pedantic-errors |
32864778 | 721 | @opindex @code{pedantic-errors} |
6de9cd9a DN |
722 | Like @option{-pedantic}, except that errors are produced rather than |
723 | warnings. | |
724 | ||
6de9cd9a | 725 | @item -Wall |
32864778 | 726 | @opindex @code{Wall} |
6de9cd9a DN |
727 | @cindex all warnings |
728 | @cindex warnings, all | |
3fbab549 JD |
729 | Enables commonly used warning options pertaining to usage that |
730 | we recommend avoiding and that we believe are easy to avoid. | |
cf21551e | 731 | This currently includes @option{-Waliasing}, @option{-Wampersand}, |
72ac1c07 | 732 | @option{-Wconversion}, @option{-Wsurprising}, @option{-Wc-binding-type}, |
cf21551e | 733 | @option{-Wintrinsics-std}, @option{-Wno-tabs}, @option{-Wintrinsic-shadow}, |
f657024b TB |
734 | @option{-Wline-truncation}, @option{-Wtarget-lifetime}, |
735 | @option{-Wreal-q-constant} and @option{-Wunused}. | |
6de9cd9a | 736 | |
6de9cd9a | 737 | @item -Waliasing |
32864778 | 738 | @opindex @code{Waliasing} |
6de9cd9a | 739 | @cindex aliasing |
32864778 | 740 | @cindex warnings, aliasing |
3010be13 AD |
741 | Warn about possible aliasing of dummy arguments. Specifically, it warns |
742 | if the same actual argument is associated with a dummy argument with | |
40746dcc | 743 | @code{INTENT(IN)} and a dummy argument with @code{INTENT(OUT)} in a call |
3010be13 AD |
744 | with an explicit interface. |
745 | ||
746 | The following example will trigger the warning. | |
6de9cd9a | 747 | @smallexample |
3010be13 AD |
748 | interface |
749 | subroutine bar(a,b) | |
750 | integer, intent(in) :: a | |
751 | integer, intent(out) :: b | |
752 | end subroutine | |
753 | end interface | |
754 | integer :: a | |
755 | ||
756 | call bar(a,a) | |
6de9cd9a DN |
757 | @end smallexample |
758 | ||
3fbab549 | 759 | @item -Wampersand |
32864778 DF |
760 | @opindex @code{Wampersand} |
761 | @cindex warnings, ampersand | |
ab940b73 | 762 | @cindex @code{&} |
3fbab549 | 763 | Warn about missing ampersand in continued character constants. The warning is |
f489fba1 FXC |
764 | given with @option{-Wampersand}, @option{-pedantic}, @option{-std=f95}, |
765 | @option{-std=f2003} and @option{-std=f2008}. Note: With no ampersand | |
766 | given in a continued character constant, GNU Fortran assumes continuation | |
767 | at the first non-comment, non-whitespace character after the ampersand | |
768 | that initiated the continuation. | |
3fbab549 | 769 | |
bdfd2ff0 TK |
770 | @item -Warray-temporaries |
771 | @opindex @code{Warray-temporaries} | |
772 | @cindex warnings, array temporaries | |
773 | Warn about array temporaries generated by the compiler. The information | |
774 | generated by this warning is sometimes useful in optimization, in order to | |
775 | avoid such temporaries. | |
776 | ||
0e193637 TB |
777 | @item -Wc-binding-type |
778 | @opindex @code{Wc-binding-type} | |
779 | @cindex warning, C binding type | |
780 | Warn if the a variable might not be C interoperable. In particular, warn if | |
781 | the variable has been declared using an intrinsic type with default kind | |
782 | instead of using a kind parameter defined for C interoperability in the | |
72ac1c07 TK |
783 | intrinsic @code{ISO_C_Binding} module. This option is implied by |
784 | @option{-Wall}. | |
0e193637 | 785 | |
276419d0 | 786 | @item -Wcharacter-truncation |
32864778 DF |
787 | @opindex @code{Wcharacter-truncation} |
788 | @cindex warnings, character truncation | |
276419d0 BM |
789 | Warn when a character assignment will truncate the assigned string. |
790 | ||
802e3f8c RW |
791 | @item -Wline-truncation |
792 | @opindex @code{Wline-truncation} | |
793 | @cindex warnings, line truncation | |
72ac1c07 TK |
794 | Warn when a source code line will be truncated. This option is |
795 | implied by @option{-Wall}. | |
802e3f8c | 796 | |
6de9cd9a | 797 | @item -Wconversion |
32864778 DF |
798 | @opindex @code{Wconversion} |
799 | @cindex warnings, conversion | |
6de9cd9a | 800 | @cindex conversion |
daf8c6f0 DF |
801 | Warn about implicit conversions that are likely to change the value of |
802 | the expression after conversion. Implied by @option{-Wall}. | |
803 | ||
804 | @item -Wconversion-extra | |
805 | @opindex @code{Wconversion-extra} | |
806 | @cindex warnings, conversion | |
807 | @cindex conversion | |
808 | Warn about implicit conversions between different types and kinds. | |
6de9cd9a | 809 | |
72ac1c07 TK |
810 | @item -Wextra |
811 | @opindex @code{Wextra} | |
812 | @cindex extra warnings | |
813 | @cindex warnings, extra | |
814 | Enables some warning options for usages of language features which | |
815 | may be problematic. This currently includes @option{-Wcompare-reals} | |
816 | and @option{-Wunused-parameter}. | |
817 | ||
6de9cd9a | 818 | @item -Wimplicit-interface |
32864778 DF |
819 | @opindex @code{Wimplicit-interface} |
820 | @cindex warnings, implicit interface | |
02712c16 | 821 | Warn if a procedure is called without an explicit interface. |
6de9cd9a DN |
822 | Note this only checks that an explicit interface is present. It does not |
823 | check that the declared interfaces are consistent across program units. | |
824 | ||
ca071303 FXC |
825 | @item -Wimplicit-procedure |
826 | @opindex @code{Wimplicit-procedure} | |
827 | @cindex warnings, implicit procedure | |
828 | Warn if a procedure is called that has neither an explicit interface | |
829 | nor has been declared as @code{EXTERNAL}. | |
830 | ||
c3005b0f DK |
831 | @item -Wintrinsics-std |
832 | @opindex @code{Wintrinsics-std} | |
1207ac67 | 833 | @cindex warnings, non-standard intrinsics |
c3005b0f DK |
834 | @cindex warnings, intrinsics of other standards |
835 | Warn if @command{gfortran} finds a procedure named like an intrinsic not | |
836 | available in the currently selected standard (with @option{-std}) and treats | |
837 | it as @code{EXTERNAL} procedure because of this. @option{-fall-intrinsics} can | |
c7d9f803 | 838 | be used to never trigger this behavior and always link to the intrinsic |
c3005b0f | 839 | regardless of the selected standard. |
b7892582 | 840 | |
5a17346a SK |
841 | @item -Wreal-q-constant |
842 | @opindex @code{Wreal-q-constant} | |
843 | @cindex warnings, @code{q} exponent-letter | |
844 | Produce a warning if a real-literal-constant contains a @code{q} | |
845 | exponent-letter. | |
846 | ||
6de9cd9a | 847 | @item -Wsurprising |
32864778 DF |
848 | @opindex @code{Wsurprising} |
849 | @cindex warnings, suspicious code | |
2d8b59df SK |
850 | Produce a warning when ``suspicious'' code constructs are encountered. |
851 | While technically legal these usually indicate that an error has been made. | |
6de9cd9a DN |
852 | |
853 | This currently produces a warning under the following circumstances: | |
854 | ||
855 | @itemize @bullet | |
856 | @item | |
ffd1953e FXC |
857 | An INTEGER SELECT construct has a CASE that can never be matched as its |
858 | lower value is greater than its upper value. | |
6de9cd9a DN |
859 | |
860 | @item | |
861 | A LOGICAL SELECT construct has three CASE statements. | |
39a184ce JD |
862 | |
863 | @item | |
864 | A TRANSFER specifies a source that is shorter than the destination. | |
fee3292b DK |
865 | |
866 | @item | |
867 | The type of a function result is declared more than once with the same type. If | |
868 | @option{-pedantic} or standard-conforming mode is enabled, this is an error. | |
5e1d6b4c DK |
869 | |
870 | @item | |
871 | A @code{CHARACTER} variable is declared with negative length. | |
6de9cd9a DN |
872 | @end itemize |
873 | ||
840bd9f7 | 874 | @item -Wtabs |
32864778 DF |
875 | @opindex @code{Wtabs} |
876 | @cindex warnings, tabs | |
e739dfac | 877 | @cindex tabulators |
840bd9f7 | 878 | By default, tabs are accepted as whitespace, but tabs are not members |
fd1935d5 TB |
879 | of the Fortran Character Set. For continuation lines, a tab followed |
880 | by a digit between 1 and 9 is supported. @option{-Wno-tabs} will cause | |
881 | a warning to be issued if a tab is encountered. Note, @option{-Wno-tabs} | |
882 | is active for @option{-pedantic}, @option{-std=f95}, @option{-std=f2003}, | |
f489fba1 | 883 | @option{-std=f2008} and @option{-Wall}. |
840bd9f7 | 884 | |
2d8b59df | 885 | @item -Wunderflow |
32864778 DF |
886 | @opindex @code{Wunderflow} |
887 | @cindex warnings, underflow | |
888 | @cindex underflow | |
2d8b59df SK |
889 | Produce a warning when numerical constant expressions are |
890 | encountered, which yield an UNDERFLOW during compilation. | |
891 | ||
c3005b0f DK |
892 | @item -Wintrinsic-shadow |
893 | @opindex @code{Wintrinsic-shadow} | |
894 | @cindex warnings, intrinsic | |
895 | @cindex intrinsic | |
896 | Warn if a user-defined procedure or module procedure has the same name as an | |
897 | intrinsic; in this case, an explicit interface or @code{EXTERNAL} or | |
898 | @code{INTRINSIC} declaration might be needed to get calls later resolved to | |
72ac1c07 | 899 | the desired intrinsic/procedure. This option is implied by @option{-Wall}. |
c3005b0f | 900 | |
4ed44ccc DF |
901 | @item -Wunused-dummy-argument |
902 | @opindex @code{Wunused-dummy-argument} | |
903 | @cindex warnings, unused dummy argument | |
904 | @cindex unused dummy argument | |
905 | @cindex dummy argument, unused | |
906 | Warn about unused dummy arguments. This option is implied by @option{-Wall}. | |
907 | ||
d92693b4 DF |
908 | @item -Wunused-parameter |
909 | @opindex @code{Wunused-parameter} | |
910 | @cindex warnings, unused parameter | |
911 | @cindex unused parameter | |
912 | Contrary to @command{gcc}'s meaning of @option{-Wunused-parameter}, | |
913 | @command{gfortran}'s implementation of this option does not warn | |
4ed44ccc DF |
914 | about unused dummy arguments (see @option{-Wunused-dummy-argument}), |
915 | but about unused @code{PARAMETER} values. @option{-Wunused-parameter} | |
916 | is not included in @option{-Wall} but is implied by @option{-Wall -Wextra}. | |
d92693b4 | 917 | |
f613cea7 JW |
918 | @item -Walign-commons |
919 | @opindex @code{Walign-commons} | |
ab940b73 RW |
920 | @cindex warnings, alignment of @code{COMMON} blocks |
921 | @cindex alignment of @code{COMMON} blocks | |
f613cea7 | 922 | By default, @command{gfortran} warns about any occasion of variables being |
ab940b73 | 923 | padded for proper alignment inside a @code{COMMON} block. This warning can be turned |
f613cea7 JW |
924 | off via @option{-Wno-align-commons}. See also @option{-falign-commons}. |
925 | ||
51a30b32 TK |
926 | @item -Wfunction-elimination |
927 | @opindex @code{Wfunction-elimination} | |
928 | @cindex function elimination | |
929 | @cindex warnings, function elimination | |
930 | Warn if any calls to functions are eliminated by the optimizations | |
931 | enabled by the @option{-ffrontend-optimize} option. | |
932 | ||
f1fb11f1 TB |
933 | @item -Wrealloc-lhs |
934 | @opindex @code{Wrealloc-lhs} | |
935 | @cindex Reallocate the LHS in assignments, notification | |
936 | Warn when the compiler might insert code to for allocation or reallocation of | |
937 | an allocatable array variable of intrinsic type in intrinsic assignments. In | |
938 | hot loops, the Fortran 2003 reallocation feature may reduce the performance. | |
939 | If the array is already allocated with the correct shape, consider using a | |
940 | whole-array array-spec (e.g. @code{(:,:,:)}) for the variable on the left-hand | |
941 | side to prevent the reallocation check. Note that in some cases the warning | |
942 | is shown, even if the compiler will optimize reallocation checks away. For | |
943 | instance, when the right-hand side contains the same variable multiplied by | |
944 | a scalar. See also @option{-frealloc-lhs}. | |
945 | ||
946 | @item -Wrealloc-lhs-all | |
947 | @opindex @code{Wrealloc-lhs-all} | |
948 | Warn when the compiler inserts code to for allocation or reallocation of an | |
949 | allocatable variable; this includes scalars and derived types. | |
51a30b32 | 950 | |
cf21551e TK |
951 | @item -Wcompare-reals |
952 | @opindex @code{Wcompare-reals} | |
953 | Warn when comparing real or complex types for equality or inequality. | |
72ac1c07 | 954 | This option is implied by @option{-Wextra}. |
cf21551e | 955 | |
f657024b TB |
956 | @item -Wtarget-lifetime |
957 | @opindex @code{Wtargt-lifetime} | |
958 | Warn if the pointer in a pointer assignment might be longer than the its | |
959 | target. This option is implied by @option{-Wall}. | |
960 | ||
0e533e50 TK |
961 | @item -Wzerotrip |
962 | @opindex @code{Wzerotrip} | |
963 | Warn if a @code{DO} loop is known to execute zero times at compile | |
964 | time. This option is implied by @option{-Wall}. | |
965 | ||
6de9cd9a | 966 | @item -Werror |
32864778 DF |
967 | @opindex @code{Werror} |
968 | @cindex warnings, to errors | |
6de9cd9a | 969 | Turns all warnings into errors. |
6de9cd9a DN |
970 | @end table |
971 | ||
4f7d9db8 | 972 | @xref{Warning Options,,Options to Request or Suppress Errors and |
592600ce BM |
973 | Warnings, gcc,Using the GNU Compiler Collection (GCC)}, for information on |
974 | more options offered by the GBE shared by @command{gfortran}, @command{gcc} | |
975 | and other GNU compilers. | |
6de9cd9a DN |
976 | |
977 | Some of these have no effect when compiling programs written in Fortran. | |
978 | ||
979 | @node Debugging Options | |
a2bef74c | 980 | @section Options for debugging your program or GNU Fortran |
6de9cd9a DN |
981 | @cindex options, debugging |
982 | @cindex debugging information options | |
983 | ||
984 | GNU Fortran has various special options that are used for debugging | |
7fc15ba5 | 985 | either your program or the GNU Fortran compiler. |
6de9cd9a DN |
986 | |
987 | @table @gcctabopt | |
1607a827 TK |
988 | @item -fdump-fortran-original |
989 | @opindex @code{fdump-fortran-original} | |
990 | Output the internal parse tree after translating the source program | |
991 | into internal representation. Only really useful for debugging the | |
992 | GNU Fortran compiler itself. | |
993 | ||
994 | @item -fdump-optimized-tree | |
995 | @opindex @code{fdump-fortran-optimized} | |
996 | Output the parse tree after front-end optimization. Only really | |
997 | useful for debugging the GNU Fortran compiler itself. | |
998 | ||
32864778 | 999 | @opindex @code{fdump-parse-tree} |
1607a827 TK |
1000 | Output the internal parse tree after translating the source program |
1001 | into internal representation. Only really useful for debugging the | |
1002 | GNU Fortran compiler itself. This option is deprecated; use | |
1003 | @code{-fdump-fortran-original} instead. | |
6de9cd9a | 1004 | |
944b8b35 | 1005 | @item -ffpe-trap=@var{list} |
32864778 | 1006 | @opindex @code{ffpe-trap=}@var{list} |
57b4d355 JB |
1007 | Specify a list of floating point exception traps to enable. On most |
1008 | systems, if a floating point exception occurs and the trap for that | |
1009 | exception is enabled, a SIGFPE signal will be sent and the program | |
1010 | being aborted, producing a core file useful for debugging. @var{list} | |
1011 | is a (possibly empty) comma-separated list of the following | |
1012 | exceptions: @samp{invalid} (invalid floating point operation, such as | |
1013 | @code{SQRT(-1.0)}), @samp{zero} (division by zero), @samp{overflow} | |
1014 | (overflow in a floating point operation), @samp{underflow} (underflow | |
1015 | in a floating point operation), @samp{inexact} (loss of precision | |
1016 | during operation), and @samp{denormal} (operation performed on a | |
1017 | denormal value). The first five exceptions correspond to the five | |
1018 | IEEE 754 exceptions, whereas the last one (@samp{denormal}) is not | |
1019 | part of the IEEE 754 standard but is available on some common | |
1020 | architectures such as x86. | |
1021 | ||
1022 | The first three exceptions (@samp{invalid}, @samp{zero}, and | |
1023 | @samp{overflow}) often indicate serious errors, and unless the program | |
1024 | has provisions for dealing with these exceptions, enabling traps for | |
1025 | these three exceptions is probably a good idea. | |
1026 | ||
1027 | Many, if not most, floating point operations incur loss of precision | |
1028 | due to rounding, and hence the @code{ffpe-trap=inexact} is likely to | |
1029 | be uninteresting in practice. | |
1030 | ||
1031 | By default no exception traps are enabled. | |
8307c61b | 1032 | |
fa86f4f9 TB |
1033 | @item -ffpe-summary=@var{list} |
1034 | @opindex @code{ffpe-summary=}@var{list} | |
1035 | Specify a list of floating-point exceptions, whose flag status is printed | |
1036 | to @code{ERROR_UNIT} when invoking @code{STOP} and @code{ERROR STOP}. | |
1037 | @var{list} can be either @samp{none}, @samp{all} or a comma-separated list | |
1038 | of the following exceptions: @samp{invalid}, @samp{zero}, @samp{overflow}, | |
1039 | @samp{underflow}, @samp{inexact} and @samp{denormal}. (See | |
1040 | @option{-ffpe-trap} for a description of the exceptions.) | |
1041 | ||
1042 | By default, a summary for all exceptions but @samp{inexact} is shown. | |
1043 | ||
de8bd142 JB |
1044 | @item -fno-backtrace |
1045 | @opindex @code{fno-backtrace} | |
868d75db FXC |
1046 | @cindex backtrace |
1047 | @cindex trace | |
de8bd142 JB |
1048 | When a serious runtime error is encountered or a deadly signal is |
1049 | emitted (segmentation fault, illegal instruction, bus error, | |
1050 | floating-point exception, and the other POSIX signals that have the | |
1051 | action @samp{core}), the Fortran runtime library tries to output a | |
1052 | backtrace of the error. @code{-fno-backtrace} disables the backtrace | |
1053 | generation. This option only has influence for compilation of the | |
1054 | Fortran main program. | |
1055 | ||
944b8b35 FXC |
1056 | @end table |
1057 | ||
6de9cd9a DN |
1058 | @xref{Debugging Options,,Options for Debugging Your Program or GCC, |
1059 | gcc,Using the GNU Compiler Collection (GCC)}, for more information on | |
1060 | debugging options. | |
1061 | ||
1062 | @node Directory Options | |
a2bef74c | 1063 | @section Options for directory search |
6de9cd9a DN |
1064 | @cindex directory, options |
1065 | @cindex options, directory search | |
1066 | @cindex search path | |
ab940b73 RW |
1067 | @cindex @code{INCLUDE} directive |
1068 | @cindex directive, @code{INCLUDE} | |
7fc15ba5 | 1069 | These options affect how GNU Fortran searches |
5724da63 | 1070 | for files specified by the @code{INCLUDE} directive and where it searches |
6de9cd9a DN |
1071 | for previously compiled modules. |
1072 | ||
1073 | It also affects the search paths used by @command{cpp} when used to preprocess | |
2d8b59df | 1074 | Fortran source. |
6de9cd9a DN |
1075 | |
1076 | @table @gcctabopt | |
6de9cd9a | 1077 | @item -I@var{dir} |
32864778 | 1078 | @opindex @code{I}@var{dir} |
6de9cd9a DN |
1079 | @cindex directory, search paths for inclusion |
1080 | @cindex inclusion, directory search paths for | |
1081 | @cindex search paths, for included files | |
1082 | @cindex paths, search | |
1083 | @cindex module search path | |
1084 | These affect interpretation of the @code{INCLUDE} directive | |
1085 | (as well as of the @code{#include} directive of the @command{cpp} | |
1086 | preprocessor). | |
1087 | ||
1088 | Also note that the general behavior of @option{-I} and | |
1089 | @code{INCLUDE} is pretty much the same as of @option{-I} with | |
1090 | @code{#include} in the @command{cpp} preprocessor, with regard to | |
1091 | looking for @file{header.gcc} files and other such things. | |
1092 | ||
40746dcc | 1093 | This path is also used to search for @file{.mod} files when previously |
6de9cd9a DN |
1094 | compiled modules are required by a @code{USE} statement. |
1095 | ||
1096 | @xref{Directory Options,,Options for Directory Search, | |
1097 | gcc,Using the GNU Compiler Collection (GCC)}, for information on the | |
1098 | @option{-I} option. | |
1099 | ||
6de9cd9a | 1100 | @item -J@var{dir} |
32864778 | 1101 | @opindex @code{J}@var{dir} |
ccc2ed87 | 1102 | @opindex @code{M}@var{dir} |
276419d0 BM |
1103 | @cindex paths, search |
1104 | @cindex module search path | |
40746dcc | 1105 | This option specifies where to put @file{.mod} files for compiled modules. |
2d8b59df | 1106 | It is also added to the list of directories to searched by an @code{USE} |
6de9cd9a DN |
1107 | statement. |
1108 | ||
1109 | The default is the current directory. | |
1110 | ||
276419d0 | 1111 | @item -fintrinsic-modules-path @var{dir} |
32864778 | 1112 | @opindex @code{fintrinsic-modules-path} @var{dir} |
276419d0 BM |
1113 | @cindex paths, search |
1114 | @cindex module search path | |
1115 | This option specifies the location of pre-compiled intrinsic modules, if | |
1116 | they are not in the default location expected by the compiler. | |
6de9cd9a DN |
1117 | @end table |
1118 | ||
70263321 | 1119 | @node Link Options |
a2bef74c | 1120 | @section Influencing the linking step |
70263321 DF |
1121 | @cindex options, linking |
1122 | @cindex linking, static | |
1123 | ||
1124 | These options come into play when the compiler links object files into an | |
1125 | executable output file. They are meaningless if the compiler is not doing | |
1126 | a link step. | |
1127 | ||
1128 | @table @gcctabopt | |
1129 | @item -static-libgfortran | |
1130 | @opindex @code{static-libgfortran} | |
1131 | On systems that provide @file{libgfortran} as a shared and a static | |
1132 | library, this option forces the use of the static version. If no | |
1133 | shared version of @file{libgfortran} was built when the compiler was | |
1134 | configured, this option has no effect. | |
1135 | @end table | |
1136 | ||
1137 | ||
eaa90d25 | 1138 | @node Runtime Options |
a2bef74c | 1139 | @section Influencing runtime behavior |
e739dfac | 1140 | @cindex options, runtime |
eaa90d25 | 1141 | |
7fc15ba5 | 1142 | These options affect the runtime behavior of programs compiled with GNU Fortran. |
4d04d67a | 1143 | |
eaa90d25 | 1144 | @table @gcctabopt |
eaa90d25 | 1145 | @item -fconvert=@var{conversion} |
32864778 | 1146 | @opindex @code{fconvert=}@var{conversion} |
eaa90d25 TK |
1147 | Specify the representation of data for unformatted files. Valid |
1148 | values for conversion are: @samp{native}, the default; @samp{swap}, | |
1149 | swap between big- and little-endian; @samp{big-endian}, use big-endian | |
1150 | representation for unformatted files; @samp{little-endian}, use little-endian | |
1151 | representation for unformatted files. | |
1152 | ||
1153 | @emph{This option has an effect only when used in the main program. | |
1154 | The @code{CONVERT} specifier and the GFORTRAN_CONVERT_UNIT environment | |
40746dcc | 1155 | variable override the default specified by @option{-fconvert}.} |
d67ab5ee | 1156 | |
d67ab5ee | 1157 | @item -frecord-marker=@var{length} |
32864778 | 1158 | @opindex @code{frecord-marker=}@var{length} |
d67ab5ee | 1159 | Specify the length of record markers for unformatted files. |
07b3bbf2 | 1160 | Valid values for @var{length} are 4 and 8. Default is 4. |
a2bef74c | 1161 | @emph{This is different from previous versions of @command{gfortran}}, |
07b3bbf2 TK |
1162 | which specified a default record marker length of 8 on most |
1163 | systems. If you want to read or write files compatible | |
a2bef74c | 1164 | with earlier versions of @command{gfortran}, use @option{-frecord-marker=8}. |
07b3bbf2 | 1165 | |
07b3bbf2 | 1166 | @item -fmax-subrecord-length=@var{length} |
32864778 | 1167 | @opindex @code{fmax-subrecord-length=}@var{length} |
07b3bbf2 TK |
1168 | Specify the maximum length for a subrecord. The maximum permitted |
1169 | value for length is 2147483639, which is also the default. Only | |
1170 | really useful for use by the gfortran testsuite. | |
0483c79f JD |
1171 | |
1172 | @item -fsign-zero | |
1173 | @opindex @code{fsign-zero} | |
60d340ef TB |
1174 | When enabled, floating point numbers of value zero with the sign bit set |
1175 | are written as negative number in formatted output and treated as | |
c5a0818e FXC |
1176 | negative in the @code{SIGN} intrinsic. @option{-fno-sign-zero} does not |
1177 | print the negative sign of zero values (or values rounded to zero for I/O) | |
1178 | and regards zero as positive number in the @code{SIGN} intrinsic for | |
1179 | compatibility with Fortran 77. The default is @option{-fsign-zero}. | |
eaa90d25 TK |
1180 | @end table |
1181 | ||
6de9cd9a | 1182 | @node Code Gen Options |
a2bef74c | 1183 | @section Options for code generation conventions |
6de9cd9a DN |
1184 | @cindex code generation, conventions |
1185 | @cindex options, code generation | |
e739dfac | 1186 | @cindex options, run-time |
6de9cd9a DN |
1187 | |
1188 | These machine-independent options control the interface conventions | |
1189 | used in code generation. | |
1190 | ||
1191 | Most of them have both positive and negative forms; the negative form | |
1192 | of @option{-ffoo} would be @option{-fno-foo}. In the table below, only | |
1193 | one of the forms is listed---the one which is not the default. You | |
1194 | can figure out the other form by either removing @option{no-} or adding | |
1195 | it. | |
1196 | ||
6de9cd9a | 1197 | @table @gcctabopt |
ee5426a4 | 1198 | @item -fno-automatic |
32864778 | 1199 | @opindex @code{fno-automatic} |
e739dfac DF |
1200 | @cindex @code{SAVE} statement |
1201 | @cindex statement, @code{SAVE} | |
1e7de83b AL |
1202 | Treat each program unit (except those marked as RECURSIVE) as if the |
1203 | @code{SAVE} statement were specified for every local variable and array | |
1204 | referenced in it. Does not affect common blocks. (Some Fortran compilers | |
1205 | provide this option under the name @option{-static} or @option{-save}.) | |
1206 | The default, which is @option{-fautomatic}, uses the stack for local | |
1207 | variables smaller than the value given by @option{-fmax-stack-var-size}. | |
1208 | Use the option @option{-frecursive} to use no static memory. | |
ee5426a4 | 1209 | |
973ff4c0 | 1210 | @item -ff2c |
e739dfac | 1211 | @opindex ff2c |
973ff4c0 TS |
1212 | @cindex calling convention |
1213 | @cindex @command{f2c} calling convention | |
1214 | @cindex @command{g77} calling convention | |
1215 | @cindex libf2c calling convention | |
1216 | Generate code designed to be compatible with code generated | |
1217 | by @command{g77} and @command{f2c}. | |
1218 | ||
1219 | The calling conventions used by @command{g77} (originally implemented | |
1220 | in @command{f2c}) require functions that return type | |
1221 | default @code{REAL} to actually return the C type @code{double}, and | |
1222 | functions that return type @code{COMPLEX} to return the values via an | |
1223 | extra argument in the calling sequence that points to where to | |
1224 | store the return value. Under the default GNU calling conventions, such | |
1225 | functions simply return their results as they would in GNU | |
8556236b | 1226 | C---default @code{REAL} functions return the C type @code{float}, and |
973ff4c0 | 1227 | @code{COMPLEX} functions return the GNU C type @code{complex}. |
a226fc2b TS |
1228 | Additionally, this option implies the @option{-fsecond-underscore} |
1229 | option, unless @option{-fno-second-underscore} is explicitly requested. | |
973ff4c0 TS |
1230 | |
1231 | This does not affect the generation of code that interfaces with | |
1232 | the @command{libgfortran} library. | |
1233 | ||
40746dcc BM |
1234 | @emph{Caution:} It is not a good idea to mix Fortran code compiled with |
1235 | @option{-ff2c} with code compiled with the default @option{-fno-f2c} | |
973ff4c0 TS |
1236 | calling conventions as, calling @code{COMPLEX} or default @code{REAL} |
1237 | functions between program parts which were compiled with different | |
1238 | calling conventions will break at execution time. | |
1239 | ||
1240 | @emph{Caution:} This will break code which passes intrinsic functions | |
1241 | of type default @code{REAL} or @code{COMPLEX} as actual arguments, as | |
40746dcc | 1242 | the library implementations use the @option{-fno-f2c} calling conventions. |
973ff4c0 | 1243 | |
6de9cd9a | 1244 | @item -fno-underscoring |
32864778 | 1245 | @opindex @code{fno-underscoring} |
6de9cd9a DN |
1246 | @cindex underscore |
1247 | @cindex symbol names, underscores | |
1248 | @cindex transforming symbol names | |
1249 | @cindex symbol names, transforming | |
1250 | Do not transform names of entities specified in the Fortran | |
1251 | source file by appending underscores to them. | |
1252 | ||
7fc15ba5 | 1253 | With @option{-funderscoring} in effect, GNU Fortran appends one |
5724da63 JD |
1254 | underscore to external names with no underscores. This is done to ensure |
1255 | compatibility with code produced by many UNIX Fortran compilers. | |
973ff4c0 | 1256 | |
7fc15ba5 | 1257 | @emph{Caution}: The default behavior of GNU Fortran is |
973ff4c0 | 1258 | incompatible with @command{f2c} and @command{g77}, please use the |
b4cbcd1a | 1259 | @option{-ff2c} option if you want object files compiled with |
7fc15ba5 | 1260 | GNU Fortran to be compatible with object code created with these |
b4cbcd1a | 1261 | tools. |
6de9cd9a DN |
1262 | |
1263 | Use of @option{-fno-underscoring} is not recommended unless you are | |
7fc15ba5 | 1264 | experimenting with issues such as integration of GNU Fortran into |
8307c61b FXC |
1265 | existing system environments (vis-@`{a}-vis existing libraries, tools, |
1266 | and so on). | |
6de9cd9a DN |
1267 | |
1268 | For example, with @option{-funderscoring}, and assuming other defaults like | |
40746dcc BM |
1269 | @option{-fcase-lower} and that @code{j()} and @code{max_count()} are |
1270 | external functions while @code{my_var} and @code{lvar} are local variables, | |
6de9cd9a | 1271 | a statement like |
6de9cd9a DN |
1272 | @smallexample |
1273 | I = J() + MAX_COUNT (MY_VAR, LVAR) | |
1274 | @end smallexample | |
6de9cd9a DN |
1275 | @noindent |
1276 | is implemented as something akin to: | |
6de9cd9a DN |
1277 | @smallexample |
1278 | i = j_() + max_count__(&my_var__, &lvar); | |
1279 | @end smallexample | |
1280 | ||
1281 | With @option{-fno-underscoring}, the same statement is implemented as: | |
1282 | ||
1283 | @smallexample | |
1284 | i = j() + max_count(&my_var, &lvar); | |
1285 | @end smallexample | |
1286 | ||
1287 | Use of @option{-fno-underscoring} allows direct specification of | |
7fc15ba5 | 1288 | user-defined names while debugging and when interfacing GNU Fortran |
6de9cd9a DN |
1289 | code with other languages. |
1290 | ||
1291 | Note that just because the names match does @emph{not} mean that the | |
7fc15ba5 | 1292 | interface implemented by GNU Fortran for an external name matches the |
6de9cd9a | 1293 | interface implemented by some other language for that same name. |
7fc15ba5 | 1294 | That is, getting code produced by GNU Fortran to link to code produced |
6de9cd9a DN |
1295 | by some other compiler using this or any other method can be only a |
1296 | small part of the overall solution---getting the code generated by | |
1297 | both compilers to agree on issues other than naming can require | |
1298 | significant effort, and, unlike naming disagreements, linkers normally | |
1299 | cannot detect disagreements in these other areas. | |
1300 | ||
1301 | Also, note that with @option{-fno-underscoring}, the lack of appended | |
1302 | underscores introduces the very real possibility that a user-defined | |
1303 | external name will conflict with a name in a system library, which | |
1304 | could make finding unresolved-reference bugs quite difficult in some | |
1305 | cases---they might occur at program run time, and show up only as | |
1306 | buggy behavior at run time. | |
1307 | ||
7fc15ba5 | 1308 | In future versions of GNU Fortran we hope to improve naming and linking |
6de9cd9a DN |
1309 | issues so that debugging always involves using the names as they appear |
1310 | in the source, even if the names as seen by the linker are mangled to | |
1311 | prevent accidental linking between procedures with incompatible | |
1312 | interfaces. | |
1313 | ||
973ff4c0 | 1314 | @item -fsecond-underscore |
32864778 | 1315 | @opindex @code{fsecond-underscore} |
6de9cd9a DN |
1316 | @cindex underscore |
1317 | @cindex symbol names, underscores | |
1318 | @cindex transforming symbol names | |
1319 | @cindex symbol names, transforming | |
973ff4c0 TS |
1320 | @cindex @command{f2c} calling convention |
1321 | @cindex @command{g77} calling convention | |
1322 | @cindex libf2c calling convention | |
7fc15ba5 BM |
1323 | By default, GNU Fortran appends an underscore to external |
1324 | names. If this option is used GNU Fortran appends two | |
973ff4c0 | 1325 | underscores to names with underscores and one underscore to external names |
7fc15ba5 | 1326 | with no underscores. GNU Fortran also appends two underscores to |
973ff4c0 TS |
1327 | internal names with underscores to avoid naming collisions with external |
1328 | names. | |
6de9cd9a DN |
1329 | |
1330 | This option has no effect if @option{-fno-underscoring} is | |
973ff4c0 | 1331 | in effect. It is implied by the @option{-ff2c} option. |
6de9cd9a | 1332 | |
40746dcc | 1333 | Otherwise, with this option, an external name such as @code{MAX_COUNT} |
6de9cd9a | 1334 | is implemented as a reference to the link-time external symbol |
40746dcc | 1335 | @code{max_count__}, instead of @code{max_count_}. This is required |
973ff4c0 TS |
1336 | for compatibility with @command{g77} and @command{f2c}, and is implied |
1337 | by use of the @option{-ff2c} option. | |
6de9cd9a | 1338 | |
f4d1d50a TB |
1339 | @item -fcoarray=@var{<keyword>} |
1340 | @opindex @code{fcoarray} | |
1341 | @cindex coarrays | |
1342 | ||
1343 | @table @asis | |
1344 | @item @samp{none} | |
1345 | Disable coarray support; using coarray declarations and image-control | |
1346 | statements will produce a compile-time error. (Default) | |
1347 | ||
1348 | @item @samp{single} | |
1349 | Single-image mode, i.e. @code{num_images()} is always one. | |
60386f50 TB |
1350 | |
1351 | @item @samp{lib} | |
1352 | Library-based coarray parallelization; a suitable GNU Fortran coarray | |
1353 | library needs to be linked. | |
f4d1d50a TB |
1354 | @end table |
1355 | ||
1356 | ||
d3d3011f FXC |
1357 | @item -fcheck=@var{<keyword>} |
1358 | @opindex @code{fcheck} | |
e739dfac | 1359 | @cindex array, bounds checking |
6de9cd9a | 1360 | @cindex bounds checking |
20460eb9 | 1361 | @cindex pointer checking |
22bdbb0f | 1362 | @cindex memory checking |
6de9cd9a | 1363 | @cindex range checking |
6de9cd9a DN |
1364 | @cindex subscript checking |
1365 | @cindex checking subscripts | |
d3d3011f FXC |
1366 | @cindex run-time checking |
1367 | @cindex checking array temporaries | |
1368 | ||
1369 | Enable the generation of run-time checks; the argument shall be | |
1370 | a comma-delimited list of the following keywords. | |
1371 | ||
1372 | @table @asis | |
1373 | @item @samp{all} | |
1374 | Enable all run-time test of @option{-fcheck}. | |
1375 | ||
1376 | @item @samp{array-temps} | |
1377 | Warns at run time when for passing an actual argument a temporary array | |
1378 | had to be generated. The information generated by this warning is | |
1379 | sometimes useful in optimization, in order to avoid such temporaries. | |
1380 | ||
1381 | Note: The warning is only printed once per location. | |
1382 | ||
1383 | @item @samp{bounds} | |
6de9cd9a DN |
1384 | Enable generation of run-time checks for array subscripts |
1385 | and against the declared minimum and maximum values. It also | |
1386 | checks array indices for assumed and deferred | |
aad9c4f4 AM |
1387 | shape arrays against the actual allocated bounds and ensures that all string |
1388 | lengths are equal for character array constructors without an explicit | |
1389 | typespec. | |
6de9cd9a | 1390 | |
d3d3011f | 1391 | Some checks require that @option{-fcheck=bounds} is set for |
8307c61b | 1392 | the compilation of the main program. |
18fe404f | 1393 | |
aad9c4f4 AM |
1394 | Note: In the future this may also include other forms of checking, e.g., |
1395 | checking substring references. | |
43998ed9 | 1396 | |
33abc845 TB |
1397 | @item @samp{do} |
1398 | Enable generation of run-time checks for invalid modification of loop | |
1399 | iteration variables. | |
1400 | ||
22bdbb0f TB |
1401 | @item @samp{mem} |
1402 | Enable generation of run-time checks for memory allocation. | |
1403 | Note: This option does not affect explicit allocations using the | |
1404 | @code{ALLOCATE} statement, which will be always checked. | |
1405 | ||
20460eb9 TB |
1406 | @item @samp{pointer} |
1407 | Enable generation of run-time checks for pointers and allocatables. | |
1408 | ||
43998ed9 TB |
1409 | @item @samp{recursion} |
1410 | Enable generation of run-time checks for recursively called subroutines and | |
1411 | functions which are not marked as recursive. See also @option{-frecursive}. | |
8b5f6dd8 | 1412 | Note: This check does not work for OpenMP programs and is disabled if used |
5b130807 | 1413 | together with @option{-frecursive} and @option{-fopenmp}. |
d3d3011f | 1414 | @end table |
6de9cd9a | 1415 | |
0d52899f | 1416 | |
d3d3011f FXC |
1417 | @item -fbounds-check |
1418 | @opindex @code{fbounds-check} | |
1419 | @c Note: This option is also referred in gcc's manpage | |
1420 | Deprecated alias for @option{-fcheck=bounds}. | |
0d52899f | 1421 | |
d3d3011f FXC |
1422 | @item -fcheck-array-temporaries |
1423 | @opindex @code{fcheck-array-temporaries} | |
1424 | Deprecated alias for @option{-fcheck=array-temps}. | |
0d52899f | 1425 | |
63346ddb SK |
1426 | @item -fmax-array-constructor=@var{n} |
1427 | @opindex @code{fmax-array-constructor} | |
1428 | This option can be used to increase the upper limit permitted in | |
1429 | array constructors. The code below requires this option to expand | |
1430 | the array at compile time. | |
1431 | ||
1432 | @smallexample | |
ab940b73 RW |
1433 | program test |
1434 | implicit none | |
1435 | integer j | |
1436 | integer, parameter :: n = 100000 | |
1437 | integer, parameter :: i(n) = (/ (2*j, j = 1, n) /) | |
1438 | print '(10(I0,1X))', i | |
1439 | end program test | |
63346ddb SK |
1440 | @end smallexample |
1441 | ||
1442 | @emph{Caution: This option can lead to long compile times and excessively | |
1443 | large object files.} | |
1444 | ||
1445 | The default value for @var{n} is 65535. | |
1446 | ||
1447 | ||
6de9cd9a | 1448 | @item -fmax-stack-var-size=@var{n} |
32864778 | 1449 | @opindex @code{fmax-stack-var-size} |
6de9cd9a | 1450 | This option specifies the size in bytes of the largest array that will be put |
1e7de83b AL |
1451 | on the stack; if the size is exceeded static memory is used (except in |
1452 | procedures marked as RECURSIVE). Use the option @option{-frecursive} to | |
1453 | allow for recursive procedures which do not have a RECURSIVE attribute or | |
1454 | for parallel programs. Use @option{-fno-automatic} to never use the stack. | |
6de9cd9a DN |
1455 | |
1456 | This option currently only affects local arrays declared with constant | |
1457 | bounds, and may not apply to all character variables. | |
7fc15ba5 | 1458 | Future versions of GNU Fortran may improve this behavior. |
6de9cd9a DN |
1459 | |
1460 | The default value for @var{n} is 32768. | |
1461 | ||
c76f8d52 MM |
1462 | @item -fstack-arrays |
1463 | @opindex @code{fstack-arrays} | |
8578f640 | 1464 | Adding this option will make the Fortran compiler put all local arrays, |
c76f8d52 | 1465 | even those of unknown size onto stack memory. If your program uses very |
c5a0818e | 1466 | large local arrays it is possible that you will have to extend your runtime |
2d8c9ad5 TB |
1467 | limits for stack memory on some operating systems. This flag is enabled |
1468 | by default at optimization level @option{-Ofast}. | |
1469 | ||
c76f8d52 | 1470 | |
5139e1e9 | 1471 | @item -fpack-derived |
32864778 DF |
1472 | @opindex @code{fpack-derived} |
1473 | @cindex structure packing | |
7fc15ba5 | 1474 | This option tells GNU Fortran to pack derived type members as closely as |
2d8b59df | 1475 | possible. Code compiled with this option is likely to be incompatible |
6de9cd9a DN |
1476 | with code compiled without this option, and may execute slower. |
1477 | ||
6de9cd9a | 1478 | @item -frepack-arrays |
32864778 DF |
1479 | @opindex @code{frepack-arrays} |
1480 | @cindex repacking arrays | |
7fc15ba5 | 1481 | In some circumstances GNU Fortran may pass assumed shape array |
02712c16 | 1482 | sections via a descriptor describing a noncontiguous area of memory. |
6de9cd9a DN |
1483 | This option adds code to the function prologue to repack the data into |
1484 | a contiguous block at runtime. | |
1485 | ||
1486 | This should result in faster accesses to the array. However it can introduce | |
1487 | significant overhead to the function call, especially when the passed data | |
02712c16 | 1488 | is noncontiguous. |
a63dad5b | 1489 | |
a63dad5b | 1490 | @item -fshort-enums |
32864778 | 1491 | @opindex @code{fshort-enums} |
a63dad5b | 1492 | This option is provided for interoperability with C code that was |
4ba96c02 | 1493 | compiled with the @option{-fshort-enums} option. It will make |
7fc15ba5 | 1494 | GNU Fortran choose the smallest @code{INTEGER} kind a given |
a63dad5b | 1495 | enumerator set will fit in, and give all its enumerators this kind. |
5a0aad31 | 1496 | |
5a0aad31 | 1497 | @item -fexternal-blas |
32864778 | 1498 | @opindex @code{fexternal-blas} |
a2bef74c DF |
1499 | This option will make @command{gfortran} generate calls to BLAS functions |
1500 | for some matrix operations like @code{MATMUL}, instead of using our own | |
5a0aad31 | 1501 | algorithms, if the size of the matrices involved is larger than a given |
4ba96c02 | 1502 | limit (see @option{-fblas-matmul-limit}). This may be profitable if an |
5a0aad31 FXC |
1503 | optimized vendor BLAS library is available. The BLAS library will have |
1504 | to be specified at link time. | |
1505 | ||
5a0aad31 | 1506 | @item -fblas-matmul-limit=@var{n} |
32864778 | 1507 | @opindex @code{fblas-matmul-limit} |
4ba96c02 | 1508 | Only significant when @option{-fexternal-blas} is in effect. |
5a0aad31 FXC |
1509 | Matrix multiplication of matrices with size larger than (or equal to) @var{n} |
1510 | will be performed by calls to BLAS functions, while others will be | |
1511 | handled by @command{gfortran} internal algorithms. If the matrices | |
1512 | involved are not square, the size comparison is performed using the | |
1513 | geometric mean of the dimensions of the argument and result matrices. | |
1514 | ||
1515 | The default value for @var{n} is 30. | |
1516 | ||
1e7de83b AL |
1517 | @item -frecursive |
1518 | @opindex @code{frecursive} | |
1519 | Allow indirect recursion by forcing all local arrays to be allocated | |
1520 | on the stack. This flag cannot be used together with | |
1521 | @option{-fmax-stack-var-size=} or @option{-fno-automatic}. | |
1522 | ||
51b09ce3 | 1523 | @item -finit-local-zero |
4d04d67a RW |
1524 | @itemx -finit-integer=@var{n} |
1525 | @itemx -finit-real=@var{<zero|inf|-inf|nan|snan>} | |
1526 | @itemx -finit-logical=@var{<true|false>} | |
1527 | @itemx -finit-character=@var{n} | |
51b09ce3 AL |
1528 | @opindex @code{finit-local-zero} |
1529 | @opindex @code{finit-integer} | |
1530 | @opindex @code{finit-real} | |
1531 | @opindex @code{finit-logical} | |
1532 | @opindex @code{finit-character} | |
1533 | The @option{-finit-local-zero} option instructs the compiler to | |
1534 | initialize local @code{INTEGER}, @code{REAL}, and @code{COMPLEX} | |
1535 | variables to zero, @code{LOGICAL} variables to false, and | |
1536 | @code{CHARACTER} variables to a string of null bytes. Finer-grained | |
1537 | initialization options are provided by the | |
1538 | @option{-finit-integer=@var{n}}, | |
346a77d1 | 1539 | @option{-finit-real=@var{<zero|inf|-inf|nan|snan>}} (which also initializes |
51b09ce3 AL |
1540 | the real and imaginary parts of local @code{COMPLEX} variables), |
1541 | @option{-finit-logical=@var{<true|false>}}, and | |
1542 | @option{-finit-character=@var{n}} (where @var{n} is an ASCII character | |
d6202322 TM |
1543 | value) options. These options do not initialize |
1544 | @itemize @bullet | |
1545 | @item | |
d6202322 TM |
1546 | allocatable arrays |
1547 | @item | |
1548 | components of derived type variables | |
1549 | @item | |
1550 | variables that appear in an @code{EQUIVALENCE} statement. | |
1551 | @end itemize | |
1552 | (These limitations may be removed in future releases). | |
51b09ce3 AL |
1553 | |
1554 | Note that the @option{-finit-real=nan} option initializes @code{REAL} | |
346a77d1 TB |
1555 | and @code{COMPLEX} variables with a quiet NaN. For a signalling NaN |
1556 | use @option{-finit-real=snan}; note, however, that compile-time | |
1557 | optimizations may convert them into quiet NaN and that trapping | |
1558 | needs to be enabled (e.g. via @option{-ffpe-trap}). | |
f613cea7 | 1559 | |
29525822 FXC |
1560 | Finally, note that enabling any of the @option{-finit-*} options will |
1561 | silence warnings that would have been emitted by @option{-Wuninitialized} | |
1562 | for the affected local variables. | |
1563 | ||
f613cea7 JW |
1564 | @item -falign-commons |
1565 | @opindex @code{falign-commons} | |
ab940b73 | 1566 | @cindex alignment of @code{COMMON} blocks |
f613cea7 | 1567 | By default, @command{gfortran} enforces proper alignment of all variables in a |
ab940b73 RW |
1568 | @code{COMMON} block by padding them as needed. On certain platforms this is mandatory, |
1569 | on others it increases performance. If a @code{COMMON} block is not declared with | |
f613cea7 | 1570 | consistent data types everywhere, this padding can cause trouble, and |
ab940b73 RW |
1571 | @option{-fno-align-commons} can be used to disable automatic alignment. The |
1572 | same form of this option should be used for all files that share a @code{COMMON} block. | |
1573 | To avoid potential alignment issues in @code{COMMON} blocks, it is recommended to order | |
4d04d67a | 1574 | objects from largest to smallest. |
72bd130e TB |
1575 | |
1576 | @item -fno-protect-parens | |
1577 | @opindex @code{fno-protect-parens} | |
4d04d67a | 1578 | @cindex re-association of parenthesized expressions |
72bd130e TB |
1579 | By default the parentheses in expression are honored for all optimization |
1580 | levels such that the compiler does not do any re-association. Using | |
ab940b73 RW |
1581 | @option{-fno-protect-parens} allows the compiler to reorder @code{REAL} and |
1582 | @code{COMPLEX} expressions to produce faster code. Note that for the re-association | |
72bd130e | 1583 | optimization @option{-fno-signed-zeros} and @option{-fno-trapping-math} |
7a994646 TB |
1584 | need to be in effect. The parentheses protection is enabled by default, unless |
1585 | @option{-Ofast} is given. | |
597553ab PT |
1586 | |
1587 | @item -frealloc-lhs | |
1588 | @opindex @code{frealloc-lhs} | |
1589 | @cindex Reallocate the LHS in assignments | |
1590 | An allocatable left-hand side of an intrinsic assignment is automatically | |
1591 | (re)allocated if it is either unallocated or has a different shape. The | |
f1fb11f1 TB |
1592 | option is enabled by default except when @option{-std=f95} is given. See |
1593 | also @option{-Wrealloc-lhs}. | |
2757d5ec TK |
1594 | |
1595 | @item -faggressive-function-elimination | |
1596 | @opindex @code{faggressive-function-elimination} | |
1597 | @cindex Elimination of functions with identical argument lists | |
1598 | Functions with identical argument lists are eliminated within | |
1599 | statements, regardless of whether these functions are marked | |
1600 | @code{PURE} or not. For example, in | |
1601 | @smallexample | |
1602 | a = f(b,c) + f(b,c) | |
1603 | @end smallexample | |
51a30b32 TK |
1604 | there will only be a single call to @code{f}. This option only works |
1605 | if @option{-ffrontend-optimize} is in effect. | |
1606 | ||
1607 | @item -ffrontend-optimize | |
1608 | @opindex @code{frontend-optimize} | |
1609 | @cindex Front-end optimization | |
1610 | This option performs front-end optimization, based on manipulating | |
1611 | parts the Fortran parse tree. Enabled by default by any @option{-O} | |
1612 | option. Optimizations enabled by this option include elimination of | |
1613 | identical function calls within expressions, removing unnecessary | |
1614 | calls to @code{TRIM} in comparisons and assignments and replacing | |
1615 | @code{TRIM(a)} with @code{a(1:LEN_TRIM(a))}. | |
1616 | It can be deselected by specifying @option{-fno-frontend-optimize}. | |
6de9cd9a DN |
1617 | @end table |
1618 | ||
1619 | @xref{Code Gen Options,,Options for Code Generation Conventions, | |
1620 | gcc,Using the GNU Compiler Collection (GCC)}, for information on more options | |
1621 | offered by the GBE | |
7fc15ba5 | 1622 | shared by @command{gfortran}, @command{gcc}, and other GNU compilers. |
6de9cd9a | 1623 | |
6de9cd9a DN |
1624 | @c man end |
1625 | ||
1626 | @node Environment Variables | |
a2bef74c | 1627 | @section Environment variables affecting @command{gfortran} |
e739dfac | 1628 | @cindex environment variable |
6de9cd9a DN |
1629 | |
1630 | @c man begin ENVIRONMENT | |
1631 | ||
7fc15ba5 | 1632 | The @command{gfortran} compiler currently does not make use of any environment |
6de9cd9a DN |
1633 | variables to control its operation above and beyond those |
1634 | that affect the operation of @command{gcc}. | |
1635 | ||
1636 | @xref{Environment Variables,,Environment Variables Affecting GCC, | |
1637 | gcc,Using the GNU Compiler Collection (GCC)}, for information on environment | |
1638 | variables. | |
1639 | ||
eaa90d25 | 1640 | @xref{Runtime}, for environment variables that affect the |
7fc15ba5 | 1641 | run-time behavior of programs compiled with GNU Fortran. |
6de9cd9a | 1642 | @c man end |