1 @c Copyright (c) 1999, 2000, 2001, 2002
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 There are no restrictions on the contents of @var{definition}, but if
21 you are invoking the preprocessor from a shell or shell-like program you
22 may need to use the shell's quoting syntax to protect characters such as
23 spaces that have a meaning in the shell syntax.
25 If you wish to define a function-like macro on the command line, write
26 its argument list with surrounding parentheses before the equals sign
27 (if any). Parentheses are meaningful to most shells, so you will need
28 to quote the option. With @command{sh} and @command{csh},
29 @option{-D'@var{name}(@var{args@dots{}})=@var{definition}'} works.
31 @option{-D} and @option{-U} options are processed in the order they
32 are given on the command line. All @option{-imacros @var{file}} and
33 @option{-include @var{file}} options are processed after all
34 @option{-D} and @option{-U} options.
38 Cancel any previous definition of @var{name}, either built in or
39 provided with a @option{-D} option.
43 Do not predefine any system-specific macros. The common predefined
44 macros remain defined.
48 Add the directory @var{dir} to the list of directories to be searched
53 Directories named by @option{-I} are searched before the standard
54 system include directories.
56 It is dangerous to specify a standard system include directory in an
57 @option{-I} option. This defeats the special treatment of system
60 (@pxref{System Headers})
62 . It can also defeat the repairs to buggy system headers which GCC
63 makes when it is installed.
67 Write output to @var{file}. This is the same as specifying @var{file}
68 as the second non-option argument to @command{cpp}. @command{gcc} has a
69 different interpretation of a second non-option argument, so you must
70 use @option{-o} to specify the output file.
74 Turns on all optional warnings which are desirable for normal code. At
75 present this is @option{-Wcomment} and @option{-Wtrigraphs}. Note that
76 many of the preprocessor's warnings are on by default and have no
77 options to control them.
83 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
84 comment, or whenever a backslash-newline appears in a @samp{//} comment.
85 (Both forms have the same effect.)
89 Warn if any trigraphs are encountered. This option used to take effect
90 only if @option{-trigraphs} was also specified, but now works
91 independently. Warnings are not given for trigraphs within comments, as
92 they do not affect the meaning of the program.
96 Warn about certain constructs that behave differently in traditional and
97 ISO C@. Also warn about ISO C constructs that have no traditional C
98 equivalent, and problematic constructs which should be avoided.
100 @xref{Traditional Mode}.
105 Warn the first time @samp{#import} is used.
109 Warn whenever an identifier which is not a macro is encountered in an
110 @samp{#if} directive, outside of @samp{defined}. Such identifiers are
113 @item -Wunused-macros
114 @opindex Wunused-macros
115 Warn about macros defined in the main file that are unused. A macro
116 is @dfn{used} if it is expanded or tested for existence at least once.
117 The preprocessor will also warn if the macro has not been used at the
118 time it is redefined or undefined.
120 Built-in macros, macros defined on the command line, and macros
121 defined in include files are not warned about.
123 @strong{Note:} If a macro is actually used, but only used in skipped
124 conditional blocks, then CPP will report it as unused. To avoid the
125 warning in such a case, you might improve the scope of the macro's
126 definition by, for example, moving it into the first skipped block.
127 Alternatively, you could provide a dummy use with something like:
130 #if defined the_macro_causing_the_warning
135 @opindex Wendif-labels
136 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
137 This usually happens in code of the form
148 The second and third @code{FOO} should be in comments, but often are not
149 in older programs. This warning is on by default.
153 Make all warnings into hard errors. Source code which triggers warnings
156 @item -Wsystem-headers
157 @opindex Wsystem-headers
158 Issue warnings for code in system headers. These are normally unhelpful
159 in finding bugs in your own code, therefore suppressed. If you are
160 responsible for the system library, you may want to see them.
164 Suppress all warnings, including those which GNU CPP issues by default.
168 Issue all the mandatory diagnostics listed in the C standard. Some of
169 them are left out by default, since they trigger frequently on harmless
172 @item -pedantic-errors
173 @opindex pedantic-errors
174 Issue all the mandatory diagnostics, and make all mandatory diagnostics
175 into errors. This includes mandatory diagnostics that GCC issues
176 without @samp{-pedantic} but treats as warnings.
181 @cindex dependencies, make
182 Instead of outputting the result of preprocessing, output a rule
183 suitable for @command{make} describing the dependencies of the main
184 source file. The preprocessor outputs one @command{make} rule containing
185 the object file name for that source file, a colon, and the names of all
186 the included files, including those coming from @option{-include} or
187 @option{-imacros} command line options.
189 Unless specified explicitly (with @option{-MT} or @option{-MQ}), the
190 object file name consists of the basename of the source file with any
191 suffix replaced with object file suffix. If there are many included
192 files then the rule is split into several lines using @samp{\}-newline.
193 The rule has no commands.
195 This option does not suppress the preprocessor's debug output, such as
196 @option{-dM}. To avoid mixing such debug output with the dependency
197 rules you should explicitly specify the dependency output file with
198 @option{-MF}, or use an environment variable like
199 @env{DEPENDENCIES_OUTPUT} (@pxref{Environment Variables}). Debug output
200 will still be sent to the regular output stream as normal.
202 Passing @option{-M} to the driver implies @option{-E}, and suppresses
203 warnings with an implicit @option{-w}.
207 Like @option{-M} but do not mention header files that are found in
208 system header directories, nor header files that are included,
209 directly or indirectly, from such a header.
211 This implies that the choice of angle brackets or double quotes in an
212 @samp{#include} directive does not in itself determine whether that
213 header will appear in @option{-MM} dependency output. This is a
214 slight change in semantics from GCC versions 3.0 and earlier.
219 When used with @option{-M} or @option{-MM}, specifies a
220 file to write the dependencies to. If no @option{-MF} switch is given
221 the preprocessor sends the rules to the same place it would have sent
224 When used with the driver options @option{-MD} or @option{-MMD},
225 @option{-MF} overrides the default dependency output file.
229 In conjunction with an option such as @option{-M} requesting
230 dependency generation, @option{-MG} assumes missing header files are
231 generated files and adds them to the dependency list without raising
232 an error. The dependency filename is taken directly from the
233 @code{#include} directive without prepending any path. @option{-MG}
234 also suppresses preprocessed output, as a missing header file renders
237 This feature is used in automatic updating of makefiles.
241 This option instructs CPP to add a phony target for each dependency
242 other than the main file, causing each to depend on nothing. These
243 dummy rules work around errors @command{make} gives if you remove header
244 files without updating the @file{Makefile} to match.
246 This is typical output:
249 test.o: test.c test.h
254 @item -MT @var{target}
257 Change the target of the rule emitted by dependency generation. By
258 default CPP takes the name of the main input file, including any path,
259 deletes any file suffix such as @samp{.c}, and appends the platform's
260 usual object suffix. The result is the target.
262 An @option{-MT} option will set the target to be exactly the string you
263 specify. If you want multiple targets, you can specify them as a single
264 argument to @option{-MT}, or use multiple @option{-MT} options.
266 For example, @option{@w{-MT '$(objpfx)foo.o'}} might give
269 $(objpfx)foo.o: foo.c
272 @item -MQ @var{target}
275 Same as @option{-MT}, but it quotes any characters which are special to
276 Make. @option{@w{-MQ '$(objpfx)foo.o'}} gives
279 $$(objpfx)foo.o: foo.c
282 The default target is automatically quoted, as if it were given with
287 @option{-MD} is equivalent to @option{-M -MF @var{file}}, except that
288 @option{-E} is not implied. The driver determines @var{file} based on
289 whether an @option{-o} option is given. If it is, the driver uses its
290 argument but with a suffix of @file{.d}, otherwise it take the
291 basename of the input file and applies a @file{.d} suffix.
293 If @option{-MD} is used in conjunction with @option{-E}, any
294 @option{-o} switch is understood to specify the dependency output file
295 (but @pxref{-MF}), but if used without @option{-E}, each @option{-o}
296 is understood to specify a target object file.
298 Since @option{-E} is not implied, @option{-MD} can be used to generate
299 a dependency output file as a side-effect of the compilation process.
303 Like @option{-MD} except mention only user header files, not system
308 @itemx -x objective-c
309 @itemx -x assembler-with-cpp
311 Specify the source language: C, C++, Objective-C, or assembly. This has
312 nothing to do with standards conformance or extensions; it merely
313 selects which base syntax to expect. If you give none of these options,
314 cpp will deduce the language from the extension of the source file:
315 @samp{.c}, @samp{.cc}, @samp{.m}, or @samp{.S}. Some other common
316 extensions for C++ and assembly are also recognized. If cpp does not
317 recognize the extension, it will treat the file as C; this is the most
320 @strong{Note:} Previous versions of cpp accepted a @option{-lang} option
321 which selected both the language and the standards conformance level.
322 This option has been removed, because it conflicts with the @option{-l}
325 @item -std=@var{standard}
329 Specify the standard to which the code should conform. Currently cpp
330 only knows about the standards for C; other language standards will be
338 The ISO C standard from 1990. @samp{c89} is the customary shorthand for
339 this version of the standard.
341 The @option{-ansi} option is equivalent to @option{-std=c89}.
344 The 1990 C standard, as amended in 1994.
350 The revised ISO C standard, published in December 1999. Before
351 publication, this was known as C9X@.
354 The 1990 C standard plus GNU extensions. This is the default.
358 The 1999 C standard plus GNU extensions.
363 Split the include path. Any directories specified with @option{-I}
364 options before @option{-I-} are searched only for headers requested with
365 @code{@w{#include "@var{file}"}}; they are not searched for
366 @code{@w{#include <@var{file}>}}. If additional directories are
367 specified with @option{-I} options after the @option{-I-}, those
368 directories are searched for all @samp{#include} directives.
370 In addition, @option{-I-} inhibits the use of the directory of the current
371 file directory as the first search directory for @code{@w{#include
379 Do not search the standard system directories for header files.
380 Only the directories you have specified with @option{-I} options
381 (and the directory of the current file, if appropriate) are searched.
385 Do not search for header files in the C++-specific standard directories,
386 but do still search the other standard directories. (This option is
387 used when building the C++ library.)
389 @item -include @var{file}
391 Process @var{file} as if @code{#include "file"} appeared as the first
392 line of the primary source file. However, the first directory searched
393 for @var{file} is the preprocessor's working directory @emph{instead of}
394 the directory containing the main source file. If not found there, it
395 is searched for in the remainder of the @code{#include "@dots{}"} search
398 If multiple @option{-include} options are given, the files are included
399 in the order they appear on the command line.
401 @item -imacros @var{file}
403 Exactly like @option{-include}, except that any output produced by
404 scanning @var{file} is thrown away. Macros it defines remain defined.
405 This allows you to acquire all the macros from a header without also
406 processing its declarations.
408 All files specified by @option{-imacros} are processed before all files
409 specified by @option{-include}.
411 @item -idirafter @var{dir}
413 Search @var{dir} for header files, but do it @emph{after} all
414 directories specified with @option{-I} and the standard system directories
415 have been exhausted. @var{dir} is treated as a system include directory.
417 @item -iprefix @var{prefix}
419 Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix}
420 options. If the prefix represents a directory, you should include the
423 @item -iwithprefix @var{dir}
424 @itemx -iwithprefixbefore @var{dir}
426 @opindex iwithprefixbefore
427 Append @var{dir} to the prefix specified previously with
428 @option{-iprefix}, and add the resulting directory to the include search
429 path. @option{-iwithprefixbefore} puts it in the same place @option{-I}
430 would; @option{-iwithprefix} puts it where @option{-idirafter} would.
432 Use of these options is discouraged.
434 @item -isystem @var{dir}
436 Search @var{dir} for header files, after all directories specified by
437 @option{-I} but before the standard system directories. Mark it
438 as a system directory, so that it gets the same special treatment as
439 is applied to the standard system directories.
441 @xref{System Headers}.
445 @opindex fpreprocessed
446 Indicate to the preprocessor that the input file has already been
447 preprocessed. This suppresses things like macro expansion, trigraph
448 conversion, escaped newline splicing, and processing of most directives.
449 The preprocessor still recognizes and removes comments, so that you can
450 pass a file preprocessed with @option{-C} to the compiler without
451 problems. In this mode the integrated preprocessor is little more than
452 a tokenizer for the front ends.
454 @option{-fpreprocessed} is implicit if the input file has one of the
455 extensions @samp{.i}, @samp{.ii} or @samp{.mi}. These are the
456 extensions that GCC uses for preprocessed files created by
457 @option{-save-temps}.
459 @item -ftabstop=@var{width}
461 Set the distance between tab stops. This helps the preprocessor report
462 correct column numbers in warnings or errors, even if tabs appear on the
463 line. If the value is less than 1 or greater than 100, the option is
464 ignored. The default is 8.
466 @item -fno-show-column
467 @opindex fno-show-column
468 Do not print column numbers in diagnostics. This may be necessary if
469 diagnostics are being scanned by a program that does not understand the
470 column numbers, such as @command{dejagnu}.
472 @item -A @var{predicate}=@var{answer}
474 Make an assertion with the predicate @var{predicate} and answer
475 @var{answer}. This form is preferred to the older form @option{-A
476 @var{predicate}(@var{answer})}, which is still supported, because
477 it does not use shell special characters.
482 @item -A -@var{predicate}=@var{answer}
483 Cancel an assertion with the predicate @var{predicate} and answer
488 Cancel all predefined assertions and all assertions preceding it on
489 the command line. Also, undefine all predefined macros and all
490 macros preceding it on the command line. (This is a historical wart and
491 may change in the future.)
494 @var{CHARS} is a sequence of one or more of the following characters,
495 and must not be preceded by a space. Other characters are interpreted
496 by the compiler proper, or reserved for future versions of GCC, and so
497 are silently ignored. If you specify characters whose behavior
498 conflicts, the result is undefined.
503 Instead of the normal output, generate a list of @samp{#define}
504 directives for all the macros defined during the execution of the
505 preprocessor, including predefined macros. This gives you a way of
506 finding out what is predefined in your version of the preprocessor.
507 Assuming you have no file @file{foo.h}, the command
510 touch foo.h; cpp -dM foo.h
514 will show all the predefined macros.
518 Like @samp{M} except in two respects: it does @emph{not} include the
519 predefined macros, and it outputs @emph{both} the @samp{#define}
520 directives and the result of preprocessing. Both kinds of output go to
521 the standard output file.
525 Like @samp{D}, but emit only the macro names, not their expansions.
529 Output @samp{#include} directives in addition to the result of
535 Inhibit generation of linemarkers in the output from the preprocessor.
536 This might be useful when running the preprocessor on something that is
537 not C code, and will be sent to a program which might be confused by the
540 @xref{Preprocessor Output}.
545 Do not discard comments. All comments are passed through to the output
546 file, except for comments in processed directives, which are deleted
547 along with the directive.
549 You should be prepared for side effects when using @option{-C}; it
550 causes the preprocessor to treat comments as tokens in their own right.
551 For example, comments appearing at the start of what would be a
552 directive line have the effect of turning that line into an ordinary
553 source line, since the first token on the line is no longer a @samp{#}.
556 Do not discard comments, including during macro expansion. This is
557 like @option{-C}, except that comments contained within macros are
558 also passed through to the output file where the macro is expanded.
560 In addition to the side-effects of the @option{-C} option, the
561 @option{-CC} option causes all C++-style comments inside a macro
562 to be converted to C-style comments. This is to prevent later use
563 of that macro from inadvertently commenting out the remainer of
566 The @option{-CC} option is generally used to support lint comments.
570 Define the macros @sc{__gnuc__}, @sc{__gnuc_minor__} and
571 @sc{__gnuc_patchlevel__}. These are defined automatically when you use
572 @command{gcc -E}; you can turn them off in that case with
575 @item -traditional-cpp
576 @opindex traditional-cpp
577 Try to imitate the behavior of old-fashioned C preprocessors, as
578 opposed to ISO C preprocessors.
580 @xref{Traditional Mode}.
585 Process trigraph sequences.
587 @xref{Initial processing}.
590 These are three-character sequences, all starting with @samp{??}, that
591 are defined by ISO C to stand for single characters. For example,
592 @samp{??/} stands for @samp{\}, so @samp{'??/n'} is a character
593 constant for a newline. By default, GCC ignores trigraphs, but in
594 standard-conforming modes it converts them. See the @option{-std} and
595 @option{-ansi} options.
597 The nine trigraphs and their replacements are
600 Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??-
601 Replacement: [ ] @{ @} # \ ^ | ~
607 Enable special code to work around file systems which only permit very
608 short file names, such as MS-DOS@.
616 Print text describing all the command line options instead of
617 preprocessing anything.
621 Verbose mode. Print out GNU CPP's version number at the beginning of
622 execution, and report the final form of the include path.
626 Print the name of each header file used, in addition to other normal
627 activities. Each name is indented to show how deep in the
628 @samp{#include} stack it is.
633 Print out GNU CPP's version number. With one dash, proceed to
634 preprocess as normal. With two dashes, exit immediately.