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138 .\" ======================================================================
141 .TH CPP 1 "gcc-2.97" "2001-01-24" "GNU"
144 cpp \- The C Preprocessor
146 .IX Header "SYNOPSIS"
147 cpp [\fB\-P\fR] [\fB\-C\fR] [\fB\-gcc\fR] [\fB\-traditional\fR]
148 [\fB\-undef\fR] [\fB\-trigraphs\fR] [\fB\-pedantic\fR]
149 [\fB\-W\fR\fIwarn\fR...] [\fB\-I\fR\fIdir\fR...]
150 [\fB\-D\fR\fImacro\fR[=\fIdefn\fR]...] [\fB\-U\fR\fImacro\fR]
151 [\fB\-A\fR\fIpredicate\fR(\fIanswer\fR)]
152 [\fB\-M\fR|\fB\-MM\fR][\fB\-MG\fR][\fB\-MF\fR\fIfilename\fR]
153 [\fB\-MP\fR][\fB\-MQ\fR\fItarget\fR...][\fB\-MT\fR\fItarget\fR...]
154 [\fB\-x\fR \fIlanguage\fR] [\fB\-std=\fR\fIstandard\fR]
155 \fIinfile\fR \fIoutfile\fR
157 Only the most useful options are listed here; see below for the remainder.
159 .IX Header "DESCRIPTION"
160 The C preprocessor is a \fImacro processor\fR that is used automatically
161 by the C compiler to transform your program before actual compilation.
162 It is called a macro processor because it allows you to define
163 \&\fImacros\fR, which are brief abbreviations for longer constructs.
165 The C preprocessor is intended only for macro processing of C, \*(C+ and
166 Objective C source files. For macro processing of other files, you are
167 strongly encouraged to use alternatives like M4, which will likely give
168 you better results and avoid many problems. For example, normally the C
169 preprocessor does not preserve arbitrary whitespace verbatim, but
170 instead replaces each sequence with a single space.
172 For use on C-like source files, the C preprocessor provides four
173 separate facilities that you can use as you see fit:
175 Inclusion of header files. These are files of declarations that can be
176 substituted into your program.
178 Macro expansion. You can define \fImacros\fR, which are abbreviations
179 for arbitrary fragments of C code, and then the C preprocessor will
180 replace the macros with their definitions throughout the program.
182 Conditional compilation. Using special preprocessing directives, you
183 can include or exclude parts of the program according to various
186 Line control. If you use a program to combine or rearrange source files
187 into an intermediate file which is then compiled, you can use line
188 control to inform the compiler of where each source line originally came
191 C preprocessors vary in some details. This manual discusses the \s-1GNU\s0 C
192 preprocessor, which provides a small superset of the features of \s-1ISO\s0
195 In its default mode, the \s-1GNU\s0 C preprocessor does not do a few things
196 required by the standard. These are features which are rarely, if ever,
197 used, and may cause surprising changes to the meaning of a program which
198 does not expect them. To get strict \s-1ISO\s0 Standard C, you should use the
199 \&\fB\-std=c89\fR or \fB\-std=c99\fR options, depending on which version
200 of the standard you want. To get all the mandatory diagnostics, you
201 must also use \fB\-pedantic\fR.
204 The C preprocessor expects two file names as arguments, \fIinfile\fR and
205 \&\fIoutfile\fR. The preprocessor reads \fIinfile\fR together with any
206 other files it specifies with \fB#include\fR. All the output generated
207 by the combined input files is written in \fIoutfile\fR.
209 Either \fIinfile\fR or \fIoutfile\fR may be \fB-\fR, which as
210 \&\fIinfile\fR means to read from standard input and as \fIoutfile\fR
211 means to write to standard output. Also, if either file is omitted, it
212 means the same as if \fB-\fR had been specified for that file.
214 Here is a table of command options accepted by the C preprocessor.
215 These options can also be given when compiling a C program; they are
216 passed along automatically to the preprocessor when it is invoked by the
220 Inhibit generation of \fB#\fR\-lines with line-number information in the
221 output from the preprocessor. This might be useful when running the
222 preprocessor on something that is not C code and will be sent to a
223 program which might be confused by the \fB#\fR\-lines.
226 Do not discard comments. All comments are passed through to the output
227 file, except for comments in processed directives, which are deleted
228 along with the directive. Comments appearing in the expansion list of a
229 macro will be preserved, and appear in place wherever the macro is
232 You should be prepared for side effects when using \fB\-C\fR; it causes
233 the preprocessor to treat comments as tokens in their own right. For
234 example, macro redefinitions that were trivial when comments were
235 replaced by a single space might become significant when comments are
236 retained. Also, comments appearing at the start of what would be a
237 directive line have the effect of turning that line into an ordinary
238 source line, since the first token on the line is no longer a \fB#\fR.
239 .Ip "\fB\-traditional\fR" 4
240 .IX Item "-traditional"
241 Try to imitate the behavior of old-fashioned C, as opposed to \s-1ISO\s0 C.
244 Traditional macro expansion pays no attention to single-quote or
245 double-quote characters; macro argument symbols are replaced by the
246 argument values even when they appear within apparent string or
249 Traditionally, it is permissible for a macro expansion to end in the
250 middle of a string or character constant. The constant continues into
251 the text surrounding the macro call.
253 However, traditionally the end of the line terminates a string or
254 character constant, with no error.
256 In traditional C, a comment is equivalent to no text at all. (In \s-1ISO\s0
257 C, a comment counts as whitespace.)
259 Traditional C does not have the concept of a ``preprocessing number''.
260 It considers \fB1.0e+4\fR to be three tokens: \fB1.0e\fR, \fB+\fR,
263 A macro is not suppressed within its own definition, in traditional C.
264 Thus, any macro that is used recursively inevitably causes an error.
266 The character \fB#\fR has no special meaning within a macro definition
269 In traditional C, the text at the end of a macro expansion can run
270 together with the text after the macro call, to produce a single token.
271 (This is impossible in \s-1ISO\s0 C.)
273 None of the \s-1GNU\s0 extensions to the preprocessor are available in
274 \&\fB\-traditional\fR mode.
278 Use the \fB\-traditional\fR option when preprocessing Fortran code, so
279 that single-quotes and double-quotes within Fortran comment lines (which
280 are generally not recognized as such by the preprocessor) do not cause
281 diagnostics about unterminated character or string constants.
283 However, this option does not prevent diagnostics about unterminated
284 comments when a C-style comment appears to start, but not end, within
285 Fortran-style commentary.
287 So, the following Fortran comment lines are accepted with
288 \&\fB\-traditional\fR:
291 \& C This isn't an unterminated character constant
292 \& C Neither is "20000000000, an octal constant
293 \& C in some dialects of Fortran
295 However, this type of comment line will likely produce a diagnostic, or
296 at least unexpected output from the preprocessor, due to the
297 unterminated comment:
300 \& C Some Fortran compilers accept /* as starting
301 \& C an inline comment.
303 Note that \f(CW\*(C`g77\*(C'\fR automatically supplies the \fB\-traditional\fR
304 option when it invokes the preprocessor. However, a future version of
305 \&\f(CW\*(C`g77\*(C'\fR might use a different, more-Fortran-aware preprocessor in
306 place of \f(CW\*(C`cpp\*(C'\fR.
308 .Ip "\fB\-trigraphs\fR" 4
309 .IX Item "-trigraphs"
310 Process \s-1ISO\s0 standard trigraph sequences. These are three-character
311 sequences, all starting with \fB??\fR, that are defined by \s-1ISO\s0 C to
312 stand for single characters. For example, \fB??/\fR stands for
313 \&\fB\e\fR, so \fB'??/n'\fR is a character constant for a newline. By
314 default, \s-1GCC\s0 ignores trigraphs, but in standard-conforming modes it
315 converts them. See the \fB\-std\fR option.
317 The nine trigraph sequences are
349 Trigraph support is not popular, so many compilers do not implement it
350 properly. Portable code should not rely on trigraphs being either
351 converted or ignored.
353 .Ip "\fB\-pedantic\fR" 4
355 Issue warnings required by the \s-1ISO\s0 C standard in certain cases such
356 as when text other than a comment follows \fB#else\fR or \fB#endif\fR.
357 .Ip "\fB\-pedantic-errors\fR" 4
358 .IX Item "-pedantic-errors"
359 Like \fB\-pedantic\fR, except that errors are produced rather than
361 .Ip "\fB\-Wcomment\fR" 4
364 .Ip "\fB\-Wcomments\fR" 4
365 .IX Item "-Wcomments"
367 (Both forms have the same effect).
368 Warn whenever a comment-start sequence \fB/*\fR appears in a \fB/*\fR
369 comment, or whenever a backslash-newline appears in a \fB//\fR comment.
370 .Ip "\fB\-Wtrigraphs\fR" 4
371 .IX Item "-Wtrigraphs"
372 Warn if any trigraphs are encountered. This option used to take effect
373 only if \fB\-trigraphs\fR was also specified, but now works
374 independently. Warnings are not given for trigraphs within comments, as
375 we feel this is obnoxious.
376 .Ip "\fB\-Wwhite-space\fR" 4
377 .IX Item "-Wwhite-space"
378 Warn about possible white space confusion, e.g. white space between a
379 backslash and a newline.
382 Requests \fB\-Wcomment\fR, \fB\-Wtrigraphs\fR, and \fB\-Wwhite-space\fR
383 (but not \fB\-Wtraditional\fR or \fB\-Wundef\fR).
384 .Ip "\fB\-Wtraditional\fR" 4
385 .IX Item "-Wtraditional"
386 Warn about certain constructs that behave differently in traditional and
388 .Ip "\fB\-Wundef\fR" 4
390 Warn if an undefined identifier is evaluated in an \fB#if\fR directive.
391 .Ip "\fB\-I\fR \fIdirectory\fR" 4
392 .IX Item "-I directory"
393 Add the directory \fIdirectory\fR to the head of the list of
394 directories to be searched for header files.
395 This can be used to override a system header file, substituting your
396 own version, since these directories are searched before the system
397 header file directories. If you use more than one \fB\-I\fR option,
398 the directories are scanned in left-to-right order; the standard
399 system directories come after.
402 Any directories specified with \fB\-I\fR options before the \fB\-I-\fR
403 option are searched only for the case of \fB#include "\fR\fIfile\fR\fB"\fR;
404 they are not searched for \fB#include <\fR\fIfile\fR\fB>\fR.
406 If additional directories are specified with \fB\-I\fR options after
407 the \fB\-I-\fR, these directories are searched for all \fB#include\fR
410 In addition, the \fB\-I-\fR option inhibits the use of the current
411 directory as the first search directory for \fB#include "\fR\fIfile\fR\fB"\fR.
412 Therefore, the current directory is searched only if it is requested
413 explicitly with \fB\-I.\fR. Specifying both \fB\-I-\fR and \fB\-I.\fR
414 allows you to control precisely which directories are searched before
415 the current one and which are searched after.
416 .Ip "\fB\-nostdinc\fR" 4
418 Do not search the standard system directories for header files.
419 Only the directories you have specified with \fB\-I\fR options
420 (and the current directory, if appropriate) are searched.
422 By using both \fB\-nostdinc\fR and \fB\-I-\fR, you can limit the include-file
423 search path to only those directories you specify explicitly.
424 .Ip "\fB\-nostdinc++\fR" 4
425 .IX Item "-nostdinc++"
426 Do not search for header files in the \*(C+\-specific standard directories,
427 but do still search the other standard directories. (This option is
428 used when building the \*(C+ library.)
429 .Ip "\fB\-remap\fR" 4
431 When searching for a header file in a directory, remap file names if a
432 file named \fIheader.gcc\fR exists in that directory. This can be used
433 to work around limitations of file systems with file name restrictions.
434 The \fIheader.gcc\fR file should contain a series of lines with two
435 tokens on each line: the first token is the name to map, and the second
436 token is the actual name to use.
437 .Ip "\fB\-D\fR \fIname\fR" 4
439 Predefine \fIname\fR as a macro, with definition \fB1\fR.
440 .Ip "\fB\-D\fR \fIname\fR\fB=\fR\fIdefinition\fR" 4
441 .IX Item "-D name=definition"
442 Predefine \fIname\fR as a macro, with definition \fIdefinition\fR.
443 There are no restrictions on the contents of \fIdefinition\fR, but if
444 you are invoking the preprocessor from a shell or shell-like program you
445 may need to use the shell's quoting syntax to protect characters such as
446 spaces that have a meaning in the shell syntax. If you use more than
447 one \fB\-D\fR for the same \fIname\fR, the rightmost definition takes
450 Any \fB\-D\fR and \fB\-U\fR options on the command line are processed in
451 order, and always before \fB\-imacros\fR \fIfile\fR, regardless of the
452 order in which they are written.
453 .Ip "\fB\-U\fR \fIname\fR" 4
455 Do not predefine \fIname\fR.
457 Any \fB\-D\fR and \fB\-U\fR options on the command line are processed in
458 order, and always before \fB\-imacros\fR \fIfile\fR, regardless of the
459 order in which they are written.
460 .Ip "\fB\-undef\fR" 4
462 Do not predefine any nonstandard macros.
465 Define the macros \fI_\|_GNUC_\|_\fR, \fI_\|_GNUC_MINOR_\|_\fR and
466 \&\fI_\|_GNUC_PATCHLEVEL_\|_\fR. These are defined automatically when you use
467 \&\fBgcc \-E\fR; you can turn them off in that case with \fB\-no-gcc\fR.
468 .Ip "\fB\-A\fR \fIpredicate\fR\fB=\fR\fIanswer\fR" 4
469 .IX Item "-A predicate=answer"
470 Make an assertion with the predicate \fIpredicate\fR and answer
471 \&\fIanswer\fR. This form is preferred to the older form \fB\-A\fR
472 \&\fIpredicate\fR\fB(\fR\fIanswer\fR\fB)\fR, which is still supported, because
473 it does not use shell special characters.
474 .Ip "\fB\-A -\fR\fIpredicate\fR\fB=\fR\fIanswer\fR" 4
475 .IX Item "-A -predicate=answer"
476 Disable an assertion with the predicate \fIpredicate\fR and answer
477 \&\fIanswer\fR. Specifying no predicate, by \fB\-A-\fR or \fB\-A -\fR,
478 disables all predefined assertions and all assertions preceding it on
479 the command line; and also undefines all predefined macros and all
480 macros preceding it on the command line.
483 Instead of outputting the result of preprocessing, output a list of
484 \&\fB#define\fR directives for all the macros defined during the
485 execution of the preprocessor, including predefined macros. This gives
486 you a way of finding out what is predefined in your version of the
487 preprocessor; assuming you have no file \fBfoo.h\fR, the command
490 \& touch foo.h; cpp -dM foo.h
492 will show the values of any predefined macros.
495 Like \fB\-dM\fR except in two respects: it does \fInot\fR include the
496 predefined macros, and it outputs \fIboth\fR the \fB#define\fR
497 directives and the result of preprocessing. Both kinds of output go to
498 the standard output file.
501 Like \fB\-dD\fR, but emit only the macro names, not their expansions.
504 Output \fB#include\fR directives in addition to the result of
508 Instead of outputting the result of preprocessing, output a rule
509 suitable for \f(CW\*(C`make\*(C'\fR describing the dependencies of the main source
510 file. The preprocessor outputs one \f(CW\*(C`make\*(C'\fR rule containing the
511 object file name for that source file, a colon, and the names of all the
512 included files, including those coming from \fB\-include\fR or
513 \&\fB\-imacros\fR command line options. If there are many included files
514 then the rule is split into several lines using \fB\e\fR\-newline.
517 Like \fB\-M\fR, but mention only the files included with \fB#include
518 "\fR\fIfile\fR\fB"\fR or with \fB\-include\fR or \fB\-imacros\fR command line
519 options. System header files included with \fB#include <\fR\fIfile\fR\fB>\fR
521 .Ip "\fB\-MF\fR \fIfile\fR" 4
523 When used with \fB\-M\fR or \fB\-MM\fR, specifies a file to write the
524 dependencies to. This allows the preprocessor to write the preprocessed
525 file to stdout normally. If no \fB\-MF\fR switch is given, \s-1CPP\s0 sends
526 the rules to stdout and suppresses normal preprocessed output.
529 When used with \fB\-M\fR or \fB\-MM\fR, \fB\-MG\fR says to treat missing
530 header files as generated files and assume they live in the same
531 directory as the source file. It suppresses preprocessed output, as a
532 missing header file is ordinarily an error.
534 This feature is used in automatic updating of makefiles.
537 This option instructs \s-1CPP\s0 to add a phony target for each dependency
538 other than the main file, causing each to depend on nothing. These
539 dummy rules work around errors \f(CW\*(C`make\*(C'\fR gives if you remove header
540 files without updating the \f(CW\*(C`Makefile\*(C'\fR to match.
542 This is typical output:\-
545 \& /tmp/test.o: /tmp/test.c /tmp/test.h
550 .Ip "\fB\-MQ\fR \fItarget\fR" 4
551 .IX Item "-MQ target"
553 .Ip "\fB\-MT\fR \fItarget\fR" 4
554 .IX Item "-MT target"
556 By default \s-1CPP\s0 uses the main file name, including any path, and appends
557 the object suffix, normally ``.o'', to it to obtain the name of the
558 target for dependency generation. With \fB\-MT\fR you can specify a
559 target yourself, overriding the default one.
561 If you want multiple targets, you can specify them as a single argument
562 to \fB\-MT\fR, or use multiple \fB\-MT\fR options.
564 The targets you specify are output in the order they appear on the
565 command line. \fB\-MQ\fR is identical to \fB\-MT\fR, except that the
566 target name is quoted for Make, but with \fB\-MT\fR it isn't. For
567 example, \-MT '$(objpfx)foo.o' gives
570 \& $(objpfx)foo.o: /tmp/foo.c
572 but \-MQ '$(objpfx)foo.o' gives
575 \& $$(objpfx)foo.o: /tmp/foo.c
577 The default target is automatically quoted, as if it were given with
581 Print the name of each header file used, in addition to other normal
583 .Ip "\fB\-imacros\fR \fIfile\fR" 4
584 .IX Item "-imacros file"
585 Process \fIfile\fR as input, discarding the resulting output, before
586 processing the regular input file. Because the output generated from
587 \&\fIfile\fR is discarded, the only effect of \fB\-imacros\fR \fIfile\fR
588 is to make the macros defined in \fIfile\fR available for use in the
590 .Ip "\fB\-include\fR \fIfile\fR" 4
591 .IX Item "-include file"
592 Process \fIfile\fR as input, and include all the resulting output,
593 before processing the regular input file.
594 .Ip "\fB\-idirafter\fR \fIdir\fR" 4
595 .IX Item "-idirafter dir"
596 Add the directory \fIdir\fR to the second include path. The directories
597 on the second include path are searched when a header file is not found
598 in any of the directories in the main include path (the one that
599 \&\fB\-I\fR adds to).
600 .Ip "\fB\-iprefix\fR \fIprefix\fR" 4
601 .IX Item "-iprefix prefix"
602 Specify \fIprefix\fR as the prefix for subsequent \fB\-iwithprefix\fR
603 options. If the prefix represents a directory, you should include the
605 .Ip "\fB\-iwithprefix\fR \fIdir\fR" 4
606 .IX Item "-iwithprefix dir"
607 Add a directory to the second include path. The directory's name is
608 made by concatenating \fIprefix\fR and \fIdir\fR, where \fIprefix\fR was
609 specified previously with \fB\-iprefix\fR.
610 .Ip "\fB\-isystem\fR \fIdir\fR" 4
611 .IX Item "-isystem dir"
612 Add a directory to the beginning of the second include path, marking it
613 as a system directory, so that it gets the same special treatment as
614 is applied to the standard system directories.
618 .Ip "\fB\-x c++\fR" 4
620 .Ip "\fB\-x objective-c\fR" 4
621 .IX Item "-x objective-c"
622 .Ip "\fB\-x assembler-with-cpp\fR" 4
623 .IX Item "-x assembler-with-cpp"
625 Specify the source language: C, \*(C+, Objective-C, or assembly. This has
626 nothing to do with standards conformance or extensions; it merely
627 selects which base syntax to expect. If you give none of these options,
628 cpp will deduce the language from the extension of the source file:
629 \&\fB.c\fR, \fB.cc\fR, \fB.m\fR, or \fB.S\fR. Some other common
630 extensions for \*(C+ and assembly are also recognized. If cpp does not
631 recognize the extension, it will treat the file as C; this is the most
634 \&\fBNote:\fR Previous versions of cpp accepted a \fB\-lang\fR option
635 which selected both the language and the standards conformance level.
636 This option has been removed, because it conflicts with the \fB\-l\fR
638 .Ip "\fB\-std=\fR\fIstandard\fR" 4
639 .IX Item "-std=standard"
644 Specify the standard to which the code should conform. Currently cpp
645 only knows about the standards for C; other language standards will be
651 .if n .Ip "\f(CW""iso9899:1990""\fR" 4
652 .el .Ip "\f(CWiso9899:1990\fR" 4
653 .IX Item "iso9899:1990"
655 .if n .Ip "\f(CW""c89""\fR" 4
656 .el .Ip "\f(CWc89\fR" 4
659 The \s-1ISO\s0 C standard from 1990. \fBc89\fR is the customary shorthand for
660 this version of the standard.
662 The \fB\-ansi\fR option is equivalent to \fB\-std=c89\fR.
663 .if n .Ip "\f(CW""iso9899:199409""\fR" 4
664 .el .Ip "\f(CWiso9899:199409\fR" 4
665 .IX Item "iso9899:199409"
666 The 1990 C standard, as amended in 1994.
667 .if n .Ip "\f(CW""iso9899:1999""\fR" 4
668 .el .Ip "\f(CWiso9899:1999\fR" 4
669 .IX Item "iso9899:1999"
671 .if n .Ip "\f(CW""c99""\fR" 4
672 .el .Ip "\f(CWc99\fR" 4
674 .if n .Ip "\f(CW""iso9899:199x""\fR" 4
675 .el .Ip "\f(CWiso9899:199x\fR" 4
676 .IX Item "iso9899:199x"
677 .if n .Ip "\f(CW""c9x""\fR" 4
678 .el .Ip "\f(CWc9x\fR" 4
681 The revised \s-1ISO\s0 C standard, published in December 1999. Before
682 publication, this was known as C9X.
683 .if n .Ip "\f(CW""gnu89""\fR" 4
684 .el .Ip "\f(CWgnu89\fR" 4
686 The 1990 C standard plus \s-1GNU\s0 extensions. This is the default.
687 .if n .Ip "\f(CW""gnu99""\fR" 4
688 .el .Ip "\f(CWgnu99\fR" 4
691 .if n .Ip "\f(CW""gnu9x""\fR" 4
692 .el .Ip "\f(CWgnu9x\fR" 4
695 The 1999 C standard plus \s-1GNU\s0 extensions.
699 .Ip "\fB\-ftabstop=NUMBER\fR" 4
700 .IX Item "-ftabstop=NUMBER"
701 Set the distance between tab stops. This helps the preprocessor
702 report correct column numbers in warnings or errors, even if tabs appear
703 on the line. Values less than 1 or greater than 100 are ignored. The
707 Forbid the use of \fB$\fR in identifiers. The C standard allows
708 implementations to define extra characters that can appear in
709 identifiers. By default the \s-1GNU\s0 C preprocessor permits \fB$\fR, a
712 .IX Header "SEE ALSO"
713 \&\fIgcc\fR\|(1), \fIas\fR\|(1), \fIld\fR\|(1), and the Info entries for \fIcpp\fR, \fIgcc\fR, and
716 .IX Header "COPYRIGHT"
717 Copyright (c) 1987, 1989, 1991, 1992, 1993, 1994, 1995, 1996,
718 1997, 1998, 1999, 2000, 2001
719 Free Software Foundation, Inc.
721 Permission is granted to make and distribute verbatim copies of
722 this manual provided the copyright notice and this permission notice
723 are preserved on all copies.
725 Permission is granted to copy and distribute modified versions of this
726 manual under the conditions for verbatim copying, provided also that
727 the entire resulting derived work is distributed under the terms of a
728 permission notice identical to this one.
730 Permission is granted to copy and distribute translations of this manual
731 into another language, under the above conditions for modified versions.
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