cppopts.texi revision 119256
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. 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}. 20There are no restrictions on the contents of @var{definition}, but if 21you are invoking the preprocessor from a shell or shell-like program you 22may need to use the shell's quoting syntax to protect characters such as 23spaces that have a meaning in the shell syntax. 24 25If you wish to define a function-like macro on the command line, write 26its argument list with surrounding parentheses before the equals sign 27(if any). Parentheses are meaningful to most shells, so you will need 28to quote the option. With @command{sh} and @command{csh}, 29@option{-D'@var{name}(@var{args@dots{}})=@var{definition}'} works. 30 31@option{-D} and @option{-U} options are processed in the order they 32are 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. 35 36@item -U @var{name} 37@opindex U 38Cancel any previous definition of @var{name}, either built in or 39provided with a @option{-D} option. 40 41@item -undef 42@opindex undef 43Do not predefine any system-specific or GCC-specific macros. The 44standard predefined macros remain defined. 45@ifset cppmanual 46@xref{Standard Predefined Macros}. 47@end ifset 48 49@item -I @var{dir} 50@opindex I 51Add the directory @var{dir} to the list of directories to be searched 52for header files. 53@ifset cppmanual 54@xref{Search Path}. 55@end ifset 56Directories named by @option{-I} are searched before the standard 57system include directories. If the directory @var{dir} is a standard 58system include directory, the option is ignored to ensure that the 59default search order for system directories and the special treatment 60of system headers are not defeated 61@ifset cppmanual 62(@pxref{System Headers}) 63@end ifset 64. 65 66@item -o @var{file} 67@opindex o 68Write output to @var{file}. This is the same as specifying @var{file} 69as the second non-option argument to @command{cpp}. @command{gcc} has a 70different interpretation of a second non-option argument, so you must 71use @option{-o} to specify the output file. 72 73@item -Wall 74@opindex Wall 75Turns on all optional warnings which are desirable for normal code. At 76present this is @option{-Wcomment} and @option{-Wtrigraphs}. Note that 77many of the preprocessor's warnings are on by default and have no 78options to control them. 79 80@item -Wcomment 81@itemx -Wcomments 82@opindex Wcomment 83@opindex Wcomments 84Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*} 85comment, or whenever a backslash-newline appears in a @samp{//} comment. 86(Both forms have the same effect.) 87 88@item -Wtrigraphs 89@opindex Wtrigraphs 90Warn if any trigraphs are encountered. This option used to take effect 91only if @option{-trigraphs} was also specified, but now works 92independently. Warnings are not given for trigraphs within comments, as 93they do not affect the meaning of the program. 94 95@item -Wtraditional 96@opindex Wtraditional 97Warn about certain constructs that behave differently in traditional and 98ISO C@. Also warn about ISO C constructs that have no traditional C 99equivalent, and problematic constructs which should be avoided. 100@ifset cppmanual 101@xref{Traditional Mode}. 102@end ifset 103 104@item -Wimport 105@opindex Wimport 106Warn the first time @samp{#import} is used. 107 108@item -Wundef 109@opindex Wundef 110Warn whenever an identifier which is not a macro is encountered in an 111@samp{#if} directive, outside of @samp{defined}. Such identifiers are 112replaced with zero. 113 114@item -Wunused-macros 115@opindex Wunused-macros 116Warn about macros defined in the main file that are unused. A macro 117is @dfn{used} if it is expanded or tested for existence at least once. 118The preprocessor will also warn if the macro has not been used at the 119time it is redefined or undefined. 120 121Built-in macros, macros defined on the command line, and macros 122defined in include files are not warned about. 123 124@strong{Note:} If a macro is actually used, but only used in skipped 125conditional blocks, then CPP will report it as unused. To avoid the 126warning in such a case, you might improve the scope of the macro's 127definition by, for example, moving it into the first skipped block. 128Alternatively, you could provide a dummy use with something like: 129 130@smallexample 131#if defined the_macro_causing_the_warning 132#endif 133@end smallexample 134 135@item -Wendif-labels 136@opindex Wendif-labels 137Warn whenever an @samp{#else} or an @samp{#endif} are followed by text. 138This usually happens in code of the form 139 140@smallexample 141#if FOO 142@dots{} 143#else FOO 144@dots{} 145#endif FOO 146@end smallexample 147 148@noindent 149The second and third @code{FOO} should be in comments, but often are not 150in older programs. This warning is on by default. 151 152@item -Werror 153@opindex Werror 154Make all warnings into hard errors. Source code which triggers warnings 155will be rejected. 156 157@item -Wsystem-headers 158@opindex Wsystem-headers 159Issue warnings for code in system headers. These are normally unhelpful 160in finding bugs in your own code, therefore suppressed. If you are 161responsible for the system library, you may want to see them. 162 163@item -w 164@opindex w 165Suppress all warnings, including those which GNU CPP issues by default. 166 167@item -pedantic 168@opindex pedantic 169Issue all the mandatory diagnostics listed in the C standard. Some of 170them are left out by default, since they trigger frequently on harmless 171code. 172 173@item -pedantic-errors 174@opindex pedantic-errors 175Issue all the mandatory diagnostics, and make all mandatory diagnostics 176into errors. This includes mandatory diagnostics that GCC issues 177without @samp{-pedantic} but treats as warnings. 178 179@item -M 180@opindex M 181@cindex make 182@cindex dependencies, make 183Instead of outputting the result of preprocessing, output a rule 184suitable for @command{make} describing the dependencies of the main 185source file. The preprocessor outputs one @command{make} rule containing 186the object file name for that source file, a colon, and the names of all 187the included files, including those coming from @option{-include} or 188@option{-imacros} command line options. 189 190Unless specified explicitly (with @option{-MT} or @option{-MQ}), the 191object file name consists of the basename of the source file with any 192suffix replaced with object file suffix. If there are many included 193files then the rule is split into several lines using @samp{\}-newline. 194The rule has no commands. 195 196This option does not suppress the preprocessor's debug output, such as 197@option{-dM}. To avoid mixing such debug output with the dependency 198rules you should explicitly specify the dependency output file with 199@option{-MF}, or use an environment variable like 200@env{DEPENDENCIES_OUTPUT} (@pxref{Environment Variables}). Debug output 201will still be sent to the regular output stream as normal. 202 203Passing @option{-M} to the driver implies @option{-E}, and suppresses 204warnings with an implicit @option{-w}. 205 206@item -MM 207@opindex MM 208Like @option{-M} but do not mention header files that are found in 209system header directories, nor header files that are included, 210directly or indirectly, from such a header. 211 212This implies that the choice of angle brackets or double quotes in an 213@samp{#include} directive does not in itself determine whether that 214header will appear in @option{-MM} dependency output. This is a 215slight change in semantics from GCC versions 3.0 and earlier. 216 217@item -MF @var{file} 218@opindex MF 219@anchor{-MF} 220When used with @option{-M} or @option{-MM}, specifies a 221file to write the dependencies to. If no @option{-MF} switch is given 222the preprocessor sends the rules to the same place it would have sent 223preprocessed output. 224 225When used with the driver options @option{-MD} or @option{-MMD}, 226@option{-MF} overrides the default dependency output file. 227 228@item -MG 229@opindex MG 230In conjunction with an option such as @option{-M} requesting 231dependency generation, @option{-MG} assumes missing header files are 232generated files and adds them to the dependency list without raising 233an error. The dependency filename is taken directly from the 234@code{#include} directive without prepending any path. @option{-MG} 235also suppresses preprocessed output, as a missing header file renders 236this useless. 237 238This feature is used in automatic updating of makefiles. 239 240@item -MP 241@opindex MP 242This option instructs CPP to add a phony target for each dependency 243other than the main file, causing each to depend on nothing. These 244dummy rules work around errors @command{make} gives if you remove header 245files without updating the @file{Makefile} to match. 246 247This is typical output: 248 249@example 250test.o: test.c test.h 251 252test.h: 253@end example 254 255@item -MT @var{target} 256@opindex MT 257 258Change the target of the rule emitted by dependency generation. By 259default CPP takes the name of the main input file, including any path, 260deletes any file suffix such as @samp{.c}, and appends the platform's 261usual object suffix. The result is the target. 262 263An @option{-MT} option will set the target to be exactly the string you 264specify. If you want multiple targets, you can specify them as a single 265argument to @option{-MT}, or use multiple @option{-MT} options. 266 267For example, @option{@w{-MT '$(objpfx)foo.o'}} might give 268 269@example 270$(objpfx)foo.o: foo.c 271@end example 272 273@item -MQ @var{target} 274@opindex MQ 275 276Same as @option{-MT}, but it quotes any characters which are special to 277Make. @option{@w{-MQ '$(objpfx)foo.o'}} gives 278 279@example 280$$(objpfx)foo.o: foo.c 281@end example 282 283The default target is automatically quoted, as if it were given with 284@option{-MQ}. 285 286@item -MD 287@opindex MD 288@option{-MD} is equivalent to @option{-M -MF @var{file}}, except that 289@option{-E} is not implied. The driver determines @var{file} based on 290whether an @option{-o} option is given. If it is, the driver uses its 291argument but with a suffix of @file{.d}, otherwise it take the 292basename of the input file and applies a @file{.d} suffix. 293 294If @option{-MD} is used in conjunction with @option{-E}, any 295@option{-o} switch is understood to specify the dependency output file 296(but @pxref{-MF}), but if used without @option{-E}, each @option{-o} 297is understood to specify a target object file. 298 299Since @option{-E} is not implied, @option{-MD} can be used to generate 300a dependency output file as a side-effect of the compilation process. 301 302@item -MMD 303@opindex MMD 304Like @option{-MD} except mention only user header files, not system 305-header files. 306 307@item -x c 308@itemx -x c++ 309@itemx -x objective-c 310@itemx -x assembler-with-cpp 311@opindex x 312Specify the source language: C, C++, Objective-C, or assembly. This has 313nothing to do with standards conformance or extensions; it merely 314selects which base syntax to expect. If you give none of these options, 315cpp will deduce the language from the extension of the source file: 316@samp{.c}, @samp{.cc}, @samp{.m}, or @samp{.S}. Some other common 317extensions for C++ and assembly are also recognized. If cpp does not 318recognize the extension, it will treat the file as C; this is the most 319generic mode. 320 321@strong{Note:} Previous versions of cpp accepted a @option{-lang} option 322which selected both the language and the standards conformance level. 323This option has been removed, because it conflicts with the @option{-l} 324option. 325 326@item -std=@var{standard} 327@itemx -ansi 328@opindex ansi 329@opindex std= 330Specify the standard to which the code should conform. Currently CPP 331knows about C and C++ standards; others may be added in the future. 332 333@var{standard} 334may be one of: 335@table @code 336@item iso9899:1990 337@itemx c89 338The ISO C standard from 1990. @samp{c89} is the customary shorthand for 339this version of the standard. 340 341The @option{-ansi} option is equivalent to @option{-std=c89}. 342 343@item iso9899:199409 344The 1990 C standard, as amended in 1994. 345 346@item iso9899:1999 347@itemx c99 348@itemx iso9899:199x 349@itemx c9x 350The revised ISO C standard, published in December 1999. Before 351publication, this was known as C9X@. 352 353@item gnu89 354The 1990 C standard plus GNU extensions. This is the default. 355 356@item gnu99 357@itemx gnu9x 358The 1999 C standard plus GNU extensions. 359 360@item c++98 361The 1998 ISO C++ standard plus amendments. 362 363@item gnu++98 364The same as @option{-std=c++98} plus GNU extensions. This is the 365default for C++ code. 366@end table 367 368@item -I- 369@opindex I- 370Split the include path. Any directories specified with @option{-I} 371options before @option{-I-} are searched only for headers requested with 372@code{@w{#include "@var{file}"}}; they are not searched for 373@code{@w{#include <@var{file}>}}. If additional directories are 374specified with @option{-I} options after the @option{-I-}, those 375directories are searched for all @samp{#include} directives. 376 377In addition, @option{-I-} inhibits the use of the directory of the current 378file directory as the first search directory for @code{@w{#include 379"@var{file}"}}. 380@ifset cppmanual 381@xref{Search Path}. 382@end ifset 383 384@item -nostdinc 385@opindex nostdinc 386Do not search the standard system directories for header files. 387Only the directories you have specified with @option{-I} options 388(and the directory of the current file, if appropriate) are searched. 389 390@item -nostdinc++ 391@opindex nostdinc++ 392Do not search for header files in the C++-specific standard directories, 393but do still search the other standard directories. (This option is 394used when building the C++ library.) 395 396@item -include @var{file} 397@opindex include 398Process @var{file} as if @code{#include "file"} appeared as the first 399line of the primary source file. However, the first directory searched 400for @var{file} is the preprocessor's working directory @emph{instead of} 401the directory containing the main source file. If not found there, it 402is searched for in the remainder of the @code{#include "@dots{}"} search 403chain as normal. 404 405If multiple @option{-include} options are given, the files are included 406in the order they appear on the command line. 407 408@item -imacros @var{file} 409@opindex imacros 410Exactly like @option{-include}, except that any output produced by 411scanning @var{file} is thrown away. Macros it defines remain defined. 412This allows you to acquire all the macros from a header without also 413processing its declarations. 414 415All files specified by @option{-imacros} are processed before all files 416specified by @option{-include}. 417 418@item -idirafter @var{dir} 419@opindex idirafter 420Search @var{dir} for header files, but do it @emph{after} all 421directories specified with @option{-I} and the standard system directories 422have been exhausted. @var{dir} is treated as a system include directory. 423 424@item -iprefix @var{prefix} 425@opindex iprefix 426Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix} 427options. If the prefix represents a directory, you should include the 428final @samp{/}. 429 430@item -iwithprefix @var{dir} 431@itemx -iwithprefixbefore @var{dir} 432@opindex iwithprefix 433@opindex iwithprefixbefore 434Append @var{dir} to the prefix specified previously with 435@option{-iprefix}, and add the resulting directory to the include search 436path. @option{-iwithprefixbefore} puts it in the same place @option{-I} 437would; @option{-iwithprefix} puts it where @option{-idirafter} would. 438 439Use of these options is discouraged. 440 441@item -isystem @var{dir} 442@opindex isystem 443Search @var{dir} for header files, after all directories specified by 444@option{-I} but before the standard system directories. Mark it 445as a system directory, so that it gets the same special treatment as 446is applied to the standard system directories. 447@ifset cppmanual 448@xref{System Headers}. 449@end ifset 450 451@item -fpreprocessed 452@opindex fpreprocessed 453Indicate to the preprocessor that the input file has already been 454preprocessed. This suppresses things like macro expansion, trigraph 455conversion, escaped newline splicing, and processing of most directives. 456The preprocessor still recognizes and removes comments, so that you can 457pass a file preprocessed with @option{-C} to the compiler without 458problems. In this mode the integrated preprocessor is little more than 459a tokenizer for the front ends. 460 461@option{-fpreprocessed} is implicit if the input file has one of the 462extensions @samp{.i}, @samp{.ii} or @samp{.mi}. These are the 463extensions that GCC uses for preprocessed files created by 464@option{-save-temps}. 465 466@item -ftabstop=@var{width} 467@opindex ftabstop 468Set the distance between tab stops. This helps the preprocessor report 469correct column numbers in warnings or errors, even if tabs appear on the 470line. If the value is less than 1 or greater than 100, the option is 471ignored. The default is 8. 472 473@item -fno-show-column 474@opindex fno-show-column 475Do not print column numbers in diagnostics. This may be necessary if 476diagnostics are being scanned by a program that does not understand the 477column numbers, such as @command{dejagnu}. 478 479@item -A @var{predicate}=@var{answer} 480@opindex A 481Make an assertion with the predicate @var{predicate} and answer 482@var{answer}. This form is preferred to the older form @option{-A 483@var{predicate}(@var{answer})}, which is still supported, because 484it does not use shell special characters. 485@ifset cppmanual 486@xref{Assertions}. 487@end ifset 488 489@item -A -@var{predicate}=@var{answer} 490Cancel an assertion with the predicate @var{predicate} and answer 491@var{answer}. 492 493@item -dCHARS 494@var{CHARS} is a sequence of one or more of the following characters, 495and must not be preceded by a space. Other characters are interpreted 496by the compiler proper, or reserved for future versions of GCC, and so 497are silently ignored. If you specify characters whose behavior 498conflicts, the result is undefined. 499 500@table @samp 501@item M 502@opindex dM 503Instead of the normal output, generate a list of @samp{#define} 504directives for all the macros defined during the execution of the 505preprocessor, including predefined macros. This gives you a way of 506finding out what is predefined in your version of the preprocessor. 507Assuming you have no file @file{foo.h}, the command 508 509@example 510touch foo.h; cpp -dM foo.h 511@end example 512 513@noindent 514will show all the predefined macros. 515 516@item D 517@opindex dD 518Like @samp{M} except in two respects: it does @emph{not} include the 519predefined macros, and it outputs @emph{both} the @samp{#define} 520directives and the result of preprocessing. Both kinds of output go to 521the standard output file. 522 523@item N 524@opindex dN 525Like @samp{D}, but emit only the macro names, not their expansions. 526 527@item I 528@opindex dI 529Output @samp{#include} directives in addition to the result of 530preprocessing. 531@end table 532 533@item -P 534@opindex P 535Inhibit generation of linemarkers in the output from the preprocessor. 536This might be useful when running the preprocessor on something that is 537not C code, and will be sent to a program which might be confused by the 538linemarkers. 539@ifset cppmanual 540@xref{Preprocessor Output}. 541@end ifset 542 543@item -C 544@opindex C 545Do not discard comments. All comments are passed through to the output 546file, except for comments in processed directives, which are deleted 547along with the directive. 548 549You should be prepared for side effects when using @option{-C}; it 550causes the preprocessor to treat comments as tokens in their own right. 551For example, comments appearing at the start of what would be a 552directive line have the effect of turning that line into an ordinary 553source line, since the first token on the line is no longer a @samp{#}. 554 555@item -CC 556Do not discard comments, including during macro expansion. This is 557like @option{-C}, except that comments contained within macros are 558also passed through to the output file where the macro is expanded. 559 560In addition to the side-effects of the @option{-C} option, the 561@option{-CC} option causes all C++-style comments inside a macro 562to be converted to C-style comments. This is to prevent later use 563of that macro from inadvertently commenting out the remainder of 564the source line. 565 566The @option{-CC} option is generally used to support lint comments. 567 568@item -traditional-cpp 569@opindex traditional-cpp 570Try to imitate the behavior of old-fashioned C preprocessors, as 571opposed to ISO C preprocessors. 572@ifset cppmanual 573@xref{Traditional Mode}. 574@end ifset 575 576@item -trigraphs 577@opindex trigraphs 578Process trigraph sequences. 579@ifset cppmanual 580@xref{Initial processing}. 581@end ifset 582@ifclear cppmanual 583These are three-character sequences, all starting with @samp{??}, that 584are defined by ISO C to stand for single characters. For example, 585@samp{??/} stands for @samp{\}, so @samp{'??/n'} is a character 586constant for a newline. By default, GCC ignores trigraphs, but in 587standard-conforming modes it converts them. See the @option{-std} and 588@option{-ansi} options. 589 590The nine trigraphs and their replacements are 591 592@smallexample 593Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??- 594Replacement: [ ] @{ @} # \ ^ | ~ 595@end smallexample 596@end ifclear 597 598@item -remap 599@opindex remap 600Enable special code to work around file systems which only permit very 601short file names, such as MS-DOS@. 602 603@itemx --help 604@itemx --target-help 605@opindex help 606@opindex target-help 607Print text describing all the command line options instead of 608preprocessing anything. 609 610@item -v 611@opindex v 612Verbose mode. Print out GNU CPP's version number at the beginning of 613execution, and report the final form of the include path. 614 615@item -H 616@opindex H 617Print the name of each header file used, in addition to other normal 618activities. Each name is indented to show how deep in the 619@samp{#include} stack it is. 620 621@item -version 622@itemx --version 623@opindex version 624Print out GNU CPP's version number. With one dash, proceed to 625preprocess as normal. With two dashes, exit immediately. 626@end table 627