[ -Idir...] [-iquotedir...]
[ -M|-MM] [-MG] [-MF filename]
[ -MP] [-MQ target...]
[ -MT target...]
infile [[-o] outfile] Only the most useful options are given above; see below for a more complete list of preprocessor-specific options. In addition, cpp accepts most gcc driver options, which are not listed here. Refer to the GCC documentation for details.
- -D name
- Predefine name as a macro, with definition 1.
- -D name=definition
- The contents of definition are tokenized and
processed as if they appeared during translation phase three in a
#define directive. In particular, the definition is truncated by
embedded newline characters.
- -U name
- Cancel any previous definition of name, either built in or provided with a -D option.
- -include file
- Process file as if "#include
"file"" appeared as the first line of the primary source
file. However, the first directory searched for file is the
preprocessor's working directory instead of the directory
containing the main source file. If not found there, it is searched for in
the remainder of the "#include "..."" search chain as
- -imacros file
- Exactly like -include, except that any output
produced by scanning file is thrown away. Macros it defines remain
defined. This allows you to acquire all the macros from a header without
also processing its declarations.
- Do not predefine any system-specific or GCC-specific macros. The standard predefined macros remain defined.
- Define additional macros required for using the POSIX threads library. You should use this option consistently for both compilation and linking. This option is supported on GNU/Linux targets, most other Unix derivatives, and also on x86 Cygwin and MinGW targets.
- Instead of outputting the result of preprocessing, output a
rule suitable for make describing the dependencies of the main
source file. The preprocessor outputs one make rule containing the
object file name for that source file, a colon, and the names of all the
included files, including those coming from -include or
-imacros command-line options.
- Like -M but do not mention header files that are
found in system header directories, nor header files that are included,
directly or indirectly, from such a header.
- -MF file
- When used with -M or -MM, specifies a file to
write the dependencies to. If no -MF switch is given the
preprocessor sends the rules to the same place it would send preprocessed
- In conjunction with an option such as -M requesting
dependency generation, -MG assumes missing header files are
generated files and adds them to the dependency list without raising an
error. The dependency filename is taken directly from the
"#include" directive without prepending any path. -MG
also suppresses preprocessed output, as a missing header file renders this
- This option instructs CPP to add a phony target for each
dependency other than the main file, causing each to depend on nothing.
These dummy rules work around errors make gives if you remove
header files without updating the Makefile to match.
test.o: test.c test.h test.h:
- -MT target
- Change the target of the rule emitted by dependency
generation. By default CPP takes the name of the main input file, deletes
any directory components and any file suffix such as .c, and
appends the platform's usual object suffix. The result is the target.
- -MQ target
- Same as -MT, but it quotes any characters which are
special to Make. -MQ '$(objpfx)foo.o' gives
- -MD is equivalent to -M -MF file,
except that -E is not implied. The driver determines file
based on whether an -o option is given. If it is, the driver uses
its argument but with a suffix of .d, otherwise it takes the name
of the input file, removes any directory components and suffix, and
applies a .d suffix.
- Like -MD except mention only user header files, not system header files.
- Indicate to the preprocessor that the input file has
already been preprocessed. This suppresses things like macro expansion,
trigraph conversion, escaped newline splicing, and processing of most
directives. The preprocessor still recognizes and removes comments, so
that you can pass a file preprocessed with -C to the compiler
without problems. In this mode the integrated preprocessor is little more
than a tokenizer for the front ends.
- When preprocessing, handle directives, but do not expand
- Accept $ in identifiers.
- Accept universal character names in identifiers. This option is enabled by default for C99 (and later C standard versions) and C++.
- When preprocessing, do not shorten system header paths with canonicalization.
- Set the distance between tab stops. This helps the preprocessor report correct column numbers in warnings or errors, even if tabs appear on the line. If the value is less than 1 or greater than 100, the option is ignored. The default is 8.
- Track locations of tokens across macro expansions. This
allows the compiler to emit diagnostic about the current macro expansion
stack when a compilation error occurs in a macro expansion. Using this
option makes the preprocessor and the compiler consume more memory. The
level parameter can be used to choose the level of precision of
token location tracking thus decreasing the memory consumption if
necessary. Value 0 of level de-activates this option. Value
1 tracks tokens locations in a degraded mode for the sake of
minimal memory overhead. In this mode all tokens resulting from the
expansion of an argument of a function-like macro have the same location.
Value 2 tracks tokens locations completely. This value is the most
memory hungry. When this option is given no argument, the default
parameter value is 2.
- When preprocessing files residing in directory old , expand the "__FILE__" and "__BASE_FILE__" macros as if the files resided in directory new instead. This can be used to change an absolute path to a relative path by using . for new which can result in more reproducible builds that are location independent. This option also affects "__builtin_FILE()" during compilation. See also -ffile-prefix-map.
- Set the execution character set, used for string and character constants. The default is UTF-8. charset can be any encoding supported by the system's "iconv" library routine.
- Set the wide execution character set, used for wide string and character constants. The default is UTF-32 or UTF-16, whichever corresponds to the width of "wchar_t". As with -fexec-charset, charset can be any encoding supported by the system's "iconv" library routine; however, you will have problems with encodings that do not fit exactly in "wchar_t".
- Set the input character set, used for translation from the character set of the input file to the source character set used by GCC. If the locale does not specify, or GCC cannot get this information from the locale, the default is UTF-8. This can be overridden by either the locale or this command-line option. Currently the command-line option takes precedence if there's a conflict. charset can be any encoding supported by the system's "iconv" library routine.
- Enable generation of linemarkers in the preprocessor output that let the compiler know the current working directory at the time of preprocessing. When this option is enabled, the preprocessor emits, after the initial linemarker, a second linemarker with the current working directory followed by two slashes. GCC uses this directory, when it's present in the preprocessed input, as the directory emitted as the current working directory in some debugging information formats. This option is implicitly enabled if debugging information is enabled, but this can be inhibited with the negated form -fno-working-directory. If the -P flag is present in the command line, this option has no effect, since no "#line" directives are emitted whatsoever.
- -A predicate=answer
- Make an assertion with the predicate predicate and answer answer. This form is preferred to the older form -A predicate(answer), which is still supported, because it does not use shell special characters.
- -A -predicate=answer
- Cancel an assertion with the predicate predicate and answer answer.
- Do not discard comments. All comments are passed through to
the output file, except for comments in processed directives, which are
deleted along with the directive.
- Do not discard comments, including during macro expansion.
This is like -C, except that comments contained within macros are
also passed through to the output file where the macro is expanded.
- Inhibit generation of linemarkers in the output from the preprocessor. This might be useful when running the preprocessor on something that is not C code, and will be sent to a program which might be confused by the linemarkers.
- Try to imitate the behavior of pre-standard C
preprocessors, as opposed to ISO C preprocessors.
- Support ISO C trigraphs. These are three-character
sequences, all starting with ??, that are defined by ISO C to stand
for single characters. For example, ??/ stands for \, so
'??/n' is a character constant for a newline.
- Enable special code to work around file systems which only permit very short file names, such as MS-DOS.
- Print the name of each header file used, in addition to other normal activities. Each name is indented to show how deep in the #include stack it is. Precompiled header files are also printed, even if they are found to be invalid; an invalid precompiled header file is printed with ...x and a valid one with ...! .
- Says to make debugging dumps during compilation as specified by letters. The flags documented here are those relevant to the preprocessor. Other letters are interpreted by the compiler proper, or reserved for future versions of GCC, and so are silently ignored. If you specify letters whose behavior conflicts, the result is undefined.
- Instead of the normal output, generate a list of
#define directives for all the macros defined during the execution
of the preprocessor, including predefined macros. This gives you a way of
finding out what is predefined in your version of the preprocessor.
Assuming you have no file foo.h, the command
touch foo.h; cpp -dM foo.h
- Like -dM except in two respects: it does not include the predefined macros, and it outputs both the #define directives and the result of preprocessing. Both kinds of output go to the standard output file.
- Like -dD, but emit only the macro names, not their expansions.
- Output #include directives in addition to the result of preprocessing.
- Like -dD except that only macros that are expanded, or whose definedness is tested in preprocessor directives, are output; the output is delayed until the use or test of the macro; and #undef directives are also output for macros tested but undefined at the time.
- This option is only useful for debugging GCC. When used
from CPP or with -E, it dumps debugging information about location
maps. Every token in the output is preceded by the dump of the map its
location belongs to.
- -I dir
- -iquote dir
- -isystem dir
- -idirafter dir
- Add the directory dir to the list of directories to
be searched for header files during preprocessing.
- For the quote form of the include directive, the directory of the current file is searched first.
- For the quote form of the include directive, the directories specified by -iquote options are searched in left-to-right order, as they appear on the command line.
- Directories specified with -I options are scanned in left-to-right order.
- Directories specified with -isystem options are scanned in left-to-right order.
- Standard system directories are scanned.
- Directories specified with -idirafter options are scanned in left-to-right order.
- Split the include path. This option has been deprecated.
Please use -iquote instead for -I directories before the
-I- and remove the -I- option.
- -iprefix prefix
- Specify prefix as the prefix for subsequent -iwithprefix options. If the prefix represents a directory, you should include the final /.
- -iwithprefix dir
- -iwithprefixbefore dir
- Append dir to the prefix specified previously with -iprefix, and add the resulting directory to the include search path. -iwithprefixbefore puts it in the same place -I would; -iwithprefix puts it where -idirafter would.
- -isysroot dir
- This option is like the --sysroot option, but applies only to header files (except for Darwin targets, where it applies to both header files and libraries). See the --sysroot option for more information.
- -imultilib dir
- Use dir as a subdirectory of the directory containing target-specific C++ headers.
- Do not search the standard system directories for header files. Only the directories explicitly specified with -I, -iquote, -isystem, and/or -idirafter options (and the directory of the current file, if appropriate) are searched.
- Do not search for header files in the C++-specific standard directories, but do still search the other standard directories. (This option is used when building the C++ library.)
- Warn whenever a comment-start sequence /* appears in a /* comment, or whenever a backslash-newline appears in a // comment. This warning is enabled by -Wall.
- Warn if any trigraphs are encountered that might change the
meaning of the program. Trigraphs within comments are not warned about,
except those that would form escaped newlines.
- Warn if an undefined identifier is evaluated in an "#if" directive. Such identifiers are replaced with zero.
- Warn whenever defined is encountered in the expansion of a macro (including the case where the macro is expanded by an #if directive). Such usage is not portable. This warning is also enabled by -Wpedantic and -Wextra.
- Warn about macros defined in the main file that are unused.
A macro is used if it is expanded or tested for existence at least
once. The preprocessor also warns if the macro has not been used at the
time it is redefined or undefined.
#if defined the_macro_causing_the_warning #endif
- Do not warn whenever an "#else" or an
"#endif" are followed by text. This sometimes happens in older
programs with code of the form
#if FOO ... #else FOO ... #endif FOO
- Each variable's value is a list of directories separated by
a special character, much like PATH, in which to look for header
files. The special character, "PATH_SEPARATOR", is
target-dependent and determined at GCC build time. For Microsoft
Windows-based targets it is a semicolon, and for almost all other targets
it is a colon.
- If this variable is set, its value specifies how to output
dependencies for Make based on the non-system header files processed by
the compiler. System header files are ignored in the dependency output.
- This variable is the same as DEPENDENCIES_OUTPUT (see above), except that system header files are not ignored, so it implies -M rather than -MM. However, the dependence on the main input file is omitted.
- If this variable is set, its value specifies a UNIX
timestamp to be used in replacement of the current date and time in the
"__DATE__" and "__TIME__" macros, so that the embedded
timestamps become reproducible.
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