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CPP(1) GNU CPP(1)

NAME

cpp - The C Preprocessor

SYNOPSIS

cpp [-DDmacro[=defn]...] [-UUmacro]

[-IIdir...] [-iiqquuootteedir...]

[-WWwarn...]

[-MM|-MMMM] [-MMGG] [-MMFF filename]

[-MMPP] [-MMQQ target...]

[-MMTT target...]

[-PP] [-ffnnoo-wwoorrkkiinngg-ddiirreeccttoorryy]

[-xx language] [-ssttdd==standard]

infile outfile Only the most useful options are listed here; see below for the remainder.

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 processor 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, apostrophes 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 significant to

C-family languages. If a Makefile is preprocessed, 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. -ttrraaddiittiioonnaall-ccpppp

mode preserves more white space, and is otherwise more permissive. Many of the problems can be avoided by writing C or C++ style comments instead of native language comments, and keeping macros simple. 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 programming languages have their own conditional compilation and 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 Standard C,

you should use the -ssttdd==cc8899 or -ssttdd==cc9999 options, depending on which

version of the standard you want. To get all the mandatory

diagnostics, you must also use -ppeeddaannttiicc.

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 TTrraaddiittiioonnaall MMooddee. For clarity, unless noted otherwise, references to CCPPPP in this manual refer to GNU CPP. OOPPTTIIOONNSS The C preprocessor expects two file names as arguments, infile and outfile. The preprocessor reads infile together with any other files

it specifies with ##iinncclluuddee. 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: -IIffoooo and -II ffoooo

have the same effect.

Many options have multi-letter names; therefore multiple single-letter

options may not be grouped: -ddMM is very different from -dd -MM.

-DD name

Predefine name as a macro, with definition 1.

-DD name==definition

The contents of definition are tokenized and processed as if they

appeared during translation phase three in a ##ddeeffiinnee 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 quoting 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 command 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 sshh and ccsshh,

-DD''name((args...))==definition'' works.

-DD and -UU options are processed in the order they are given on the

command line. All -iimmaaccrrooss file and -iinncclluuddee file options are

processed after all -DD and -UU options.

-UU name

Cancel any previous definition of name, either built in or provided

with a -DD option.

-uunnddeeff

Do not predefine any system-specific or GCC-specific macros. The

standard predefined macros remain defined.

-II dir

Add the directory dir to the list of directories to be searched for header files.

Directories named by -II 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 .

-oo file

Write output to file. This is the same as specifying file as the

second non-option argument to ccpppp. ggcccc has a different

interpretation of a second non-option argument, so you must use -oo

to specify the output file.

-WWaallll

Turns on all optional warnings which are desirable for normal code.

At present this is -WWccoommmmeenntt, -WWttrriiggrraapphhss, -WWmmuullttiicchhaarr and a

warning about integer promotion causing 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.

-WWccoommmmeenntt

-WWccoommmmeennttss

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.)

-WWttrriiggrraapphhss

@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 newlines produce warnings inside a comment.

This option is implied by -WWaallll. If -WWaallll is not given, this

option is still enabled unless trigraphs are enabled. To get

trigraph conversion without warnings, but get the other -WWaallll

warnings, use -ttrriiggrraapphhss -WWaallll -WWnnoo-ttrriiggrraapphhss.

-WWttrraaddiittiioonnaall

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.

-WWiimmppoorrtt

Warn the first time ##iimmppoorrtt is used.

-WWuunnddeeff

Warn whenever an identifier which is not a macro is encountered in

an ##iiff directive, outside of ddeeffiinneedd. Such identifiers are

replaced with zero.

-WWuunnuusseedd-mmaaccrrooss

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 redefined 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. Alternatively, you could provide a dummy use with something like:

#if defined themacrocausingthewarning

#endif

-WWeennddiiff-llaabbeellss

Warn whenever an ##eellssee or an ##eennddiiff 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.

-WWeerrrroorr

Make all warnings into hard errors. Source code which triggers warnings will be rejected.

-WWssyysstteemm-hheeaaddeerrss

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.

-ww Suppress all warnings, including those which GNU CPP issues by

default.

-ppeeddaannttiicc

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.

-ppeeddaannttiicc-eerrrroorrss

Issue all the mandatory diagnostics, and make all mandatory diagnostics into errors. This includes mandatory diagnostics that

GCC issues without -ppeeddaannttiicc but treats as warnings.

-MM Instead of outputting the result of preprocessing, output a rule

suitable for mmaakkee describing the dependencies of the main source file. The preprocessor outputs one mmaakkee rule containing the object file name for that source file, a colon, and the names of all the

included files, including those coming from -iinncclluuddee or -iimmaaccrrooss

command line options.

Unless specified explicitly (with -MMTT or -MMQQ), 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 commands. This option does not suppress the preprocessor's debug output, such

as -ddMM. To avoid mixing such debug output with the dependency

rules you should explicitly specify the dependency output file with

-MMFF, or use an environment variable like DDEEPPEENNDDEENNCCIIEESSOOUUTTPPUUTT.

Debug output will still be sent to the regular output stream as normal.

Passing -MM to the driver implies -EE, and suppresses warnings with

an implicit -ww.

-MMMM Like -MM 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 ##iinncclluuddee directive does not in itself determine whether that

header will appear in -MMMM dependency output. This is a slight

change in semantics from GCC versions 3.0 and earlier. @anchor{dashMF}

-MMFF file

When used with -MM or -MMMM, specifies a file to write the

dependencies to. If no -MMFF switch is given the preprocessor sends

the rules to the same place it would have sent preprocessed output.

When used with the driver options -MMDD or -MMMMDD, -MMFF overrides the

default dependency output file.

-ddeeppeennddeennccyy-ffiillee

Like -MMFF. (APPLE ONLY)

-MMGG In conjunction with an option such as -MM requesting dependency

generation, -MMGG 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. -MMGG also suppresses preprocessed

output, as a missing header file renders this useless. This feature is used in automatic updating of makefiles.

-MMPP 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 mmaakkee gives if you remove header files without updating the Makefile to match. This is typical output: test.o: test.c test.h test.h:

-MMTT target

Change the target of the rule emitted by dependency generation. By default CPP takes the name of the main input file, including any path, deletes any file suffix such as ..cc, and appends the platform's usual object suffix. The result is the target.

An -MMTT 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 -MMTT, or use multiple -MMTT options.

For example, -MMTT ''$$((oobbjjppffxx))ffoooo..oo'' might give

$(objpfx)foo.o: foo.c

-MMQQ target

Same as -MMTT, but it quotes any characters which are special to

Make. -MMQQ ''$$((oobbjjppffxx))ffoooo..oo'' gives

$$(objpfx)foo.o: foo.c

The default target is automatically quoted, as if it were given

with -MMQQ.

-MMDD -MMDD is equivalent to -MM -MMFF file, except that -EE is not implied.

The driver determines file based on whether an -oo option is given.

If it is, the driver uses its argument but with a suffix of .d, otherwise it take the basename of the input file and applies a .d suffix.

If -MMDD is used in conjunction with -EE, any -oo switch is understood

to specify the dependency output file, but if used without -EE, each

-oo is understood to specify a target object file.

Since -EE is not implied, -MMDD can be used to generate a dependency

output file as a side-effect of the compilation process.

-MMMMDD

Like -MMDD except mention only user header files, not system header

files.

-xx cc

-xx cc++++

-xx oobbjjeeccttiivvee-cc

-xx oobbjjeeccttiivvee-cc++++

-xx aasssseemmbblleerr-wwiitthh-ccpppp

Specify the source language: C, C++, Objective-C, Objective-C++, or

assembly. This has nothing to do with standards conformance 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: ..cc, ..cccc, ..mm, ..mmmm, or ..SS. 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 -llaanngg option which

selected both the language and the standards conformance level.

This option has been removed, because it conflicts with the -ll

option.

-ssttdd==standard

-aannssii

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. cc8899 is the customary shorthand for this version of the standard.

The -aannssii option is equivalent to -ssttdd==cc8899.

"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. "c++98" The 1998 ISO C++ standard plus amendments. "gnu++98"

The same as -ssttdd==cc++++9988 plus GNU extensions. This is the

default for C++ code.

-II- Split the include path. Any directories specified with -II options

before -II- are searched only for headers requested with

"#include "file""; they are not searched for "#include ". If

additional directories are specified with -II options after the -II-,

those directories are searched for all ##iinncclluuddee directives.

In addition, -II- inhibits the use of the directory of the current

file directory as the first search directory for "#include "file"".

This option has been deprecated.

-nnoossttddiinncc

Do not search the standard system directories for header files.

Only the directories you have specified with -II options (and the

directory of the current file, if appropriate) are searched.

-nnoossttddiinncc++++

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.)

-iinncclluuddee 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 -iinncclluuddee options are given, the files are included in

the order they appear on the command line.

-iimmaaccrrooss file

Exactly like -iinncclluuddee, 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.

All files specified by -iimmaaccrrooss are processed before all files

specified by -iinncclluuddee.

-iiddiirraafftteerr dir

Search dir for header files, but do it after all directories

specified with -II and the standard system directories have been

exhausted. dir is treated as a system include directory.

-iipprreeffiixx prefix

Specify prefix as the prefix for subsequent -iiwwiitthhpprreeffiixx options.

If the prefix represents a directory, you should include the final //.

-iiwwiitthhpprreeffiixx dir

-iiwwiitthhpprreeffiixxbbeeffoorree dir

Append dir to the prefix specified previously with -iipprreeffiixx, and

add the resulting directory to the include search path.

-iiwwiitthhpprreeffiixxbbeeffoorree puts it in the same place -II would; -iiwwiitthhpprreeffiixx

puts it where -iiddiirraafftteerr would.

-iissyysstteemm dir

Search dir for header files, after all directories specified by -II

but before the standard system directories. Mark it as a system directory, so that it gets the same special treatment as is applied to the standard system directories.

-iiqquuoottee dir

Search dir only for header files requested with "#include "file"";

they are not searched for "#include ", before all directories

specified by -II and before the standard system directories.

-ffddoollllaarrss-iinn-iiddeennttiiffiieerrss

@anchor{fdollars-in-identifiers} Accept $$ in identifiers.

-ffpprreepprroocceesssseedd

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 -CC to the

compiler without problems. In this mode the integrated preprocessor is little more than a tokenizer for the front ends.

-ffpprreepprroocceesssseedd is implicit if the input file has one of the

extensions ..ii, ..iiii or ..mmii. These are the extensions that GCC uses

for preprocessed files created by -ssaavvee-tteemmppss.

-ffttaabbssttoopp==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.

-ffeexxeecc-cchhaarrsseett==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.

-ffwwiiddee-eexxeecc-cchhaarrsseett==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 "wchart". As with -ffeexxeecc-cchhaarrsseett,

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 "wchart".

-ffiinnppuutt-cchhaarrsseett==charset

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.

-ffwwoorrkkiinngg-ddiirreeccttoorryy

Enable generation of linemarkers in the preprocessor output that will let the compiler know the current working 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 -ffnnoo-wwoorrkkiinngg-ddiirreeccttoorryy. If

the -PP flag is present in the command line, this option has no

effect, since no "#line" directives are emitted whatsoever.

-ffnnoo-sshhooww-ccoolluummnn

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 ddeejjaaggnnuu.

-AA predicate==answer

Make an assertion with the predicate predicate and answer answer.

This form is preferred to the older form -AA predicate((answer)),

which is still supported, because it does not use shell special characters.

-AA -predicate==answer

Cancel an assertion with the predicate predicate and answer answer.

-ddCCHHAARRSS

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 conflicts, the result is undefined.

MM Instead of the normal output, generate a list of ##ddeeffiinnee

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

will show all the predefined macros. DD Like MM except in two respects: it does not include the

predefined macros, and it outputs both the ##ddeeffiinnee directives

and the result of preprocessing. Both kinds of output go to the standard output file. NN Like DD, but emit only the macro names, not their expansions.

II Output ##iinncclluuddee directives in addition to the result of

preprocessing.

-PP 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.

-CC 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.

You should be prepared for side effects when using -CC; 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 line, since the first token on the line is no

longer a ##.

-CCCC Do not discard comments, including during macro expansion. This is

like -CC, 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 -CC option, the -CCCC 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 -CCCC option is generally used to support lint comments.

-ttrraaddiittiioonnaall-ccpppp

Try to imitate the behavior of old-fashioned C preprocessors, as

opposed to ISO C preprocessors.

-ttrriiggrraapphhss

Process trigraph sequences.

-rreemmaapp

Enable special code to work around file systems which only permit

very short file names, such as MS-DOS.

--hheellpp

--ttaarrggeett-hheellpp

Print text describing all the command line options instead of preprocessing anything.

-vv Verbose mode. Print out GNU CPP's version number at the beginning

of execution, and report the final form of the include path.

-HH Print the name of each header file used, in addition to other

normal activities. Each name is indented to show how deep in the

##iinncclluuddee 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 ......xx and a valid one with ......!! .

-vveerrssiioonn

--vveerrssiioonn

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 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

-II, and control dependency output with options like -MM. These take

precedence over environment variables, which in turn take precedence over the configuration of GCC. CCPPAATTHH CCIINNCCLLUUDDEEPPAATTHH CCPPLLUUSSIINNCCLLUUDDEEPPAATTHH OOBBJJCCIINNCCLLUUDDEEPPAATTHH Each variable's value is a list of directories separated by a special character, much like PPAATTHH, in which to look for header

files. The special character, "PATHSEPARATOR", 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. CCPPAATTHH specifies a list of directories to be searched as if

specified with -II, but after any paths given with -II options on the

command line. This environment variable is used regardless of which language is being preprocessed. 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 -iissyysstteemm, but after

any paths given with -iissyysstteemm 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 CCPPAATTHH is ":/special/include", that has the same effect as

-II.. -II//ssppeecciiaall//iinncclluuddee.

DDEEPPEENNDDEENNCCIIEESSOOUUTTPPUUTT 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. The value of DDEEPPEENNDDEENNCCIIEESSOOUUTTPPUUTT 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 target as the target name. In other words, this environment variable is equivalent to

combining the options -MMMM and -MMFF, with an optional -MMTT switch too.

SSUUNNPPRROODDEEPPEENNDDEENNCCIIEESS This variable is the same as DDEEPPEENNDDEENNCCIIEESSOOUUTTPPUUTT (see above),

except that system header files are not ignored, so it implies -MM

rather than -MMMM. However, the dependence on the main input file is

omitted.

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-4.0.1 2009-02-04 CPP(1)