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
114 @opindex Wendif-labels
115 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
116 This usually happens in code of the form
127 The second and third @code{FOO} should be in comments, but often are not
128 in older programs. This warning is on by default.
132 Make all warnings into hard errors. Source code which triggers warnings
135 @item -Wsystem-headers
136 @opindex Wsystem-headers
137 Issue warnings for code in system headers. These are normally unhelpful
138 in finding bugs in your own code, therefore suppressed. If you are
139 responsible for the system library, you may want to see them.
143 Suppress all warnings, including those which GNU CPP issues by default.
147 Issue all the mandatory diagnostics listed in the C standard. Some of
148 them are left out by default, since they trigger frequently on harmless
151 @item -pedantic-errors
152 @opindex pedantic-errors
153 Issue all the mandatory diagnostics, and make all mandatory diagnostics
154 into errors. This includes mandatory diagnostics that GCC issues
155 without @samp{-pedantic} but treats as warnings.
160 @cindex dependencies, make
161 Instead of outputting the result of preprocessing, output a rule
162 suitable for @command{make} describing the dependencies of the main
163 source file. The preprocessor outputs one @command{make} rule containing
164 the object file name for that source file, a colon, and the names of all
165 the included files, including those coming from @option{-include} or
166 @option{-imacros} command line options.
168 Unless specified explicitly (with @option{-MT} or @option{-MQ}), the
169 object file name consists of the basename of the source file with any
170 suffix replaced with object file suffix. If there are many included
171 files then the rule is split into several lines using @samp{\}-newline.
172 The rule has no commands.
174 This option does not suppress the preprocessor's debug output, such as
175 @option{-dM}. To avoid mixing such debug output with the dependency
176 rules you should explicitly specify the dependency output file with
177 @option{-MF}, or use an environment variable like
178 @env{DEPENDENCIES_OUTPUT} (@pxref{Environment Variables}). Debug output
179 will still be sent to the regular output stream as normal.
181 Passing @option{-M} to the driver implies @option{-E}.
185 Like @option{-M} but do not mention header files that are found in
186 system header directories, nor header files that are included,
187 directly or indirectly, from such a header.
189 This implies that the choice of angle brackets or double quotes in an
190 @samp{#include} directive does not in itself determine whether that
191 header will appear in @option{-MM} dependency output. This is a
192 slight change in semantics from GCC versions 3.0 and earlier.
197 When used with @option{-M} or @option{-MM}, specifies a
198 file to write the dependencies to. If no @option{-MF} switch is given
199 the preprocessor sends the rules to the same place it would have sent
202 When used with the driver options @option{-MD} or @option{-MMD},
203 @option{-MF} overrides the default dependency output file.
207 In conjunction with an option such as @option{-M} requesting
208 dependency generation, @option{-MG} assumes missing header files are
209 generated files and adds them to the dependency list without raising
210 an error. The dependency filename is taken directly from the
211 @code{#include} directive without prepending any path. @option{-MG}
212 also suppresses preprocessed output, as a missing header file renders
215 This feature is used in automatic updating of makefiles.
219 This option instructs CPP to add a phony target for each dependency
220 other than the main file, causing each to depend on nothing. These
221 dummy rules work around errors @command{make} gives if you remove header
222 files without updating the @file{Makefile} to match.
224 This is typical output:
227 test.o: test.c test.h
232 @item -MT @var{target}
235 Change the target of the rule emitted by dependency generation. By
236 default CPP takes the name of the main input file, including any path,
237 deletes any file suffix such as @samp{.c}, and appends the platform's
238 usual object suffix. The result is the target.
240 An @option{-MT} option will set the target to be exactly the string you
241 specify. If you want multiple targets, you can specify them as a single
242 argument to @option{-MT}, or use multiple @option{-MT} options.
244 For example, @option{@w{-MT '$(objpfx)foo.o'}} might give
247 $(objpfx)foo.o: foo.c
250 @item -MQ @var{target}
253 Same as @option{-MT}, but it quotes any characters which are special to
254 Make. @option{@w{-MQ '$(objpfx)foo.o'}} gives
257 $$(objpfx)foo.o: foo.c
260 The default target is automatically quoted, as if it were given with
265 @option{-MD} is equivalent to @option{-M -MF @var{file}}, except that
266 @option{-E} is not implied. The driver determines @var{file} based on
267 whether an @option{-o} option is given. If it is, the driver uses its
268 argument but with a suffix of @file{.d}, otherwise it take the
269 basename of the input file and applies a @file{.d} suffix.
271 If @option{-MD} is used in conjunction with @option{-E}, any
272 @option{-o} switch is understood to specify the dependency output file
273 (but @pxref{-MF}), but if used without @option{-E}, each @option{-o}
274 is understood to specify a target object file.
276 Since @option{-E} is not implied, @option{-MD} can be used to generate
277 a dependency output file as a side-effect of the compilation process.
281 Like @option{-MD} except mention only user header files, not system
286 @itemx -x objective-c
287 @itemx -x assembler-with-cpp
289 Specify the source language: C, C++, Objective-C, or assembly. This has
290 nothing to do with standards conformance or extensions; it merely
291 selects which base syntax to expect. If you give none of these options,
292 cpp will deduce the language from the extension of the source file:
293 @samp{.c}, @samp{.cc}, @samp{.m}, or @samp{.S}. Some other common
294 extensions for C++ and assembly are also recognized. If cpp does not
295 recognize the extension, it will treat the file as C; this is the most
298 @strong{Note:} Previous versions of cpp accepted a @option{-lang} option
299 which selected both the language and the standards conformance level.
300 This option has been removed, because it conflicts with the @option{-l}
303 @item -std=@var{standard}
307 Specify the standard to which the code should conform. Currently cpp
308 only knows about the standards for C; other language standards will be
316 The ISO C standard from 1990. @samp{c89} is the customary shorthand for
317 this version of the standard.
319 The @option{-ansi} option is equivalent to @option{-std=c89}.
322 The 1990 C standard, as amended in 1994.
328 The revised ISO C standard, published in December 1999. Before
329 publication, this was known as C9X@.
332 The 1990 C standard plus GNU extensions. This is the default.
336 The 1999 C standard plus GNU extensions.
341 Split the include path. Any directories specified with @option{-I}
342 options before @option{-I-} are searched only for headers requested with
343 @code{@w{#include "@var{file}"}}; they are not searched for
344 @code{@w{#include <@var{file}>}}. If additional directories are
345 specified with @option{-I} options after the @option{-I-}, those
346 directories are searched for all @samp{#include} directives.
348 In addition, @option{-I-} inhibits the use of the directory of the current
349 file directory as the first search directory for @code{@w{#include
357 Do not search the standard system directories for header files.
358 Only the directories you have specified with @option{-I} options
359 (and the directory of the current file, if appropriate) are searched.
363 Do not search for header files in the C++-specific standard directories,
364 but do still search the other standard directories. (This option is
365 used when building the C++ library.)
367 @item -include @var{file}
369 Process @var{file} as if @code{#include "file"} appeared as the first
370 line of the primary source file. However, the first directory searched
371 for @var{file} is the preprocessor's working directory @emph{instead of}
372 the directory containing the main source file. If not found there, it
373 is searched for in the remainder of the @code{#include "@dots{}"} search
376 If multiple @option{-include} options are given, the files are included
377 in the order they appear on the command line.
379 @item -imacros @var{file}
381 Exactly like @option{-include}, except that any output produced by
382 scanning @var{file} is thrown away. Macros it defines remain defined.
383 This allows you to acquire all the macros from a header without also
384 processing its declarations.
386 All files specified by @option{-imacros} are processed before all files
387 specified by @option{-include}.
389 @item -idirafter @var{dir}
391 Search @var{dir} for header files, but do it @emph{after} all
392 directories specified with @option{-I} and the standard system directories
393 have been exhausted. @var{dir} is treated as a system include directory.
395 @item -iprefix @var{prefix}
397 Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix}
398 options. If the prefix represents a directory, you should include the
401 @item -iwithprefix @var{dir}
402 @itemx -iwithprefixbefore @var{dir}
404 @opindex iwithprefixbefore
405 Append @var{dir} to the prefix specified previously with
406 @option{-iprefix}, and add the resulting directory to the include search
407 path. @option{-iwithprefixbefore} puts it in the same place @option{-I}
408 would; @option{-iwithprefix} puts it where @option{-idirafter} would.
410 Use of these options is discouraged.
412 @item -isystem @var{dir}
414 Search @var{dir} for header files, after all directories specified by
415 @option{-I} but before the standard system directories. Mark it
416 as a system directory, so that it gets the same special treatment as
417 is applied to the standard system directories.
419 @xref{System Headers}.
423 @opindex fpreprocessed
424 Indicate to the preprocessor that the input file has already been
425 preprocessed. This suppresses things like macro expansion, trigraph
426 conversion, escaped newline splicing, and processing of most directives.
427 The preprocessor still recognizes and removes comments, so that you can
428 pass a file preprocessed with @option{-C} to the compiler without
429 problems. In this mode the integrated preprocessor is little more than
430 a tokenizer for the front ends.
432 @option{-fpreprocessed} is implicit if the input file has one of the
433 extensions @samp{.i}, @samp{.ii} or @samp{.mi}. These are the
434 extensions that GCC uses for preprocessed files created by
435 @option{-save-temps}.
437 @item -ftabstop=@var{width}
439 Set the distance between tab stops. This helps the preprocessor report
440 correct column numbers in warnings or errors, even if tabs appear on the
441 line. If the value is less than 1 or greater than 100, the option is
442 ignored. The default is 8.
444 @item -fno-show-column
445 @opindex fno-show-column
446 Do not print column numbers in diagnostics. This may be necessary if
447 diagnostics are being scanned by a program that does not understand the
448 column numbers, such as @command{dejagnu}.
450 @item -A @var{predicate}=@var{answer}
452 Make an assertion with the predicate @var{predicate} and answer
453 @var{answer}. This form is preferred to the older form @option{-A
454 @var{predicate}(@var{answer})}, which is still supported, because
455 it does not use shell special characters.
460 @item -A -@var{predicate}=@var{answer}
461 Cancel an assertion with the predicate @var{predicate} and answer
466 Cancel all predefined assertions and all assertions preceding it on
467 the command line. Also, undefine all predefined macros and all
468 macros preceding it on the command line. (This is a historical wart and
469 may change in the future.)
472 @var{CHARS} is a sequence of one or more of the following characters,
473 and must not be preceded by a space. Other characters are interpreted
474 by the compiler proper, or reserved for future versions of GCC, and so
475 are silently ignored. If you specify characters whose behavior
476 conflicts, the result is undefined.
481 Instead of the normal output, generate a list of @samp{#define}
482 directives for all the macros defined during the execution of the
483 preprocessor, including predefined macros. This gives you a way of
484 finding out what is predefined in your version of the preprocessor.
485 Assuming you have no file @file{foo.h}, the command
488 touch foo.h; cpp -dM foo.h
492 will show all the predefined macros.
496 Like @samp{M} except in two respects: it does @emph{not} include the
497 predefined macros, and it outputs @emph{both} the @samp{#define}
498 directives and the result of preprocessing. Both kinds of output go to
499 the standard output file.
503 Like @samp{D}, but emit only the macro names, not their expansions.
507 Output @samp{#include} directives in addition to the result of
513 Inhibit generation of linemarkers in the output from the preprocessor.
514 This might be useful when running the preprocessor on something that is
515 not C code, and will be sent to a program which might be confused by the
518 @xref{Preprocessor Output}.
523 Do not discard comments. All comments are passed through to the output
524 file, except for comments in processed directives, which are deleted
525 along with the directive.
527 You should be prepared for side effects when using @option{-C}; it
528 causes the preprocessor to treat comments as tokens in their own right.
529 For example, comments appearing at the start of what would be a
530 directive line have the effect of turning that line into an ordinary
531 source line, since the first token on the line is no longer a @samp{#}.
534 Do not discard comments, including during macro expansion. This is
535 like @option{-C}, except that comments contained within macros are
536 also passed through to the output file where the macro is expanded.
538 In addition to the side-effects of the @option{-C} option, the
539 @option{-CC} option causes all C++-style comments inside a macro
540 to be converted to C-style comments. This is to prevent later use
541 of that macro from inadvertently commenting out the remainer of
544 The @option{-CC} option is generally used to support lint comments.
548 Define the macros @sc{__gnuc__}, @sc{__gnuc_minor__} and
549 @sc{__gnuc_patchlevel__}. These are defined automatically when you use
550 @command{gcc -E}; you can turn them off in that case with
555 Try to imitate the behavior of old-fashioned C, as opposed to ISO
558 @xref{Traditional Mode}.
563 Process trigraph sequences.
565 @xref{Initial processing}.
568 These are three-character sequences, all starting with @samp{??}, that
569 are defined by ISO C to stand for single characters. For example,
570 @samp{??/} stands for @samp{\}, so @samp{'??/n'} is a character
571 constant for a newline. By default, GCC ignores trigraphs, but in
572 standard-conforming modes it converts them. See the @option{-std} and
573 @option{-ansi} options.
575 The nine trigraphs and their replacements are
578 Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??-
579 Replacement: [ ] @{ @} # \ ^ | ~
585 Enable special code to work around file systems which only permit very
586 short file names, such as MS-DOS@.
590 Forbid the use of @samp{$} in identifiers. The C standard allows
591 implementations to define extra characters that can appear in
592 identifiers. By default GNU CPP permits @samp{$}, a common extension.
600 Print text describing all the command line options instead of
601 preprocessing anything.
605 Verbose mode. Print out GNU CPP's version number at the beginning of
606 execution, and report the final form of the include path.
610 Print the name of each header file used, in addition to other normal
611 activities. Each name is indented to show how deep in the
612 @samp{#include} stack it is.
617 Print out GNU CPP's version number. With one dash, proceed to
618 preprocess as normal. With two dashes, exit immediately.