1 @c Copyright (c) 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007
2 @c Free Software Foundation, Inc.
3 @c This is part of the CPP and GCC manuals.
4 @c For copying conditions, see the file gcc.texi.
6 @c ---------------------------------------------------------------------
7 @c Options affecting the preprocessor
8 @c ---------------------------------------------------------------------
10 @c If this file is included with the flag ``cppmanual'' set, it is
11 @c formatted for inclusion in the CPP manual; otherwise the main GCC manual.
16 Predefine @var{name} as a macro, with definition @code{1}.
18 @item -D @var{name}=@var{definition}
19 The contents of @var{definition} are tokenized and processed as if
20 they appeared during translation phase three in a @samp{#define}
21 directive. In particular, the definition will be truncated by
22 embedded newline characters.
24 If you are invoking the preprocessor from a shell or shell-like
25 program you may need to use the shell's quoting syntax to protect
26 characters such as spaces that have a meaning in the shell syntax.
28 If you wish to define a function-like macro on the command line, write
29 its argument list with surrounding parentheses before the equals sign
30 (if any). Parentheses are meaningful to most shells, so you will need
31 to quote the option. With @command{sh} and @command{csh},
32 @option{-D'@var{name}(@var{args@dots{}})=@var{definition}'} works.
34 @option{-D} and @option{-U} options are processed in the order they
35 are given on the command line. All @option{-imacros @var{file}} and
36 @option{-include @var{file}} options are processed after all
37 @option{-D} and @option{-U} options.
41 Cancel any previous definition of @var{name}, either built in or
42 provided with a @option{-D} option.
46 Do not predefine any system-specific or GCC-specific macros. The
47 standard predefined macros remain defined.
49 @xref{Standard Predefined Macros}.
54 Add the directory @var{dir} to the list of directories to be searched
59 Directories named by @option{-I} are searched before the standard
60 system include directories. If the directory @var{dir} is a standard
61 system include directory, the option is ignored to ensure that the
62 default search order for system directories and the special treatment
63 of system headers are not defeated
65 (@pxref{System Headers})
71 Write output to @var{file}. This is the same as specifying @var{file}
72 as the second non-option argument to @command{cpp}. @command{gcc} has a
73 different interpretation of a second non-option argument, so you must
74 use @option{-o} to specify the output file.
78 Turns on all optional warnings which are desirable for normal code.
79 At present this is @option{-Wcomment}, @option{-Wtrigraphs},
80 @option{-Wmultichar} and a warning about integer promotion causing a
81 change of sign in @code{#if} expressions. Note that many of the
82 preprocessor's warnings are on by default and have no options to
89 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
90 comment, or whenever a backslash-newline appears in a @samp{//} comment.
91 (Both forms have the same effect.)
96 Most trigraphs in comments cannot affect the meaning of the program.
97 However, a trigraph that would form an escaped newline (@samp{??/} at
98 the end of a line) can, by changing where the comment begins or ends.
99 Therefore, only trigraphs that would form escaped newlines produce
100 warnings inside a comment.
102 This option is implied by @option{-Wall}. If @option{-Wall} is not
103 given, this option is still enabled unless trigraphs are enabled. To
104 get trigraph conversion without warnings, but get the other
105 @option{-Wall} warnings, use @samp{-trigraphs -Wall -Wno-trigraphs}.
108 @opindex Wtraditional
109 Warn about certain constructs that behave differently in traditional and
110 ISO C@. Also warn about ISO C constructs that have no traditional C
111 equivalent, and problematic constructs which should be avoided.
113 @xref{Traditional Mode}.
118 Warn the first time @samp{#import} is used.
122 Warn whenever an identifier which is not a macro is encountered in an
123 @samp{#if} directive, outside of @samp{defined}. Such identifiers are
126 @item -Wunused-macros
127 @opindex Wunused-macros
128 Warn about macros defined in the main file that are unused. A macro
129 is @dfn{used} if it is expanded or tested for existence at least once.
130 The preprocessor will also warn if the macro has not been used at the
131 time it is redefined or undefined.
133 Built-in macros, macros defined on the command line, and macros
134 defined in include files are not warned about.
136 @emph{Note:} If a macro is actually used, but only used in skipped
137 conditional blocks, then CPP will report it as unused. To avoid the
138 warning in such a case, you might improve the scope of the macro's
139 definition by, for example, moving it into the first skipped block.
140 Alternatively, you could provide a dummy use with something like:
143 #if defined the_macro_causing_the_warning
148 @opindex Wendif-labels
149 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
150 This usually happens in code of the form
161 The second and third @code{FOO} should be in comments, but often are not
162 in older programs. This warning is on by default.
166 Make all warnings into hard errors. Source code which triggers warnings
169 @item -Wsystem-headers
170 @opindex Wsystem-headers
171 Issue warnings for code in system headers. These are normally unhelpful
172 in finding bugs in your own code, therefore suppressed. If you are
173 responsible for the system library, you may want to see them.
177 Suppress all warnings, including those which GNU CPP issues by default.
181 Issue all the mandatory diagnostics listed in the C standard. Some of
182 them are left out by default, since they trigger frequently on harmless
185 @item -pedantic-errors
186 @opindex pedantic-errors
187 Issue all the mandatory diagnostics, and make all mandatory diagnostics
188 into errors. This includes mandatory diagnostics that GCC issues
189 without @samp{-pedantic} but treats as warnings.
194 @cindex dependencies, make
195 Instead of outputting the result of preprocessing, output a rule
196 suitable for @command{make} describing the dependencies of the main
197 source file. The preprocessor outputs one @command{make} rule containing
198 the object file name for that source file, a colon, and the names of all
199 the included files, including those coming from @option{-include} or
200 @option{-imacros} command line options.
202 Unless specified explicitly (with @option{-MT} or @option{-MQ}), the
203 object file name consists of the name of the source file with any
204 suffix replaced with object file suffix and with any leading directory
205 parts removed. If there are many included files then the rule is
206 split into several lines using @samp{\}-newline. The rule has no
209 This option does not suppress the preprocessor's debug output, such as
210 @option{-dM}. To avoid mixing such debug output with the dependency
211 rules you should explicitly specify the dependency output file with
212 @option{-MF}, or use an environment variable like
213 @env{DEPENDENCIES_OUTPUT} (@pxref{Environment Variables}). Debug output
214 will still be sent to the regular output stream as normal.
216 Passing @option{-M} to the driver implies @option{-E}, and suppresses
217 warnings with an implicit @option{-w}.
221 Like @option{-M} but do not mention header files that are found in
222 system header directories, nor header files that are included,
223 directly or indirectly, from such a header.
225 This implies that the choice of angle brackets or double quotes in an
226 @samp{#include} directive does not in itself determine whether that
227 header will appear in @option{-MM} dependency output. This is a
228 slight change in semantics from GCC versions 3.0 and earlier.
233 When used with @option{-M} or @option{-MM}, specifies a
234 file to write the dependencies to. If no @option{-MF} switch is given
235 the preprocessor sends the rules to the same place it would have sent
238 When used with the driver options @option{-MD} or @option{-MMD},
239 @option{-MF} overrides the default dependency output file.
243 In conjunction with an option such as @option{-M} requesting
244 dependency generation, @option{-MG} assumes missing header files are
245 generated files and adds them to the dependency list without raising
246 an error. The dependency filename is taken directly from the
247 @code{#include} directive without prepending any path. @option{-MG}
248 also suppresses preprocessed output, as a missing header file renders
251 This feature is used in automatic updating of makefiles.
255 This option instructs CPP to add a phony target for each dependency
256 other than the main file, causing each to depend on nothing. These
257 dummy rules work around errors @command{make} gives if you remove header
258 files without updating the @file{Makefile} to match.
260 This is typical output:
263 test.o: test.c test.h
268 @item -MT @var{target}
271 Change the target of the rule emitted by dependency generation. By
272 default CPP takes the name of the main input file, deletes any
273 directory components and any file suffix such as @samp{.c}, and
274 appends the platform's usual object suffix. The result is the target.
276 An @option{-MT} option will set the target to be exactly the string you
277 specify. If you want multiple targets, you can specify them as a single
278 argument to @option{-MT}, or use multiple @option{-MT} options.
280 For example, @option{@w{-MT '$(objpfx)foo.o'}} might give
283 $(objpfx)foo.o: foo.c
286 @item -MQ @var{target}
289 Same as @option{-MT}, but it quotes any characters which are special to
290 Make. @option{@w{-MQ '$(objpfx)foo.o'}} gives
293 $$(objpfx)foo.o: foo.c
296 The default target is automatically quoted, as if it were given with
301 @option{-MD} is equivalent to @option{-M -MF @var{file}}, except that
302 @option{-E} is not implied. The driver determines @var{file} based on
303 whether an @option{-o} option is given. If it is, the driver uses its
304 argument but with a suffix of @file{.d}, otherwise it takes the name
305 of the input file, removes any directory components and suffix, and
306 applies a @file{.d} suffix.
308 If @option{-MD} is used in conjunction with @option{-E}, any
309 @option{-o} switch is understood to specify the dependency output file
310 (@pxref{dashMF,,-MF}), but if used without @option{-E}, each @option{-o}
311 is understood to specify a target object file.
313 Since @option{-E} is not implied, @option{-MD} can be used to generate
314 a dependency output file as a side-effect of the compilation process.
318 Like @option{-MD} except mention only user header files, not system
324 When using precompiled headers (@pxref{Precompiled Headers}), this flag
325 will cause the dependency-output flags to also list the files from the
326 precompiled header's dependencies. If not specified only the
327 precompiled header would be listed and not the files that were used to
328 create it because those files are not consulted when a precompiled
331 @item -fpch-preprocess
332 @opindex fpch-preprocess
333 This option allows use of a precompiled header (@pxref{Precompiled
334 Headers}) together with @option{-E}. It inserts a special @code{#pragma},
335 @code{#pragma GCC pch_preprocess "<filename>"} in the output to mark
336 the place where the precompiled header was found, and its filename. When
337 @option{-fpreprocessed} is in use, GCC recognizes this @code{#pragma} and
340 This option is off by default, because the resulting preprocessed output
341 is only really suitable as input to GCC@. It is switched on by
342 @option{-save-temps}.
344 You should not write this @code{#pragma} in your own code, but it is
345 safe to edit the filename if the PCH file is available in a different
346 location. The filename may be absolute or it may be relative to GCC's
352 @itemx -x objective-c
353 @itemx -x assembler-with-cpp
355 Specify the source language: C, C++, Objective-C, or assembly. This has
356 nothing to do with standards conformance or extensions; it merely
357 selects which base syntax to expect. If you give none of these options,
358 cpp will deduce the language from the extension of the source file:
359 @samp{.c}, @samp{.cc}, @samp{.m}, or @samp{.S}. Some other common
360 extensions for C++ and assembly are also recognized. If cpp does not
361 recognize the extension, it will treat the file as C; this is the most
364 @emph{Note:} Previous versions of cpp accepted a @option{-lang} option
365 which selected both the language and the standards conformance level.
366 This option has been removed, because it conflicts with the @option{-l}
369 @item -std=@var{standard}
373 Specify the standard to which the code should conform. Currently CPP
374 knows about C and C++ standards; others may be added in the future.
381 The ISO C standard from 1990. @samp{c89} is the customary shorthand for
382 this version of the standard.
384 The @option{-ansi} option is equivalent to @option{-std=c89}.
387 The 1990 C standard, as amended in 1994.
393 The revised ISO C standard, published in December 1999. Before
394 publication, this was known as C9X@.
397 The 1990 C standard plus GNU extensions. This is the default.
401 The 1999 C standard plus GNU extensions.
404 The 1998 ISO C++ standard plus amendments.
407 The same as @option{-std=c++98} plus GNU extensions. This is the
408 default for C++ code.
413 Split the include path. Any directories specified with @option{-I}
414 options before @option{-I-} are searched only for headers requested with
415 @code{@w{#include "@var{file}"}}; they are not searched for
416 @code{@w{#include <@var{file}>}}. If additional directories are
417 specified with @option{-I} options after the @option{-I-}, those
418 directories are searched for all @samp{#include} directives.
420 In addition, @option{-I-} inhibits the use of the directory of the current
421 file directory as the first search directory for @code{@w{#include
426 This option has been deprecated.
430 Do not search the standard system directories for header files.
431 Only the directories you have specified with @option{-I} options
432 (and the directory of the current file, if appropriate) are searched.
436 Do not search for header files in the C++-specific standard directories,
437 but do still search the other standard directories. (This option is
438 used when building the C++ library.)
440 @item -include @var{file}
442 Process @var{file} as if @code{#include "file"} appeared as the first
443 line of the primary source file. However, the first directory searched
444 for @var{file} is the preprocessor's working directory @emph{instead of}
445 the directory containing the main source file. If not found there, it
446 is searched for in the remainder of the @code{#include "@dots{}"} search
449 If multiple @option{-include} options are given, the files are included
450 in the order they appear on the command line.
452 @item -imacros @var{file}
454 Exactly like @option{-include}, except that any output produced by
455 scanning @var{file} is thrown away. Macros it defines remain defined.
456 This allows you to acquire all the macros from a header without also
457 processing its declarations.
459 All files specified by @option{-imacros} are processed before all files
460 specified by @option{-include}.
462 @item -idirafter @var{dir}
464 Search @var{dir} for header files, but do it @emph{after} all
465 directories specified with @option{-I} and the standard system directories
466 have been exhausted. @var{dir} is treated as a system include directory.
468 @item -iprefix @var{prefix}
470 Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix}
471 options. If the prefix represents a directory, you should include the
474 @item -iwithprefix @var{dir}
475 @itemx -iwithprefixbefore @var{dir}
477 @opindex iwithprefixbefore
478 Append @var{dir} to the prefix specified previously with
479 @option{-iprefix}, and add the resulting directory to the include search
480 path. @option{-iwithprefixbefore} puts it in the same place @option{-I}
481 would; @option{-iwithprefix} puts it where @option{-idirafter} would.
483 @item -isysroot @var{dir}
485 This option is like the @option{--sysroot} option, but applies only to
486 header files. See the @option{--sysroot} option for more information.
488 @item -imultilib @var{dir}
490 Use @var{dir} as a subdirectory of the directory containing
491 target-specific C++ headers.
493 @item -isystem @var{dir}
495 Search @var{dir} for header files, after all directories specified by
496 @option{-I} but before the standard system directories. Mark it
497 as a system directory, so that it gets the same special treatment as
498 is applied to the standard system directories.
500 @xref{System Headers}.
503 @item -iquote @var{dir}
505 Search @var{dir} only for header files requested with
506 @code{@w{#include "@var{file}"}}; they are not searched for
507 @code{@w{#include <@var{file}>}}, before all directories specified by
508 @option{-I} and before the standard system directories.
513 @item -fdollars-in-identifiers
514 @opindex fdollars-in-identifiers
515 @anchor{fdollars-in-identifiers}
516 Accept @samp{$} in identifiers.
518 @xref{Identifier characters}.
521 @item -fextended-identifiers
522 @opindex fextended-identifiers
523 Accept universal character names in identifiers. This option is
524 experimental; in a future version of GCC, it will be enabled by
525 default for C99 and C++.
528 @opindex fpreprocessed
529 Indicate to the preprocessor that the input file has already been
530 preprocessed. This suppresses things like macro expansion, trigraph
531 conversion, escaped newline splicing, and processing of most directives.
532 The preprocessor still recognizes and removes comments, so that you can
533 pass a file preprocessed with @option{-C} to the compiler without
534 problems. In this mode the integrated preprocessor is little more than
535 a tokenizer for the front ends.
537 @option{-fpreprocessed} is implicit if the input file has one of the
538 extensions @samp{.i}, @samp{.ii} or @samp{.mi}. These are the
539 extensions that GCC uses for preprocessed files created by
540 @option{-save-temps}.
542 @item -ftabstop=@var{width}
544 Set the distance between tab stops. This helps the preprocessor report
545 correct column numbers in warnings or errors, even if tabs appear on the
546 line. If the value is less than 1 or greater than 100, the option is
547 ignored. The default is 8.
549 @item -fexec-charset=@var{charset}
550 @opindex fexec-charset
551 @cindex character set, execution
552 Set the execution character set, used for string and character
553 constants. The default is UTF-8. @var{charset} can be any encoding
554 supported by the system's @code{iconv} library routine.
556 @item -fwide-exec-charset=@var{charset}
557 @opindex fwide-exec-charset
558 @cindex character set, wide execution
559 Set the wide execution character set, used for wide string and
560 character constants. The default is UTF-32 or UTF-16, whichever
561 corresponds to the width of @code{wchar_t}. As with
562 @option{-fexec-charset}, @var{charset} can be any encoding supported
563 by the system's @code{iconv} library routine; however, you will have
564 problems with encodings that do not fit exactly in @code{wchar_t}.
566 @item -finput-charset=@var{charset}
567 @opindex finput-charset
568 @cindex character set, input
569 Set the input character set, used for translation from the character
570 set of the input file to the source character set used by GCC@. If the
571 locale does not specify, or GCC cannot get this information from the
572 locale, the default is UTF-8. This can be overridden by either the locale
573 or this command line option. Currently the command line option takes
574 precedence if there's a conflict. @var{charset} can be any encoding
575 supported by the system's @code{iconv} library routine.
577 @item -fworking-directory
578 @opindex fworking-directory
579 @opindex fno-working-directory
580 Enable generation of linemarkers in the preprocessor output that will
581 let the compiler know the current working directory at the time of
582 preprocessing. When this option is enabled, the preprocessor will
583 emit, after the initial linemarker, a second linemarker with the
584 current working directory followed by two slashes. GCC will use this
585 directory, when it's present in the preprocessed input, as the
586 directory emitted as the current working directory in some debugging
587 information formats. This option is implicitly enabled if debugging
588 information is enabled, but this can be inhibited with the negated
589 form @option{-fno-working-directory}. If the @option{-P} flag is
590 present in the command line, this option has no effect, since no
591 @code{#line} directives are emitted whatsoever.
593 @item -fno-show-column
594 @opindex fno-show-column
595 Do not print column numbers in diagnostics. This may be necessary if
596 diagnostics are being scanned by a program that does not understand the
597 column numbers, such as @command{dejagnu}.
599 @item -A @var{predicate}=@var{answer}
601 Make an assertion with the predicate @var{predicate} and answer
602 @var{answer}. This form is preferred to the older form @option{-A
603 @var{predicate}(@var{answer})}, which is still supported, because
604 it does not use shell special characters.
609 @item -A -@var{predicate}=@var{answer}
610 Cancel an assertion with the predicate @var{predicate} and answer
614 @var{CHARS} is a sequence of one or more of the following characters,
615 and must not be preceded by a space. Other characters are interpreted
616 by the compiler proper, or reserved for future versions of GCC, and so
617 are silently ignored. If you specify characters whose behavior
618 conflicts, the result is undefined.
623 Instead of the normal output, generate a list of @samp{#define}
624 directives for all the macros defined during the execution of the
625 preprocessor, including predefined macros. This gives you a way of
626 finding out what is predefined in your version of the preprocessor.
627 Assuming you have no file @file{foo.h}, the command
630 touch foo.h; cpp -dM foo.h
634 will show all the predefined macros.
638 Like @samp{M} except in two respects: it does @emph{not} include the
639 predefined macros, and it outputs @emph{both} the @samp{#define}
640 directives and the result of preprocessing. Both kinds of output go to
641 the standard output file.
645 Like @samp{D}, but emit only the macro names, not their expansions.
649 Output @samp{#include} directives in addition to the result of
655 Inhibit generation of linemarkers in the output from the preprocessor.
656 This might be useful when running the preprocessor on something that is
657 not C code, and will be sent to a program which might be confused by the
660 @xref{Preprocessor Output}.
665 Do not discard comments. All comments are passed through to the output
666 file, except for comments in processed directives, which are deleted
667 along with the directive.
669 You should be prepared for side effects when using @option{-C}; it
670 causes the preprocessor to treat comments as tokens in their own right.
671 For example, comments appearing at the start of what would be a
672 directive line have the effect of turning that line into an ordinary
673 source line, since the first token on the line is no longer a @samp{#}.
676 Do not discard comments, including during macro expansion. This is
677 like @option{-C}, except that comments contained within macros are
678 also passed through to the output file where the macro is expanded.
680 In addition to the side-effects of the @option{-C} option, the
681 @option{-CC} option causes all C++-style comments inside a macro
682 to be converted to C-style comments. This is to prevent later use
683 of that macro from inadvertently commenting out the remainder of
686 The @option{-CC} option is generally used to support lint comments.
688 @item -traditional-cpp
689 @opindex traditional-cpp
690 Try to imitate the behavior of old-fashioned C preprocessors, as
691 opposed to ISO C preprocessors.
693 @xref{Traditional Mode}.
698 Process trigraph sequences.
700 @xref{Initial processing}.
703 These are three-character sequences, all starting with @samp{??}, that
704 are defined by ISO C to stand for single characters. For example,
705 @samp{??/} stands for @samp{\}, so @samp{'??/n'} is a character
706 constant for a newline. By default, GCC ignores trigraphs, but in
707 standard-conforming modes it converts them. See the @option{-std} and
708 @option{-ansi} options.
710 The nine trigraphs and their replacements are
713 Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??-
714 Replacement: [ ] @{ @} # \ ^ | ~
720 Enable special code to work around file systems which only permit very
721 short file names, such as MS-DOS@.
727 Print text describing all the command line options instead of
728 preprocessing anything.
732 Verbose mode. Print out GNU CPP's version number at the beginning of
733 execution, and report the final form of the include path.
737 Print the name of each header file used, in addition to other normal
738 activities. Each name is indented to show how deep in the
739 @samp{#include} stack it is. Precompiled header files are also
740 printed, even if they are found to be invalid; an invalid precompiled
741 header file is printed with @samp{...x} and a valid one with @samp{...!} .
746 Print out GNU CPP's version number. With one dash, proceed to
747 preprocess as normal. With two dashes, exit immediately.