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. If the directory @var{dir} is a standard
55 system include directory, the option is ignored to ensure that the
56 default search order for system directories and the special treatment
57 of system headers are not defeated
59 (@pxref{System Headers})
65 Write output to @var{file}. This is the same as specifying @var{file}
66 as the second non-option argument to @command{cpp}. @command{gcc} has a
67 different interpretation of a second non-option argument, so you must
68 use @option{-o} to specify the output file.
72 Turns on all optional warnings which are desirable for normal code.
73 At present this is @option{-Wcomment}, @option{-Wtrigraphs},
74 @option{-Wmultichar} and a warning about integer promotion causing a
75 change of sign in @code{#if} expressions. Note that many of the
76 preprocessor's warnings are on by default and have no options to
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.)
90 Warn if any trigraphs that may change the meaning of a program are
91 encountered. This option is in effect unless trigraphs are turned on,
92 and is implied by @option{-Wall}. With the exception of a trigraph
93 that would form an escaped newline, warnings are not given for
94 trigraphs within comments as they do not affect the meaning of the
99 Warn about certain constructs that behave differently in traditional and
100 ISO C@. Also warn about ISO C constructs that have no traditional C
101 equivalent, and problematic constructs which should be avoided.
103 @xref{Traditional Mode}.
108 Warn the first time @samp{#import} is used.
112 Warn whenever an identifier which is not a macro is encountered in an
113 @samp{#if} directive, outside of @samp{defined}. Such identifiers are
116 @item -Wunused-macros
117 @opindex Wunused-macros
118 Warn about macros defined in the main file that are unused. A macro
119 is @dfn{used} if it is expanded or tested for existence at least once.
120 The preprocessor will also warn if the macro has not been used at the
121 time it is redefined or undefined.
123 Built-in macros, macros defined on the command line, and macros
124 defined in include files are not warned about.
126 @strong{Note:} If a macro is actually used, but only used in skipped
127 conditional blocks, then CPP will report it as unused. To avoid the
128 warning in such a case, you might improve the scope of the macro's
129 definition by, for example, moving it into the first skipped block.
130 Alternatively, you could provide a dummy use with something like:
133 #if defined the_macro_causing_the_warning
138 @opindex Wendif-labels
139 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
140 This usually happens in code of the form
151 The second and third @code{FOO} should be in comments, but often are not
152 in older programs. This warning is on by default.
156 Make all warnings into hard errors. Source code which triggers warnings
159 @item -Wsystem-headers
160 @opindex Wsystem-headers
161 Issue warnings for code in system headers. These are normally unhelpful
162 in finding bugs in your own code, therefore suppressed. If you are
163 responsible for the system library, you may want to see them.
167 Suppress all warnings, including those which GNU CPP issues by default.
171 Issue all the mandatory diagnostics listed in the C standard. Some of
172 them are left out by default, since they trigger frequently on harmless
175 @item -pedantic-errors
176 @opindex pedantic-errors
177 Issue all the mandatory diagnostics, and make all mandatory diagnostics
178 into errors. This includes mandatory diagnostics that GCC issues
179 without @samp{-pedantic} but treats as warnings.
184 @cindex dependencies, make
185 Instead of outputting the result of preprocessing, output a rule
186 suitable for @command{make} describing the dependencies of the main
187 source file. The preprocessor outputs one @command{make} rule containing
188 the object file name for that source file, a colon, and the names of all
189 the included files, including those coming from @option{-include} or
190 @option{-imacros} command line options.
192 Unless specified explicitly (with @option{-MT} or @option{-MQ}), the
193 object file name consists of the basename of the source file with any
194 suffix replaced with object file suffix. If there are many included
195 files then the rule is split into several lines using @samp{\}-newline.
196 The rule has no commands.
198 This option does not suppress the preprocessor's debug output, such as
199 @option{-dM}. To avoid mixing such debug output with the dependency
200 rules you should explicitly specify the dependency output file with
201 @option{-MF}, or use an environment variable like
202 @env{DEPENDENCIES_OUTPUT} (@pxref{Environment Variables}). Debug output
203 will still be sent to the regular output stream as normal.
205 Passing @option{-M} to the driver implies @option{-E}, and suppresses
206 warnings with an implicit @option{-w}.
210 Like @option{-M} but do not mention header files that are found in
211 system header directories, nor header files that are included,
212 directly or indirectly, from such a header.
214 This implies that the choice of angle brackets or double quotes in an
215 @samp{#include} directive does not in itself determine whether that
216 header will appear in @option{-MM} dependency output. This is a
217 slight change in semantics from GCC versions 3.0 and earlier.
222 When used with @option{-M} or @option{-MM}, specifies a
223 file to write the dependencies to. If no @option{-MF} switch is given
224 the preprocessor sends the rules to the same place it would have sent
227 When used with the driver options @option{-MD} or @option{-MMD},
228 @option{-MF} overrides the default dependency output file.
232 In conjunction with an option such as @option{-M} requesting
233 dependency generation, @option{-MG} assumes missing header files are
234 generated files and adds them to the dependency list without raising
235 an error. The dependency filename is taken directly from the
236 @code{#include} directive without prepending any path. @option{-MG}
237 also suppresses preprocessed output, as a missing header file renders
240 This feature is used in automatic updating of makefiles.
244 This option instructs CPP to add a phony target for each dependency
245 other than the main file, causing each to depend on nothing. These
246 dummy rules work around errors @command{make} gives if you remove header
247 files without updating the @file{Makefile} to match.
249 This is typical output:
252 test.o: test.c test.h
257 @item -MT @var{target}
260 Change the target of the rule emitted by dependency generation. By
261 default CPP takes the name of the main input file, including any path,
262 deletes any file suffix such as @samp{.c}, and appends the platform's
263 usual object suffix. The result is the target.
265 An @option{-MT} option will set the target to be exactly the string you
266 specify. If you want multiple targets, you can specify them as a single
267 argument to @option{-MT}, or use multiple @option{-MT} options.
269 For example, @option{@w{-MT '$(objpfx)foo.o'}} might give
272 $(objpfx)foo.o: foo.c
275 @item -MQ @var{target}
278 Same as @option{-MT}, but it quotes any characters which are special to
279 Make. @option{@w{-MQ '$(objpfx)foo.o'}} gives
282 $$(objpfx)foo.o: foo.c
285 The default target is automatically quoted, as if it were given with
290 @option{-MD} is equivalent to @option{-M -MF @var{file}}, except that
291 @option{-E} is not implied. The driver determines @var{file} based on
292 whether an @option{-o} option is given. If it is, the driver uses its
293 argument but with a suffix of @file{.d}, otherwise it take the
294 basename of the input file and applies a @file{.d} suffix.
296 If @option{-MD} is used in conjunction with @option{-E}, any
297 @option{-o} switch is understood to specify the dependency output file
298 (but @pxref{-MF}), but if used without @option{-E}, each @option{-o}
299 is understood to specify a target object file.
301 Since @option{-E} is not implied, @option{-MD} can be used to generate
302 a dependency output file as a side-effect of the compilation process.
306 Like @option{-MD} except mention only user header files, not system
312 When using precompiled headers (@pxref{Precompiled Headers}), this flag
313 will cause the dependency-output flags to also list the files from the
314 precompiled header's dependencies. If not specified only the
315 precompiled header would be listed and not the files that were used to
316 create it because those files are not consulted when a precompiled
322 @itemx -x objective-c
323 @itemx -x assembler-with-cpp
325 Specify the source language: C, C++, Objective-C, or assembly. This has
326 nothing to do with standards conformance or extensions; it merely
327 selects which base syntax to expect. If you give none of these options,
328 cpp will deduce the language from the extension of the source file:
329 @samp{.c}, @samp{.cc}, @samp{.m}, or @samp{.S}. Some other common
330 extensions for C++ and assembly are also recognized. If cpp does not
331 recognize the extension, it will treat the file as C; this is the most
334 @strong{Note:} Previous versions of cpp accepted a @option{-lang} option
335 which selected both the language and the standards conformance level.
336 This option has been removed, because it conflicts with the @option{-l}
339 @item -std=@var{standard}
343 Specify the standard to which the code should conform. Currently CPP
344 knows about C and C++ standards; others may be added in the future.
351 The ISO C standard from 1990. @samp{c89} is the customary shorthand for
352 this version of the standard.
354 The @option{-ansi} option is equivalent to @option{-std=c89}.
357 The 1990 C standard, as amended in 1994.
363 The revised ISO C standard, published in December 1999. Before
364 publication, this was known as C9X@.
367 The 1990 C standard plus GNU extensions. This is the default.
371 The 1999 C standard plus GNU extensions.
374 The 1998 ISO C++ standard plus amendments.
377 The same as @option{-std=c++98} plus GNU extensions. This is the
378 default for C++ code.
383 Split the include path. Any directories specified with @option{-I}
384 options before @option{-I-} are searched only for headers requested with
385 @code{@w{#include "@var{file}"}}; they are not searched for
386 @code{@w{#include <@var{file}>}}. If additional directories are
387 specified with @option{-I} options after the @option{-I-}, those
388 directories are searched for all @samp{#include} directives.
390 In addition, @option{-I-} inhibits the use of the directory of the current
391 file directory as the first search directory for @code{@w{#include
399 Do not search the standard system directories for header files.
400 Only the directories you have specified with @option{-I} options
401 (and the directory of the current file, if appropriate) are searched.
405 Do not search for header files in the C++-specific standard directories,
406 but do still search the other standard directories. (This option is
407 used when building the C++ library.)
409 @item -include @var{file}
411 Process @var{file} as if @code{#include "file"} appeared as the first
412 line of the primary source file. However, the first directory searched
413 for @var{file} is the preprocessor's working directory @emph{instead of}
414 the directory containing the main source file. If not found there, it
415 is searched for in the remainder of the @code{#include "@dots{}"} search
418 If multiple @option{-include} options are given, the files are included
419 in the order they appear on the command line.
421 @item -imacros @var{file}
423 Exactly like @option{-include}, except that any output produced by
424 scanning @var{file} is thrown away. Macros it defines remain defined.
425 This allows you to acquire all the macros from a header without also
426 processing its declarations.
428 All files specified by @option{-imacros} are processed before all files
429 specified by @option{-include}.
431 @item -idirafter @var{dir}
433 Search @var{dir} for header files, but do it @emph{after} all
434 directories specified with @option{-I} and the standard system directories
435 have been exhausted. @var{dir} is treated as a system include directory.
437 @item -iprefix @var{prefix}
439 Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix}
440 options. If the prefix represents a directory, you should include the
443 @item -iwithprefix @var{dir}
444 @itemx -iwithprefixbefore @var{dir}
446 @opindex iwithprefixbefore
447 Append @var{dir} to the prefix specified previously with
448 @option{-iprefix}, and add the resulting directory to the include search
449 path. @option{-iwithprefixbefore} puts it in the same place @option{-I}
450 would; @option{-iwithprefix} puts it where @option{-idirafter} would.
452 Use of these options is discouraged.
454 @item -isystem @var{dir}
456 Search @var{dir} for header files, after all directories specified by
457 @option{-I} but before the standard system directories. Mark it
458 as a system directory, so that it gets the same special treatment as
459 is applied to the standard system directories.
461 @xref{System Headers}.
465 @opindex fpreprocessed
466 Indicate to the preprocessor that the input file has already been
467 preprocessed. This suppresses things like macro expansion, trigraph
468 conversion, escaped newline splicing, and processing of most directives.
469 The preprocessor still recognizes and removes comments, so that you can
470 pass a file preprocessed with @option{-C} to the compiler without
471 problems. In this mode the integrated preprocessor is little more than
472 a tokenizer for the front ends.
474 @option{-fpreprocessed} is implicit if the input file has one of the
475 extensions @samp{.i}, @samp{.ii} or @samp{.mi}. These are the
476 extensions that GCC uses for preprocessed files created by
477 @option{-save-temps}.
479 @item -ftabstop=@var{width}
481 Set the distance between tab stops. This helps the preprocessor report
482 correct column numbers in warnings or errors, even if tabs appear on the
483 line. If the value is less than 1 or greater than 100, the option is
484 ignored. The default is 8.
486 @item -fno-show-column
487 @opindex fno-show-column
488 Do not print column numbers in diagnostics. This may be necessary if
489 diagnostics are being scanned by a program that does not understand the
490 column numbers, such as @command{dejagnu}.
492 @item -A @var{predicate}=@var{answer}
494 Make an assertion with the predicate @var{predicate} and answer
495 @var{answer}. This form is preferred to the older form @option{-A
496 @var{predicate}(@var{answer})}, which is still supported, because
497 it does not use shell special characters.
502 @item -A -@var{predicate}=@var{answer}
503 Cancel an assertion with the predicate @var{predicate} and answer
507 @var{CHARS} is a sequence of one or more of the following characters,
508 and must not be preceded by a space. Other characters are interpreted
509 by the compiler proper, or reserved for future versions of GCC, and so
510 are silently ignored. If you specify characters whose behavior
511 conflicts, the result is undefined.
516 Instead of the normal output, generate a list of @samp{#define}
517 directives for all the macros defined during the execution of the
518 preprocessor, including predefined macros. This gives you a way of
519 finding out what is predefined in your version of the preprocessor.
520 Assuming you have no file @file{foo.h}, the command
523 touch foo.h; cpp -dM foo.h
527 will show all the predefined macros.
531 Like @samp{M} except in two respects: it does @emph{not} include the
532 predefined macros, and it outputs @emph{both} the @samp{#define}
533 directives and the result of preprocessing. Both kinds of output go to
534 the standard output file.
538 Like @samp{D}, but emit only the macro names, not their expansions.
542 Output @samp{#include} directives in addition to the result of
548 Inhibit generation of linemarkers in the output from the preprocessor.
549 This might be useful when running the preprocessor on something that is
550 not C code, and will be sent to a program which might be confused by the
553 @xref{Preprocessor Output}.
558 Do not discard comments. All comments are passed through to the output
559 file, except for comments in processed directives, which are deleted
560 along with the directive.
562 You should be prepared for side effects when using @option{-C}; it
563 causes the preprocessor to treat comments as tokens in their own right.
564 For example, comments appearing at the start of what would be a
565 directive line have the effect of turning that line into an ordinary
566 source line, since the first token on the line is no longer a @samp{#}.
569 Do not discard comments, including during macro expansion. This is
570 like @option{-C}, except that comments contained within macros are
571 also passed through to the output file where the macro is expanded.
573 In addition to the side-effects of the @option{-C} option, the
574 @option{-CC} option causes all C++-style comments inside a macro
575 to be converted to C-style comments. This is to prevent later use
576 of that macro from inadvertently commenting out the remainder of
579 The @option{-CC} option is generally used to support lint comments.
583 Define the macros @sc{__gnuc__}, @sc{__gnuc_minor__} and
584 @sc{__gnuc_patchlevel__}. These are defined automatically when you use
585 @command{gcc -E}; you can turn them off in that case with
588 @item -traditional-cpp
589 @opindex traditional-cpp
590 Try to imitate the behavior of old-fashioned C preprocessors, as
591 opposed to ISO C preprocessors.
593 @xref{Traditional Mode}.
598 Process trigraph sequences.
600 @xref{Initial processing}.
603 These are three-character sequences, all starting with @samp{??}, that
604 are defined by ISO C to stand for single characters. For example,
605 @samp{??/} stands for @samp{\}, so @samp{'??/n'} is a character
606 constant for a newline. By default, GCC ignores trigraphs, but in
607 standard-conforming modes it converts them. See the @option{-std} and
608 @option{-ansi} options.
610 The nine trigraphs and their replacements are
613 Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??-
614 Replacement: [ ] @{ @} # \ ^ | ~
620 Enable special code to work around file systems which only permit very
621 short file names, such as MS-DOS@.
627 Print text describing all the command line options instead of
628 preprocessing anything.
632 Verbose mode. Print out GNU CPP's version number at the beginning of
633 execution, and report the final form of the include path.
637 Print the name of each header file used, in addition to other normal
638 activities. Each name is indented to show how deep in the
639 @samp{#include} stack it is.
644 Print out GNU CPP's version number. With one dash, proceed to
645 preprocess as normal. With two dashes, exit immediately.