1 @c Copyright (c) 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008,
2 @c 2010, 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 whenever an identifier which is not a macro is encountered in an
121 @samp{#if} directive, outside of @samp{defined}. Such identifiers are
124 @item -Wunused-macros
125 @opindex Wunused-macros
126 Warn about macros defined in the main file that are unused. A macro
127 is @dfn{used} if it is expanded or tested for existence at least once.
128 The preprocessor will also warn if the macro has not been used at the
129 time it is redefined or undefined.
131 Built-in macros, macros defined on the command line, and macros
132 defined in include files are not warned about.
134 @emph{Note:} If a macro is actually used, but only used in skipped
135 conditional blocks, then CPP will report it as unused. To avoid the
136 warning in such a case, you might improve the scope of the macro's
137 definition by, for example, moving it into the first skipped block.
138 Alternatively, you could provide a dummy use with something like:
141 #if defined the_macro_causing_the_warning
146 @opindex Wendif-labels
147 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
148 This usually happens in code of the form
159 The second and third @code{FOO} should be in comments, but often are not
160 in older programs. This warning is on by default.
164 Make all warnings into hard errors. Source code which triggers warnings
167 @item -Wsystem-headers
168 @opindex Wsystem-headers
169 Issue warnings for code in system headers. These are normally unhelpful
170 in finding bugs in your own code, therefore suppressed. If you are
171 responsible for the system library, you may want to see them.
175 Suppress all warnings, including those which GNU CPP issues by default.
179 Issue all the mandatory diagnostics listed in the C standard. Some of
180 them are left out by default, since they trigger frequently on harmless
183 @item -pedantic-errors
184 @opindex pedantic-errors
185 Issue all the mandatory diagnostics, and make all mandatory diagnostics
186 into errors. This includes mandatory diagnostics that GCC issues
187 without @samp{-pedantic} but treats as warnings.
191 @cindex @command{make}
192 @cindex dependencies, @command{make}
193 Instead of outputting the result of preprocessing, output a rule
194 suitable for @command{make} describing the dependencies of the main
195 source file. The preprocessor outputs one @command{make} rule containing
196 the object file name for that source file, a colon, and the names of all
197 the included files, including those coming from @option{-include} or
198 @option{-imacros} command line options.
200 Unless specified explicitly (with @option{-MT} or @option{-MQ}), the
201 object file name consists of the name of the source file with any
202 suffix replaced with object file suffix and with any leading directory
203 parts removed. If there are many included files then the rule is
204 split into several lines using @samp{\}-newline. The rule has no
207 This option does not suppress the preprocessor's debug output, such as
208 @option{-dM}. To avoid mixing such debug output with the dependency
209 rules you should explicitly specify the dependency output file with
210 @option{-MF}, or use an environment variable like
211 @env{DEPENDENCIES_OUTPUT} (@pxref{Environment Variables}). Debug output
212 will still be sent to the regular output stream as normal.
214 Passing @option{-M} to the driver implies @option{-E}, and suppresses
215 warnings with an implicit @option{-w}.
219 Like @option{-M} but do not mention header files that are found in
220 system header directories, nor header files that are included,
221 directly or indirectly, from such a header.
223 This implies that the choice of angle brackets or double quotes in an
224 @samp{#include} directive does not in itself determine whether that
225 header will appear in @option{-MM} dependency output. This is a
226 slight change in semantics from GCC versions 3.0 and earlier.
231 When used with @option{-M} or @option{-MM}, specifies a
232 file to write the dependencies to. If no @option{-MF} switch is given
233 the preprocessor sends the rules to the same place it would have sent
236 When used with the driver options @option{-MD} or @option{-MMD},
237 @option{-MF} overrides the default dependency output file.
241 In conjunction with an option such as @option{-M} requesting
242 dependency generation, @option{-MG} assumes missing header files are
243 generated files and adds them to the dependency list without raising
244 an error. The dependency filename is taken directly from the
245 @code{#include} directive without prepending any path. @option{-MG}
246 also suppresses preprocessed output, as a missing header file renders
249 This feature is used in automatic updating of makefiles.
253 This option instructs CPP to add a phony target for each dependency
254 other than the main file, causing each to depend on nothing. These
255 dummy rules work around errors @command{make} gives if you remove header
256 files without updating the @file{Makefile} to match.
258 This is typical output:
261 test.o: test.c test.h
266 @item -MT @var{target}
269 Change the target of the rule emitted by dependency generation. By
270 default CPP takes the name of the main input file, deletes any
271 directory components and any file suffix such as @samp{.c}, and
272 appends the platform's usual object suffix. The result is the target.
274 An @option{-MT} option will set the target to be exactly the string you
275 specify. If you want multiple targets, you can specify them as a single
276 argument to @option{-MT}, or use multiple @option{-MT} options.
278 For example, @option{@w{-MT '$(objpfx)foo.o'}} might give
281 $(objpfx)foo.o: foo.c
284 @item -MQ @var{target}
287 Same as @option{-MT}, but it quotes any characters which are special to
288 Make. @option{@w{-MQ '$(objpfx)foo.o'}} gives
291 $$(objpfx)foo.o: foo.c
294 The default target is automatically quoted, as if it were given with
299 @option{-MD} is equivalent to @option{-M -MF @var{file}}, except that
300 @option{-E} is not implied. The driver determines @var{file} based on
301 whether an @option{-o} option is given. If it is, the driver uses its
302 argument but with a suffix of @file{.d}, otherwise it takes the name
303 of the input file, removes any directory components and suffix, and
304 applies a @file{.d} suffix.
306 If @option{-MD} is used in conjunction with @option{-E}, any
307 @option{-o} switch is understood to specify the dependency output file
308 (@pxref{dashMF,,-MF}), but if used without @option{-E}, each @option{-o}
309 is understood to specify a target object file.
311 Since @option{-E} is not implied, @option{-MD} can be used to generate
312 a dependency output file as a side-effect of the compilation process.
316 Like @option{-MD} except mention only user header files, not system
322 When using precompiled headers (@pxref{Precompiled Headers}), this flag
323 will cause the dependency-output flags to also list the files from the
324 precompiled header's dependencies. If not specified only the
325 precompiled header would be listed and not the files that were used to
326 create it because those files are not consulted when a precompiled
329 @item -fpch-preprocess
330 @opindex fpch-preprocess
331 This option allows use of a precompiled header (@pxref{Precompiled
332 Headers}) together with @option{-E}. It inserts a special @code{#pragma},
333 @code{#pragma GCC pch_preprocess "@var{filename}"} in the output to mark
334 the place where the precompiled header was found, and its @var{filename}.
335 When @option{-fpreprocessed} is in use, GCC recognizes this @code{#pragma}
338 This option is off by default, because the resulting preprocessed output
339 is only really suitable as input to GCC@. It is switched on by
340 @option{-save-temps}.
342 You should not write this @code{#pragma} in your own code, but it is
343 safe to edit the filename if the PCH file is available in a different
344 location. The filename may be absolute or it may be relative to GCC's
350 @itemx -x objective-c
351 @itemx -x assembler-with-cpp
353 Specify the source language: C, C++, Objective-C, or assembly. This has
354 nothing to do with standards conformance or extensions; it merely
355 selects which base syntax to expect. If you give none of these options,
356 cpp will deduce the language from the extension of the source file:
357 @samp{.c}, @samp{.cc}, @samp{.m}, or @samp{.S}. Some other common
358 extensions for C++ and assembly are also recognized. If cpp does not
359 recognize the extension, it will treat the file as C; this is the most
362 @emph{Note:} Previous versions of cpp accepted a @option{-lang} option
363 which selected both the language and the standards conformance level.
364 This option has been removed, because it conflicts with the @option{-l}
367 @item -std=@var{standard}
371 Specify the standard to which the code should conform. Currently CPP
372 knows about C and C++ standards; others may be added in the future.
380 The ISO C standard from 1990. @samp{c90} is the customary shorthand for
381 this version of the standard.
383 The @option{-ansi} option is equivalent to @option{-std=c90}.
386 The 1990 C standard, as amended in 1994.
392 The revised ISO C standard, published in December 1999. Before
393 publication, this was known as C9X@.
398 The revised ISO C standard, published in December 2011. Before
399 publication, this was known as C1X@.
403 The 1990 C standard plus GNU extensions. This is the default.
407 The 1999 C standard plus GNU extensions.
411 The 2011 C standard plus GNU extensions.
414 The 1998 ISO C++ standard plus amendments.
417 The same as @option{-std=c++98} plus GNU extensions. This is the
418 default for C++ code.
423 Split the include path. Any directories specified with @option{-I}
424 options before @option{-I-} are searched only for headers requested with
425 @code{@w{#include "@var{file}"}}; they are not searched for
426 @code{@w{#include <@var{file}>}}. If additional directories are
427 specified with @option{-I} options after the @option{-I-}, those
428 directories are searched for all @samp{#include} directives.
430 In addition, @option{-I-} inhibits the use of the directory of the current
431 file directory as the first search directory for @code{@w{#include
436 This option has been deprecated.
440 Do not search the standard system directories for header files.
441 Only the directories you have specified with @option{-I} options
442 (and the directory of the current file, if appropriate) are searched.
446 Do not search for header files in the C++-specific standard directories,
447 but do still search the other standard directories. (This option is
448 used when building the C++ library.)
450 @item -include @var{file}
452 Process @var{file} as if @code{#include "file"} appeared as the first
453 line of the primary source file. However, the first directory searched
454 for @var{file} is the preprocessor's working directory @emph{instead of}
455 the directory containing the main source file. If not found there, it
456 is searched for in the remainder of the @code{#include "@dots{}"} search
459 If multiple @option{-include} options are given, the files are included
460 in the order they appear on the command line.
462 @item -imacros @var{file}
464 Exactly like @option{-include}, except that any output produced by
465 scanning @var{file} is thrown away. Macros it defines remain defined.
466 This allows you to acquire all the macros from a header without also
467 processing its declarations.
469 All files specified by @option{-imacros} are processed before all files
470 specified by @option{-include}.
472 @item -idirafter @var{dir}
474 Search @var{dir} for header files, but do it @emph{after} all
475 directories specified with @option{-I} and the standard system directories
476 have been exhausted. @var{dir} is treated as a system include directory.
477 If @var{dir} begins with @code{=}, then the @code{=} will be replaced
478 by the sysroot prefix; see @option{--sysroot} and @option{-isysroot}.
480 @item -iprefix @var{prefix}
482 Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix}
483 options. If the prefix represents a directory, you should include the
486 @item -iwithprefix @var{dir}
487 @itemx -iwithprefixbefore @var{dir}
489 @opindex iwithprefixbefore
490 Append @var{dir} to the prefix specified previously with
491 @option{-iprefix}, and add the resulting directory to the include search
492 path. @option{-iwithprefixbefore} puts it in the same place @option{-I}
493 would; @option{-iwithprefix} puts it where @option{-idirafter} would.
495 @item -isysroot @var{dir}
497 This option is like the @option{--sysroot} option, but applies only to
498 header files (except for Darwin targets, where it applies to both header
499 files and libraries). See the @option{--sysroot} option for more
502 @item -imultilib @var{dir}
504 Use @var{dir} as a subdirectory of the directory containing
505 target-specific C++ headers.
507 @item -isystem @var{dir}
509 Search @var{dir} for header files, after all directories specified by
510 @option{-I} but before the standard system directories. Mark it
511 as a system directory, so that it gets the same special treatment as
512 is applied to the standard system directories.
514 @xref{System Headers}.
516 If @var{dir} begins with @code{=}, then the @code{=} will be replaced
517 by the sysroot prefix; see @option{--sysroot} and @option{-isysroot}.
519 @item -iquote @var{dir}
521 Search @var{dir} only for header files requested with
522 @code{@w{#include "@var{file}"}}; they are not searched for
523 @code{@w{#include <@var{file}>}}, before all directories specified by
524 @option{-I} and before the standard system directories.
528 If @var{dir} begins with @code{=}, then the @code{=} will be replaced
529 by the sysroot prefix; see @option{--sysroot} and @option{-isysroot}.
531 @item -fdirectives-only
532 @opindex fdirectives-only
533 When preprocessing, handle directives, but do not expand macros.
535 The option's behavior depends on the @option{-E} and @option{-fpreprocessed}
538 With @option{-E}, preprocessing is limited to the handling of directives
539 such as @code{#define}, @code{#ifdef}, and @code{#error}. Other
540 preprocessor operations, such as macro expansion and trigraph
541 conversion are not performed. In addition, the @option{-dD} option is
544 With @option{-fpreprocessed}, predefinition of command line and most
545 builtin macros is disabled. Macros such as @code{__LINE__}, which are
546 contextually dependent, are handled normally. This enables compilation of
547 files previously preprocessed with @code{-E -fdirectives-only}.
549 With both @option{-E} and @option{-fpreprocessed}, the rules for
550 @option{-fpreprocessed} take precedence. This enables full preprocessing of
551 files previously preprocessed with @code{-E -fdirectives-only}.
553 @item -fdollars-in-identifiers
554 @opindex fdollars-in-identifiers
555 @anchor{fdollars-in-identifiers}
556 Accept @samp{$} in identifiers.
558 @xref{Identifier characters}.
561 @item -fextended-identifiers
562 @opindex fextended-identifiers
563 Accept universal character names in identifiers. This option is
564 experimental; in a future version of GCC, it will be enabled by
565 default for C99 and C++.
568 @opindex fpreprocessed
569 Indicate to the preprocessor that the input file has already been
570 preprocessed. This suppresses things like macro expansion, trigraph
571 conversion, escaped newline splicing, and processing of most directives.
572 The preprocessor still recognizes and removes comments, so that you can
573 pass a file preprocessed with @option{-C} to the compiler without
574 problems. In this mode the integrated preprocessor is little more than
575 a tokenizer for the front ends.
577 @option{-fpreprocessed} is implicit if the input file has one of the
578 extensions @samp{.i}, @samp{.ii} or @samp{.mi}. These are the
579 extensions that GCC uses for preprocessed files created by
580 @option{-save-temps}.
582 @item -ftabstop=@var{width}
584 Set the distance between tab stops. This helps the preprocessor report
585 correct column numbers in warnings or errors, even if tabs appear on the
586 line. If the value is less than 1 or greater than 100, the option is
587 ignored. The default is 8.
591 This option is only useful for debugging GCC. When used with
592 @option{-E}, dumps debugging information about location maps. Every
593 token in the output is preceded by the dump of the map its location
594 belongs to. The dump of the map holding the location of a token would
597 @{@samp{P}:@file{/file/path};@samp{F}:@file{/includer/path};@samp{L}:@var{line_num};@samp{C}:@var{col_num};@samp{S}:@var{system_header_p};@samp{M}:@var{map_address};@samp{E}:@var{macro_expansion_p},@samp{loc}:@var{location}@}
600 When used without @option{-E}, this option has no effect.
602 @item -ftrack-macro-expansion@r{[}=@var{level}@r{]}
603 @opindex ftrack-macro-expansion
604 Track locations of tokens across macro expansions. This allows the
605 compiler to emit diagnostic about the current macro expansion stack
606 when a compilation error occurs in a macro expansion. Using this
607 option makes the preprocessor and the compiler consume more
608 memory. The @var{level} parameter can be used to choose the level of
609 precision of token location tracking thus decreasing the memory
610 consumption if necessary. Value @samp{0} of @var{level} de-activates
611 this option just as if no @option{-ftrack-macro-expansion} was present
612 on the command line. Value @samp{1} tracks tokens locations in a
613 degraded mode for the sake of minimal memory overhead. In this mode
614 all tokens resulting from the expansion of an argument of a
615 function-like macro have the same location. Value @samp{2} tracks
616 tokens locations completely. This value is the most memory hungry.
617 When this option is given no argument, the default parameter value is
620 @item -fexec-charset=@var{charset}
621 @opindex fexec-charset
622 @cindex character set, execution
623 Set the execution character set, used for string and character
624 constants. The default is UTF-8. @var{charset} can be any encoding
625 supported by the system's @code{iconv} library routine.
627 @item -fwide-exec-charset=@var{charset}
628 @opindex fwide-exec-charset
629 @cindex character set, wide execution
630 Set the wide execution character set, used for wide string and
631 character constants. The default is UTF-32 or UTF-16, whichever
632 corresponds to the width of @code{wchar_t}. As with
633 @option{-fexec-charset}, @var{charset} can be any encoding supported
634 by the system's @code{iconv} library routine; however, you will have
635 problems with encodings that do not fit exactly in @code{wchar_t}.
637 @item -finput-charset=@var{charset}
638 @opindex finput-charset
639 @cindex character set, input
640 Set the input character set, used for translation from the character
641 set of the input file to the source character set used by GCC@. If the
642 locale does not specify, or GCC cannot get this information from the
643 locale, the default is UTF-8. This can be overridden by either the locale
644 or this command line option. Currently the command line option takes
645 precedence if there's a conflict. @var{charset} can be any encoding
646 supported by the system's @code{iconv} library routine.
648 @item -fworking-directory
649 @opindex fworking-directory
650 @opindex fno-working-directory
651 Enable generation of linemarkers in the preprocessor output that will
652 let the compiler know the current working directory at the time of
653 preprocessing. When this option is enabled, the preprocessor will
654 emit, after the initial linemarker, a second linemarker with the
655 current working directory followed by two slashes. GCC will use this
656 directory, when it's present in the preprocessed input, as the
657 directory emitted as the current working directory in some debugging
658 information formats. This option is implicitly enabled if debugging
659 information is enabled, but this can be inhibited with the negated
660 form @option{-fno-working-directory}. If the @option{-P} flag is
661 present in the command line, this option has no effect, since no
662 @code{#line} directives are emitted whatsoever.
664 @item -fno-show-column
665 @opindex fno-show-column
666 Do not print column numbers in diagnostics. This may be necessary if
667 diagnostics are being scanned by a program that does not understand the
668 column numbers, such as @command{dejagnu}.
670 @item -A @var{predicate}=@var{answer}
672 Make an assertion with the predicate @var{predicate} and answer
673 @var{answer}. This form is preferred to the older form @option{-A
674 @var{predicate}(@var{answer})}, which is still supported, because
675 it does not use shell special characters.
677 @xref{Obsolete Features}.
680 @item -A -@var{predicate}=@var{answer}
681 Cancel an assertion with the predicate @var{predicate} and answer
685 @var{CHARS} is a sequence of one or more of the following characters,
686 and must not be preceded by a space. Other characters are interpreted
687 by the compiler proper, or reserved for future versions of GCC, and so
688 are silently ignored. If you specify characters whose behavior
689 conflicts, the result is undefined.
694 Instead of the normal output, generate a list of @samp{#define}
695 directives for all the macros defined during the execution of the
696 preprocessor, including predefined macros. This gives you a way of
697 finding out what is predefined in your version of the preprocessor.
698 Assuming you have no file @file{foo.h}, the command
701 touch foo.h; cpp -dM foo.h
705 will show all the predefined macros.
707 If you use @option{-dM} without the @option{-E} option, @option{-dM} is
708 interpreted as a synonym for @option{-fdump-rtl-mach}.
709 @xref{Debugging Options, , ,gcc}.
713 Like @samp{M} except in two respects: it does @emph{not} include the
714 predefined macros, and it outputs @emph{both} the @samp{#define}
715 directives and the result of preprocessing. Both kinds of output go to
716 the standard output file.
720 Like @samp{D}, but emit only the macro names, not their expansions.
724 Output @samp{#include} directives in addition to the result of
729 Like @samp{D} except that only macros that are expanded, or whose
730 definedness is tested in preprocessor directives, are output; the
731 output is delayed until the use or test of the macro; and
732 @samp{#undef} directives are also output for macros tested but
733 undefined at the time.
738 Inhibit generation of linemarkers in the output from the preprocessor.
739 This might be useful when running the preprocessor on something that is
740 not C code, and will be sent to a program which might be confused by the
743 @xref{Preprocessor Output}.
748 Do not discard comments. All comments are passed through to the output
749 file, except for comments in processed directives, which are deleted
750 along with the directive.
752 You should be prepared for side effects when using @option{-C}; it
753 causes the preprocessor to treat comments as tokens in their own right.
754 For example, comments appearing at the start of what would be a
755 directive line have the effect of turning that line into an ordinary
756 source line, since the first token on the line is no longer a @samp{#}.
759 Do not discard comments, including during macro expansion. This is
760 like @option{-C}, except that comments contained within macros are
761 also passed through to the output file where the macro is expanded.
763 In addition to the side-effects of the @option{-C} option, the
764 @option{-CC} option causes all C++-style comments inside a macro
765 to be converted to C-style comments. This is to prevent later use
766 of that macro from inadvertently commenting out the remainder of
769 The @option{-CC} option is generally used to support lint comments.
771 @item -traditional-cpp
772 @opindex traditional-cpp
773 Try to imitate the behavior of old-fashioned C preprocessors, as
774 opposed to ISO C preprocessors.
776 @xref{Traditional Mode}.
781 Process trigraph sequences.
783 @xref{Initial processing}.
786 These are three-character sequences, all starting with @samp{??}, that
787 are defined by ISO C to stand for single characters. For example,
788 @samp{??/} stands for @samp{\}, so @samp{'??/n'} is a character
789 constant for a newline. By default, GCC ignores trigraphs, but in
790 standard-conforming modes it converts them. See the @option{-std} and
791 @option{-ansi} options.
793 The nine trigraphs and their replacements are
796 Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??-
797 Replacement: [ ] @{ @} # \ ^ | ~
803 Enable special code to work around file systems which only permit very
804 short file names, such as MS-DOS@.
810 Print text describing all the command line options instead of
811 preprocessing anything.
815 Verbose mode. Print out GNU CPP's version number at the beginning of
816 execution, and report the final form of the include path.
820 Print the name of each header file used, in addition to other normal
821 activities. Each name is indented to show how deep in the
822 @samp{#include} stack it is. Precompiled header files are also
823 printed, even if they are found to be invalid; an invalid precompiled
824 header file is printed with @samp{...x} and a valid one with @samp{...!} .
829 Print out GNU CPP's version number. With one dash, proceed to
830 preprocess as normal. With two dashes, exit immediately.