1@c Copyright (c) 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2@c 2010, 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. 5 6@c --------------------------------------------------------------------- 7@c Options affecting the preprocessor 8@c --------------------------------------------------------------------- 9 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. 12 13@table @gcctabopt 14@item -D @var{name} 15@opindex D 16Predefine @var{name} as a macro, with definition @code{1}. 17 18@item -D @var{name}=@var{definition} 19The contents of @var{definition} are tokenized and processed as if 20they appeared during translation phase three in a @samp{#define} 21directive. In particular, the definition will be truncated by 22embedded newline characters. 23 24If you are invoking the preprocessor from a shell or shell-like 25program you may need to use the shell's quoting syntax to protect 26characters such as spaces that have a meaning in the shell syntax. 27 28If you wish to define a function-like macro on the command line, write 29its argument list with surrounding parentheses before the equals sign 30(if any). Parentheses are meaningful to most shells, so you will need 31to quote the option. With @command{sh} and @command{csh}, 32@option{-D'@var{name}(@var{args@dots{}})=@var{definition}'} works. 33 34@option{-D} and @option{-U} options are processed in the order they 35are given on the command line. All @option{-imacros @var{file}} and 36@option{-include @var{file}} options are processed after all 37@option{-D} and @option{-U} options. 38 39@item -U @var{name} 40@opindex U 41Cancel any previous definition of @var{name}, either built in or 42provided with a @option{-D} option. 43 44@item -undef 45@opindex undef 46Do not predefine any system-specific or GCC-specific macros. The 47standard predefined macros remain defined. 48@ifset cppmanual 49@xref{Standard Predefined Macros}. 50@end ifset 51 52@item -I @var{dir} 53@opindex I 54Add the directory @var{dir} to the list of directories to be searched 55for header files. 56@ifset cppmanual 57@xref{Search Path}. 58@end ifset 59Directories named by @option{-I} are searched before the standard 60system include directories. If the directory @var{dir} is a standard 61system include directory, the option is ignored to ensure that the 62default search order for system directories and the special treatment 63of system headers are not defeated 64@ifset cppmanual 65(@pxref{System Headers}) 66@end ifset 67. 68If @var{dir} begins with @code{=}, then the @code{=} will be replaced 69by the sysroot prefix; see @option{--sysroot} and @option{-isysroot}. 70 71@item -o @var{file} 72@opindex o 73Write output to @var{file}. This is the same as specifying @var{file} 74as the second non-option argument to @command{cpp}. @command{gcc} has a 75different interpretation of a second non-option argument, so you must 76use @option{-o} to specify the output file. 77 78@item -Wall 79@opindex Wall 80Turns on all optional warnings which are desirable for normal code. 81At present this is @option{-Wcomment}, @option{-Wtrigraphs}, 82@option{-Wmultichar} and a warning about integer promotion causing a 83change of sign in @code{#if} expressions. Note that many of the 84preprocessor's warnings are on by default and have no options to 85control them. 86 87@item -Wcomment 88@itemx -Wcomments 89@opindex Wcomment 90@opindex Wcomments 91Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*} 92comment, or whenever a backslash-newline appears in a @samp{//} comment. 93(Both forms have the same effect.) 94 95@item -Wtrigraphs 96@opindex Wtrigraphs 97@anchor{Wtrigraphs} 98Most trigraphs in comments cannot affect the meaning of the program. 99However, a trigraph that would form an escaped newline (@samp{??/} at 100the end of a line) can, by changing where the comment begins or ends. 101Therefore, only trigraphs that would form escaped newlines produce 102warnings inside a comment. 103 104This option is implied by @option{-Wall}. If @option{-Wall} is not 105given, this option is still enabled unless trigraphs are enabled. To 106get trigraph conversion without warnings, but get the other 107@option{-Wall} warnings, use @samp{-trigraphs -Wall -Wno-trigraphs}. 108 109@item -Wtraditional 110@opindex Wtraditional 111Warn about certain constructs that behave differently in traditional and 112ISO C@. Also warn about ISO C constructs that have no traditional C 113equivalent, and problematic constructs which should be avoided. 114@ifset cppmanual 115@xref{Traditional Mode}. 116@end ifset 117 118@item -Wundef 119@opindex Wundef 120Warn whenever an identifier which is not a macro is encountered in an 121@samp{#if} directive, outside of @samp{defined}. Such identifiers are 122replaced with zero. 123 124@item -Wunused-macros 125@opindex Wunused-macros 126Warn about macros defined in the main file that are unused. A macro 127is @dfn{used} if it is expanded or tested for existence at least once. 128The preprocessor will also warn if the macro has not been used at the 129time it is redefined or undefined. 130 131Built-in macros, macros defined on the command line, and macros 132defined in include files are not warned about. 133 134@emph{Note:} If a macro is actually used, but only used in skipped 135conditional blocks, then CPP will report it as unused. To avoid the 136warning in such a case, you might improve the scope of the macro's 137definition by, for example, moving it into the first skipped block. 138Alternatively, you could provide a dummy use with something like: 139 140@smallexample 141#if defined the_macro_causing_the_warning 142#endif 143@end smallexample 144 145@item -Wendif-labels 146@opindex Wendif-labels 147Warn whenever an @samp{#else} or an @samp{#endif} are followed by text. 148This usually happens in code of the form 149 150@smallexample 151#if FOO 152@dots{} 153#else FOO 154@dots{} 155#endif FOO 156@end smallexample 157 158@noindent 159The second and third @code{FOO} should be in comments, but often are not 160in older programs. This warning is on by default. 161 162@item -Werror 163@opindex Werror 164Make all warnings into hard errors. Source code which triggers warnings 165will be rejected. 166 167@item -Wsystem-headers 168@opindex Wsystem-headers 169Issue warnings for code in system headers. These are normally unhelpful 170in finding bugs in your own code, therefore suppressed. If you are 171responsible for the system library, you may want to see them. 172 173@item -w 174@opindex w 175Suppress all warnings, including those which GNU CPP issues by default. 176 177@item -pedantic 178@opindex pedantic 179Issue all the mandatory diagnostics listed in the C standard. Some of 180them are left out by default, since they trigger frequently on harmless 181code. 182 183@item -pedantic-errors 184@opindex pedantic-errors 185Issue all the mandatory diagnostics, and make all mandatory diagnostics 186into errors. This includes mandatory diagnostics that GCC issues 187without @samp{-pedantic} but treats as warnings. 188 189@item -M 190@opindex M 191@cindex @command{make} 192@cindex dependencies, @command{make} 193Instead of outputting the result of preprocessing, output a rule 194suitable for @command{make} describing the dependencies of the main 195source file. The preprocessor outputs one @command{make} rule containing 196the object file name for that source file, a colon, and the names of all 197the included files, including those coming from @option{-include} or 198@option{-imacros} command line options. 199 200Unless specified explicitly (with @option{-MT} or @option{-MQ}), the 201object file name consists of the name of the source file with any 202suffix replaced with object file suffix and with any leading directory 203parts removed. If there are many included files then the rule is 204split into several lines using @samp{\}-newline. The rule has no 205commands. 206 207This option does not suppress the preprocessor's debug output, such as 208@option{-dM}. To avoid mixing such debug output with the dependency 209rules you should explicitly specify the dependency output file with 210@option{-MF}, or use an environment variable like 211@env{DEPENDENCIES_OUTPUT} (@pxref{Environment Variables}). Debug output 212will still be sent to the regular output stream as normal. 213 214Passing @option{-M} to the driver implies @option{-E}, and suppresses 215warnings with an implicit @option{-w}. 216 217@item -MM 218@opindex MM 219Like @option{-M} but do not mention header files that are found in 220system header directories, nor header files that are included, 221directly or indirectly, from such a header. 222 223This implies that the choice of angle brackets or double quotes in an 224@samp{#include} directive does not in itself determine whether that 225header will appear in @option{-MM} dependency output. This is a 226slight change in semantics from GCC versions 3.0 and earlier. 227 228@anchor{dashMF} 229@item -MF @var{file} 230@opindex MF 231When used with @option{-M} or @option{-MM}, specifies a 232file to write the dependencies to. If no @option{-MF} switch is given 233the preprocessor sends the rules to the same place it would have sent 234preprocessed output. 235 236When used with the driver options @option{-MD} or @option{-MMD}, 237@option{-MF} overrides the default dependency output file. 238 239@item -MG 240@opindex MG 241In conjunction with an option such as @option{-M} requesting 242dependency generation, @option{-MG} assumes missing header files are 243generated files and adds them to the dependency list without raising 244an error. The dependency filename is taken directly from the 245@code{#include} directive without prepending any path. @option{-MG} 246also suppresses preprocessed output, as a missing header file renders 247this useless. 248 249This feature is used in automatic updating of makefiles. 250 251@item -MP 252@opindex MP 253This option instructs CPP to add a phony target for each dependency 254other than the main file, causing each to depend on nothing. These 255dummy rules work around errors @command{make} gives if you remove header 256files without updating the @file{Makefile} to match. 257 258This is typical output: 259 260@smallexample 261test.o: test.c test.h 262 263test.h: 264@end smallexample 265 266@item -MT @var{target} 267@opindex MT 268 269Change the target of the rule emitted by dependency generation. By 270default CPP takes the name of the main input file, deletes any 271directory components and any file suffix such as @samp{.c}, and 272appends the platform's usual object suffix. The result is the target. 273 274An @option{-MT} option will set the target to be exactly the string you 275specify. If you want multiple targets, you can specify them as a single 276argument to @option{-MT}, or use multiple @option{-MT} options. 277 278For example, @option{@w{-MT '$(objpfx)foo.o'}} might give 279 280@smallexample 281$(objpfx)foo.o: foo.c 282@end smallexample 283 284@item -MQ @var{target} 285@opindex MQ 286 287Same as @option{-MT}, but it quotes any characters which are special to 288Make. @option{@w{-MQ '$(objpfx)foo.o'}} gives 289 290@smallexample 291$$(objpfx)foo.o: foo.c 292@end smallexample 293 294The default target is automatically quoted, as if it were given with 295@option{-MQ}. 296 297@item -MD 298@opindex MD 299@option{-MD} is equivalent to @option{-M -MF @var{file}}, except that 300@option{-E} is not implied. The driver determines @var{file} based on 301whether an @option{-o} option is given. If it is, the driver uses its 302argument but with a suffix of @file{.d}, otherwise it takes the name 303of the input file, removes any directory components and suffix, and 304applies a @file{.d} suffix. 305 306If @option{-MD} is used in conjunction with @option{-E}, any 307@option{-o} switch is understood to specify the dependency output file 308(@pxref{dashMF,,-MF}), but if used without @option{-E}, each @option{-o} 309is understood to specify a target object file. 310 311Since @option{-E} is not implied, @option{-MD} can be used to generate 312a dependency output file as a side-effect of the compilation process. 313 314@item -MMD 315@opindex MMD 316Like @option{-MD} except mention only user header files, not system 317header files. 318 319@ifclear cppmanual 320@item -fpch-deps 321@opindex fpch-deps 322When using precompiled headers (@pxref{Precompiled Headers}), this flag 323will cause the dependency-output flags to also list the files from the 324precompiled header's dependencies. If not specified only the 325precompiled header would be listed and not the files that were used to 326create it because those files are not consulted when a precompiled 327header is used. 328 329@item -fpch-preprocess 330@opindex fpch-preprocess 331This option allows use of a precompiled header (@pxref{Precompiled 332Headers}) together with @option{-E}. It inserts a special @code{#pragma}, 333@code{#pragma GCC pch_preprocess "@var{filename}"} in the output to mark 334the place where the precompiled header was found, and its @var{filename}. 335When @option{-fpreprocessed} is in use, GCC recognizes this @code{#pragma} 336and loads the PCH@. 337 338This option is off by default, because the resulting preprocessed output 339is only really suitable as input to GCC@. It is switched on by 340@option{-save-temps}. 341 342You should not write this @code{#pragma} in your own code, but it is 343safe to edit the filename if the PCH file is available in a different 344location. The filename may be absolute or it may be relative to GCC's 345current directory. 346 347@end ifclear 348@item -x c 349@itemx -x c++ 350@itemx -x objective-c 351@itemx -x assembler-with-cpp 352@opindex x 353Specify the source language: C, C++, Objective-C, or assembly. This has 354nothing to do with standards conformance or extensions; it merely 355selects which base syntax to expect. If you give none of these options, 356cpp will deduce the language from the extension of the source file: 357@samp{.c}, @samp{.cc}, @samp{.m}, or @samp{.S}. Some other common 358extensions for C++ and assembly are also recognized. If cpp does not 359recognize the extension, it will treat the file as C; this is the most 360generic mode. 361 362@emph{Note:} Previous versions of cpp accepted a @option{-lang} option 363which selected both the language and the standards conformance level. 364This option has been removed, because it conflicts with the @option{-l} 365option. 366 367@item -std=@var{standard} 368@itemx -ansi 369@opindex ansi 370@opindex std= 371Specify the standard to which the code should conform. Currently CPP 372knows about C and C++ standards; others may be added in the future. 373 374@var{standard} 375may be one of: 376@table @code 377@item c90 378@itemx c89 379@itemx iso9899:1990 380The ISO C standard from 1990. @samp{c90} is the customary shorthand for 381this version of the standard. 382 383The @option{-ansi} option is equivalent to @option{-std=c90}. 384 385@item iso9899:199409 386The 1990 C standard, as amended in 1994. 387 388@item iso9899:1999 389@itemx c99 390@itemx iso9899:199x 391@itemx c9x 392The revised ISO C standard, published in December 1999. Before 393publication, this was known as C9X@. 394 395@item iso9899:2011 396@itemx c11 397@itemx c1x 398The revised ISO C standard, published in December 2011. Before 399publication, this was known as C1X@. 400 401@item gnu90 402@itemx gnu89 403The 1990 C standard plus GNU extensions. This is the default. 404 405@item gnu99 406@itemx gnu9x 407The 1999 C standard plus GNU extensions. 408 409@item gnu11 410@itemx gnu1x 411The 2011 C standard plus GNU extensions. 412 413@item c++98 414The 1998 ISO C++ standard plus amendments. 415 416@item gnu++98 417The same as @option{-std=c++98} plus GNU extensions. This is the 418default for C++ code. 419@end table 420 421@item -I- 422@opindex I- 423Split the include path. Any directories specified with @option{-I} 424options before @option{-I-} are searched only for headers requested with 425@code{@w{#include "@var{file}"}}; they are not searched for 426@code{@w{#include <@var{file}>}}. If additional directories are 427specified with @option{-I} options after the @option{-I-}, those 428directories are searched for all @samp{#include} directives. 429 430In addition, @option{-I-} inhibits the use of the directory of the current 431file directory as the first search directory for @code{@w{#include 432"@var{file}"}}. 433@ifset cppmanual 434@xref{Search Path}. 435@end ifset 436This option has been deprecated. 437 438@item -nostdinc 439@opindex nostdinc 440Do not search the standard system directories for header files. 441Only the directories you have specified with @option{-I} options 442(and the directory of the current file, if appropriate) are searched. 443 444@item -nostdinc++ 445@opindex nostdinc++ 446Do not search for header files in the C++-specific standard directories, 447but do still search the other standard directories. (This option is 448used when building the C++ library.) 449 450@item -include @var{file} 451@opindex include 452Process @var{file} as if @code{#include "file"} appeared as the first 453line of the primary source file. However, the first directory searched 454for @var{file} is the preprocessor's working directory @emph{instead of} 455the directory containing the main source file. If not found there, it 456is searched for in the remainder of the @code{#include "@dots{}"} search 457chain as normal. 458 459If multiple @option{-include} options are given, the files are included 460in the order they appear on the command line. 461 462@item -imacros @var{file} 463@opindex imacros 464Exactly like @option{-include}, except that any output produced by 465scanning @var{file} is thrown away. Macros it defines remain defined. 466This allows you to acquire all the macros from a header without also 467processing its declarations. 468 469All files specified by @option{-imacros} are processed before all files 470specified by @option{-include}. 471 472@item -idirafter @var{dir} 473@opindex idirafter 474Search @var{dir} for header files, but do it @emph{after} all 475directories specified with @option{-I} and the standard system directories 476have been exhausted. @var{dir} is treated as a system include directory. 477If @var{dir} begins with @code{=}, then the @code{=} will be replaced 478by the sysroot prefix; see @option{--sysroot} and @option{-isysroot}. 479 480@item -iprefix @var{prefix} 481@opindex iprefix 482Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix} 483options. If the prefix represents a directory, you should include the 484final @samp{/}. 485 486@item -iwithprefix @var{dir} 487@itemx -iwithprefixbefore @var{dir} 488@opindex iwithprefix 489@opindex iwithprefixbefore 490Append @var{dir} to the prefix specified previously with 491@option{-iprefix}, and add the resulting directory to the include search 492path. @option{-iwithprefixbefore} puts it in the same place @option{-I} 493would; @option{-iwithprefix} puts it where @option{-idirafter} would. 494 495@item -isysroot @var{dir} 496@opindex isysroot 497This option is like the @option{--sysroot} option, but applies only to 498header files (except for Darwin targets, where it applies to both header 499files and libraries). See the @option{--sysroot} option for more 500information. 501 502@item -imultilib @var{dir} 503@opindex imultilib 504Use @var{dir} as a subdirectory of the directory containing 505target-specific C++ headers. 506 507@item -isystem @var{dir} 508@opindex isystem 509Search @var{dir} for header files, after all directories specified by 510@option{-I} but before the standard system directories. Mark it 511as a system directory, so that it gets the same special treatment as 512is applied to the standard system directories. 513@ifset cppmanual 514@xref{System Headers}. 515@end ifset 516If @var{dir} begins with @code{=}, then the @code{=} will be replaced 517by the sysroot prefix; see @option{--sysroot} and @option{-isysroot}. 518 519@item -iquote @var{dir} 520@opindex iquote 521Search @var{dir} only for header files requested with 522@code{@w{#include "@var{file}"}}; they are not searched for 523@code{@w{#include <@var{file}>}}, before all directories specified by 524@option{-I} and before the standard system directories. 525@ifset cppmanual 526@xref{Search Path}. 527@end ifset 528If @var{dir} begins with @code{=}, then the @code{=} will be replaced 529by the sysroot prefix; see @option{--sysroot} and @option{-isysroot}. 530 531@item -fdirectives-only 532@opindex fdirectives-only 533When preprocessing, handle directives, but do not expand macros. 534 535The option's behavior depends on the @option{-E} and @option{-fpreprocessed} 536options. 537 538With @option{-E}, preprocessing is limited to the handling of directives 539such as @code{#define}, @code{#ifdef}, and @code{#error}. Other 540preprocessor operations, such as macro expansion and trigraph 541conversion are not performed. In addition, the @option{-dD} option is 542implicitly enabled. 543 544With @option{-fpreprocessed}, predefinition of command line and most 545builtin macros is disabled. Macros such as @code{__LINE__}, which are 546contextually dependent, are handled normally. This enables compilation of 547files previously preprocessed with @code{-E -fdirectives-only}. 548 549With both @option{-E} and @option{-fpreprocessed}, the rules for 550@option{-fpreprocessed} take precedence. This enables full preprocessing of 551files previously preprocessed with @code{-E -fdirectives-only}. 552 553@item -fdollars-in-identifiers 554@opindex fdollars-in-identifiers 555@anchor{fdollars-in-identifiers} 556Accept @samp{$} in identifiers. 557@ifset cppmanual 558@xref{Identifier characters}. 559@end ifset 560 561@item -fextended-identifiers 562@opindex fextended-identifiers 563Accept universal character names in identifiers. This option is 564experimental; in a future version of GCC, it will be enabled by 565default for C99 and C++. 566 567@item -fpreprocessed 568@opindex fpreprocessed 569Indicate to the preprocessor that the input file has already been 570preprocessed. This suppresses things like macro expansion, trigraph 571conversion, escaped newline splicing, and processing of most directives. 572The preprocessor still recognizes and removes comments, so that you can 573pass a file preprocessed with @option{-C} to the compiler without 574problems. In this mode the integrated preprocessor is little more than 575a tokenizer for the front ends. 576 577@option{-fpreprocessed} is implicit if the input file has one of the 578extensions @samp{.i}, @samp{.ii} or @samp{.mi}. These are the 579extensions that GCC uses for preprocessed files created by 580@option{-save-temps}. 581 582@item -ftabstop=@var{width} 583@opindex ftabstop 584Set the distance between tab stops. This helps the preprocessor report 585correct column numbers in warnings or errors, even if tabs appear on the 586line. If the value is less than 1 or greater than 100, the option is 587ignored. The default is 8. 588 589@item -fdebug-cpp 590@opindex fdebug-cpp 591This option is only useful for debugging GCC. When used with 592@option{-E}, dumps debugging information about location maps. Every 593token in the output is preceded by the dump of the map its location 594belongs to. The dump of the map holding the location of a token would 595be: 596@smallexample 597@{@samp{P}:@file{/file/path};@samp{F}:@file{/includer/path};@samp{L}:@var{line_num};@samp{C}:@var{col_num};@samp{S}:@var{system_header_p};@samp{M}:@var{map_address};@samp{E}:@var{macro_expansion_p},@samp{loc}:@var{location}@} 598@end smallexample 599 600When used without @option{-E}, this option has no effect. 601 602@item -ftrack-macro-expansion@r{[}=@var{level}@r{]} 603@opindex ftrack-macro-expansion 604Track locations of tokens across macro expansions. This allows the 605compiler to emit diagnostic about the current macro expansion stack 606when a compilation error occurs in a macro expansion. Using this 607option makes the preprocessor and the compiler consume more 608memory. The @var{level} parameter can be used to choose the level of 609precision of token location tracking thus decreasing the memory 610consumption if necessary. Value @samp{0} of @var{level} de-activates 611this option just as if no @option{-ftrack-macro-expansion} was present 612on the command line. Value @samp{1} tracks tokens locations in a 613degraded mode for the sake of minimal memory overhead. In this mode 614all tokens resulting from the expansion of an argument of a 615function-like macro have the same location. Value @samp{2} tracks 616tokens locations completely. This value is the most memory hungry. 617When this option is given no argument, the default parameter value is 618@samp{2}. 619 620@item -fexec-charset=@var{charset} 621@opindex fexec-charset 622@cindex character set, execution 623Set the execution character set, used for string and character 624constants. The default is UTF-8. @var{charset} can be any encoding 625supported by the system's @code{iconv} library routine. 626 627@item -fwide-exec-charset=@var{charset} 628@opindex fwide-exec-charset 629@cindex character set, wide execution 630Set the wide execution character set, used for wide string and 631character constants. The default is UTF-32 or UTF-16, whichever 632corresponds to the width of @code{wchar_t}. As with 633@option{-fexec-charset}, @var{charset} can be any encoding supported 634by the system's @code{iconv} library routine; however, you will have 635problems with encodings that do not fit exactly in @code{wchar_t}. 636 637@item -finput-charset=@var{charset} 638@opindex finput-charset 639@cindex character set, input 640Set the input character set, used for translation from the character 641set of the input file to the source character set used by GCC@. If the 642locale does not specify, or GCC cannot get this information from the 643locale, the default is UTF-8. This can be overridden by either the locale 644or this command line option. Currently the command line option takes 645precedence if there's a conflict. @var{charset} can be any encoding 646supported by the system's @code{iconv} library routine. 647 648@item -fworking-directory 649@opindex fworking-directory 650@opindex fno-working-directory 651Enable generation of linemarkers in the preprocessor output that will 652let the compiler know the current working directory at the time of 653preprocessing. When this option is enabled, the preprocessor will 654emit, after the initial linemarker, a second linemarker with the 655current working directory followed by two slashes. GCC will use this 656directory, when it's present in the preprocessed input, as the 657directory emitted as the current working directory in some debugging 658information formats. This option is implicitly enabled if debugging 659information is enabled, but this can be inhibited with the negated 660form @option{-fno-working-directory}. If the @option{-P} flag is 661present in the command line, this option has no effect, since no 662@code{#line} directives are emitted whatsoever. 663 664@item -fno-show-column 665@opindex fno-show-column 666Do not print column numbers in diagnostics. This may be necessary if 667diagnostics are being scanned by a program that does not understand the 668column numbers, such as @command{dejagnu}. 669 670@item -A @var{predicate}=@var{answer} 671@opindex A 672Make an assertion with the predicate @var{predicate} and answer 673@var{answer}. This form is preferred to the older form @option{-A 674@var{predicate}(@var{answer})}, which is still supported, because 675it does not use shell special characters. 676@ifset cppmanual 677@xref{Obsolete Features}. 678@end ifset 679 680@item -A -@var{predicate}=@var{answer} 681Cancel an assertion with the predicate @var{predicate} and answer 682@var{answer}. 683 684@item -dCHARS 685@var{CHARS} is a sequence of one or more of the following characters, 686and must not be preceded by a space. Other characters are interpreted 687by the compiler proper, or reserved for future versions of GCC, and so 688are silently ignored. If you specify characters whose behavior 689conflicts, the result is undefined. 690 691@table @samp 692@item M 693@opindex dM 694Instead of the normal output, generate a list of @samp{#define} 695directives for all the macros defined during the execution of the 696preprocessor, including predefined macros. This gives you a way of 697finding out what is predefined in your version of the preprocessor. 698Assuming you have no file @file{foo.h}, the command 699 700@smallexample 701touch foo.h; cpp -dM foo.h 702@end smallexample 703 704@noindent 705will show all the predefined macros. 706 707If you use @option{-dM} without the @option{-E} option, @option{-dM} is 708interpreted as a synonym for @option{-fdump-rtl-mach}. 709@xref{Debugging Options, , ,gcc}. 710 711@item D 712@opindex dD 713Like @samp{M} except in two respects: it does @emph{not} include the 714predefined macros, and it outputs @emph{both} the @samp{#define} 715directives and the result of preprocessing. Both kinds of output go to 716the standard output file. 717 718@item N 719@opindex dN 720Like @samp{D}, but emit only the macro names, not their expansions. 721 722@item I 723@opindex dI 724Output @samp{#include} directives in addition to the result of 725preprocessing. 726 727@item U 728@opindex dU 729Like @samp{D} except that only macros that are expanded, or whose 730definedness is tested in preprocessor directives, are output; the 731output is delayed until the use or test of the macro; and 732@samp{#undef} directives are also output for macros tested but 733undefined at the time. 734@end table 735 736@item -P 737@opindex P 738Inhibit generation of linemarkers in the output from the preprocessor. 739This might be useful when running the preprocessor on something that is 740not C code, and will be sent to a program which might be confused by the 741linemarkers. 742@ifset cppmanual 743@xref{Preprocessor Output}. 744@end ifset 745 746@item -C 747@opindex C 748Do not discard comments. All comments are passed through to the output 749file, except for comments in processed directives, which are deleted 750along with the directive. 751 752You should be prepared for side effects when using @option{-C}; it 753causes the preprocessor to treat comments as tokens in their own right. 754For example, comments appearing at the start of what would be a 755directive line have the effect of turning that line into an ordinary 756source line, since the first token on the line is no longer a @samp{#}. 757 758@item -CC 759Do not discard comments, including during macro expansion. This is 760like @option{-C}, except that comments contained within macros are 761also passed through to the output file where the macro is expanded. 762 763In addition to the side-effects of the @option{-C} option, the 764@option{-CC} option causes all C++-style comments inside a macro 765to be converted to C-style comments. This is to prevent later use 766of that macro from inadvertently commenting out the remainder of 767the source line. 768 769The @option{-CC} option is generally used to support lint comments. 770 771@item -traditional-cpp 772@opindex traditional-cpp 773Try to imitate the behavior of old-fashioned C preprocessors, as 774opposed to ISO C preprocessors. 775@ifset cppmanual 776@xref{Traditional Mode}. 777@end ifset 778 779@item -trigraphs 780@opindex trigraphs 781Process trigraph sequences. 782@ifset cppmanual 783@xref{Initial processing}. 784@end ifset 785@ifclear cppmanual 786These are three-character sequences, all starting with @samp{??}, that 787are defined by ISO C to stand for single characters. For example, 788@samp{??/} stands for @samp{\}, so @samp{'??/n'} is a character 789constant for a newline. By default, GCC ignores trigraphs, but in 790standard-conforming modes it converts them. See the @option{-std} and 791@option{-ansi} options. 792 793The nine trigraphs and their replacements are 794 795@smallexample 796Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??- 797Replacement: [ ] @{ @} # \ ^ | ~ 798@end smallexample 799@end ifclear 800 801@item -remap 802@opindex remap 803Enable special code to work around file systems which only permit very 804short file names, such as MS-DOS@. 805 806@item --help 807@itemx --target-help 808@opindex help 809@opindex target-help 810Print text describing all the command line options instead of 811preprocessing anything. 812 813@item -v 814@opindex v 815Verbose mode. Print out GNU CPP's version number at the beginning of 816execution, and report the final form of the include path. 817 818@item -H 819@opindex H 820Print the name of each header file used, in addition to other normal 821activities. Each name is indented to show how deep in the 822@samp{#include} stack it is. Precompiled header files are also 823printed, even if they are found to be invalid; an invalid precompiled 824header file is printed with @samp{...x} and a valid one with @samp{...!} . 825 826@item -version 827@itemx --version 828@opindex version 829Print out GNU CPP's version number. With one dash, proceed to 830preprocess as normal. With two dashes, exit immediately. 831@end table 832