CPP(1) GNU CPP(1)NAMEmcpp - The GNU C Preprocessor
SYNOPSIS
cpp [-Dmacro[=defn]...] [-Umacro]
[-Idir...] [-Wwarn...]
[-M|-MM] [-MG] [-MF filename]
[-MP] [-MQ target...]
[-MT target...]
[-P] [-fno-working-directory]
[-x language] [-std=standard]
infile outfile
Only the most useful options are listed here; see below for
the remainder.
On MirOS, /usr/bin/cpp calls GNU cpp (/usr/bin/mcpp) if it
exists, and if not, /usr/libexec/cpp (Reiser CCCP). This
usage is deprecated, and a separate cpp binary might vanish
soon.
DESCRIPTION
The C preprocessor, often known as cpp, is a macro processor
that is used automatically by the C compiler to transform
your program before compilation. It is called a macro pro-
cessor because it allows you to define macros, which are
brief abbreviations for longer constructs.
The C preprocessor is intended to be used only with C, C++,
and Objective-C source code. In the past, it has been
abused as a general text processor. It will choke on input
which does not obey C's lexical rules. For example, apos-
trophes will be interpreted as the beginning of character
constants, and cause errors. Also, you cannot rely on it
preserving characteristics of the input which are not signi-
ficant to C-family languages. If a Makefile is prepro-
cessed, all the hard tabs will be removed, and the Makefile
will not work.
Having said that, you can often get away with using cpp on
things which are not C. Other Algol-ish programming
languages are often safe (Pascal, Ada, etc.) So is assembly,
with caution. -traditional-cpp mode preserves more white
space, and is otherwise more permissive. Many of the prob-
lems can be avoided by writing C or C++ style comments
instead of native language comments, and keeping macros sim-
ple.
Wherever possible, you should use a preprocessor geared to
the language you are writing in. Modern versions of the GNU
assembler have macro facilities. Most high level program-
ming languages have their own conditional compilation and
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inclusion mechanism. If all else fails, try a true general
text processor, such as GNU M4.
C preprocessors vary in some details. This manual discusses
the GNU C preprocessor, which provides a small superset of
the features of ISO Standard C. In its default mode, the
GNU C preprocessor does not do a few things required by the
standard. These are features which are rarely, if ever,
used, and may cause surprising changes to the meaning of a
program which does not expect them. To get strict ISO Stan-
dard C, you should use the -std=c89 or -std=c99 options,
depending on which version of the standard you want. To get
all the mandatory diagnostics, you must also use -pedantic.
This manual describes the behavior of the ISO preprocessor.
To minimize gratuitous differences, where the ISO
preprocessor's behavior does not conflict with traditional
semantics, the traditional preprocessor should behave the
same way. The various differences that do exist are
detailed in the section Traditional Mode.
For clarity, unless noted otherwise, references to CPP in
this manual refer to GNU CPP.
OPTIONS
The C preprocessor expects two file names as arguments,
infile and outfile. The preprocessor reads infile together
with any other files it specifies with #include. All the
output generated by the combined input files is written in
outfile.
Either infile or outfile may be -, which as infile means to
read from standard input and as outfile means to write to
standard output. Also, if either file is omitted, it means
the same as if - had been specified for that file.
Unless otherwise noted, or the option ends in =, all options
which take an argument may have that argument appear either
immediately after the option, or with a space between option
and argument: -Ifoo and -I foo have the same effect.
Many options have multi-letter names; therefore multiple
single-letter options may not be grouped: -dM is very dif-
ferent from -d -M.
-D name
Predefine name as a macro, with definition 1.
-D name=definition
Predefine name as a macro, with definition definition.
The contents of definition are tokenized and processed
as if they appeared during translation phase three in a
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#define directive. In particular, the definition will
be truncated by embedded newline characters.
If you are invoking the preprocessor from a shell or
shell-like program you may need to use the shell's quot-
ing syntax to protect characters such as spaces that
have a meaning in the shell syntax.
If you wish to define a function-like macro on the com-
mand line, write its argument list with surrounding
parentheses before the equals sign (if any).
Parentheses are meaningful to most shells, so you will
need to quote the option. With sh and csh,
-D'name(args...)=definition' works.
-D and -U options are processed in the order they are
given on the command line. All -imacros file and
-include file options are processed after all -D and -U
options.
-U name
Cancel any previous definition of name, either built in
or provided with a -D option.
-undef
Do not predefine any system-specific or GCC-specific
macros. The standard predefined macros remain defined.
-I dir
Add the directory dir to the list of directories to be
searched for header files.
Directories named by -I are searched before the standard
system include directories. If the directory dir is a
standard system include directory, the option is ignored
to ensure that the default search order for system
directories and the special treatment of system headers
are not defeated .
-o file
Write output to file. This is the same as specifying
file as the second non-option argument to cpp. gcc has
a different interpretation of a second non-option argu-
ment, so you must use -o to specify the output file.
-Wall
Turns on all optional warnings which are desirable for
normal code. At present this is -Wcomment, -Wtrigraphs,
-Wmultichar and a warning about integer promotion caus-
ing a change of sign in "#if" expressions. Note that
many of the preprocessor's warnings are on by default
and have no options to control them.
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-Wcomments
Warn whenever a comment-start sequence /* appears in a
/* comment, or whenever a backslash-newline appears in a
// comment. (Both forms have the same effect.)
-Wtrigraphs
@anchor{Wtrigraphs} Most trigraphs in comments cannot
affect the meaning of the program. However, a trigraph
that would form an escaped newline (??/ at the end of a
line) can, by changing where the comment begins or ends.
Therefore, only trigraphs that would form escaped new-
lines produce warnings inside a comment.
This option is implied by -Wall. If -Wall is not given,
this option is still enabled unless trigraphs are
enabled. To get trigraph conversion without warnings,
but get the other -Wall warnings, use -trigraphs -Wall
-Wno-trigraphs.
-Wtraditional
Warn about certain constructs that behave differently in
traditional and ISO C. Also warn about ISO C constructs
that have no traditional C equivalent, and problematic
constructs which should be avoided.
-Wimport
Warn the first time #import is used.
-Wundef
Warn whenever an identifier which is not a macro is
encountered in an #if directive, outside of defined.
Such identifiers are replaced with zero.
-Wunused-macros
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 will also warn
if the macro has not been used at the time it is rede-
fined or undefined.
Built-in macros, macros defined on the command line, and
macros defined in include files are not warned about.
Note: If a macro is actually used, but only used in
skipped conditional blocks, then CPP will report it as
unused. To avoid the warning in such a case, you might
improve the scope of the macro's definition by, for
example, moving it into the first skipped block. Alter-
natively, you could provide a dummy use with something
like:
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#if defined the_macro_causing_the_warning
#endif
-Wendif-labels
Warn whenever an #else or an #endif are followed by
text. This usually happens in code of the form
#if FOO
...
#else FOO
...
#endif FOO
The second and third "FOO" should be in comments, but
often are not in older programs. This warning is on by
default.
-Werror
Make all warnings into hard errors. Source code which
triggers warnings will be rejected.
-Werror-maybe-reset
Act like -Wno-error if the GCC_NO_WERROR environment
variable is set to anything other than 0 or empty.
-Wsystem-headers
Issue warnings for code in system headers. These are
normally unhelpful in finding bugs in your own code,
therefore suppressed. If you are responsible for the
system library, you may want to see them.
-w Suppress all warnings, including those which GNU CPP
issues by default.
-pedantic
Issue all the mandatory diagnostics listed in the C
standard. Some of them are left out by default, since
they trigger frequently on harmless code.
-pedantic-errors
Issue all the mandatory diagnostics, and make all manda-
tory diagnostics into errors. This includes mandatory
diagnostics that GCC issues without -pedantic but treats
as warnings.
-M Instead of outputting the result of preprocessing, out-
put 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.
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Unless specified explicitly (with -MT or -MQ), the
object file name consists of the basename of the source
file with any suffix replaced with object file suffix.
If there are many included files then the rule is split
into several lines using \-newline. The rule has no com-
mands.
This option does not suppress the preprocessor's debug
output, such as -dM. To avoid mixing such debug output
with the dependency rules you should explicitly specify
the dependency output file with -MF, or use an environ-
ment variable like DEPENDENCIES_OUTPUT. Debug output
will still be sent to the regular output stream as nor-
mal.
Passing -M to the driver implies -E, and suppresses
warnings with an implicit -w.
-MM 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.
This implies that the choice of angle brackets or double
quotes in an #include directive does not in itself
determine whether that header will appear in -MM depen-
dency output. This is a slight change in semantics from
GCC versions 3.0 and earlier.
@anchor{dashMF}
-MF file
When used with -M or -MM, specifies a file to write the
dependencies to. If no -MF switch is given the prepro-
cessor sends the rules to the same place it would have
sent preprocessed output.
When used with the driver options -MD or -MMD, -MF over-
rides the default dependency output file.
-MG 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 useless.
This feature is used in automatic updating of makefiles.
-MP 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
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make gives if you remove header files without updating
the Makefile to match.
This is typical output:
test.o: test.c test.h
test.h:
-MT target
Change the target of the rule emitted by dependency gen-
eration. By default CPP takes the name of the main
input file, including any path, deletes any file suffix
such as .c, and appends the platform's usual object suf-
fix. The result is the target.
An -MT option will set the target to be exactly the
string you specify. If you want multiple targets, you
can specify them as a single argument to -MT, or use
multiple -MT options.
For example, -MT '$(objpfx)foo.o' might give
$(objpfx)foo.o: foo.c
-MQ target
Same as -MT, but it quotes any characters which are spe-
cial to Make. -MQ '$(objpfx)foo.o' gives
$$(objpfx)foo.o: foo.c
The default target is automatically quoted, as if it
were given with -MQ.
-MD -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 argu-
ment but with a suffix of .d, otherwise it take the
basename of the input file and applies a .d suffix.
If -MD is used in conjunction with -E, any -o switch is
understood to specify the dependency output file (but
@pxref{dashMF,,-MF}), but if used without -E, each -o is
understood to specify a target object file.
Since -E is not implied, -MD can be used to generate a
dependency output file as a side-effect of the compila-
tion process.
-MMD
Like -MD except mention only user header files, not sys-
tem -header files.
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-x c++
-x objective-c
-x assembler-with-cpp
Specify the source language: C, C++, Objective-C, or
assembly. This has nothing to do with standards confor-
mance or extensions; it merely selects which base syntax
to expect. If you give none of these options, cpp will
deduce the language from the extension of the source
file: .c, .cc, .m, or .S. Some other common extensions
for C++ and assembly are also recognized. If cpp does
not recognize the extension, it will treat the file as
C; this is the most generic mode.
Note: Previous versions of cpp accepted a -lang option
which selected both the language and the standards con-
formance level. This option has been removed, because it
conflicts with the -l option.
-std=standard
-ansi
Specify the standard to which the code should conform.
Currently CPP knows about C and C++ standards; others
may be added in the future.
standard may be one of:
"iso9899:1990"
"c89"
The ISO C standard from 1990. c89 is the customary
shorthand for this version of the standard.
The -ansi option is equivalent to -std=c89.
"iso9899:199409"
The 1990 C standard, as amended in 1994.
"iso9899:1999"
"c99"
"iso9899:199x"
"c9x"
The revised ISO C standard, published in December
1999. Before publication, this was known as C9X.
"gnu89"
The 1990 C standard plus GNU extensions. This is
the default.
"gnu99"
"gnu9x"
The 1999 C standard plus GNU extensions.
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"c++98"
The 1998 ISO C++ standard plus amendments.
"gnu++98"
The same as -std=c++98 plus GNU extensions. This is
the default for C++ code.
-I- Split the include path. Any directories specified with
-I options before -I- are searched only for headers
requested with "#include "file""; they are not searched
for "#include <file>". If additional directories are
specified with -I options after the -I-, those direc-
tories are searched for all #include directives.
In addition, -I- inhibits the use of the directory of
the current file directory as the first search directory
for "#include "file"".
-nostdinc
Do not search the standard system directories for header
files. Only the directories you have specified with -I
options (and the directory of the current file, if
appropriate) are searched.
-nostdinc++
Do not search for header files in the C++-specific stan-
dard directories, but do still search the other standard
directories. (This option is used when building the C++
library.)
-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 normal.
If multiple -include options are given, the files are
included in the order they appear on the command line.
-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 mac-
ros from a header without also processing its declara-
tions.
All files specified by -imacros are processed before all
files specified by -include.
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CPP(1) GNU CPP(1)-idirafter dir
Search dir for header files, but do it after all direc-
tories specified with -I and the standard system direc-
tories have been exhausted. dir is treated as a system
include directory.
-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.
-isystem dir
Search dir for header files, after all directories
specified by -I but before the standard system direc-
tories. Mark it as a system directory, so that it gets
the same special treatment as is applied to the standard
system directories.
-fdollars-in-identifiers
@anchor{fdollars-in-identifiers} Accept $ in identif-
iers.
-fpreprocessed
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 prepro-
cessor 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 prepro-
cessor is little more than a tokenizer for the front
ends.
-fpreprocessed is implicit if the input file has one of
the extensions .i, .ii or .mi. These are the extensions
that GCC uses for preprocessed files created by
-save-temps.
-ftabstop=width
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.
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-fexec-charset=charset
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.
-fwide-exec-charset=charset
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 -ftarget-charset, charset can be any
encoding supported by the system's "iconv" library rou-
tine; however, you will have problems with encodings
that do not fit exactly in "wchar_t".
-finput-charset=charset
Set the input character set, used for translation from
the character set of the input file to the source char-
acter 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 com-
mand line option takes precedence if there's a conflict.
charset can be any encoding supported by the system's
"iconv" library routine.
-fworking-directory
Enable generation of linemarkers in the preprocessor
output that will let the compiler know the current work-
ing directory at the time of preprocessing. When this
option is enabled, the preprocessor will emit, after the
initial linemarker, a second linemarker with the current
working directory followed by two slashes. GCC will use
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.
-fno-show-column
Do not print column numbers in diagnostics. This may be
necessary if diagnostics are being scanned by a program
that does not understand the column numbers, such as
dejagnu.
-A predicate=answer
Make an assertion with the predicate predicate and
answer answer. This form is preferred to the older form
-Apredicate(answer), which is still supported, because
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it does not use shell special characters.
-A -predicate=answer
Cancel an assertion with the predicate predicate and
answer answer.
-dCHARS
CHARS is a sequence of one or more of the following
characters, and must not be preceded by a space. Other
characters are interpreted by the compiler proper, or
reserved for future versions of GCC, and so are silently
ignored. If you specify characters whose behavior con-
flicts, the result is undefined.
M Instead of the normal output, generate a list of
#define directives for all the macros defined during
the execution of the preprocessor, including prede-
fined macros. This gives you a way of finding out
what is predefined in your version of the preproces-
sor. Assuming you have no file foo.h, the command
touch foo.h; cpp -dM foo.h
will show all the predefined macros.
D Like M 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.
N Like D, but emit only the macro names, not their
expansions.
I Output #include directives in addition to the result
of preprocessing.
-P 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.
-C Do not discard comments. All comments are passed
through to the output file, except for comments in pro-
cessed directives, which are deleted along with the
directive.
You should be prepared for side effects when using -C;
it causes the preprocessor to treat comments as tokens
in their own right. For example, comments appearing at
the start of what would be a directive line have the
effect of turning that line into an ordinary source
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line, since the first token on the line is no longer a
#.
-CC Do not discard comments, including during macro expan-
sion. This is like -C, except that comments contained
within macros are also passed through to the output file
where the macro is expanded.
In addition to the side-effects of the -C option, the
-CC option causes all C++-style comments inside a macro
to be converted to C-style comments. This is to prevent
later use of that macro from inadvertently commenting
out the remainder of the source line.
The -CC option is generally used to support lint com-
ments.
-traditional-cpp
Try to imitate the behavior of old-fashioned C prepro-
cessors, as opposed to ISO C preprocessors.
-trigraphs
Process trigraph sequences.
-remap
Enable special code to work around file systems which
only permit very short file names, such as MS-DOS.
--help
--target-help
Print text describing all the command line options
instead of preprocessing anything.
-v Verbose mode. Print out GNU CPP's version number at the
beginning of execution, and report the final form of the
include path.
-H 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 ...! .
-version
--version
Print out GNU CPP's version number. With one dash,
proceed to preprocess as normal. With two dashes, exit
immediately.
ENVIRONMENT
This section describes the environment variables that affect
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how CPP operates. You can use them to specify directories
or prefixes to use when searching for include files, or to
control dependency output.
Note that you can also specify places to search using
options such as -I, and control dependency output with
options like -M. These take precedence over environment
variables, which in turn take precedence over the configura-
tion of GCC.
CPATH
C_INCLUDE_PATH
CPLUS_INCLUDE_PATH
OBJC_INCLUDE_PATH
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.
CPATH specifies a list of directories to be searched as
if specified with -I, but after any paths given with -I
options on the command line. This environment variable
is used regardless of which language is being prepro-
cessed.
The remaining environment variables apply only when
preprocessing the particular language indicated. Each
specifies a list of directories to be searched as if
specified with -isystem, but after any paths given with
-isystem options on the command line.
In all these variables, an empty element instructs the
compiler to search its current working directory. Empty
elements can appear at the beginning or end of a path.
For instance, if the value of CPATH is
":/special/include", that has the same effect as
-I. -I/special/include.
DEPENDENCIES_OUTPUT
If this variable is set, its value specifies how to out-
put dependencies for Make based on the non-system header
files processed by the compiler. System header files
are ignored in the dependency output.
The value of DEPENDENCIES_OUTPUT can be just a file
name, in which case the Make rules are written to that
file, guessing the target name from the source file
name. Or the value can have the form file target, in
which case the rules are written to file file using
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target as the target name.
In other words, this environment variable is equivalent
to combining the options -MM and -MF, with an optional
-MT switch too.
SUNPRO_DEPENDENCIES
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 depen-
dence on the main input file is omitted.
SEE ALSOgpl(7), gfdl(7), fsf-funding(7), gcc(1), as(1), ld(1), and
the Info entries for cpp, gcc, and binutils.
COPYRIGHT
Copyright (c) 1987, 1989, 1991, 1992, 1993, 1994, 1995,
1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation
License, Version 1.1 or any later version published by the
Free Software Foundation. A copy of the license is included
in the man page gfdl(7). This manual contains no Invariant
Sections. The Front-Cover Texts are (a) (see below), and
the Back-Cover Texts are (b) (see below).
(a) The FSF's Front-Cover Text is:
A GNU Manual
(b) The FSF's Back-Cover Text is:
You have freedom to copy and modify this GNU Manual, like GNU
software. Copies published by the Free Software Foundation raise
funds for GNU development.
gcc-3.4.6 2011-08-18 15
