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.\" ========================================================================
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.\"
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.IX Title "GFORTRAN 1"
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.TH GFORTRAN 1 "2007-10-07" "gcc-4.2.2" "GNU"
133
.SH "NAME"
134
gfortran \- GNU Fortran compiler
135
.SH "SYNOPSIS"
136
.IX Header "SYNOPSIS"
137
gfortran [\fB\-c\fR|\fB\-S\fR|\fB\-E\fR]
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         [\fB\-g\fR] [\fB\-pg\fR] [\fB\-O\fR\fIlevel\fR]
139
         [\fB\-W\fR\fIwarn\fR...] [\fB\-pedantic\fR]
140
         [\fB\-I\fR\fIdir\fR...] [\fB\-L\fR\fIdir\fR...]
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         [\fB\-D\fR\fImacro\fR[=\fIdefn\fR]...] [\fB\-U\fR\fImacro\fR]
142
         [\fB\-f\fR\fIoption\fR...]
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         [\fB\-m\fR\fImachine-option\fR...]
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         [\fB\-o\fR \fIoutfile\fR] \fIinfile\fR...
145
.PP
146
Only the most useful options are listed here; see below for the
147
remainder.
148
.SH "DESCRIPTION"
149
.IX Header "DESCRIPTION"
150
The \fBgfortran\fR command supports all the options supported by the
151
\&\fBgcc\fR command.  Only options specific to \s-1GNU\s0 Fortran are documented here.
152
.PP
153
All \s-1GCC\s0 and \s-1GNU\s0 Fortran options
154
are accepted both by \fBgfortran\fR and by \fBgcc\fR
155
(as well as any other drivers built at the same time,
156
such as \fBg++\fR),
157
since adding \s-1GNU\s0 Fortran to the \s-1GCC\s0 distribution
158
enables acceptance of \s-1GNU\s0 Fortran options
159
by all of the relevant drivers.
160
.PP
161
In some cases, options have positive and negative forms;
162
the negative form of \fB\-ffoo\fR would be \fB\-fno\-foo\fR.
163
This manual documents only one of these two forms, whichever
164
one is not the default.
165
.SH "OPTIONS"
166
.IX Header "OPTIONS"
167
Here is a summary of all the options specific to \s-1GNU\s0 Fortran, grouped
168
by type.  Explanations are in the following sections.
169
.IP "\fIFortran Language Options\fR" 4
170
.IX Item "Fortran Language Options"
171
\&\fB\-fall\-intrinsics  \-ffree\-form  \-fno\-fixed\-form
172
\&\-fdollar\-ok  \-fimplicit\-none  \-fmax\-identifier\-length
173
\&\-std=\fR\fIstd\fR \fB\-fd\-lines\-as\-code  \-fd\-lines\-as\-comments
174
\&\-ffixed\-line\-length\-\fR\fIn\fR  \fB\-ffixed\-line\-length\-none
175
\&\-ffree\-line\-length\-\fR\fIn\fR  \fB\-ffree\-line\-length\-none
176
\&\-fdefault\-double\-8  \-fdefault\-integer\-8  \-fdefault\-real\-8
177
\&\-fcray\-pointer  \-fopenmp  \-frange\-check \-fno\-backslash\fR
178
.IP "\fIError and Warning Options\fR" 4
179
.IX Item "Error and Warning Options"
180
\&\fB\-fmax\-errors=\fR\fIn\fR
181
\&\fB\-fsyntax\-only  \-pedantic  \-pedantic\-errors
182
\&\-Wall  \-Waliasing  \-Wampersand  \-Wcharacter\-truncation  \-Wconversion
183
\&\-Wimplicit\-interface  \-Wline\-truncation  \-Wnonstd\-intrinsics  \-Wsurprising
184
\&\-Wno\-tabs  \-Wunderflow\fR
185
.IP "\fIDebugging Options\fR" 4
186
.IX Item "Debugging Options"
187
\&\fB\-fdump\-parse\-tree  \-ffpe\-trap=\fR\fIlist\fR
188
.IP "\fIDirectory Options\fR" 4
189
.IX Item "Directory Options"
190
\&\fB\-I\fR\fIdir\fR  \fB\-J\fR\fIdir\fR  \fB\-M\fR\fIdir\fR
191
.IP "\fIRuntime Options\fR" 4
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.IX Item "Runtime Options"
193
\&\fB\-fconvert=\fR\fIconversion\fR  \fB\-frecord\-marker=\fR\fIlength\fR
194
\&\fB\-fmax\-subrecord\-length=\fR\fIlength\fR
195
.IP "\fICode Generation Options\fR" 4
196
.IX Item "Code Generation Options"
197
\&\fB\-fno\-automatic  \-ff2c  \-fno\-underscoring
198
\&\-fsecond\-underscore
199
\&\-fbounds\-check  \-fmax\-stack\-var\-size=\fR\fIn\fR
200
\&\fB\-fpack\-derived  \-frepack\-arrays  \-fshort\-enums\fR
201
.Sh "Options controlling Fortran dialect"
202
.IX Subsection "Options controlling Fortran dialect"
203
The following options control the details of the Fortran dialect
204
accepted by the compiler:
205
.IP "\fB\-ffree\-form\fR" 4
206
.IX Item "-ffree-form"
207
.PD 0
208
.IP "\fB\-ffixed\-form\fR" 4
209
.IX Item "-ffixed-form"
210
.PD
211
Specify the layout used by the source file.  The free form layout
212
was introduced in Fortran 90.  Fixed form was traditionally used in
213
older Fortran programs.  When neither option is specified, the source
214
form is determined by the file extension.
215
.IP "\fB\-fall\-intrinsics\fR" 4
216
.IX Item "-fall-intrinsics"
217
Accept all of the intrinsic procedures provided in libgfortran
218
without regard to the setting of \fB\-std\fR.  In particular,
219
this option can be quite useful with \fB\-std=f95\fR.  Additionally,
220
\&\fBgfortran\fR will ignore \fB\-Wnonstd\-intrinsics\fR.
221
.IP "\fB\-fd\-lines\-as\-code\fR" 4
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.IX Item "-fd-lines-as-code"
223
.PD 0
224
.IP "\fB\-fd\-lines\-as\-comments\fR" 4
225
.IX Item "-fd-lines-as-comments"
226
.PD
227
Enable special treatment for lines beginning with \f(CW\*(C`d\*(C'\fR or \f(CW\*(C`D\*(C'\fR
228
in fixed form sources.  If the \fB\-fd\-lines\-as\-code\fR option is
229
given they are treated as if the first column contained a blank.  If the
230
\&\fB\-fd\-lines\-as\-comments\fR option is given, they are treated as
231
comment lines.
232
.IP "\fB\-fdefault\-double\-8\fR" 4
233
.IX Item "-fdefault-double-8"
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Set the \f(CW\*(C`DOUBLE PRECISION\*(C'\fR type to an 8 byte wide type.
235
.IP "\fB\-fdefault\-integer\-8\fR" 4
236
.IX Item "-fdefault-integer-8"
237
Set the default integer and logical types to an 8 byte wide type.
238
Do nothing if this is already the default.
239
.IP "\fB\-fdefault\-real\-8\fR" 4
240
.IX Item "-fdefault-real-8"
241
Set the default real type to an 8 byte wide type.
242
Do nothing if this is already the default.
243
.IP "\fB\-fdollar\-ok\fR" 4
244
.IX Item "-fdollar-ok"
245
Allow \fB$\fR as a valid character in a symbol name.
246
.IP "\fB\-fno\-backslash\fR" 4
247
.IX Item "-fno-backslash"
248
Change the interpretation of backslashes in string literals from
249
\&\*(L"C\-style\*(R" escape characters to a single backslash character.
250
.IP "\fB\-ffixed\-line\-length\-\fR\fIn\fR" 4
251
.IX Item "-ffixed-line-length-n"
252
Set column after which characters are ignored in typical fixed-form
253
lines in the source file, and through which spaces are assumed (as
254
if padded to that length) after the ends of short fixed-form lines.
255
.Sp
256
Popular values for \fIn\fR include 72 (the
257
standard and the default), 80 (card image), and 132 (corresponding
258
to \*(L"extended\-source\*(R" options in some popular compilers).
259
\&\fIn\fR may also be \fBnone\fR, meaning that the entire line is meaningful
260
and that continued character constants never have implicit spaces appended
261
to them to fill out the line.
262
\&\fB\-ffixed\-line\-length\-0\fR means the same thing as
263
\&\fB\-ffixed\-line\-length\-none\fR.
264
.IP "\fB\-ffree\-line\-length\-\fR\fIn\fR" 4
265
.IX Item "-ffree-line-length-n"
266
Set column after which characters are ignored in typical free-form
267
lines in the source file. The default value is 132.
268
\&\fIn\fR may be \fBnone\fR, meaning that the entire line is meaningful.
269
\&\fB\-ffree\-line\-length\-0\fR means the same thing as
270
\&\fB\-ffree\-line\-length\-none\fR.
271
.IP "\fB\-fmax\-identifier\-length=\fR\fIn\fR" 4
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.IX Item "-fmax-identifier-length=n"
273
Specify the maximum allowed identifier length. Typical values are
274
31 (Fortran 95) and 63 (Fortran 2003).
275
.IP "\fB\-fimplicit\-none\fR" 4
276
.IX Item "-fimplicit-none"
277
Specify that no implicit typing is allowed, unless overridden by explicit
278
\&\f(CW\*(C`IMPLICIT\*(C'\fR statements.  This is the equivalent of adding
279
\&\f(CW\*(C`implicit none\*(C'\fR to the start of every procedure.
280
.IP "\fB\-fcray\-pointer\fR" 4
281
.IX Item "-fcray-pointer"
282
Enable the Cray pointer extension, which provides C\-like pointer
283
functionality.
284
.IP "\fB\-fopenmp\fR" 4
285
.IX Item "-fopenmp"
286
Enable the OpenMP extensions.  This includes OpenMP \f(CW\*(C`!$omp\*(C'\fR directives
287
in free form
288
and \f(CW\*(C`c$omp\*(C'\fR, \f(CW*$omp\fR and \f(CW\*(C`!$omp\*(C'\fR directives in fixed form,
289
\&\f(CW\*(C`!$\*(C'\fR conditional compilation sentinels in free form
290
and \f(CW\*(C`c$\*(C'\fR, \f(CW\*(C`*$\*(C'\fR and \f(CW\*(C`!$\*(C'\fR sentinels in fixed form,
291
and when linking arranges for the OpenMP runtime library to be linked
292
in.
293
.IP "\fB\-frange\-check\fR" 4
294
.IX Item "-frange-check"
295
Enable range checking on results of simplification of constant
296
expressions during compilation.  For example, by default, \s-1GNU\s0 Fortran
297
will give an overflow error at compile time when simplifying \f(CW\*(C`a =
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EXP(1000)\*(C'\fR. With \fB\-fno\-range\-check\fR, no error will be given and
299
the variable \f(CW\*(C`a\*(C'\fR will be assigned the value \f(CW\*(C`+Infinity\*(C'\fR.
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Similarly, \f(CW\*(C`DATA i/Z'FFFFFFFF'/\*(C'\fR will result in an integer overflow
301
on most systems, but with \fB\-fno\-range\-check\fR the value will
302
\&\*(L"wrap around\*(R" and \f(CW\*(C`i\*(C'\fR will be initialized to \-1 instead.
303
.IP "\fB\-std=\fR\fIstd\fR" 4
304
.IX Item "-std=std"
305
Specify the standard to which the program is expected to conform, which
306
may be one of \fBf95\fR, \fBf2003\fR, \fBgnu\fR, or \fBlegacy\fR.
307
The default value for \fIstd\fR is \fBgnu\fR, which specifies a
308
superset of the Fortran 95 standard that includes all of the extensions
309
supported by \s-1GNU\s0 Fortran, although warnings will be given for obsolete
310
extensions not recommended for use in new code.  The \fBlegacy\fR value
311
is equivalent but without the warnings for obsolete extensions, and may
312
be useful for old non-standard programs.  The \fBf95\fR and
313
\&\fBf2003\fR values specify strict conformance to the Fortran 95 and
314
Fortran 2003 standards, respectively; errors are given for all
315
extensions beyond the relevant language standard, and warnings are given
316
for the Fortran 77 features that are permitted but obsolescent in later
317
standards.
318
.Sh "Options to request or suppress errors and warnings"
319
.IX Subsection "Options to request or suppress errors and warnings"
320
Errors are diagnostic messages that report that the \s-1GNU\s0 Fortran compiler
321
cannot compile the relevant piece of source code.  The compiler will
322
continue to process the program in an attempt to report further errors
323
to aid in debugging, but will not produce any compiled output.
324
.PP
325
Warnings are diagnostic messages that report constructions which
326
are not inherently erroneous but which are risky or suggest there is
327
likely to be a bug in the program.  Unless \fB\-Werror\fR is specified,
328
they do not prevent compilation of the program.
329
.PP
330
You can request many specific warnings with options beginning \fB\-W\fR,
331
for example \fB\-Wimplicit\fR to request warnings on implicit
332
declarations.  Each of these specific warning options also has a
333
negative form beginning \fB\-Wno\-\fR to turn off warnings;
334
for example, \fB\-Wno\-implicit\fR.  This manual lists only one of the
335
two forms, whichever is not the default.
336
.PP
337
These options control the amount and kinds of errors and warnings produced
338
by \s-1GNU\s0 Fortran:
339
.IP "\fB\-fmax\-errors\-\fR\fIn\fR" 4
340
.IX Item "-fmax-errors-n"
341
Limits the maximum number of error messages to \fIn\fR, at which point
342
\&\s-1GNU\s0 Fortran bails out rather than attempting to continue processing the
343
source code.  If \fIn\fR is 0, there is no limit on the number of error
344
messages produced.
345
.IP "\fB\-fsyntax\-only\fR" 4
346
.IX Item "-fsyntax-only"
347
Check the code for syntax errors, but don't do anything beyond that.
348
.IP "\fB\-pedantic\fR" 4
349
.IX Item "-pedantic"
350
Issue warnings for uses of extensions to Fortran 95.
351
\&\fB\-pedantic\fR also applies to C\-language constructs where they
352
occur in \s-1GNU\s0 Fortran source files, such as use of \fB\ee\fR in a
353
character constant within a directive like \f(CW\*(C`#include\*(C'\fR.
354
.Sp
355
Valid Fortran 95 programs should compile properly with or without
356
this option.
357
However, without this option, certain \s-1GNU\s0 extensions and traditional
358
Fortran features are supported as well.
359
With this option, many of them are rejected.
360
.Sp
361
Some users try to use \fB\-pedantic\fR to check programs for conformance.
362
They soon find that it does not do quite what they want\-\-\-it finds some
363
nonstandard practices, but not all.
364
However, improvements to \s-1GNU\s0 Fortran in this area are welcome.
365
.Sp
366
This should be used in conjunction with \fB\-std=f95\fR or
367
\&\fB\-std=f2003\fR.
368
.IP "\fB\-pedantic\-errors\fR" 4
369
.IX Item "-pedantic-errors"
370
Like \fB\-pedantic\fR, except that errors are produced rather than
371
warnings.
372
.IP "\fB\-Wall\fR" 4
373
.IX Item "-Wall"
374
Enables commonly used warning options pertaining to usage that
375
we recommend avoiding and that we believe are easy to avoid.
376
This currently includes \fB\-Waliasing\fR,
377
\&\fB\-Wampersand\fR, \fB\-Wsurprising\fR, \fB\-Wnonstd\-intrinsics\fR,
378
\&\fB\-Wno\-tabs\fR, and \fB\-Wline\-truncation\fR.
379
.IP "\fB\-Waliasing\fR" 4
380
.IX Item "-Waliasing"
381
Warn about possible aliasing of dummy arguments. Specifically, it warns
382
if the same actual argument is associated with a dummy argument with
383
\&\f(CW\*(C`INTENT(IN)\*(C'\fR and a dummy argument with \f(CW\*(C`INTENT(OUT)\*(C'\fR in a call
384
with an explicit interface.
385
.Sp
386
The following example will trigger the warning.
387
.Sp
388
.Vb 7
389
\&          interface
390
\&            subroutine bar(a,b)
391
\&              integer, intent(in) :: a
392
\&              integer, intent(out) :: b
393
\&            end subroutine
394
\&          end interface
395
\&          integer :: a
396
.Ve
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.Sp
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.Vb 1
399
\&          call bar(a,a)
400
.Ve
401
.IP "\fB\-Wampersand\fR" 4
402
.IX Item "-Wampersand"
403
Warn about missing ampersand in continued character constants. The warning is
404
given with \fB\-Wampersand\fR, \fB\-pedantic\fR, \fB\-std=f95\fR, and
405
\&\fB\-std=f2003\fR. Note: With no ampersand given in a continued character
406
constant, \s-1GNU\s0 Fortran assumes continuation at the first non\-comment,
407
non-whitespace character after the ampersand that initiated the continuation.
408
.IP "\fB\-Wcharacter\-truncation\fR" 4
409
.IX Item "-Wcharacter-truncation"
410
Warn when a character assignment will truncate the assigned string.
411
.IP "\fB\-Wconversion\fR" 4
412
.IX Item "-Wconversion"
413
Warn about implicit conversions between different types.
414
.IP "\fB\-Wimplicit\-interface\fR" 4
415
.IX Item "-Wimplicit-interface"
416
Warn if a procedure is called without an explicit interface.
417
Note this only checks that an explicit interface is present.  It does not
418
check that the declared interfaces are consistent across program units.
419
.IP "\fB\-Wnonstd\-intrinsics\fR" 4
420
.IX Item "-Wnonstd-intrinsics"
421
Warn if the user tries to use an intrinsic that does not belong to the
422
standard the user has chosen via the \fB\-std\fR option.
423
.IP "\fB\-Wsurprising\fR" 4
424
.IX Item "-Wsurprising"
425
Produce a warning when \*(L"suspicious\*(R" code constructs are encountered.
426
While technically legal these usually indicate that an error has been made.
427
.Sp
428
This currently produces a warning under the following circumstances:
429
.RS 4
430
.IP "*" 4
431
An \s-1INTEGER\s0 \s-1SELECT\s0 construct has a \s-1CASE\s0 that can never be matched as its
432
lower value is greater than its upper value.
433
.IP "*" 4
434
A \s-1LOGICAL\s0 \s-1SELECT\s0 construct has three \s-1CASE\s0 statements.
435
.RE
436
.RS 4
437
.RE
438
.IP "\fB\-Wtabs\fR" 4
439
.IX Item "-Wtabs"
440
By default, tabs are accepted as whitespace, but tabs are not members
441
of the Fortran Character Set.  \fB\-Wno\-tabs\fR will cause a warning
442
to be issued if a tab is encountered. Note, \fB\-Wno\-tabs\fR is active
443
for \fB\-pedantic\fR, \fB\-std=f95\fR, \fB\-std=f2003\fR, and
444
\&\fB\-Wall\fR.
445
.IP "\fB\-Wunderflow\fR" 4
446
.IX Item "-Wunderflow"
447
Produce a warning when numerical constant expressions are
448
encountered, which yield an \s-1UNDERFLOW\s0 during compilation.
449
.IP "\fB\-Werror\fR" 4
450
.IX Item "-Werror"
451
Turns all warnings into errors.
452
.PP
453
Some of these have no effect when compiling programs written in Fortran.
454
.Sh "Options for debugging your program or \s-1GNU\s0 Fortran"
455
.IX Subsection "Options for debugging your program or GNU Fortran"
456
\&\s-1GNU\s0 Fortran has various special options that are used for debugging
457
either your program or the \s-1GNU\s0 Fortran compiler.
458
.IP "\fB\-fdump\-parse\-tree\fR" 4
459
.IX Item "-fdump-parse-tree"
460
Output the internal parse tree before starting code generation.  Only
461
really useful for debugging the \s-1GNU\s0 Fortran compiler itself.
462
.IP "\fB\-ffpe\-trap=\fR\fIlist\fR" 4
463
.IX Item "-ffpe-trap=list"
464
Specify a list of \s-1IEEE\s0 exceptions when a Floating Point Exception
465
(\s-1FPE\s0) should be raised.  On most systems, this will result in a \s-1SIGFPE\s0
466
signal being sent and the program being interrupted, producing a core
467
file useful for debugging.  \fIlist\fR is a (possibly empty) comma-separated
468
list of the following \s-1IEEE\s0 exceptions: \fBinvalid\fR (invalid floating
469
point operation, such as \f(CW\*(C`SQRT(\-1.0)\*(C'\fR), \fBzero\fR (division by
470
zero), \fBoverflow\fR (overflow in a floating point operation),
471
\&\fBunderflow\fR (underflow in a floating point operation),
472
\&\fBprecision\fR (loss of precision during operation) and \fBdenormal\fR
473
(operation produced a denormal value).
474
.Sh "Options for directory search"
475
.IX Subsection "Options for directory search"
476
These options affect how \s-1GNU\s0 Fortran searches
477
for files specified by the \f(CW\*(C`INCLUDE\*(C'\fR directive and where it searches
478
for previously compiled modules.
479
.PP
480
It also affects the search paths used by \fBcpp\fR when used to preprocess
481
Fortran source.
482
.IP "\fB\-I\fR\fIdir\fR" 4
483
.IX Item "-Idir"
484
These affect interpretation of the \f(CW\*(C`INCLUDE\*(C'\fR directive
485
(as well as of the \f(CW\*(C`#include\*(C'\fR directive of the \fBcpp\fR
486
preprocessor).
487
.Sp
488
Also note that the general behavior of \fB\-I\fR and
489
\&\f(CW\*(C`INCLUDE\*(C'\fR is pretty much the same as of \fB\-I\fR with
490
\&\f(CW\*(C`#include\*(C'\fR in the \fBcpp\fR preprocessor, with regard to
491
looking for \fIheader.gcc\fR files and other such things.
492
.Sp
493
This path is also used to search for \fI.mod\fR files when previously
494
compiled modules are required by a \f(CW\*(C`USE\*(C'\fR statement.
495
.IP "\fB\-M\fR\fIdir\fR" 4
496
.IX Item "-Mdir"
497
.PD 0
498
.IP "\fB\-J\fR\fIdir\fR" 4
499
.IX Item "-Jdir"
500
.PD
501
This option specifies where to put \fI.mod\fR files for compiled modules.
502
It is also added to the list of directories to searched by an \f(CW\*(C`USE\*(C'\fR
503
statement.
504
.Sp
505
The default is the current directory.
506
.Sp
507
\&\fB\-J\fR is an alias for \fB\-M\fR to avoid conflicts with existing
508
\&\s-1GCC\s0 options.
509
.Sh "Influencing runtime behavior"
510
.IX Subsection "Influencing runtime behavior"
511
These options affect the runtime behavior of programs compiled with \s-1GNU\s0 Fortran.
512
.IP "\fB\-fconvert=\fR\fIconversion\fR" 4
513
.IX Item "-fconvert=conversion"
514
Specify the representation of data for unformatted files.  Valid
515
values for conversion are: \fBnative\fR, the default; \fBswap\fR,
516
swap between big\- and little\-endian; \fBbig-endian\fR, use big-endian
517
representation for unformatted files; \fBlittle-endian\fR, use little-endian
518
representation for unformatted files.
519
.Sp
520
\&\fIThis option has an effect only when used in the main program.
521
The \f(CI\*(C`CONVERT\*(C'\fI specifier and the \s-1GFORTRAN_CONVERT_UNIT\s0 environment
522
variable override the default specified by \f(BI\-fconvert\fI.\fR
523
.IP "\fB\-frecord\-marker=\fR\fIlength\fR" 4
524
.IX Item "-frecord-marker=length"
525
Specify the length of record markers for unformatted files.
526
Valid values for \fIlength\fR are 4 and 8.  Default is 4.
527
\&\fIThis is different from previous versions of\fR \fBgfortran\fR,
528
which specified a default record marker length of 8 on most
529
systems.  If you want to read or write files compatible
530
with earlier versions of \fBgfortran\fR, use \fB\-frecord\-marker=8\fR.
531
.IP "\fB\-fmax\-subrecord\-length=\fR\fIlength\fR" 4
532
.IX Item "-fmax-subrecord-length=length"
533
Specify the maximum length for a subrecord.  The maximum permitted
534
value for length is 2147483639, which is also the default.  Only
535
really useful for use by the gfortran testsuite.
536
.Sh "Options for code generation conventions"
537
.IX Subsection "Options for code generation conventions"
538
These machine-independent options control the interface conventions
539
used in code generation.
540
.PP
541
Most of them have both positive and negative forms; the negative form
542
of \fB\-ffoo\fR would be \fB\-fno\-foo\fR.  In the table below, only
543
one of the forms is listed\-\-\-the one which is not the default.  You
544
can figure out the other form by either removing \fBno\-\fR or adding
545
it.
546
.IP "\fB\-fno\-automatic\fR" 4
547
.IX Item "-fno-automatic"
548
Treat each program unit as if the \f(CW\*(C`SAVE\*(C'\fR statement was specified for
549
every local variable and array referenced in it. Does not affect common
550
blocks. (Some Fortran compilers provide this option under the name
551
\&\fB\-static\fR.)
552
.IP "\fB\-ff2c\fR" 4
553
.IX Item "-ff2c"
554
Generate code designed to be compatible with code generated
555
by \fBg77\fR and \fBf2c\fR.
556
.Sp
557
The calling conventions used by \fBg77\fR (originally implemented
558
in \fBf2c\fR) require functions that return type
559
default \f(CW\*(C`REAL\*(C'\fR to actually return the C type \f(CW\*(C`double\*(C'\fR, and
560
functions that return type \f(CW\*(C`COMPLEX\*(C'\fR to return the values via an
561
extra argument in the calling sequence that points to where to
562
store the return value.  Under the default \s-1GNU\s0 calling conventions, such
563
functions simply return their results as they would in \s-1GNU\s0
564
C\-\-\-default \f(CW\*(C`REAL\*(C'\fR functions return the C type \f(CW\*(C`float\*(C'\fR, and
565
\&\f(CW\*(C`COMPLEX\*(C'\fR functions return the \s-1GNU\s0 C type \f(CW\*(C`complex\*(C'\fR.
566
Additionally, this option implies the \fB\-fsecond\-underscore\fR
567
option, unless \fB\-fno\-second\-underscore\fR is explicitly requested.
568
.Sp
569
This does not affect the generation of code that interfaces with
570
the \fBlibgfortran\fR library.
571
.Sp
572
\&\fICaution:\fR It is not a good idea to mix Fortran code compiled with
573
\&\fB\-ff2c\fR with code compiled with the default \fB\-fno\-f2c\fR
574
calling conventions as, calling \f(CW\*(C`COMPLEX\*(C'\fR or default \f(CW\*(C`REAL\*(C'\fR
575
functions between program parts which were compiled with different
576
calling conventions will break at execution time.
577
.Sp
578
\&\fICaution:\fR This will break code which passes intrinsic functions
579
of type default \f(CW\*(C`REAL\*(C'\fR or \f(CW\*(C`COMPLEX\*(C'\fR as actual arguments, as
580
the library implementations use the \fB\-fno\-f2c\fR calling conventions.
581
.IP "\fB\-fno\-underscoring\fR" 4
582
.IX Item "-fno-underscoring"
583
Do not transform names of entities specified in the Fortran
584
source file by appending underscores to them.
585
.Sp
586
With \fB\-funderscoring\fR in effect, \s-1GNU\s0 Fortran appends one
587
underscore to external names with no underscores.  This is done to ensure
588
compatibility with code produced by many \s-1UNIX\s0 Fortran compilers.
589
.Sp
590
\&\fICaution\fR: The default behavior of \s-1GNU\s0 Fortran is
591
incompatible with \fBf2c\fR and \fBg77\fR, please use the
592
\&\fB\-ff2c\fR option if you want object files compiled with
593
\&\s-1GNU\s0 Fortran to be compatible with object code created with these
594
tools.
595
.Sp
596
Use of \fB\-fno\-underscoring\fR is not recommended unless you are
597
experimenting with issues such as integration of \s-1GNU\s0 Fortran into
598
existing system environments (vis\-a\-vis existing libraries, tools, and
599
so on).
600
.Sp
601
For example, with \fB\-funderscoring\fR, and assuming other defaults like
602
\&\fB\-fcase\-lower\fR and that \f(CW\*(C`j()\*(C'\fR and \f(CW\*(C`max_count()\*(C'\fR are
603
external functions while \f(CW\*(C`my_var\*(C'\fR and \f(CW\*(C`lvar\*(C'\fR are local variables,
604
a statement like
605
.Sp
606
.Vb 1
607
\&        I = J() + MAX_COUNT (MY_VAR, LVAR)
608
.Ve
609
.Sp
610
is implemented as something akin to:
611
.Sp
612
.Vb 1
613
\&        i = j_() + max_count__(&my_var__, &lvar);
614
.Ve
615
.Sp
616
With \fB\-fno\-underscoring\fR, the same statement is implemented as:
617
.Sp
618
.Vb 1
619
\&        i = j() + max_count(&my_var, &lvar);
620
.Ve
621
.Sp
622
Use of \fB\-fno\-underscoring\fR allows direct specification of
623
user-defined names while debugging and when interfacing \s-1GNU\s0 Fortran
624
code with other languages.
625
.Sp
626
Note that just because the names match does \fInot\fR mean that the
627
interface implemented by \s-1GNU\s0 Fortran for an external name matches the
628
interface implemented by some other language for that same name.
629
That is, getting code produced by \s-1GNU\s0 Fortran to link to code produced
630
by some other compiler using this or any other method can be only a
631
small part of the overall solution\-\-\-getting the code generated by
632
both compilers to agree on issues other than naming can require
633
significant effort, and, unlike naming disagreements, linkers normally
634
cannot detect disagreements in these other areas.
635
.Sp
636
Also, note that with \fB\-fno\-underscoring\fR, the lack of appended
637
underscores introduces the very real possibility that a user-defined
638
external name will conflict with a name in a system library, which
639
could make finding unresolved-reference bugs quite difficult in some
640
cases\-\-\-they might occur at program run time, and show up only as
641
buggy behavior at run time.
642
.Sp
643
In future versions of \s-1GNU\s0 Fortran we hope to improve naming and linking
644
issues so that debugging always involves using the names as they appear
645
in the source, even if the names as seen by the linker are mangled to
646
prevent accidental linking between procedures with incompatible
647
interfaces.
648
.IP "\fB\-fsecond\-underscore\fR" 4
649
.IX Item "-fsecond-underscore"
650
By default, \s-1GNU\s0 Fortran appends an underscore to external
651
names.  If this option is used \s-1GNU\s0 Fortran appends two
652
underscores to names with underscores and one underscore to external names
653
with no underscores.  \s-1GNU\s0 Fortran also appends two underscores to
654
internal names with underscores to avoid naming collisions with external
655
names.
656
.Sp
657
This option has no effect if \fB\-fno\-underscoring\fR is
658
in effect.  It is implied by the \fB\-ff2c\fR option.
659
.Sp
660
Otherwise, with this option, an external name such as \f(CW\*(C`MAX_COUNT\*(C'\fR
661
is implemented as a reference to the link-time external symbol
662
\&\f(CW\*(C`max_count_\|_\*(C'\fR, instead of \f(CW\*(C`max_count_\*(C'\fR.  This is required
663
for compatibility with \fBg77\fR and \fBf2c\fR, and is implied
664
by use of the \fB\-ff2c\fR option.
665
.IP "\fB\-fbounds\-check\fR" 4
666
.IX Item "-fbounds-check"
667
Enable generation of run-time checks for array subscripts
668
and against the declared minimum and maximum values.  It also
669
checks array indices for assumed and deferred
670
shape arrays against the actual allocated bounds.
671
.Sp
672
In the future this may also include other forms of checking, e.g., checking
673
substring references.
674
.IP "\fB\-fmax\-stack\-var\-size=\fR\fIn\fR" 4
675
.IX Item "-fmax-stack-var-size=n"
676
This option specifies the size in bytes of the largest array that will be put
677
on the stack.
678
.Sp
679
This option currently only affects local arrays declared with constant
680
bounds, and may not apply to all character variables.
681
Future versions of \s-1GNU\s0 Fortran may improve this behavior.
682
.Sp
683
The default value for \fIn\fR is 32768.
684
.IP "\fB\-fpack\-derived\fR" 4
685
.IX Item "-fpack-derived"
686
This option tells \s-1GNU\s0 Fortran to pack derived type members as closely as
687
possible.  Code compiled with this option is likely to be incompatible
688
with code compiled without this option, and may execute slower.
689
.IP "\fB\-frepack\-arrays\fR" 4
690
.IX Item "-frepack-arrays"
691
In some circumstances \s-1GNU\s0 Fortran may pass assumed shape array
692
sections via a descriptor describing a noncontiguous area of memory.
693
This option adds code to the function prologue to repack the data into
694
a contiguous block at runtime.
695
.Sp
696
This should result in faster accesses to the array.  However it can introduce
697
significant overhead to the function call, especially  when the passed data
698
is noncontiguous.
699
.IP "\fB\-fshort\-enums\fR" 4
700
.IX Item "-fshort-enums"
701
This option is provided for interoperability with C code that was
702
compiled with the \fB\-fshort\-enums\fR option.  It will make
703
\&\s-1GNU\s0 Fortran choose the smallest \f(CW\*(C`INTEGER\*(C'\fR kind a given
704
enumerator set will fit in, and give all its enumerators this kind.
705
.SH "ENVIRONMENT"
706
.IX Header "ENVIRONMENT"
707
The \fBgfortran\fR compiler currently does not make use of any environment
708
variables to control its operation above and beyond those
709
that affect the operation of \fBgcc\fR.
710
.SH "BUGS"
711
.IX Header "BUGS"
712
For instructions on reporting bugs, see
713
<\fBhttp://gcc.gnu.org/bugs.html\fR>.
714
.SH "SEE ALSO"
715
.IX Header "SEE ALSO"
716
\&\fIgpl\fR\|(7), \fIgfdl\fR\|(7), \fIfsf\-funding\fR\|(7),
717
\&\fIcpp\fR\|(1), \fIgcov\fR\|(1), \fIgcc\fR\|(1), \fIas\fR\|(1), \fIld\fR\|(1), \fIgdb\fR\|(1), \fIadb\fR\|(1), \fIdbx\fR\|(1), \fIsdb\fR\|(1)
718
and the Info entries for \fIgcc\fR, \fIcpp\fR, \fIgfortran\fR, \fIas\fR,
719
\&\fIld\fR, \fIbinutils\fR and \fIgdb\fR.
720
.SH "AUTHOR"
721
.IX Header "AUTHOR"
722
See the Info entry for \fBgfortran\fR for contributors to \s-1GCC\s0 and
723
\&\s-1GNU\s0 Fortran.
724
.SH "COPYRIGHT"
725
.IX Header "COPYRIGHT"
726
Copyright (c) 2004, 2005, 2006, 2007
727
Free Software Foundation, Inc.
728
.PP
729
Permission is granted to copy, distribute and/or modify this document
730
under the terms of the \s-1GNU\s0 Free Documentation License, Version 1.2 or
731
any later version published by the Free Software Foundation; with the
732
Invariant Sections being \*(L"\s-1GNU\s0 General Public License\*(R" and \*(L"Funding
733
Free Software\*(R", the Front-Cover texts being (a) (see below), and with
734
the Back-Cover Texts being (b) (see below).  A copy of the license is
735
included in the \fIgfdl\fR\|(7) man page.
736
.PP
737
(a) The \s-1FSF\s0's Front-Cover Text is:
738
.PP
739
.Vb 1
740
\&     A GNU Manual
741
.Ve
742
.PP
743
(b) The \s-1FSF\s0's Back-Cover Text is:
744
.PP
745
.Vb 3
746
\&     You have freedom to copy and modify this GNU Manual, like GNU
747
\&     software.  Copies published by the Free Software Foundation raise
748
\&     funds for GNU development.
749
.Ve

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