cppopts.texi revision 103445
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 macros. The common predefined 44macros remain defined. 45 46@item -I @var{dir} 47@opindex I 48Add the directory @var{dir} to the list of directories to be searched 49for header files. 50@ifset cppmanual 51@xref{Search Path}. 52@end ifset 53Directories named by @option{-I} are searched before the standard 54system include directories. 55 56It is dangerous to specify a standard system include directory in an 57@option{-I} option. This defeats the special treatment of system 58headers 59@ifset cppmanual 60(@pxref{System Headers}) 61@end ifset 62. It can also defeat the repairs to buggy system headers which GCC 63makes when it is installed. 64 65@item -o @var{file} 66@opindex o 67Write output to @var{file}. This is the same as specifying @var{file} 68as the second non-option argument to @command{cpp}. @command{gcc} has a 69different interpretation of a second non-option argument, so you must 70use @option{-o} to specify the output file. 71 72@item -Wall 73@opindex Wall 74Turns on all optional warnings which are desirable for normal code. At 75present this is @option{-Wcomment} and @option{-Wtrigraphs}. Note that 76many of the preprocessor's warnings are on by default and have no 77options to control them. 78 79@item -Wcomment 80@itemx -Wcomments 81@opindex Wcomment 82@opindex Wcomments 83Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*} 84comment, or whenever a backslash-newline appears in a @samp{//} comment. 85(Both forms have the same effect.) 86 87@item -Wtrigraphs 88@opindex Wtrigraphs 89Warn if any trigraphs are encountered. This option used to take effect 90only if @option{-trigraphs} was also specified, but now works 91independently. Warnings are not given for trigraphs within comments, as 92they do not affect the meaning of the program. 93 94@item -Wtraditional 95@opindex Wtraditional 96Warn about certain constructs that behave differently in traditional and 97ISO C@. Also warn about ISO C constructs that have no traditional C 98equivalent, and problematic constructs which should be avoided. 99@ifset cppmanual 100@xref{Traditional Mode}. 101@end ifset 102 103@item -Wimport 104@opindex Wimport 105Warn the first time @samp{#import} is used. 106 107@item -Wundef 108@opindex Wundef 109Warn whenever an identifier which is not a macro is encountered in an 110@samp{#if} directive, outside of @samp{defined}. Such identifiers are 111replaced with zero. 112 113@item -Werror 114@opindex Werror 115Make all warnings into hard errors. Source code which triggers warnings 116will be rejected. 117 118@item -Wsystem-headers 119@opindex Wsystem-headers 120Issue warnings for code in system headers. These are normally unhelpful 121in finding bugs in your own code, therefore suppressed. If you are 122responsible for the system library, you may want to see them. 123 124@item -w 125@opindex w 126Suppress all warnings, including those which GNU CPP issues by default. 127 128@item -pedantic 129@opindex pedantic 130Issue all the mandatory diagnostics listed in the C standard. Some of 131them are left out by default, since they trigger frequently on harmless 132code. 133 134@item -pedantic-errors 135@opindex pedantic-errors 136Issue all the mandatory diagnostics, and make all mandatory diagnostics 137into errors. This includes mandatory diagnostics that GCC issues 138without @samp{-pedantic} but treats as warnings. 139 140@item -M 141@opindex M 142@cindex make 143@cindex dependencies, make 144Instead of outputting the result of preprocessing, output a rule 145suitable for @command{make} describing the dependencies of the main 146source file. The preprocessor outputs one @command{make} rule containing 147the object file name for that source file, a colon, and the names of all 148the included files, including those coming from @option{-include} or 149@option{-imacros} command line options. 150 151Unless specified explicitly (with @option{-MT} or @option{-MQ}), the 152object file name consists of the basename of the source file with any 153suffix replaced with object file suffix. If there are many included 154files then the rule is split into several lines using @samp{\}-newline. 155The rule has no commands. 156 157This option does not suppress the preprocessor's debug output, such as 158@option{-dM}. To avoid mixing such debug output with the dependency 159rules you should explicitly specify the dependency output file with 160@option{-MF}, or use an environment variable like 161@env{DEPENDENCIES_OUTPUT} (@pxref{DEPENDENCIES_OUTPUT}). Debug output 162will still be sent to the regular output stream as normal. 163 164Passing @option{-M} to the driver implies @option{-E}. 165 166@item -MM 167@opindex MM 168Like @option{-M} but do not mention header files that are found in 169system header directories, nor header files that are included, 170directly or indirectly, from such a header. 171 172This implies that the choice of angle brackets or double quotes in an 173@samp{#include} directive does not in itself determine whether that 174header will appear in @option{-MM} dependency output. This is a 175slight change in semantics from GCC versions 3.0 and earlier. 176 177@item -MF @var{file} 178@opindex MF 179@anchor{-MF} 180When used with @option{-M} or @option{-MM}, specifies a 181file to write the dependencies to. If no @option{-MF} switch is given 182the preprocessor sends the rules to the same place it would have sent 183preprocessed output. 184 185When used with the driver options @option{-MD} or @option{-MMD}, 186@option{-MF} overrides the default dependency output file. 187 188@item -MG 189@opindex MG 190When used with @option{-M} or @option{-MM}, @option{-MG} says to treat missing 191header files as generated files and assume they live in the same 192directory as the source file. It suppresses preprocessed output, as a 193missing header file is ordinarily an error. 194 195This feature is used in automatic updating of makefiles. 196 197@item -MP 198@opindex MP 199This option instructs CPP to add a phony target for each dependency 200other than the main file, causing each to depend on nothing. These 201dummy rules work around errors @command{make} gives if you remove header 202files without updating the @file{Makefile} to match. 203 204This is typical output: 205 206@example 207test.o: test.c test.h 208 209test.h: 210@end example 211 212@item -MT @var{target} 213@opindex MT 214 215Change the target of the rule emitted by dependency generation. By 216default CPP takes the name of the main input file, including any path, 217deletes any file suffix such as @samp{.c}, and appends the platform's 218usual object suffix. The result is the target. 219 220An @option{-MT} option will set the target to be exactly the string you 221specify. If you want multiple targets, you can specify them as a single 222argument to @option{-MT}, or use multiple @option{-MT} options. 223 224For example, @option{@w{-MT '$(objpfx)foo.o'}} might give 225 226@example 227$(objpfx)foo.o: foo.c 228@end example 229 230@item -MQ @var{target} 231@opindex MQ 232 233Same as @option{-MT}, but it quotes any characters which are special to 234Make. @option{@w{-MQ '$(objpfx)foo.o'}} gives 235 236@example 237$$(objpfx)foo.o: foo.c 238@end example 239 240The default target is automatically quoted, as if it were given with 241@option{-MQ}. 242 243@item -MD 244@opindex MD 245@option{-MD} is equivalent to @option{-M -MF @var{file}}, except that 246@option{-E} is not implied. The driver determines @var{file} based on 247whether an @option{-o} option is given. If it is, the driver uses its 248argument but with a suffix of @file{.d}, otherwise it take the 249basename of the input file and applies a @file{.d} suffix. 250 251If @option{-MD} is used in conjunction with @option{-E}, any 252@option{-o} switch is understood to specify the dependency output file 253(but @pxref{-MF}), but if used without @option{-E}, each @option{-o} 254is understood to specify a target object file. 255 256Since @option{-E} is not implied, @option{-MD} can be used to generate 257a dependency output file as a side-effect of the compilation process. 258 259@item -MMD 260@opindex MMD 261Like @option{-MD} except mention only user header files, not system 262-header files. 263 264@item -x c 265@itemx -x c++ 266@itemx -x objective-c 267@itemx -x assembler-with-cpp 268@opindex x 269Specify the source language: C, C++, Objective-C, or assembly. This has 270nothing to do with standards conformance or extensions; it merely 271selects which base syntax to expect. If you give none of these options, 272cpp will deduce the language from the extension of the source file: 273@samp{.c}, @samp{.cc}, @samp{.m}, or @samp{.S}. Some other common 274extensions for C++ and assembly are also recognized. If cpp does not 275recognize the extension, it will treat the file as C; this is the most 276generic mode. 277 278@strong{Note:} Previous versions of cpp accepted a @option{-lang} option 279which selected both the language and the standards conformance level. 280This option has been removed, because it conflicts with the @option{-l} 281option. 282 283@item -std=@var{standard} 284@itemx -ansi 285@opindex ansi 286@opindex std= 287Specify the standard to which the code should conform. Currently cpp 288only knows about the standards for C; other language standards will be 289added in the future. 290 291@var{standard} 292may be one of: 293@table @code 294@item iso9899:1990 295@itemx c89 296The ISO C standard from 1990. @samp{c89} is the customary shorthand for 297this version of the standard. 298 299The @option{-ansi} option is equivalent to @option{-std=c89}. 300 301@item iso9899:199409 302The 1990 C standard, as amended in 1994. 303 304@item iso9899:1999 305@itemx c99 306@itemx iso9899:199x 307@itemx c9x 308The revised ISO C standard, published in December 1999. Before 309publication, this was known as C9X@. 310 311@item gnu89 312The 1990 C standard plus GNU extensions. This is the default. 313 314@item gnu99 315@itemx gnu9x 316The 1999 C standard plus GNU extensions. 317@end table 318 319@item -I- 320@opindex I- 321Split the include path. Any directories specified with @option{-I} 322options before @option{-I-} are searched only for headers requested with 323@code{@w{#include "@var{file}"}}; they are not searched for 324@code{@w{#include <@var{file}>}}. If additional directories are 325specified with @option{-I} options after the @option{-I-}, those 326directories are searched for all @samp{#include} directives. 327 328In addition, @option{-I-} inhibits the use of the directory of the current 329file directory as the first search directory for @code{@w{#include 330"@var{file}"}}. 331@ifset cppmanual 332@xref{Search Path}. 333@end ifset 334 335@item -nostdinc 336@opindex nostdinc 337Do not search the standard system directories for header files. 338Only the directories you have specified with @option{-I} options 339(and the directory of the current file, if appropriate) are searched. 340 341@item -nostdinc++ 342@opindex nostdinc++ 343Do not search for header files in the C++-specific standard directories, 344but do still search the other standard directories. (This option is 345used when building the C++ library.) 346 347@item -include @var{file} 348@opindex include 349Process @var{file} as if @code{#include "file"} appeared as the first 350line of the primary source file. However, the first directory searched 351for @var{file} is the preprocessor's working directory @emph{instead of} 352the directory containing the main source file. If not found there, it 353is searched for in the remainder of the @code{#include "@dots{}"} search 354chain as normal. 355 356If multiple @option{-include} options are given, the files are included 357in the order they appear on the command line. 358 359@item -imacros @var{file} 360@opindex imacros 361Exactly like @option{-include}, except that any output produced by 362scanning @var{file} is thrown away. Macros it defines remain defined. 363This allows you to acquire all the macros from a header without also 364processing its declarations. 365 366All files specified by @option{-imacros} are processed before all files 367specified by @option{-include}. 368 369@item -idirafter @var{dir} 370@opindex idirafter 371Search @var{dir} for header files, but do it @emph{after} all 372directories specified with @option{-I} and the standard system directories 373have been exhausted. @var{dir} is treated as a system include directory. 374 375@item -iprefix @var{prefix} 376@opindex iprefix 377Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix} 378options. If the prefix represents a directory, you should include the 379final @samp{/}. 380 381@item -iwithprefix @var{dir} 382@itemx -iwithprefixbefore @var{dir} 383@opindex iwithprefix 384@opindex iwithprefixbefore 385Append @var{dir} to the prefix specified previously with 386@option{-iprefix}, and add the resulting directory to the include search 387path. @option{-iwithprefixbefore} puts it in the same place @option{-I} 388would; @option{-iwithprefix} puts it where @option{-idirafter} would. 389 390Use of these options is discouraged. 391 392@item -isystem @var{dir} 393@opindex isystem 394Search @var{dir} for header files, after all directories specified by 395@option{-I} but before the standard system directories. Mark it 396as a system directory, so that it gets the same special treatment as 397is applied to the standard system directories. 398@ifset cppmanual 399@xref{System Headers}. 400@end ifset 401 402@item -fpreprocessed 403@opindex fpreprocessed 404Indicate to the preprocessor that the input file has already been 405preprocessed. This suppresses things like macro expansion, trigraph 406conversion, escaped newline splicing, and processing of most directives. 407The preprocessor still recognizes and removes comments, so that you can 408pass a file preprocessed with @option{-C} to the compiler without 409problems. In this mode the integrated preprocessor is little more than 410a tokenizer for the front ends. 411 412@option{-fpreprocessed} is implicit if the input file has one of the 413extensions @samp{.i}, @samp{.ii} or @samp{.mi}. These are the 414extensions that GCC uses for preprocessed files created by 415@option{-save-temps}. 416 417@item -ftabstop=@var{width} 418@opindex ftabstop 419Set the distance between tab stops. This helps the preprocessor report 420correct column numbers in warnings or errors, even if tabs appear on the 421line. If the value is less than 1 or greater than 100, the option is 422ignored. The default is 8. 423 424@item -fno-show-column 425@opindex fno-show-column 426Do not print column numbers in diagnostics. This may be necessary if 427diagnostics are being scanned by a program that does not understand the 428column numbers, such as @command{dejagnu}. 429 430@item -A @var{predicate}=@var{answer} 431@opindex A 432Make an assertion with the predicate @var{predicate} and answer 433@var{answer}. This form is preferred to the older form @option{-A 434@var{predicate}(@var{answer})}, which is still supported, because 435it does not use shell special characters. 436@ifset cppmanual 437@xref{Assertions}. 438@end ifset 439 440@item -A -@var{predicate}=@var{answer} 441Cancel an assertion with the predicate @var{predicate} and answer 442@var{answer}. 443 444@item -A- 445@opindex A- 446Cancel all predefined assertions and all assertions preceding it on 447the command line. Also, undefine all predefined macros and all 448macros preceding it on the command line. (This is a historical wart and 449may change in the future.) 450 451@item -dCHARS 452@var{CHARS} is a sequence of one or more of the following characters, 453and must not be preceded by a space. Other characters are interpreted 454by the compiler proper, or reserved for future versions of GCC, and so 455are silently ignored. If you specify characters whose behavior 456conflicts, the result is undefined. 457 458@table @samp 459@item M 460@opindex dM 461Instead of the normal output, generate a list of @samp{#define} 462directives for all the macros defined during the execution of the 463preprocessor, including predefined macros. This gives you a way of 464finding out what is predefined in your version of the preprocessor. 465Assuming you have no file @file{foo.h}, the command 466 467@example 468touch foo.h; cpp -dM foo.h 469@end example 470 471@noindent 472will show all the predefined macros. 473 474@item D 475@opindex dD 476Like @samp{M} except in two respects: it does @emph{not} include the 477predefined macros, and it outputs @emph{both} the @samp{#define} 478directives and the result of preprocessing. Both kinds of output go to 479the standard output file. 480 481@item N 482@opindex dN 483Like @samp{D}, but emit only the macro names, not their expansions. 484 485@item I 486@opindex dI 487Output @samp{#include} directives in addition to the result of 488preprocessing. 489@end table 490 491@item -P 492@opindex P 493Inhibit generation of linemarkers in the output from the preprocessor. 494This might be useful when running the preprocessor on something that is 495not C code, and will be sent to a program which might be confused by the 496linemarkers. 497@ifset cppmanual 498@xref{Preprocessor Output}. 499@end ifset 500 501@item -C 502@opindex C 503Do not discard comments. All comments are passed through to the output 504file, except for comments in processed directives, which are deleted 505along with the directive. 506 507You should be prepared for side effects when using @option{-C}; it 508causes the preprocessor to treat comments as tokens in their own right. 509For example, comments appearing at the start of what would be a 510directive line have the effect of turning that line into an ordinary 511source line, since the first token on the line is no longer a @samp{#}. 512 513@item -gcc 514@opindex gcc 515Define the macros @sc{__gnuc__}, @sc{__gnuc_minor__} and 516@sc{__gnuc_patchlevel__}. These are defined automatically when you use 517@command{gcc -E}; you can turn them off in that case with 518@option{-no-gcc}. 519 520@item -traditional 521@opindex traditional 522Try to imitate the behavior of old-fashioned C, as opposed to ISO 523C@. 524@ifset cppmanual 525@xref{Traditional Mode}. 526@end ifset 527 528@item -trigraphs 529@opindex trigraphs 530Process trigraph sequences. 531@ifset cppmanual 532@xref{Initial processing}. 533@end ifset 534@ifclear cppmanual 535These are three-character sequences, all starting with @samp{??}, that 536are defined by ISO C to stand for single characters. For example, 537@samp{??/} stands for @samp{\}, so @samp{'??/n'} is a character 538constant for a newline. By default, GCC ignores trigraphs, but in 539standard-conforming modes it converts them. See the @option{-std} and 540@option{-ansi} options. 541 542The nine trigraphs and their replacements are 543 544@smallexample 545Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??- 546Replacement: [ ] @{ @} # \ ^ | ~ 547@end smallexample 548@end ifclear 549 550@item -remap 551@opindex remap 552Enable special code to work around file systems which only permit very 553short file names, such as MS-DOS@. 554 555@item -$ 556@opindex $ 557Forbid the use of @samp{$} in identifiers. The C standard allows 558implementations to define extra characters that can appear in 559identifiers. By default GNU CPP permits @samp{$}, a common extension. 560 561@item -h 562@itemx --help 563@itemx --target-help 564@opindex h 565@opindex help 566@opindex target-help 567Print text describing all the command line options instead of 568preprocessing anything. 569 570@item -v 571@opindex v 572Verbose mode. Print out GNU CPP's version number at the beginning of 573execution, and report the final form of the include path. 574 575@item -H 576@opindex H 577Print the name of each header file used, in addition to other normal 578activities. Each name is indented to show how deep in the 579@samp{#include} stack it is. 580 581@item -version 582@itemx --version 583@opindex version 584Print out GNU CPP's version number. With one dash, proceed to 585preprocess as normal. With two dashes, exit immediately. 586@end table 587