cppopts.texi revision 132718
1@c Copyright (c) 1999, 2000, 2001, 2002, 2003, 2004 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} 19Predefine @var{name} as a macro, with definition @var{definition}. 20The contents of @var{definition} are tokenized and processed as if 21they appeared during translation phase three in a @samp{#define} 22directive. In particular, the definition will be truncated by 23embedded newline characters. 24 25If you are invoking the preprocessor from a shell or shell-like 26program you may need to use the shell's quoting syntax to protect 27characters such as spaces that have a meaning in the shell syntax. 28 29If you wish to define a function-like macro on the command line, write 30its argument list with surrounding parentheses before the equals sign 31(if any). Parentheses are meaningful to most shells, so you will need 32to quote the option. With @command{sh} and @command{csh}, 33@option{-D'@var{name}(@var{args@dots{}})=@var{definition}'} works. 34 35@option{-D} and @option{-U} options are processed in the order they 36are given on the command line. All @option{-imacros @var{file}} and 37@option{-include @var{file}} options are processed after all 38@option{-D} and @option{-U} options. 39 40@item -U @var{name} 41@opindex U 42Cancel any previous definition of @var{name}, either built in or 43provided with a @option{-D} option. 44 45@item -undef 46@opindex undef 47Do not predefine any system-specific or GCC-specific macros. The 48standard predefined macros remain defined. 49@ifset cppmanual 50@xref{Standard Predefined Macros}. 51@end ifset 52 53@item -I @var{dir} 54@opindex I 55Add the directory @var{dir} to the list of directories to be searched 56for header files. 57@ifset cppmanual 58@xref{Search Path}. 59@end ifset 60Directories named by @option{-I} are searched before the standard 61system include directories. If the directory @var{dir} is a standard 62system include directory, the option is ignored to ensure that the 63default search order for system directories and the special treatment 64of system headers are not defeated 65@ifset cppmanual 66(@pxref{System Headers}) 67@end ifset 68. 69 70@item -o @var{file} 71@opindex o 72Write output to @var{file}. This is the same as specifying @var{file} 73as the second non-option argument to @command{cpp}. @command{gcc} has a 74different interpretation of a second non-option argument, so you must 75use @option{-o} to specify the output file. 76 77@item -Wall 78@opindex Wall 79Turns on all optional warnings which are desirable for normal code. 80At present this is @option{-Wcomment}, @option{-Wtrigraphs}, 81@option{-Wmultichar} and a warning about integer promotion causing a 82change of sign in @code{#if} expressions. Note that many of the 83preprocessor's warnings are on by default and have no options to 84control them. 85 86@item -Wcomment 87@itemx -Wcomments 88@opindex Wcomment 89@opindex Wcomments 90Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*} 91comment, or whenever a backslash-newline appears in a @samp{//} comment. 92(Both forms have the same effect.) 93 94@item -Wtrigraphs 95@opindex Wtrigraphs 96@anchor{Wtrigraphs} 97Most trigraphs in comments cannot affect the meaning of the program. 98However, a trigraph that would form an escaped newline (@samp{??/} at 99the end of a line) can, by changing where the comment begins or ends. 100Therefore, only trigraphs that would form escaped newlines produce 101warnings inside a comment. 102 103This option is implied by @option{-Wall}. If @option{-Wall} is not 104given, this option is still enabled unless trigraphs are enabled. To 105get trigraph conversion without warnings, but get the other 106@option{-Wall} warnings, use @samp{-trigraphs -Wall -Wno-trigraphs}. 107 108@item -Wtraditional 109@opindex Wtraditional 110Warn about certain constructs that behave differently in traditional and 111ISO C@. Also warn about ISO C constructs that have no traditional C 112equivalent, and problematic constructs which should be avoided. 113@ifset cppmanual 114@xref{Traditional Mode}. 115@end ifset 116 117@item -Wimport 118@opindex Wimport 119Warn the first time @samp{#import} is used. 120 121@item -Wundef 122@opindex Wundef 123Warn whenever an identifier which is not a macro is encountered in an 124@samp{#if} directive, outside of @samp{defined}. Such identifiers are 125replaced with zero. 126 127@item -Wunused-macros 128@opindex Wunused-macros 129Warn about macros defined in the main file that are unused. A macro 130is @dfn{used} if it is expanded or tested for existence at least once. 131The preprocessor will also warn if the macro has not been used at the 132time it is redefined or undefined. 133 134Built-in macros, macros defined on the command line, and macros 135defined in include files are not warned about. 136 137@strong{Note:} If a macro is actually used, but only used in skipped 138conditional blocks, then CPP will report it as unused. To avoid the 139warning in such a case, you might improve the scope of the macro's 140definition by, for example, moving it into the first skipped block. 141Alternatively, you could provide a dummy use with something like: 142 143@smallexample 144#if defined the_macro_causing_the_warning 145#endif 146@end smallexample 147 148@item -Wendif-labels 149@opindex Wendif-labels 150Warn whenever an @samp{#else} or an @samp{#endif} are followed by text. 151This usually happens in code of the form 152 153@smallexample 154#if FOO 155@dots{} 156#else FOO 157@dots{} 158#endif FOO 159@end smallexample 160 161@noindent 162The second and third @code{FOO} should be in comments, but often are not 163in older programs. This warning is on by default. 164 165@item -Werror 166@opindex Werror 167Make all warnings into hard errors. Source code which triggers warnings 168will be rejected. 169 170@item -Wsystem-headers 171@opindex Wsystem-headers 172Issue warnings for code in system headers. These are normally unhelpful 173in finding bugs in your own code, therefore suppressed. If you are 174responsible for the system library, you may want to see them. 175 176@item -w 177@opindex w 178Suppress all warnings, including those which GNU CPP issues by default. 179 180@item -pedantic 181@opindex pedantic 182Issue all the mandatory diagnostics listed in the C standard. Some of 183them are left out by default, since they trigger frequently on harmless 184code. 185 186@item -pedantic-errors 187@opindex pedantic-errors 188Issue all the mandatory diagnostics, and make all mandatory diagnostics 189into errors. This includes mandatory diagnostics that GCC issues 190without @samp{-pedantic} but treats as warnings. 191 192@item -M 193@opindex M 194@cindex make 195@cindex dependencies, make 196Instead of outputting the result of preprocessing, output a rule 197suitable for @command{make} describing the dependencies of the main 198source file. The preprocessor outputs one @command{make} rule containing 199the object file name for that source file, a colon, and the names of all 200the included files, including those coming from @option{-include} or 201@option{-imacros} command line options. 202 203Unless specified explicitly (with @option{-MT} or @option{-MQ}), the 204object file name consists of the basename of the source file with any 205suffix replaced with object file suffix. If there are many included 206files then the rule is split into several lines using @samp{\}-newline. 207The rule has no commands. 208 209This option does not suppress the preprocessor's debug output, such as 210@option{-dM}. To avoid mixing such debug output with the dependency 211rules you should explicitly specify the dependency output file with 212@option{-MF}, or use an environment variable like 213@env{DEPENDENCIES_OUTPUT} (@pxref{Environment Variables}). Debug output 214will still be sent to the regular output stream as normal. 215 216Passing @option{-M} to the driver implies @option{-E}, and suppresses 217warnings with an implicit @option{-w}. 218 219@item -MM 220@opindex MM 221Like @option{-M} but do not mention header files that are found in 222system header directories, nor header files that are included, 223directly or indirectly, from such a header. 224 225This implies that the choice of angle brackets or double quotes in an 226@samp{#include} directive does not in itself determine whether that 227header will appear in @option{-MM} dependency output. This is a 228slight change in semantics from GCC versions 3.0 and earlier. 229 230@anchor{dashMF} 231@item -MF @var{file} 232@opindex MF 233When used with @option{-M} or @option{-MM}, specifies a 234file to write the dependencies to. If no @option{-MF} switch is given 235the preprocessor sends the rules to the same place it would have sent 236preprocessed output. 237 238When used with the driver options @option{-MD} or @option{-MMD}, 239@option{-MF} overrides the default dependency output file. 240 241@item -MG 242@opindex MG 243In conjunction with an option such as @option{-M} requesting 244dependency generation, @option{-MG} assumes missing header files are 245generated files and adds them to the dependency list without raising 246an error. The dependency filename is taken directly from the 247@code{#include} directive without prepending any path. @option{-MG} 248also suppresses preprocessed output, as a missing header file renders 249this useless. 250 251This feature is used in automatic updating of makefiles. 252 253@item -MP 254@opindex MP 255This option instructs CPP to add a phony target for each dependency 256other than the main file, causing each to depend on nothing. These 257dummy rules work around errors @command{make} gives if you remove header 258files without updating the @file{Makefile} to match. 259 260This is typical output: 261 262@smallexample 263test.o: test.c test.h 264 265test.h: 266@end smallexample 267 268@item -MT @var{target} 269@opindex MT 270 271Change the target of the rule emitted by dependency generation. By 272default CPP takes the name of the main input file, including any path, 273deletes any file suffix such as @samp{.c}, and appends the platform's 274usual object suffix. The result is the target. 275 276An @option{-MT} option will set the target to be exactly the string you 277specify. If you want multiple targets, you can specify them as a single 278argument to @option{-MT}, or use multiple @option{-MT} options. 279 280For example, @option{@w{-MT '$(objpfx)foo.o'}} might give 281 282@smallexample 283$(objpfx)foo.o: foo.c 284@end smallexample 285 286@item -MQ @var{target} 287@opindex MQ 288 289Same as @option{-MT}, but it quotes any characters which are special to 290Make. @option{@w{-MQ '$(objpfx)foo.o'}} gives 291 292@smallexample 293$$(objpfx)foo.o: foo.c 294@end smallexample 295 296The default target is automatically quoted, as if it were given with 297@option{-MQ}. 298 299@item -MD 300@opindex MD 301@option{-MD} is equivalent to @option{-M -MF @var{file}}, except that 302@option{-E} is not implied. The driver determines @var{file} based on 303whether an @option{-o} option is given. If it is, the driver uses its 304argument but with a suffix of @file{.d}, otherwise it take the 305basename of the input file and applies a @file{.d} suffix. 306 307If @option{-MD} is used in conjunction with @option{-E}, any 308@option{-o} switch is understood to specify the dependency output file 309(but @pxref{dashMF,,-MF}), but if used without @option{-E}, each @option{-o} 310is understood to specify a target object file. 311 312Since @option{-E} is not implied, @option{-MD} can be used to generate 313a dependency output file as a side-effect of the compilation process. 314 315@item -MMD 316@opindex MMD 317Like @option{-MD} except mention only user header files, not system 318-header files. 319 320@ifclear cppmanual 321@item -fpch-deps 322@opindex fpch-deps 323When using precompiled headers (@pxref{Precompiled Headers}), this flag 324will cause the dependency-output flags to also list the files from the 325precompiled header's dependencies. If not specified only the 326precompiled header would be listed and not the files that were used to 327create it because those files are not consulted when a precompiled 328header is used. 329 330@end ifclear 331@item -x c 332@itemx -x c++ 333@itemx -x objective-c 334@itemx -x assembler-with-cpp 335@opindex x 336Specify the source language: C, C++, Objective-C, or assembly. This has 337nothing to do with standards conformance or extensions; it merely 338selects which base syntax to expect. If you give none of these options, 339cpp will deduce the language from the extension of the source file: 340@samp{.c}, @samp{.cc}, @samp{.m}, or @samp{.S}. Some other common 341extensions for C++ and assembly are also recognized. If cpp does not 342recognize the extension, it will treat the file as C; this is the most 343generic mode. 344 345@strong{Note:} Previous versions of cpp accepted a @option{-lang} option 346which selected both the language and the standards conformance level. 347This option has been removed, because it conflicts with the @option{-l} 348option. 349 350@item -std=@var{standard} 351@itemx -ansi 352@opindex ansi 353@opindex std= 354Specify the standard to which the code should conform. Currently CPP 355knows about C and C++ standards; others may be added in the future. 356 357@var{standard} 358may be one of: 359@table @code 360@item iso9899:1990 361@itemx c89 362The ISO C standard from 1990. @samp{c89} is the customary shorthand for 363this version of the standard. 364 365The @option{-ansi} option is equivalent to @option{-std=c89}. 366 367@item iso9899:199409 368The 1990 C standard, as amended in 1994. 369 370@item iso9899:1999 371@itemx c99 372@itemx iso9899:199x 373@itemx c9x 374The revised ISO C standard, published in December 1999. Before 375publication, this was known as C9X@. 376 377@item gnu89 378The 1990 C standard plus GNU extensions. This is the default. 379 380@item gnu99 381@itemx gnu9x 382The 1999 C standard plus GNU extensions. 383 384@item c++98 385The 1998 ISO C++ standard plus amendments. 386 387@item gnu++98 388The same as @option{-std=c++98} plus GNU extensions. This is the 389default for C++ code. 390@end table 391 392@item -I- 393@opindex I- 394Split the include path. Any directories specified with @option{-I} 395options before @option{-I-} are searched only for headers requested with 396@code{@w{#include "@var{file}"}}; they are not searched for 397@code{@w{#include <@var{file}>}}. If additional directories are 398specified with @option{-I} options after the @option{-I-}, those 399directories are searched for all @samp{#include} directives. 400 401In addition, @option{-I-} inhibits the use of the directory of the current 402file directory as the first search directory for @code{@w{#include 403"@var{file}"}}. 404@ifset cppmanual 405@xref{Search Path}. 406@end ifset 407 408@item -nostdinc 409@opindex nostdinc 410Do not search the standard system directories for header files. 411Only the directories you have specified with @option{-I} options 412(and the directory of the current file, if appropriate) are searched. 413 414@item -nostdinc++ 415@opindex nostdinc++ 416Do not search for header files in the C++-specific standard directories, 417but do still search the other standard directories. (This option is 418used when building the C++ library.) 419 420@item -include @var{file} 421@opindex include 422Process @var{file} as if @code{#include "file"} appeared as the first 423line of the primary source file. However, the first directory searched 424for @var{file} is the preprocessor's working directory @emph{instead of} 425the directory containing the main source file. If not found there, it 426is searched for in the remainder of the @code{#include "@dots{}"} search 427chain as normal. 428 429If multiple @option{-include} options are given, the files are included 430in the order they appear on the command line. 431 432@item -imacros @var{file} 433@opindex imacros 434Exactly like @option{-include}, except that any output produced by 435scanning @var{file} is thrown away. Macros it defines remain defined. 436This allows you to acquire all the macros from a header without also 437processing its declarations. 438 439All files specified by @option{-imacros} are processed before all files 440specified by @option{-include}. 441 442@item -idirafter @var{dir} 443@opindex idirafter 444Search @var{dir} for header files, but do it @emph{after} all 445directories specified with @option{-I} and the standard system directories 446have been exhausted. @var{dir} is treated as a system include directory. 447 448@item -iprefix @var{prefix} 449@opindex iprefix 450Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix} 451options. If the prefix represents a directory, you should include the 452final @samp{/}. 453 454@item -iwithprefix @var{dir} 455@itemx -iwithprefixbefore @var{dir} 456@opindex iwithprefix 457@opindex iwithprefixbefore 458Append @var{dir} to the prefix specified previously with 459@option{-iprefix}, and add the resulting directory to the include search 460path. @option{-iwithprefixbefore} puts it in the same place @option{-I} 461would; @option{-iwithprefix} puts it where @option{-idirafter} would. 462 463@item -isystem @var{dir} 464@opindex isystem 465Search @var{dir} for header files, after all directories specified by 466@option{-I} but before the standard system directories. Mark it 467as a system directory, so that it gets the same special treatment as 468is applied to the standard system directories. 469@ifset cppmanual 470@xref{System Headers}. 471@end ifset 472 473@item -fdollars-in-identifiers 474@opindex fdollars-in-identifiers 475@anchor{fdollars-in-identifiers} 476Accept @samp{$} in identifiers. 477@ifset cppmanual 478 @xref{Identifier characters}. 479@end ifset 480 481@item -fpreprocessed 482@opindex fpreprocessed 483Indicate to the preprocessor that the input file has already been 484preprocessed. This suppresses things like macro expansion, trigraph 485conversion, escaped newline splicing, and processing of most directives. 486The preprocessor still recognizes and removes comments, so that you can 487pass a file preprocessed with @option{-C} to the compiler without 488problems. In this mode the integrated preprocessor is little more than 489a tokenizer for the front ends. 490 491@option{-fpreprocessed} is implicit if the input file has one of the 492extensions @samp{.i}, @samp{.ii} or @samp{.mi}. These are the 493extensions that GCC uses for preprocessed files created by 494@option{-save-temps}. 495 496@item -ftabstop=@var{width} 497@opindex ftabstop 498Set the distance between tab stops. This helps the preprocessor report 499correct column numbers in warnings or errors, even if tabs appear on the 500line. If the value is less than 1 or greater than 100, the option is 501ignored. The default is 8. 502 503@item -fexec-charset=@var{charset} 504@opindex fexec-charset 505Set the execution character set, used for string and character 506constants. The default is UTF-8. @var{charset} can be any encoding 507supported by the system's @code{iconv} library routine. 508 509@item -fwide-exec-charset=@var{charset} 510@opindex fwide-exec-charset 511Set the wide execution character set, used for wide string and 512character constants. The default is UTF-32 or UTF-16, whichever 513corresponds to the width of @code{wchar_t}. As with 514@option{-ftarget-charset}, @var{charset} can be any encoding supported 515by the system's @code{iconv} library routine; however, you will have 516problems with encodings that do not fit exactly in @code{wchar_t}. 517 518@item -finput-charset=@var{charset} 519@opindex finput-charset 520Set the input character set, used for translation from the character 521set of the input file to the source character set used by GCC. If the 522locale does not specify, or GCC cannot get this information from the 523locale, the default is UTF-8. This can be overridden by either the locale 524or this command line option. Currently the command line option takes 525precedence if there's a conflict. @var{charset} can be any encoding 526supported by the system's @code{iconv} library routine. 527 528@item -fworking-directory 529@opindex fworking-directory 530@opindex fno-working-directory 531Enable generation of linemarkers in the preprocessor output that will 532let the compiler know the current working directory at the time of 533preprocessing. When this option is enabled, the preprocessor will 534emit, after the initial linemarker, a second linemarker with the 535current working directory followed by two slashes. GCC will use this 536directory, when it's present in the preprocessed input, as the 537directory emitted as the current working directory in some debugging 538information formats. This option is implicitly enabled if debugging 539information is enabled, but this can be inhibited with the negated 540form @option{-fno-working-directory}. If the @option{-P} flag is 541present in the command line, this option has no effect, since no 542@code{#line} directives are emitted whatsoever. 543 544@item -fno-show-column 545@opindex fno-show-column 546Do not print column numbers in diagnostics. This may be necessary if 547diagnostics are being scanned by a program that does not understand the 548column numbers, such as @command{dejagnu}. 549 550@item -A @var{predicate}=@var{answer} 551@opindex A 552Make an assertion with the predicate @var{predicate} and answer 553@var{answer}. This form is preferred to the older form @option{-A 554@var{predicate}(@var{answer})}, which is still supported, because 555it does not use shell special characters. 556@ifset cppmanual 557@xref{Assertions}. 558@end ifset 559 560@item -A -@var{predicate}=@var{answer} 561Cancel an assertion with the predicate @var{predicate} and answer 562@var{answer}. 563 564@item -dCHARS 565@var{CHARS} is a sequence of one or more of the following characters, 566and must not be preceded by a space. Other characters are interpreted 567by the compiler proper, or reserved for future versions of GCC, and so 568are silently ignored. If you specify characters whose behavior 569conflicts, the result is undefined. 570 571@table @samp 572@item M 573@opindex dM 574Instead of the normal output, generate a list of @samp{#define} 575directives for all the macros defined during the execution of the 576preprocessor, including predefined macros. This gives you a way of 577finding out what is predefined in your version of the preprocessor. 578Assuming you have no file @file{foo.h}, the command 579 580@smallexample 581touch foo.h; cpp -dM foo.h 582@end smallexample 583 584@noindent 585will show all the predefined macros. 586 587@item D 588@opindex dD 589Like @samp{M} except in two respects: it does @emph{not} include the 590predefined macros, and it outputs @emph{both} the @samp{#define} 591directives and the result of preprocessing. Both kinds of output go to 592the standard output file. 593 594@item N 595@opindex dN 596Like @samp{D}, but emit only the macro names, not their expansions. 597 598@item I 599@opindex dI 600Output @samp{#include} directives in addition to the result of 601preprocessing. 602@end table 603 604@item -P 605@opindex P 606Inhibit generation of linemarkers in the output from the preprocessor. 607This might be useful when running the preprocessor on something that is 608not C code, and will be sent to a program which might be confused by the 609linemarkers. 610@ifset cppmanual 611@xref{Preprocessor Output}. 612@end ifset 613 614@item -C 615@opindex C 616Do not discard comments. All comments are passed through to the output 617file, except for comments in processed directives, which are deleted 618along with the directive. 619 620You should be prepared for side effects when using @option{-C}; it 621causes the preprocessor to treat comments as tokens in their own right. 622For example, comments appearing at the start of what would be a 623directive line have the effect of turning that line into an ordinary 624source line, since the first token on the line is no longer a @samp{#}. 625 626@item -CC 627Do not discard comments, including during macro expansion. This is 628like @option{-C}, except that comments contained within macros are 629also passed through to the output file where the macro is expanded. 630 631In addition to the side-effects of the @option{-C} option, the 632@option{-CC} option causes all C++-style comments inside a macro 633to be converted to C-style comments. This is to prevent later use 634of that macro from inadvertently commenting out the remainder of 635the source line. 636 637The @option{-CC} option is generally used to support lint comments. 638 639@item -traditional-cpp 640@opindex traditional-cpp 641Try to imitate the behavior of old-fashioned C preprocessors, as 642opposed to ISO C preprocessors. 643@ifset cppmanual 644@xref{Traditional Mode}. 645@end ifset 646 647@item -trigraphs 648@opindex trigraphs 649Process trigraph sequences. 650@ifset cppmanual 651@xref{Initial processing}. 652@end ifset 653@ifclear cppmanual 654These are three-character sequences, all starting with @samp{??}, that 655are defined by ISO C to stand for single characters. For example, 656@samp{??/} stands for @samp{\}, so @samp{'??/n'} is a character 657constant for a newline. By default, GCC ignores trigraphs, but in 658standard-conforming modes it converts them. See the @option{-std} and 659@option{-ansi} options. 660 661The nine trigraphs and their replacements are 662 663@smallexample 664Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??- 665Replacement: [ ] @{ @} # \ ^ | ~ 666@end smallexample 667@end ifclear 668 669@item -remap 670@opindex remap 671Enable special code to work around file systems which only permit very 672short file names, such as MS-DOS@. 673 674@itemx --help 675@itemx --target-help 676@opindex help 677@opindex target-help 678Print text describing all the command line options instead of 679preprocessing anything. 680 681@item -v 682@opindex v 683Verbose mode. Print out GNU CPP's version number at the beginning of 684execution, and report the final form of the include path. 685 686@item -H 687@opindex H 688Print the name of each header file used, in addition to other normal 689activities. Each name is indented to show how deep in the 690@samp{#include} stack it is. Precompiled header files are also 691printed, even if they are found to be invalid; an invalid precompiled 692header file is printed with @samp{...x} and a valid one with @samp{...!} . 693 694@item -version 695@itemx --version 696@opindex version 697Print out GNU CPP's version number. With one dash, proceed to 698preprocess as normal. With two dashes, exit immediately. 699@end table 700