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})
68 If @var{dir} begins with @code{=}, then the @code{=} will be replaced
69 by the sysroot prefix; see @option{--sysroot} and @option{-isysroot}.
73 Write output to @var{file}. This is the same as specifying @var{file}
74 as the second non-option argument to @command{cpp}. @command{gcc} has a
75 different interpretation of a second non-option argument, so you must
76 use @option{-o} to specify the output file.
80 Turns on all optional warnings which are desirable for normal code.
81 At present this is @option{-Wcomment}, @option{-Wtrigraphs},
82 @option{-Wmultichar} and a warning about integer promotion causing a
83 change of sign in @code{#if} expressions. Note that many of the
84 preprocessor's warnings are on by default and have no options to
91 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
92 comment, or whenever a backslash-newline appears in a @samp{//} comment.
93 (Both forms have the same effect.)
98 Most trigraphs in comments cannot affect the meaning of the program.
99 However, a trigraph that would form an escaped newline (@samp{??/} at
100 the end of a line) can, by changing where the comment begins or ends.
101 Therefore, only trigraphs that would form escaped newlines produce
102 warnings inside a comment.
104 This option is implied by @option{-Wall}. If @option{-Wall} is not
105 given, this option is still enabled unless trigraphs are enabled. To
106 get trigraph conversion without warnings, but get the other
107 @option{-Wall} warnings, use @samp{-trigraphs -Wall -Wno-trigraphs}.
110 @opindex Wtraditional
111 Warn about certain constructs that behave differently in traditional and
112 ISO C@. Also warn about ISO C constructs that have no traditional C
113 equivalent, and problematic constructs which should be avoided.
115 @xref{Traditional Mode}.
120 Warn the first time @samp{#import} is used.
124 Warn whenever an identifier which is not a macro is encountered in an
125 @samp{#if} directive, outside of @samp{defined}. Such identifiers are
128 @item -Wunused-macros
129 @opindex Wunused-macros
130 Warn about macros defined in the main file that are unused. A macro
131 is @dfn{used} if it is expanded or tested for existence at least once.
132 The preprocessor will also warn if the macro has not been used at the
133 time it is redefined or undefined.
135 Built-in macros, macros defined on the command line, and macros
136 defined in include files are not warned about.
138 @emph{Note:} If a macro is actually used, but only used in skipped
139 conditional blocks, then CPP will report it as unused. To avoid the
140 warning in such a case, you might improve the scope of the macro's
141 definition by, for example, moving it into the first skipped block.
142 Alternatively, you could provide a dummy use with something like:
145 #if defined the_macro_causing_the_warning
150 @opindex Wendif-labels
151 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
152 This usually happens in code of the form
163 The second and third @code{FOO} should be in comments, but often are not
164 in older programs. This warning is on by default.
168 Make all warnings into hard errors. Source code which triggers warnings
171 @item -Wsystem-headers
172 @opindex Wsystem-headers
173 Issue warnings for code in system headers. These are normally unhelpful
174 in finding bugs in your own code, therefore suppressed. If you are
175 responsible for the system library, you may want to see them.
179 Suppress all warnings, including those which GNU CPP issues by default.
183 Issue all the mandatory diagnostics listed in the C standard. Some of
184 them are left out by default, since they trigger frequently on harmless
187 @item -pedantic-errors
188 @opindex pedantic-errors
189 Issue all the mandatory diagnostics, and make all mandatory diagnostics
190 into errors. This includes mandatory diagnostics that GCC issues
191 without @samp{-pedantic} but treats as warnings.
196 @cindex dependencies, make
197 Instead of outputting the result of preprocessing, output a rule
198 suitable for @command{make} describing the dependencies of the main
199 source file. The preprocessor outputs one @command{make} rule containing
200 the object file name for that source file, a colon, and the names of all
201 the included files, including those coming from @option{-include} or
202 @option{-imacros} command line options.
204 Unless specified explicitly (with @option{-MT} or @option{-MQ}), the
205 object file name consists of the name of the source file with any
206 suffix replaced with object file suffix and with any leading directory
207 parts removed. If there are many included files then the rule is
208 split into several lines using @samp{\}-newline. The rule has no
211 This option does not suppress the preprocessor's debug output, such as
212 @option{-dM}. To avoid mixing such debug output with the dependency
213 rules you should explicitly specify the dependency output file with
214 @option{-MF}, or use an environment variable like
215 @env{DEPENDENCIES_OUTPUT} (@pxref{Environment Variables}). Debug output
216 will still be sent to the regular output stream as normal.
218 Passing @option{-M} to the driver implies @option{-E}, and suppresses
219 warnings with an implicit @option{-w}.
223 Like @option{-M} but do not mention header files that are found in
224 system header directories, nor header files that are included,
225 directly or indirectly, from such a header.
227 This implies that the choice of angle brackets or double quotes in an
228 @samp{#include} directive does not in itself determine whether that
229 header will appear in @option{-MM} dependency output. This is a
230 slight change in semantics from GCC versions 3.0 and earlier.
235 When used with @option{-M} or @option{-MM}, specifies a
236 file to write the dependencies to. If no @option{-MF} switch is given
237 the preprocessor sends the rules to the same place it would have sent
240 When used with the driver options @option{-MD} or @option{-MMD},
241 @option{-MF} overrides the default dependency output file.
245 In conjunction with an option such as @option{-M} requesting
246 dependency generation, @option{-MG} assumes missing header files are
247 generated files and adds them to the dependency list without raising
248 an error. The dependency filename is taken directly from the
249 @code{#include} directive without prepending any path. @option{-MG}
250 also suppresses preprocessed output, as a missing header file renders
253 This feature is used in automatic updating of makefiles.
257 This option instructs CPP to add a phony target for each dependency
258 other than the main file, causing each to depend on nothing. These
259 dummy rules work around errors @command{make} gives if you remove header
260 files without updating the @file{Makefile} to match.
262 This is typical output:
265 test.o: test.c test.h
270 @item -MT @var{target}
273 Change the target of the rule emitted by dependency generation. By
274 default CPP takes the name of the main input file, deletes any
275 directory components and any file suffix such as @samp{.c}, and
276 appends the platform's usual object suffix. The result is the target.
278 An @option{-MT} option will set the target to be exactly the string you
279 specify. If you want multiple targets, you can specify them as a single
280 argument to @option{-MT}, or use multiple @option{-MT} options.
282 For example, @option{@w{-MT '$(objpfx)foo.o'}} might give
285 $(objpfx)foo.o: foo.c
288 @item -MQ @var{target}
291 Same as @option{-MT}, but it quotes any characters which are special to
292 Make. @option{@w{-MQ '$(objpfx)foo.o'}} gives
295 $$(objpfx)foo.o: foo.c
298 The default target is automatically quoted, as if it were given with
303 @option{-MD} is equivalent to @option{-M -MF @var{file}}, except that
304 @option{-E} is not implied. The driver determines @var{file} based on
305 whether an @option{-o} option is given. If it is, the driver uses its
306 argument but with a suffix of @file{.d}, otherwise it takes the name
307 of the input file, removes any directory components and suffix, and
308 applies a @file{.d} suffix.
310 If @option{-MD} is used in conjunction with @option{-E}, any
311 @option{-o} switch is understood to specify the dependency output file
312 (@pxref{dashMF,,-MF}), but if used without @option{-E}, each @option{-o}
313 is understood to specify a target object file.
315 Since @option{-E} is not implied, @option{-MD} can be used to generate
316 a dependency output file as a side-effect of the compilation process.
320 Like @option{-MD} except mention only user header files, not system
326 When using precompiled headers (@pxref{Precompiled Headers}), this flag
327 will cause the dependency-output flags to also list the files from the
328 precompiled header's dependencies. If not specified only the
329 precompiled header would be listed and not the files that were used to
330 create it because those files are not consulted when a precompiled
333 @item -fpch-preprocess
334 @opindex fpch-preprocess
335 This option allows use of a precompiled header (@pxref{Precompiled
336 Headers}) together with @option{-E}. It inserts a special @code{#pragma},
337 @code{#pragma GCC pch_preprocess "<filename>"} in the output to mark
338 the place where the precompiled header was found, and its filename. When
339 @option{-fpreprocessed} is in use, GCC recognizes this @code{#pragma} and
342 This option is off by default, because the resulting preprocessed output
343 is only really suitable as input to GCC@. It is switched on by
344 @option{-save-temps}.
346 You should not write this @code{#pragma} in your own code, but it is
347 safe to edit the filename if the PCH file is available in a different
348 location. The filename may be absolute or it may be relative to GCC's
354 @itemx -x objective-c
355 @itemx -x assembler-with-cpp
357 Specify the source language: C, C++, Objective-C, or assembly. This has
358 nothing to do with standards conformance or extensions; it merely
359 selects which base syntax to expect. If you give none of these options,
360 cpp will deduce the language from the extension of the source file:
361 @samp{.c}, @samp{.cc}, @samp{.m}, or @samp{.S}. Some other common
362 extensions for C++ and assembly are also recognized. If cpp does not
363 recognize the extension, it will treat the file as C; this is the most
366 @emph{Note:} Previous versions of cpp accepted a @option{-lang} option
367 which selected both the language and the standards conformance level.
368 This option has been removed, because it conflicts with the @option{-l}
371 @item -std=@var{standard}
375 Specify the standard to which the code should conform. Currently CPP
376 knows about C and C++ standards; others may be added in the future.
383 The ISO C standard from 1990. @samp{c89} is the customary shorthand for
384 this version of the standard.
386 The @option{-ansi} option is equivalent to @option{-std=c89}.
389 The 1990 C standard, as amended in 1994.
395 The revised ISO C standard, published in December 1999. Before
396 publication, this was known as C9X@.
399 The 1990 C standard plus GNU extensions. This is the default.
403 The 1999 C standard plus GNU extensions.
406 The 1998 ISO C++ standard plus amendments.
409 The same as @option{-std=c++98} plus GNU extensions. This is the
410 default for C++ code.
415 Split the include path. Any directories specified with @option{-I}
416 options before @option{-I-} are searched only for headers requested with
417 @code{@w{#include "@var{file}"}}; they are not searched for
418 @code{@w{#include <@var{file}>}}. If additional directories are
419 specified with @option{-I} options after the @option{-I-}, those
420 directories are searched for all @samp{#include} directives.
422 In addition, @option{-I-} inhibits the use of the directory of the current
423 file directory as the first search directory for @code{@w{#include
428 This option has been deprecated.
432 Do not search the standard system directories for header files.
433 Only the directories you have specified with @option{-I} options
434 (and the directory of the current file, if appropriate) are searched.
438 Do not search for header files in the C++-specific standard directories,
439 but do still search the other standard directories. (This option is
440 used when building the C++ library.)
442 @item -include @var{file}
444 Process @var{file} as if @code{#include "file"} appeared as the first
445 line of the primary source file. However, the first directory searched
446 for @var{file} is the preprocessor's working directory @emph{instead of}
447 the directory containing the main source file. If not found there, it
448 is searched for in the remainder of the @code{#include "@dots{}"} search
451 If multiple @option{-include} options are given, the files are included
452 in the order they appear on the command line.
454 @item -imacros @var{file}
456 Exactly like @option{-include}, except that any output produced by
457 scanning @var{file} is thrown away. Macros it defines remain defined.
458 This allows you to acquire all the macros from a header without also
459 processing its declarations.
461 All files specified by @option{-imacros} are processed before all files
462 specified by @option{-include}.
464 @item -idirafter @var{dir}
466 Search @var{dir} for header files, but do it @emph{after} all
467 directories specified with @option{-I} and the standard system directories
468 have been exhausted. @var{dir} is treated as a system include directory.
469 If @var{dir} begins with @code{=}, then the @code{=} will be replaced
470 by the sysroot prefix; see @option{--sysroot} and @option{-isysroot}.
472 @item -iprefix @var{prefix}
474 Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix}
475 options. If the prefix represents a directory, you should include the
478 @item -iwithprefix @var{dir}
479 @itemx -iwithprefixbefore @var{dir}
481 @opindex iwithprefixbefore
482 Append @var{dir} to the prefix specified previously with
483 @option{-iprefix}, and add the resulting directory to the include search
484 path. @option{-iwithprefixbefore} puts it in the same place @option{-I}
485 would; @option{-iwithprefix} puts it where @option{-idirafter} would.
487 @item -isysroot @var{dir}
489 This option is like the @option{--sysroot} option, but applies only to
490 header files. See the @option{--sysroot} option for more information.
492 @item -imultilib @var{dir}
494 Use @var{dir} as a subdirectory of the directory containing
495 target-specific C++ headers.
497 @item -isystem @var{dir}
499 Search @var{dir} for header files, after all directories specified by
500 @option{-I} but before the standard system directories. Mark it
501 as a system directory, so that it gets the same special treatment as
502 is applied to the standard system directories.
504 @xref{System Headers}.
506 If @var{dir} begins with @code{=}, then the @code{=} will be replaced
507 by the sysroot prefix; see @option{--sysroot} and @option{-isysroot}.
509 @item -iquote @var{dir}
511 Search @var{dir} only for header files requested with
512 @code{@w{#include "@var{file}"}}; they are not searched for
513 @code{@w{#include <@var{file}>}}, before all directories specified by
514 @option{-I} and before the standard system directories.
518 If @var{dir} begins with @code{=}, then the @code{=} will be replaced
519 by the sysroot prefix; see @option{--sysroot} and @option{-isysroot}.
521 @item -fdirectives-only
522 @opindex fdirectives-only
523 When preprocessing, handle directives, but do not expand macros.
525 The option's behavior depends on the @option{-E} and @option{-fpreprocessed}
528 With @option{-E}, preprocessing is limited to the handling of directives
529 such as @code{#define}, @code{#ifdef}, and @code{#error}. Other
530 preprocessor operations, such as macro expansion and trigraph
531 conversion are not performed. In addition, the @option{-dD} option is
534 With @option{-fpreprocessed}, predefinition of command line and most
535 builtin macros is disabled. Macros such as @code{__LINE__}, which are
536 contextually dependent, are handled normally. This enables compilation of
537 files previously preprocessed with @code{-E -fdirectives-only}.
539 With both @option{-E} and @option{-fpreprocessed}, the rules for
540 @option{-fpreprocessed} take precedence. This enables full preprocessing of
541 files previously preprocessed with @code{-E -fdirectives-only}.
543 @item -fdollars-in-identifiers
544 @opindex fdollars-in-identifiers
545 @anchor{fdollars-in-identifiers}
546 Accept @samp{$} in identifiers.
548 @xref{Identifier characters}.
551 @item -fextended-identifiers
552 @opindex fextended-identifiers
553 Accept universal character names in identifiers. This option is
554 experimental; in a future version of GCC, it will be enabled by
555 default for C99 and C++.
558 @opindex fpreprocessed
559 Indicate to the preprocessor that the input file has already been
560 preprocessed. This suppresses things like macro expansion, trigraph
561 conversion, escaped newline splicing, and processing of most directives.
562 The preprocessor still recognizes and removes comments, so that you can
563 pass a file preprocessed with @option{-C} to the compiler without
564 problems. In this mode the integrated preprocessor is little more than
565 a tokenizer for the front ends.
567 @option{-fpreprocessed} is implicit if the input file has one of the
568 extensions @samp{.i}, @samp{.ii} or @samp{.mi}. These are the
569 extensions that GCC uses for preprocessed files created by
570 @option{-save-temps}.
572 @item -ftabstop=@var{width}
574 Set the distance between tab stops. This helps the preprocessor report
575 correct column numbers in warnings or errors, even if tabs appear on the
576 line. If the value is less than 1 or greater than 100, the option is
577 ignored. The default is 8.
579 @item -fexec-charset=@var{charset}
580 @opindex fexec-charset
581 @cindex character set, execution
582 Set the execution character set, used for string and character
583 constants. The default is UTF-8. @var{charset} can be any encoding
584 supported by the system's @code{iconv} library routine.
586 @item -fwide-exec-charset=@var{charset}
587 @opindex fwide-exec-charset
588 @cindex character set, wide execution
589 Set the wide execution character set, used for wide string and
590 character constants. The default is UTF-32 or UTF-16, whichever
591 corresponds to the width of @code{wchar_t}. As with
592 @option{-fexec-charset}, @var{charset} can be any encoding supported
593 by the system's @code{iconv} library routine; however, you will have
594 problems with encodings that do not fit exactly in @code{wchar_t}.
596 @item -finput-charset=@var{charset}
597 @opindex finput-charset
598 @cindex character set, input
599 Set the input character set, used for translation from the character
600 set of the input file to the source character set used by GCC@. If the
601 locale does not specify, or GCC cannot get this information from the
602 locale, the default is UTF-8. This can be overridden by either the locale
603 or this command line option. Currently the command line option takes
604 precedence if there's a conflict. @var{charset} can be any encoding
605 supported by the system's @code{iconv} library routine.
607 @item -fworking-directory
608 @opindex fworking-directory
609 @opindex fno-working-directory
610 Enable generation of linemarkers in the preprocessor output that will
611 let the compiler know the current working directory at the time of
612 preprocessing. When this option is enabled, the preprocessor will
613 emit, after the initial linemarker, a second linemarker with the
614 current working directory followed by two slashes. GCC will use this
615 directory, when it's present in the preprocessed input, as the
616 directory emitted as the current working directory in some debugging
617 information formats. This option is implicitly enabled if debugging
618 information is enabled, but this can be inhibited with the negated
619 form @option{-fno-working-directory}. If the @option{-P} flag is
620 present in the command line, this option has no effect, since no
621 @code{#line} directives are emitted whatsoever.
623 @item -fno-show-column
624 @opindex fno-show-column
625 Do not print column numbers in diagnostics. This may be necessary if
626 diagnostics are being scanned by a program that does not understand the
627 column numbers, such as @command{dejagnu}.
629 @item -A @var{predicate}=@var{answer}
631 Make an assertion with the predicate @var{predicate} and answer
632 @var{answer}. This form is preferred to the older form @option{-A
633 @var{predicate}(@var{answer})}, which is still supported, because
634 it does not use shell special characters.
639 @item -A -@var{predicate}=@var{answer}
640 Cancel an assertion with the predicate @var{predicate} and answer
644 @var{CHARS} is a sequence of one or more of the following characters,
645 and must not be preceded by a space. Other characters are interpreted
646 by the compiler proper, or reserved for future versions of GCC, and so
647 are silently ignored. If you specify characters whose behavior
648 conflicts, the result is undefined.
653 Instead of the normal output, generate a list of @samp{#define}
654 directives for all the macros defined during the execution of the
655 preprocessor, including predefined macros. This gives you a way of
656 finding out what is predefined in your version of the preprocessor.
657 Assuming you have no file @file{foo.h}, the command
660 touch foo.h; cpp -dM foo.h
664 will show all the predefined macros.
666 If you use @option{-dM} without the @option{-E} option, @option{-dM} is
667 interpreted as a synonym for @option{-fdump-rtl-mach}.
668 @xref{Debugging Options, , ,gcc}.
672 Like @samp{M} except in two respects: it does @emph{not} include the
673 predefined macros, and it outputs @emph{both} the @samp{#define}
674 directives and the result of preprocessing. Both kinds of output go to
675 the standard output file.
679 Like @samp{D}, but emit only the macro names, not their expansions.
683 Output @samp{#include} directives in addition to the result of
688 Like @samp{D} except that only macros that are expanded, or whose
689 definedness is tested in preprocessor directives, are output; the
690 output is delayed until the use or test of the macro; and
691 @samp{#undef} directives are also output for macros tested but
692 undefined at the time.
697 Inhibit generation of linemarkers in the output from the preprocessor.
698 This might be useful when running the preprocessor on something that is
699 not C code, and will be sent to a program which might be confused by the
702 @xref{Preprocessor Output}.
707 Do not discard comments. All comments are passed through to the output
708 file, except for comments in processed directives, which are deleted
709 along with the directive.
711 You should be prepared for side effects when using @option{-C}; it
712 causes the preprocessor to treat comments as tokens in their own right.
713 For example, comments appearing at the start of what would be a
714 directive line have the effect of turning that line into an ordinary
715 source line, since the first token on the line is no longer a @samp{#}.
718 Do not discard comments, including during macro expansion. This is
719 like @option{-C}, except that comments contained within macros are
720 also passed through to the output file where the macro is expanded.
722 In addition to the side-effects of the @option{-C} option, the
723 @option{-CC} option causes all C++-style comments inside a macro
724 to be converted to C-style comments. This is to prevent later use
725 of that macro from inadvertently commenting out the remainder of
728 The @option{-CC} option is generally used to support lint comments.
730 @item -traditional-cpp
731 @opindex traditional-cpp
732 Try to imitate the behavior of old-fashioned C preprocessors, as
733 opposed to ISO C preprocessors.
735 @xref{Traditional Mode}.
740 Process trigraph sequences.
742 @xref{Initial processing}.
745 These are three-character sequences, all starting with @samp{??}, that
746 are defined by ISO C to stand for single characters. For example,
747 @samp{??/} stands for @samp{\}, so @samp{'??/n'} is a character
748 constant for a newline. By default, GCC ignores trigraphs, but in
749 standard-conforming modes it converts them. See the @option{-std} and
750 @option{-ansi} options.
752 The nine trigraphs and their replacements are
755 Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??-
756 Replacement: [ ] @{ @} # \ ^ | ~
762 Enable special code to work around file systems which only permit very
763 short file names, such as MS-DOS@.
769 Print text describing all the command line options instead of
770 preprocessing anything.
774 Verbose mode. Print out GNU CPP's version number at the beginning of
775 execution, and report the final form of the include path.
779 Print the name of each header file used, in addition to other normal
780 activities. Each name is indented to show how deep in the
781 @samp{#include} stack it is. Precompiled header files are also
782 printed, even if they are found to be invalid; an invalid precompiled
783 header file is printed with @samp{...x} and a valid one with @samp{...!} .
788 Print out GNU CPP's version number. With one dash, proceed to
789 preprocess as normal. With two dashes, exit immediately.