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 or GCC-specific macros. The
44 standard predefined macros remain defined.
46 @xref{Standard Predefined Macros}.
51 Add the directory @var{dir} to the list of directories to be searched
56 Directories named by @option{-I} are searched before the standard
57 system include directories. If the directory @var{dir} is a standard
58 system include directory, the option is ignored to ensure that the
59 default search order for system directories and the special treatment
60 of system headers are not defeated
62 (@pxref{System Headers})
68 Write output to @var{file}. This is the same as specifying @var{file}
69 as the second non-option argument to @command{cpp}. @command{gcc} has a
70 different interpretation of a second non-option argument, so you must
71 use @option{-o} to specify the output file.
75 Turns on all optional warnings which are desirable for normal code.
76 At present this is @option{-Wcomment}, @option{-Wtrigraphs},
77 @option{-Wmultichar} and a warning about integer promotion causing a
78 change of sign in @code{#if} expressions. Note that many of the
79 preprocessor's warnings are on by default and have no options to
86 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
87 comment, or whenever a backslash-newline appears in a @samp{//} comment.
88 (Both forms have the same effect.)
93 Most trigraphs in comments cannot affect the meaning of the program.
94 However, a trigraph that would form an escaped newline (@samp{??/} at
95 the end of a line) can, by changing where the comment begins or ends.
96 Therefore, only trigraphs that would form escaped newlines produce
97 warnings inside a comment.
99 This option is implied by @option{-Wall}. If @option{-Wall} is not
100 given, this option is still enabled unless trigraphs are enabled. To
101 get trigraph conversion without warnings, but get the other
102 @option{-Wall} warnings, use @samp{-trigraphs -Wall -Wno-trigraphs}.
105 @opindex Wtraditional
106 Warn about certain constructs that behave differently in traditional and
107 ISO C@. Also warn about ISO C constructs that have no traditional C
108 equivalent, and problematic constructs which should be avoided.
110 @xref{Traditional Mode}.
115 Warn the first time @samp{#import} is used.
119 Warn whenever an identifier which is not a macro is encountered in an
120 @samp{#if} directive, outside of @samp{defined}. Such identifiers are
123 @item -Wunused-macros
124 @opindex Wunused-macros
125 Warn about macros defined in the main file that are unused. A macro
126 is @dfn{used} if it is expanded or tested for existence at least once.
127 The preprocessor will also warn if the macro has not been used at the
128 time it is redefined or undefined.
130 Built-in macros, macros defined on the command line, and macros
131 defined in include files are not warned about.
133 @strong{Note:} If a macro is actually used, but only used in skipped
134 conditional blocks, then CPP will report it as unused. To avoid the
135 warning in such a case, you might improve the scope of the macro's
136 definition by, for example, moving it into the first skipped block.
137 Alternatively, you could provide a dummy use with something like:
140 #if defined the_macro_causing_the_warning
145 @opindex Wendif-labels
146 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
147 This usually happens in code of the form
158 The second and third @code{FOO} should be in comments, but often are not
159 in older programs. This warning is on by default.
163 Make all warnings into hard errors. Source code which triggers warnings
166 @item -Wsystem-headers
167 @opindex Wsystem-headers
168 Issue warnings for code in system headers. These are normally unhelpful
169 in finding bugs in your own code, therefore suppressed. If you are
170 responsible for the system library, you may want to see them.
174 Suppress all warnings, including those which GNU CPP issues by default.
178 Issue all the mandatory diagnostics listed in the C standard. Some of
179 them are left out by default, since they trigger frequently on harmless
182 @item -pedantic-errors
183 @opindex pedantic-errors
184 Issue all the mandatory diagnostics, and make all mandatory diagnostics
185 into errors. This includes mandatory diagnostics that GCC issues
186 without @samp{-pedantic} but treats as warnings.
191 @cindex dependencies, make
192 Instead of outputting the result of preprocessing, output a rule
193 suitable for @command{make} describing the dependencies of the main
194 source file. The preprocessor outputs one @command{make} rule containing
195 the object file name for that source file, a colon, and the names of all
196 the included files, including those coming from @option{-include} or
197 @option{-imacros} command line options.
199 Unless specified explicitly (with @option{-MT} or @option{-MQ}), the
200 object file name consists of the basename of the source file with any
201 suffix replaced with object file suffix. If there are many included
202 files then the rule is split into several lines using @samp{\}-newline.
203 The rule has no commands.
205 This option does not suppress the preprocessor's debug output, such as
206 @option{-dM}. To avoid mixing such debug output with the dependency
207 rules you should explicitly specify the dependency output file with
208 @option{-MF}, or use an environment variable like
209 @env{DEPENDENCIES_OUTPUT} (@pxref{Environment Variables}). Debug output
210 will still be sent to the regular output stream as normal.
212 Passing @option{-M} to the driver implies @option{-E}, and suppresses
213 warnings with an implicit @option{-w}.
217 Like @option{-M} but do not mention header files that are found in
218 system header directories, nor header files that are included,
219 directly or indirectly, from such a header.
221 This implies that the choice of angle brackets or double quotes in an
222 @samp{#include} directive does not in itself determine whether that
223 header will appear in @option{-MM} dependency output. This is a
224 slight change in semantics from GCC versions 3.0 and earlier.
229 When used with @option{-M} or @option{-MM}, specifies a
230 file to write the dependencies to. If no @option{-MF} switch is given
231 the preprocessor sends the rules to the same place it would have sent
234 When used with the driver options @option{-MD} or @option{-MMD},
235 @option{-MF} overrides the default dependency output file.
239 In conjunction with an option such as @option{-M} requesting
240 dependency generation, @option{-MG} assumes missing header files are
241 generated files and adds them to the dependency list without raising
242 an error. The dependency filename is taken directly from the
243 @code{#include} directive without prepending any path. @option{-MG}
244 also suppresses preprocessed output, as a missing header file renders
247 This feature is used in automatic updating of makefiles.
251 This option instructs CPP to add a phony target for each dependency
252 other than the main file, causing each to depend on nothing. These
253 dummy rules work around errors @command{make} gives if you remove header
254 files without updating the @file{Makefile} to match.
256 This is typical output:
259 test.o: test.c test.h
264 @item -MT @var{target}
267 Change the target of the rule emitted by dependency generation. By
268 default CPP takes the name of the main input file, including any path,
269 deletes any file suffix such as @samp{.c}, and appends the platform's
270 usual object suffix. The result is the target.
272 An @option{-MT} option will set the target to be exactly the string you
273 specify. If you want multiple targets, you can specify them as a single
274 argument to @option{-MT}, or use multiple @option{-MT} options.
276 For example, @option{@w{-MT '$(objpfx)foo.o'}} might give
279 $(objpfx)foo.o: foo.c
282 @item -MQ @var{target}
285 Same as @option{-MT}, but it quotes any characters which are special to
286 Make. @option{@w{-MQ '$(objpfx)foo.o'}} gives
289 $$(objpfx)foo.o: foo.c
292 The default target is automatically quoted, as if it were given with
297 @option{-MD} is equivalent to @option{-M -MF @var{file}}, except that
298 @option{-E} is not implied. The driver determines @var{file} based on
299 whether an @option{-o} option is given. If it is, the driver uses its
300 argument but with a suffix of @file{.d}, otherwise it take the
301 basename of the input file and applies a @file{.d} suffix.
303 If @option{-MD} is used in conjunction with @option{-E}, any
304 @option{-o} switch is understood to specify the dependency output file
305 (but @pxref{-MF}), but if used without @option{-E}, each @option{-o}
306 is understood to specify a target object file.
308 Since @option{-E} is not implied, @option{-MD} can be used to generate
309 a dependency output file as a side-effect of the compilation process.
313 Like @option{-MD} except mention only user header files, not system
319 When using precompiled headers (@pxref{Precompiled Headers}), this flag
320 will cause the dependency-output flags to also list the files from the
321 precompiled header's dependencies. If not specified only the
322 precompiled header would be listed and not the files that were used to
323 create it because those files are not consulted when a precompiled
329 @itemx -x objective-c
330 @itemx -x assembler-with-cpp
332 Specify the source language: C, C++, Objective-C, or assembly. This has
333 nothing to do with standards conformance or extensions; it merely
334 selects which base syntax to expect. If you give none of these options,
335 cpp will deduce the language from the extension of the source file:
336 @samp{.c}, @samp{.cc}, @samp{.m}, or @samp{.S}. Some other common
337 extensions for C++ and assembly are also recognized. If cpp does not
338 recognize the extension, it will treat the file as C; this is the most
341 @strong{Note:} Previous versions of cpp accepted a @option{-lang} option
342 which selected both the language and the standards conformance level.
343 This option has been removed, because it conflicts with the @option{-l}
346 @item -std=@var{standard}
350 Specify the standard to which the code should conform. Currently CPP
351 knows about C and C++ standards; others may be added in the future.
358 The ISO C standard from 1990. @samp{c89} is the customary shorthand for
359 this version of the standard.
361 The @option{-ansi} option is equivalent to @option{-std=c89}.
364 The 1990 C standard, as amended in 1994.
370 The revised ISO C standard, published in December 1999. Before
371 publication, this was known as C9X@.
374 The 1990 C standard plus GNU extensions. This is the default.
378 The 1999 C standard plus GNU extensions.
381 The 1998 ISO C++ standard plus amendments.
384 The same as @option{-std=c++98} plus GNU extensions. This is the
385 default for C++ code.
390 Split the include path. Any directories specified with @option{-I}
391 options before @option{-I-} are searched only for headers requested with
392 @code{@w{#include "@var{file}"}}; they are not searched for
393 @code{@w{#include <@var{file}>}}. If additional directories are
394 specified with @option{-I} options after the @option{-I-}, those
395 directories are searched for all @samp{#include} directives.
397 In addition, @option{-I-} inhibits the use of the directory of the current
398 file directory as the first search directory for @code{@w{#include
406 Do not search the standard system directories for header files.
407 Only the directories you have specified with @option{-I} options
408 (and the directory of the current file, if appropriate) are searched.
412 Do not search for header files in the C++-specific standard directories,
413 but do still search the other standard directories. (This option is
414 used when building the C++ library.)
416 @item -include @var{file}
418 Process @var{file} as if @code{#include "file"} appeared as the first
419 line of the primary source file. However, the first directory searched
420 for @var{file} is the preprocessor's working directory @emph{instead of}
421 the directory containing the main source file. If not found there, it
422 is searched for in the remainder of the @code{#include "@dots{}"} search
425 If multiple @option{-include} options are given, the files are included
426 in the order they appear on the command line.
428 @item -imacros @var{file}
430 Exactly like @option{-include}, except that any output produced by
431 scanning @var{file} is thrown away. Macros it defines remain defined.
432 This allows you to acquire all the macros from a header without also
433 processing its declarations.
435 All files specified by @option{-imacros} are processed before all files
436 specified by @option{-include}.
438 @item -idirafter @var{dir}
440 Search @var{dir} for header files, but do it @emph{after} all
441 directories specified with @option{-I} and the standard system directories
442 have been exhausted. @var{dir} is treated as a system include directory.
444 @item -iprefix @var{prefix}
446 Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix}
447 options. If the prefix represents a directory, you should include the
450 @item -iwithprefix @var{dir}
451 @itemx -iwithprefixbefore @var{dir}
453 @opindex iwithprefixbefore
454 Append @var{dir} to the prefix specified previously with
455 @option{-iprefix}, and add the resulting directory to the include search
456 path. @option{-iwithprefixbefore} puts it in the same place @option{-I}
457 would; @option{-iwithprefix} puts it where @option{-idirafter} would.
459 Use of these options is discouraged.
461 @item -isystem @var{dir}
463 Search @var{dir} for header files, after all directories specified by
464 @option{-I} but before the standard system directories. Mark it
465 as a system directory, so that it gets the same special treatment as
466 is applied to the standard system directories.
468 @xref{System Headers}.
472 @opindex fpreprocessed
473 Indicate to the preprocessor that the input file has already been
474 preprocessed. This suppresses things like macro expansion, trigraph
475 conversion, escaped newline splicing, and processing of most directives.
476 The preprocessor still recognizes and removes comments, so that you can
477 pass a file preprocessed with @option{-C} to the compiler without
478 problems. In this mode the integrated preprocessor is little more than
479 a tokenizer for the front ends.
481 @option{-fpreprocessed} is implicit if the input file has one of the
482 extensions @samp{.i}, @samp{.ii} or @samp{.mi}. These are the
483 extensions that GCC uses for preprocessed files created by
484 @option{-save-temps}.
486 @item -ftabstop=@var{width}
488 Set the distance between tab stops. This helps the preprocessor report
489 correct column numbers in warnings or errors, even if tabs appear on the
490 line. If the value is less than 1 or greater than 100, the option is
491 ignored. The default is 8.
493 @item -fno-show-column
494 @opindex fno-show-column
495 Do not print column numbers in diagnostics. This may be necessary if
496 diagnostics are being scanned by a program that does not understand the
497 column numbers, such as @command{dejagnu}.
499 @item -A @var{predicate}=@var{answer}
501 Make an assertion with the predicate @var{predicate} and answer
502 @var{answer}. This form is preferred to the older form @option{-A
503 @var{predicate}(@var{answer})}, which is still supported, because
504 it does not use shell special characters.
509 @item -A -@var{predicate}=@var{answer}
510 Cancel an assertion with the predicate @var{predicate} and answer
514 @var{CHARS} is a sequence of one or more of the following characters,
515 and must not be preceded by a space. Other characters are interpreted
516 by the compiler proper, or reserved for future versions of GCC, and so
517 are silently ignored. If you specify characters whose behavior
518 conflicts, the result is undefined.
523 Instead of the normal output, generate a list of @samp{#define}
524 directives for all the macros defined during the execution of the
525 preprocessor, including predefined macros. This gives you a way of
526 finding out what is predefined in your version of the preprocessor.
527 Assuming you have no file @file{foo.h}, the command
530 touch foo.h; cpp -dM foo.h
534 will show all the predefined macros.
538 Like @samp{M} except in two respects: it does @emph{not} include the
539 predefined macros, and it outputs @emph{both} the @samp{#define}
540 directives and the result of preprocessing. Both kinds of output go to
541 the standard output file.
545 Like @samp{D}, but emit only the macro names, not their expansions.
549 Output @samp{#include} directives in addition to the result of
555 Inhibit generation of linemarkers in the output from the preprocessor.
556 This might be useful when running the preprocessor on something that is
557 not C code, and will be sent to a program which might be confused by the
560 @xref{Preprocessor Output}.
565 Do not discard comments. All comments are passed through to the output
566 file, except for comments in processed directives, which are deleted
567 along with the directive.
569 You should be prepared for side effects when using @option{-C}; it
570 causes the preprocessor to treat comments as tokens in their own right.
571 For example, comments appearing at the start of what would be a
572 directive line have the effect of turning that line into an ordinary
573 source line, since the first token on the line is no longer a @samp{#}.
576 Do not discard comments, including during macro expansion. This is
577 like @option{-C}, except that comments contained within macros are
578 also passed through to the output file where the macro is expanded.
580 In addition to the side-effects of the @option{-C} option, the
581 @option{-CC} option causes all C++-style comments inside a macro
582 to be converted to C-style comments. This is to prevent later use
583 of that macro from inadvertently commenting out the remainder of
586 The @option{-CC} option is generally used to support lint comments.
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. Precompiled header files are also
640 printed, even if they are found to be invalid; an invalid precompiled
641 header file is printed with @samp{...x} and a valid one with @samp{...!} .
646 Print out GNU CPP's version number. With one dash, proceed to
647 preprocess as normal. With two dashes, exit immediately.