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