1 @c Copyright (C) 1999-2024 Free Software Foundation, Inc.
2 @c This is part of the CPP and GCC manuals.
3 @c For copying conditions, see the file gcc.texi.
5 @c ---------------------------------------------------------------------
6 @c Options affecting the preprocessor
7 @c ---------------------------------------------------------------------
9 @c If this file is included with the flag ``cppmanual'' set, it is
10 @c formatted for inclusion in the CPP manual; otherwise the main GCC manual.
14 Predefine @var{name} as a macro, with definition @code{1}.
16 @item -D @var{name}=@var{definition}
17 The contents of @var{definition} are tokenized and processed as if
18 they appeared during translation phase three in a @samp{#define}
19 directive. In particular, the definition is truncated by
20 embedded newline characters.
22 If you are invoking the preprocessor from a shell or shell-like
23 program you may need to use the shell's quoting syntax to protect
24 characters such as spaces that have a meaning in the shell syntax.
26 If you wish to define a function-like macro on the command line, write
27 its argument list with surrounding parentheses before the equals sign
28 (if any). Parentheses are meaningful to most shells, so you should
29 quote the option. With @command{sh} and @command{csh},
30 @option{-D'@var{name}(@var{args@dots{}})=@var{definition}'} works.
32 @option{-D} and @option{-U} options are processed in the order they
33 are given on the command line. All @option{-imacros @var{file}} and
34 @option{-include @var{file}} options are processed after all
35 @option{-D} and @option{-U} options.
39 Cancel any previous definition of @var{name}, either built in or
40 provided with a @option{-D} option.
43 @item -include @var{file}
44 Process @var{file} as if @code{#include "file"} appeared as the first
45 line of the primary source file. However, the first directory searched
46 for @var{file} is the preprocessor's working directory @emph{instead of}
47 the directory containing the main source file. If not found there, it
48 is searched for in the remainder of the @code{#include "@dots{}"} search
51 If multiple @option{-include} options are given, the files are included
52 in the order they appear on the command line.
55 @item -imacros @var{file}
56 Exactly like @option{-include}, except that any output produced by
57 scanning @var{file} is thrown away. Macros it defines remain defined.
58 This allows you to acquire all the macros from a header without also
59 processing its declarations.
61 All files specified by @option{-imacros} are processed before all files
62 specified by @option{-include}.
66 Do not predefine any system-specific or GCC-specific macros. The
67 standard predefined macros remain defined.
69 @xref{Standard Predefined Macros}.
74 Define additional macros required for using the POSIX threads library.
75 You should use this option consistently for both compilation and linking.
76 This option is supported on GNU/Linux targets, most other Unix derivatives,
77 and also on x86 Cygwin and MinGW targets.
80 @cindex @command{make}
81 @cindex dependencies, @command{make}
83 Instead of outputting the result of preprocessing, output a rule
84 suitable for @command{make} describing the dependencies of the main
85 source file. The preprocessor outputs one @command{make} rule containing
86 the object file name for that source file, a colon, and the names of all
87 the included files, including those coming from @option{-include} or
88 @option{-imacros} command-line options.
90 Unless specified explicitly (with @option{-MT} or @option{-MQ}), the
91 object file name consists of the name of the source file with any
92 suffix replaced with object file suffix and with any leading directory
93 parts removed. If there are many included files then the rule is
94 split into several lines using @samp{\}-newline. The rule has no
97 This option does not suppress the preprocessor's debug output, such as
98 @option{-dM}. To avoid mixing such debug output with the dependency
99 rules you should explicitly specify the dependency output file with
100 @option{-MF}, or use an environment variable like
101 @env{DEPENDENCIES_OUTPUT} (@pxref{Environment Variables}). Debug output
102 is still sent to the regular output stream as normal.
104 Passing @option{-M} to the driver implies @option{-E}, and suppresses
105 warnings with an implicit @option{-w}.
109 Like @option{-M} but do not mention header files that are found in
110 system header directories, nor header files that are included,
111 directly or indirectly, from such a header.
113 This implies that the choice of angle brackets or double quotes in an
114 @samp{#include} directive does not in itself determine whether that
115 header appears in @option{-MM} dependency output.
120 When used with @option{-M} or @option{-MM}, specifies a
121 file to write the dependencies to. If no @option{-MF} switch is given
122 the preprocessor sends the rules to the same place it would send
125 When used with the driver options @option{-MD} or @option{-MMD},
126 @option{-MF} overrides the default dependency output file.
128 If @var{file} is @file{-}, then the dependencies are written to @file{stdout}.
132 In conjunction with an option such as @option{-M} requesting
133 dependency generation, @option{-MG} assumes missing header files are
134 generated files and adds them to the dependency list without raising
135 an error. The dependency filename is taken directly from the
136 @code{#include} directive without prepending any path. @option{-MG}
137 also suppresses preprocessed output, as a missing header file renders
140 This feature is used in automatic updating of makefiles.
144 Disable dependency generation for compiled module interfaces.
148 This option instructs CPP to add a phony target for each dependency
149 other than the main file, causing each to depend on nothing. These
150 dummy rules work around errors @command{make} gives if you remove header
151 files without updating the @file{Makefile} to match.
153 This is typical output:
156 test.o: test.c test.h
162 @item -MT @var{target}
164 Change the target of the rule emitted by dependency generation. By
165 default CPP takes the name of the main input file, deletes any
166 directory components and any file suffix such as @samp{.c}, and
167 appends the platform's usual object suffix. The result is the target.
169 An @option{-MT} option sets the target to be exactly the string you
170 specify. If you want multiple targets, you can specify them as a single
171 argument to @option{-MT}, or use multiple @option{-MT} options.
173 For example, @option{@w{-MT '$(objpfx)foo.o'}} might give
176 $(objpfx)foo.o: foo.c
180 @item -MQ @var{target}
182 Same as @option{-MT}, but it quotes any characters which are special to
183 Make. @option{@w{-MQ '$(objpfx)foo.o'}} gives
186 $$(objpfx)foo.o: foo.c
189 The default target is automatically quoted, as if it were given with
194 @option{-MD} is equivalent to @option{-M -MF @var{file}}, except that
195 @option{-E} is not implied. The driver determines @var{file} based on
196 whether an @option{-o} option is given. If it is, the driver uses its
197 argument but with a suffix of @file{.d}, otherwise it takes the name
198 of the input file, removes any directory components and suffix, and
199 applies a @file{.d} suffix.
201 If @option{-MD} is used in conjunction with @option{-E}, any
202 @option{-o} switch is understood to specify the dependency output file
203 (@pxref{dashMF,,-MF}), but if used without @option{-E}, each @option{-o}
204 is understood to specify a target object file.
206 Since @option{-E} is not implied, @option{-MD} can be used to generate
207 a dependency output file as a side effect of the compilation process.
211 Like @option{-MD} except mention only user header files, not system
214 @opindex fpreprocessed
216 Indicate to the preprocessor that the input file has already been
217 preprocessed. This suppresses things like macro expansion, trigraph
218 conversion, escaped newline splicing, and processing of most directives.
219 The preprocessor still recognizes and removes comments, so that you can
220 pass a file preprocessed with @option{-C} to the compiler without
221 problems. In this mode the integrated preprocessor is little more than
222 a tokenizer for the front ends.
224 @option{-fpreprocessed} is implicit if the input file has one of the
225 extensions @samp{.i}, @samp{.ii} or @samp{.mi}. These are the
226 extensions that GCC uses for preprocessed files created by
227 @option{-save-temps}.
229 @opindex fdirectives-only
230 @item -fdirectives-only
231 When preprocessing, handle directives, but do not expand macros.
233 The option's behavior depends on the @option{-E} and @option{-fpreprocessed}
236 With @option{-E}, preprocessing is limited to the handling of directives
237 such as @code{#define}, @code{#ifdef}, and @code{#error}. Other
238 preprocessor operations, such as macro expansion and trigraph
239 conversion are not performed. In addition, the @option{-dD} option is
242 With @option{-fpreprocessed}, predefinition of command line and most
243 builtin macros is disabled. Macros such as @code{__LINE__}, which are
244 contextually dependent, are handled normally. This enables compilation of
245 files previously preprocessed with @code{-E -fdirectives-only}.
247 With both @option{-E} and @option{-fpreprocessed}, the rules for
248 @option{-fpreprocessed} take precedence. This enables full preprocessing of
249 files previously preprocessed with @code{-E -fdirectives-only}.
251 @opindex fdollars-in-identifiers
252 @item -fdollars-in-identifiers
253 @anchor{fdollars-in-identifiers}
254 Accept @samp{$} in identifiers.
256 @xref{Identifier characters}.
259 @opindex fextended-identifiers
260 @item -fextended-identifiers
261 Accept universal character names and extended characters in
262 identifiers. This option is enabled by default for C99 (and later C
263 standard versions) and C++.
265 @opindex fno-canonical-system-headers
266 @item -fno-canonical-system-headers
267 When preprocessing, do not shorten system header paths with canonicalization.
269 @opindex fmax-include-depth
270 @item -fmax-include-depth=@var{depth}
271 Set the maximum depth of the nested #include. The default is 200.
274 @item -ftabstop=@var{width}
275 Set the distance between tab stops. This helps the preprocessor report
276 correct column numbers in warnings or errors, even if tabs appear on the
277 line. If the value is less than 1 or greater than 100, the option is
278 ignored. The default is 8.
280 @opindex ftrack-macro-expansion
281 @item -ftrack-macro-expansion@r{[}=@var{level}@r{]}
282 Track locations of tokens across macro expansions. This allows the
283 compiler to emit diagnostic about the current macro expansion stack
284 when a compilation error occurs in a macro expansion. Using this
285 option makes the preprocessor and the compiler consume more
286 memory. The @var{level} parameter can be used to choose the level of
287 precision of token location tracking thus decreasing the memory
288 consumption if necessary. Value @samp{0} of @var{level} de-activates
289 this option. Value @samp{1} tracks tokens locations in a
290 degraded mode for the sake of minimal memory overhead. In this mode
291 all tokens resulting from the expansion of an argument of a
292 function-like macro have the same location. Value @samp{2} tracks
293 tokens locations completely. This value is the most memory hungry.
294 When this option is given no argument, the default parameter value is
297 Note that @code{-ftrack-macro-expansion=2} is activated by default.
299 @opindex fmacro-prefix-map
300 @item -fmacro-prefix-map=@var{old}=@var{new}
301 When preprocessing files residing in directory @file{@var{old}},
302 expand the @code{__FILE__} and @code{__BASE_FILE__} macros as if the
303 files resided in directory @file{@var{new}} instead. This can be used
304 to change an absolute path to a relative path by using @file{.} for
305 @var{new} which can result in more reproducible builds that are
306 location independent. This option also affects
307 @code{__builtin_FILE()} during compilation. See also
308 @option{-ffile-prefix-map} and @option{-fcanon-prefix-map}.
310 @opindex fexec-charset
311 @cindex character set, execution
312 @item -fexec-charset=@var{charset}
313 Set the execution character set, used for string and character
314 constants. The default is UTF-8. @var{charset} can be any encoding
315 supported by the system's @code{iconv} library routine.
317 @opindex fwide-exec-charset
318 @cindex character set, wide execution
319 @item -fwide-exec-charset=@var{charset}
320 Set the wide execution character set, used for wide string and
321 character constants. The default is one of UTF-32BE, UTF-32LE, UTF-16BE,
322 or UTF-16LE, whichever corresponds to the width of @code{wchar_t} and the
323 big-endian or little-endian byte order being used for code generation. As
324 with @option{-fexec-charset}, @var{charset} can be any encoding supported
325 by the system's @code{iconv} library routine; however, you will have
326 problems with encodings that do not fit exactly in @code{wchar_t}.
328 @opindex finput-charset
329 @cindex character set, input
330 @item -finput-charset=@var{charset}
331 Set the input character set, used for translation from the character
332 set of the input file to the source character set used by GCC@. If the
333 locale does not specify, or GCC cannot get this information from the
334 locale, the default is UTF-8. This can be overridden by either the locale
335 or this command-line option. Currently the command-line option takes
336 precedence if there's a conflict. @var{charset} can be any encoding
337 supported by the system's @code{iconv} library routine.
342 When using precompiled headers (@pxref{Precompiled Headers}), this flag
343 causes the dependency-output flags to also list the files from the
344 precompiled header's dependencies. If not specified, only the
345 precompiled header are listed and not the files that were used to
346 create it, because those files are not consulted when a precompiled
349 @opindex fpch-preprocess
350 @item -fpch-preprocess
351 This option allows use of a precompiled header (@pxref{Precompiled
352 Headers}) together with @option{-E}. It inserts a special @code{#pragma},
353 @code{#pragma GCC pch_preprocess "@var{filename}"} in the output to mark
354 the place where the precompiled header was found, and its @var{filename}.
355 When @option{-fpreprocessed} is in use, GCC recognizes this @code{#pragma}
358 This option is off by default, because the resulting preprocessed output
359 is only really suitable as input to GCC@. It is switched on by
360 @option{-save-temps}.
362 You should not write this @code{#pragma} in your own code, but it is
363 safe to edit the filename if the PCH file is available in a different
364 location. The filename may be absolute or it may be relative to GCC's
368 @opindex fworking-directory
369 @opindex fno-working-directory
370 @item -fworking-directory
371 Enable generation of linemarkers in the preprocessor output that
372 let the compiler know the current working directory at the time of
373 preprocessing. When this option is enabled, the preprocessor
374 emits, after the initial linemarker, a second linemarker with the
375 current working directory followed by two slashes. GCC uses this
376 directory, when it's present in the preprocessed input, as the
377 directory emitted as the current working directory in some debugging
378 information formats. This option is implicitly enabled if debugging
379 information is enabled, but this can be inhibited with the negated
380 form @option{-fno-working-directory}. If the @option{-P} flag is
381 present in the command line, this option has no effect, since no
382 @code{#line} directives are emitted whatsoever.
385 @item -A @var{predicate}=@var{answer}
386 Make an assertion with the predicate @var{predicate} and answer
387 @var{answer}. This form is preferred to the older form @option{-A
388 @var{predicate}(@var{answer})}, which is still supported, because
389 it does not use shell special characters.
391 @xref{Obsolete Features}.
394 @item -A -@var{predicate}=@var{answer}
395 Cancel an assertion with the predicate @var{predicate} and answer
400 Do not discard comments. All comments are passed through to the output
401 file, except for comments in processed directives, which are deleted
402 along with the directive.
404 You should be prepared for side effects when using @option{-C}; it
405 causes the preprocessor to treat comments as tokens in their own right.
406 For example, comments appearing at the start of what would be a
407 directive line have the effect of turning that line into an ordinary
408 source line, since the first token on the line is no longer a @samp{#}.
412 Do not discard comments, including during macro expansion. This is
413 like @option{-C}, except that comments contained within macros are
414 also passed through to the output file where the macro is expanded.
416 In addition to the side effects of the @option{-C} option, the
417 @option{-CC} option causes all C++-style comments inside a macro
418 to be converted to C-style comments. This is to prevent later use
419 of that macro from inadvertently commenting out the remainder of
422 The @option{-CC} option is generally used to support lint comments.
426 Inhibit generation of linemarkers in the output from the preprocessor.
427 This might be useful when running the preprocessor on something that is
428 not C code, and will be sent to a program which might be confused by the
431 @xref{Preprocessor Output}.
434 @cindex traditional C language
435 @cindex C language, traditional
436 @opindex traditional-cpp
439 @itemx -traditional-cpp
441 Try to imitate the behavior of pre-standard C preprocessors, as
442 opposed to ISO C preprocessors.
444 @xref{Traditional Mode}.
447 See the GNU CPP manual for details.
450 Note that GCC does not otherwise attempt to emulate a pre-standard
451 C compiler, and these options are only supported with the @option{-E}
452 switch, or when invoking CPP explicitly.
456 Support ISO C trigraphs.
457 These are three-character sequences, all starting with @samp{??}, that
458 are defined by ISO C to stand for single characters. For example,
459 @samp{??/} stands for @samp{\}, so @samp{'??/n'} is a character
460 constant for a newline.
462 @xref{Initial processing}.
466 The nine trigraphs and their replacements are
469 Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??-
470 Replacement: [ ] @{ @} # \ ^ | ~
474 By default, GCC ignores trigraphs, but in
475 standard-conforming modes it converts them. See the @option{-std} and
476 @option{-ansi} options.
480 Enable special code to work around file systems which only permit very
481 short file names, such as MS-DOS@.
485 Print the name of each header file used, in addition to other normal
486 activities. Each name is indented to show how deep in the
487 @samp{#include} stack it is. Precompiled header files are also
488 printed, even if they are found to be invalid; an invalid precompiled
489 header file is printed with @samp{...x} and a valid one with @samp{...!} .
492 @item -d@var{letters}
493 Says to make debugging dumps during compilation as specified by
494 @var{letters}. The flags documented here are those relevant to the
495 preprocessor. Other @var{letters} are interpreted
496 by the compiler proper, or reserved for future versions of GCC, and so
497 are silently ignored. If you specify @var{letters} whose behavior
498 conflicts, the result is undefined.
500 @xref{Developer Options}, for more information.
506 Instead of the normal output, generate a list of @samp{#define}
507 directives for all the macros defined during the execution of the
508 preprocessor, including predefined macros. This gives you a way of
509 finding out what is predefined in your version of the preprocessor.
510 Assuming you have no file @file{foo.h}, the command
513 touch foo.h; cpp -dM foo.h
517 shows all the predefined macros.
520 If you use @option{-dM} without the @option{-E} option, @option{-dM} is
521 interpreted as a synonym for @option{-fdump-rtl-mach}.
522 @xref{Developer Options, , ,gcc}.
527 Like @option{-dM} except in two respects: it does @emph{not} include the
528 predefined macros, and it outputs @emph{both} the @samp{#define}
529 directives and the result of preprocessing. Both kinds of output go to
530 the standard output file.
534 Like @option{-dD}, but emit only the macro names, not their expansions.
538 Output @samp{#include} directives in addition to the result of
543 Like @option{-dD} except that only macros that are expanded, or whose
544 definedness is tested in preprocessor directives, are output; the
545 output is delayed until the use or test of the macro; and
546 @samp{#undef} directives are also output for macros tested but
547 undefined at the time.
552 This option is only useful for debugging GCC. When used from CPP or with
553 @option{-E}, it dumps debugging information about location maps. Every
554 token in the output is preceded by the dump of the map its location
557 When used from GCC without @option{-E}, this option has no effect.