1 @c Copyright (c) 1999, 2000, 2001, 2002, 2003, 2004
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 Predefine @var{name} as a macro, with definition @var{definition}.
20 The contents of @var{definition} are tokenized and processed as if
21 they appeared during translation phase three in a @samp{#define}
22 directive. In particular, the definition will be truncated by
23 embedded newline characters.
25 If you are invoking the preprocessor from a shell or shell-like
26 program you may need to use the shell's quoting syntax to protect
27 characters such as spaces that have a meaning in the shell syntax.
29 If you wish to define a function-like macro on the command line, write
30 its argument list with surrounding parentheses before the equals sign
31 (if any). Parentheses are meaningful to most shells, so you will need
32 to quote the option. With @command{sh} and @command{csh},
33 @option{-D'@var{name}(@var{args@dots{}})=@var{definition}'} works.
35 @option{-D} and @option{-U} options are processed in the order they
36 are given on the command line. All @option{-imacros @var{file}} and
37 @option{-include @var{file}} options are processed after all
38 @option{-D} and @option{-U} options.
42 Cancel any previous definition of @var{name}, either built in or
43 provided with a @option{-D} option.
47 Do not predefine any system-specific or GCC-specific macros. The
48 standard predefined macros remain defined.
50 @xref{Standard Predefined Macros}.
55 Add the directory @var{dir} to the list of directories to be searched
60 Directories named by @option{-I} are searched before the standard
61 system include directories. If the directory @var{dir} is a standard
62 system include directory, the option is ignored to ensure that the
63 default search order for system directories and the special treatment
64 of system headers are not defeated
66 (@pxref{System Headers})
72 Write output to @var{file}. This is the same as specifying @var{file}
73 as the second non-option argument to @command{cpp}. @command{gcc} has a
74 different interpretation of a second non-option argument, so you must
75 use @option{-o} to specify the output file.
79 Turns on all optional warnings which are desirable for normal code.
80 At present this is @option{-Wcomment}, @option{-Wtrigraphs},
81 @option{-Wmultichar} and a warning about integer promotion causing a
82 change of sign in @code{#if} expressions. Note that many of the
83 preprocessor's warnings are on by default and have no options to
90 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
91 comment, or whenever a backslash-newline appears in a @samp{//} comment.
92 (Both forms have the same effect.)
97 Most trigraphs in comments cannot affect the meaning of the program.
98 However, a trigraph that would form an escaped newline (@samp{??/} at
99 the end of a line) can, by changing where the comment begins or ends.
100 Therefore, only trigraphs that would form escaped newlines produce
101 warnings inside a comment.
103 This option is implied by @option{-Wall}. If @option{-Wall} is not
104 given, this option is still enabled unless trigraphs are enabled. To
105 get trigraph conversion without warnings, but get the other
106 @option{-Wall} warnings, use @samp{-trigraphs -Wall -Wno-trigraphs}.
109 @opindex Wtraditional
110 Warn about certain constructs that behave differently in traditional and
111 ISO C@. Also warn about ISO C constructs that have no traditional C
112 equivalent, and problematic constructs which should be avoided.
114 @xref{Traditional Mode}.
119 Warn the first time @samp{#import} is used.
123 Warn whenever an identifier which is not a macro is encountered in an
124 @samp{#if} directive, outside of @samp{defined}. Such identifiers are
127 @item -Wunused-macros
128 @opindex Wunused-macros
129 Warn about macros defined in the main file that are unused. A macro
130 is @dfn{used} if it is expanded or tested for existence at least once.
131 The preprocessor will also warn if the macro has not been used at the
132 time it is redefined or undefined.
134 Built-in macros, macros defined on the command line, and macros
135 defined in include files are not warned about.
137 @strong{Note:} If a macro is actually used, but only used in skipped
138 conditional blocks, then CPP will report it as unused. To avoid the
139 warning in such a case, you might improve the scope of the macro's
140 definition by, for example, moving it into the first skipped block.
141 Alternatively, you could provide a dummy use with something like:
144 #if defined the_macro_causing_the_warning
149 @opindex Wendif-labels
150 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
151 This usually happens in code of the form
162 The second and third @code{FOO} should be in comments, but often are not
163 in older programs. This warning is on by default.
167 Make all warnings into hard errors. Source code which triggers warnings
170 @item -Wsystem-headers
171 @opindex Wsystem-headers
172 Issue warnings for code in system headers. These are normally unhelpful
173 in finding bugs in your own code, therefore suppressed. If you are
174 responsible for the system library, you may want to see them.
178 Suppress all warnings, including those which GNU CPP issues by default.
182 Issue all the mandatory diagnostics listed in the C standard. Some of
183 them are left out by default, since they trigger frequently on harmless
186 @item -pedantic-errors
187 @opindex pedantic-errors
188 Issue all the mandatory diagnostics, and make all mandatory diagnostics
189 into errors. This includes mandatory diagnostics that GCC issues
190 without @samp{-pedantic} but treats as warnings.
195 @cindex dependencies, make
196 Instead of outputting the result of preprocessing, output a rule
197 suitable for @command{make} describing the dependencies of the main
198 source file. The preprocessor outputs one @command{make} rule containing
199 the object file name for that source file, a colon, and the names of all
200 the included files, including those coming from @option{-include} or
201 @option{-imacros} command line options.
203 Unless specified explicitly (with @option{-MT} or @option{-MQ}), the
204 object file name consists of the basename of the source file with any
205 suffix replaced with object file suffix. If there are many included
206 files then the rule is split into several lines using @samp{\}-newline.
207 The rule has no commands.
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, including any path,
273 deletes any file suffix such as @samp{.c}, and appends the platform's
274 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 take the
305 basename of the input file and applies a @file{.d} suffix.
307 If @option{-MD} is used in conjunction with @option{-E}, any
308 @option{-o} switch is understood to specify the dependency output file
309 (but @pxref{dashMF,,-MF}), but if used without @option{-E}, each @option{-o}
310 is understood to specify a target object file.
312 Since @option{-E} is not implied, @option{-MD} can be used to generate
313 a dependency output file as a side-effect of the compilation process.
317 Like @option{-MD} except mention only user header files, not system
323 When using precompiled headers (@pxref{Precompiled Headers}), this flag
324 will cause the dependency-output flags to also list the files from the
325 precompiled header's dependencies. If not specified only the
326 precompiled header would be listed and not the files that were used to
327 create it because those files are not consulted when a precompiled
333 @itemx -x objective-c
334 @itemx -x assembler-with-cpp
336 Specify the source language: C, C++, Objective-C, or assembly. This has
337 nothing to do with standards conformance or extensions; it merely
338 selects which base syntax to expect. If you give none of these options,
339 cpp will deduce the language from the extension of the source file:
340 @samp{.c}, @samp{.cc}, @samp{.m}, or @samp{.S}. Some other common
341 extensions for C++ and assembly are also recognized. If cpp does not
342 recognize the extension, it will treat the file as C; this is the most
345 @strong{Note:} Previous versions of cpp accepted a @option{-lang} option
346 which selected both the language and the standards conformance level.
347 This option has been removed, because it conflicts with the @option{-l}
350 @item -std=@var{standard}
354 Specify the standard to which the code should conform. Currently CPP
355 knows about C and C++ standards; others may be added in the future.
362 The ISO C standard from 1990. @samp{c89} is the customary shorthand for
363 this version of the standard.
365 The @option{-ansi} option is equivalent to @option{-std=c89}.
368 The 1990 C standard, as amended in 1994.
374 The revised ISO C standard, published in December 1999. Before
375 publication, this was known as C9X@.
378 The 1990 C standard plus GNU extensions. This is the default.
382 The 1999 C standard plus GNU extensions.
385 The 1998 ISO C++ standard plus amendments.
388 The same as @option{-std=c++98} plus GNU extensions. This is the
389 default for C++ code.
394 Split the include path. Any directories specified with @option{-I}
395 options before @option{-I-} are searched only for headers requested with
396 @code{@w{#include "@var{file}"}}; they are not searched for
397 @code{@w{#include <@var{file}>}}. If additional directories are
398 specified with @option{-I} options after the @option{-I-}, those
399 directories are searched for all @samp{#include} directives.
401 In addition, @option{-I-} inhibits the use of the directory of the current
402 file directory as the first search directory for @code{@w{#include
410 Do not search the standard system directories for header files.
411 Only the directories you have specified with @option{-I} options
412 (and the directory of the current file, if appropriate) are searched.
416 Do not search for header files in the C++-specific standard directories,
417 but do still search the other standard directories. (This option is
418 used when building the C++ library.)
420 @item -include @var{file}
422 Process @var{file} as if @code{#include "file"} appeared as the first
423 line of the primary source file. However, the first directory searched
424 for @var{file} is the preprocessor's working directory @emph{instead of}
425 the directory containing the main source file. If not found there, it
426 is searched for in the remainder of the @code{#include "@dots{}"} search
429 If multiple @option{-include} options are given, the files are included
430 in the order they appear on the command line.
432 @item -imacros @var{file}
434 Exactly like @option{-include}, except that any output produced by
435 scanning @var{file} is thrown away. Macros it defines remain defined.
436 This allows you to acquire all the macros from a header without also
437 processing its declarations.
439 All files specified by @option{-imacros} are processed before all files
440 specified by @option{-include}.
442 @item -idirafter @var{dir}
444 Search @var{dir} for header files, but do it @emph{after} all
445 directories specified with @option{-I} and the standard system directories
446 have been exhausted. @var{dir} is treated as a system include directory.
448 @item -iprefix @var{prefix}
450 Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix}
451 options. If the prefix represents a directory, you should include the
454 @item -iwithprefix @var{dir}
455 @itemx -iwithprefixbefore @var{dir}
457 @opindex iwithprefixbefore
458 Append @var{dir} to the prefix specified previously with
459 @option{-iprefix}, and add the resulting directory to the include search
460 path. @option{-iwithprefixbefore} puts it in the same place @option{-I}
461 would; @option{-iwithprefix} puts it where @option{-idirafter} would.
463 @item -isystem @var{dir}
465 Search @var{dir} for header files, after all directories specified by
466 @option{-I} but before the standard system directories. Mark it
467 as a system directory, so that it gets the same special treatment as
468 is applied to the standard system directories.
470 @xref{System Headers}.
473 @item -fdollars-in-identifiers
474 @opindex fdollars-in-identifiers
475 @anchor{fdollars-in-identifiers}
476 Accept @samp{$} in identifiers.
478 @xref{Identifier characters}.
482 @opindex fpreprocessed
483 Indicate to the preprocessor that the input file has already been
484 preprocessed. This suppresses things like macro expansion, trigraph
485 conversion, escaped newline splicing, and processing of most directives.
486 The preprocessor still recognizes and removes comments, so that you can
487 pass a file preprocessed with @option{-C} to the compiler without
488 problems. In this mode the integrated preprocessor is little more than
489 a tokenizer for the front ends.
491 @option{-fpreprocessed} is implicit if the input file has one of the
492 extensions @samp{.i}, @samp{.ii} or @samp{.mi}. These are the
493 extensions that GCC uses for preprocessed files created by
494 @option{-save-temps}.
496 @item -ftabstop=@var{width}
498 Set the distance between tab stops. This helps the preprocessor report
499 correct column numbers in warnings or errors, even if tabs appear on the
500 line. If the value is less than 1 or greater than 100, the option is
501 ignored. The default is 8.
503 @item -fexec-charset=@var{charset}
504 @opindex fexec-charset
505 Set the execution character set, used for string and character
506 constants. The default is UTF-8. @var{charset} can be any encoding
507 supported by the system's @code{iconv} library routine.
509 @item -fwide-exec-charset=@var{charset}
510 @opindex fwide-exec-charset
511 Set the wide execution character set, used for wide string and
512 character constants. The default is UTF-32 or UTF-16, whichever
513 corresponds to the width of @code{wchar_t}. As with
514 @option{-ftarget-charset}, @var{charset} can be any encoding supported
515 by the system's @code{iconv} library routine; however, you will have
516 problems with encodings that do not fit exactly in @code{wchar_t}.
518 @item -finput-charset=@var{charset}
519 @opindex finput-charset
520 Set the input character set, used for translation from the character
521 set of the input file to the source character set used by GCC. If the
522 locale does not specify, or GCC cannot get this information from the
523 locale, the default is UTF-8. This can be overridden by either the locale
524 or this command line option. Currently the command line option takes
525 precedence if there's a conflict. @var{charset} can be any encoding
526 supported by the system's @code{iconv} library routine.
528 @item -fworking-directory
529 @opindex fworking-directory
530 @opindex fno-working-directory
531 Enable generation of linemarkers in the preprocessor output that will
532 let the compiler know the current working directory at the time of
533 preprocessing. When this option is enabled, the preprocessor will
534 emit, after the initial linemarker, a second linemarker with the
535 current working directory followed by two slashes. GCC will use this
536 directory, when it's present in the preprocessed input, as the
537 directory emitted as the current working directory in some debugging
538 information formats. This option is implicitly enabled if debugging
539 information is enabled, but this can be inhibited with the negated
540 form @option{-fno-working-directory}. If the @option{-P} flag is
541 present in the command line, this option has no effect, since no
542 @code{#line} directives are emitted whatsoever.
544 @item -fno-show-column
545 @opindex fno-show-column
546 Do not print column numbers in diagnostics. This may be necessary if
547 diagnostics are being scanned by a program that does not understand the
548 column numbers, such as @command{dejagnu}.
550 @item -A @var{predicate}=@var{answer}
552 Make an assertion with the predicate @var{predicate} and answer
553 @var{answer}. This form is preferred to the older form @option{-A
554 @var{predicate}(@var{answer})}, which is still supported, because
555 it does not use shell special characters.
560 @item -A -@var{predicate}=@var{answer}
561 Cancel an assertion with the predicate @var{predicate} and answer
565 @var{CHARS} is a sequence of one or more of the following characters,
566 and must not be preceded by a space. Other characters are interpreted
567 by the compiler proper, or reserved for future versions of GCC, and so
568 are silently ignored. If you specify characters whose behavior
569 conflicts, the result is undefined.
574 Instead of the normal output, generate a list of @samp{#define}
575 directives for all the macros defined during the execution of the
576 preprocessor, including predefined macros. This gives you a way of
577 finding out what is predefined in your version of the preprocessor.
578 Assuming you have no file @file{foo.h}, the command
581 touch foo.h; cpp -dM foo.h
585 will show all the predefined macros.
589 Like @samp{M} except in two respects: it does @emph{not} include the
590 predefined macros, and it outputs @emph{both} the @samp{#define}
591 directives and the result of preprocessing. Both kinds of output go to
592 the standard output file.
596 Like @samp{D}, but emit only the macro names, not their expansions.
600 Output @samp{#include} directives in addition to the result of
606 Inhibit generation of linemarkers in the output from the preprocessor.
607 This might be useful when running the preprocessor on something that is
608 not C code, and will be sent to a program which might be confused by the
611 @xref{Preprocessor Output}.
616 Do not discard comments. All comments are passed through to the output
617 file, except for comments in processed directives, which are deleted
618 along with the directive.
620 You should be prepared for side effects when using @option{-C}; it
621 causes the preprocessor to treat comments as tokens in their own right.
622 For example, comments appearing at the start of what would be a
623 directive line have the effect of turning that line into an ordinary
624 source line, since the first token on the line is no longer a @samp{#}.
627 Do not discard comments, including during macro expansion. This is
628 like @option{-C}, except that comments contained within macros are
629 also passed through to the output file where the macro is expanded.
631 In addition to the side-effects of the @option{-C} option, the
632 @option{-CC} option causes all C++-style comments inside a macro
633 to be converted to C-style comments. This is to prevent later use
634 of that macro from inadvertently commenting out the remainder of
637 The @option{-CC} option is generally used to support lint comments.
639 @item -traditional-cpp
640 @opindex traditional-cpp
641 Try to imitate the behavior of old-fashioned C preprocessors, as
642 opposed to ISO C preprocessors.
644 @xref{Traditional Mode}.
649 Process trigraph sequences.
651 @xref{Initial processing}.
654 These are three-character sequences, all starting with @samp{??}, that
655 are defined by ISO C to stand for single characters. For example,
656 @samp{??/} stands for @samp{\}, so @samp{'??/n'} is a character
657 constant for a newline. By default, GCC ignores trigraphs, but in
658 standard-conforming modes it converts them. See the @option{-std} and
659 @option{-ansi} options.
661 The nine trigraphs and their replacements are
664 Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??-
665 Replacement: [ ] @{ @} # \ ^ | ~
671 Enable special code to work around file systems which only permit very
672 short file names, such as MS-DOS@.
678 Print text describing all the command line options instead of
679 preprocessing anything.
683 Verbose mode. Print out GNU CPP's version number at the beginning of
684 execution, and report the final form of the include path.
688 Print the name of each header file used, in addition to other normal
689 activities. Each name is indented to show how deep in the
690 @samp{#include} stack it is. Precompiled header files are also
691 printed, even if they are found to be invalid; an invalid precompiled
692 header file is printed with @samp{...x} and a valid one with @samp{...!} .
697 Print out GNU CPP's version number. With one dash, proceed to
698 preprocess as normal. With two dashes, exit immediately.