cpp3.1   [plain text]

.\" Automatically generated by Pod::Man version 1.15
.\" Wed Jun 19 19:36:25 2002
.\" Standard preamble:
.\" ======================================================================
.de Sh \" Subsection heading
.if t .Sp
.ne 5
.de Sp \" Vertical space (when we can't use .PP)
.if t .sp .5v
.if n .sp
.de Ip \" List item
.ie \\n(.$>=3 .ne \\$3
.el .ne 3
.IP "\\$1" \\$2
.de Vb \" Begin verbatim text
.ft CW
.ne \\$1
.de Ve \" End verbatim text
.ft R

.\" Set up some character translations and predefined strings.  \*(-- will
.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
.\" double quote, and \*(R" will give a right double quote.  | will give a
.\" real vertical bar.  \*(C+ will give a nicer C++.  Capital omega is used
.\" to do unbreakable dashes and therefore won't be available.  \*(C` and
.\" \*(C' expand to `' in nroff, nothing in troff, for use with C<>
.tr \(*W-|\(bv\*(Tr
.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
.ie n \{\
.    ds -- \(*W-
.    ds PI pi
.    if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
.    if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\"  diablo 12 pitch
.    ds L" ""
.    ds R" ""
.    ds C` ""
.    ds C' ""
.    ds -- \|\(em\|
.    ds PI \(*p
.    ds L" ``
.    ds R" ''
.\" If the F register is turned on, we'll generate index entries on stderr
.\" for titles (.TH), headers (.SH), subsections (.Sh), items (.Ip), and
.\" index entries marked with X<> in POD.  Of course, you'll have to process
.\" the output yourself in some meaningful fashion.
.if \nF \{\
.    de IX
.    tm Index:\\$1\t\\n%\t"\\$2"
.    nr % 0
.    rr F
.\" For nroff, turn off justification.  Always turn off hyphenation; it
.\" makes way too many mistakes in technical documents.
.hy 0
.if n .na
.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2).
.\" Fear.  Run.  Save yourself.  No user-serviceable parts.
.bd B 3
.    \" fudge factors for nroff and troff
.if n \{\
.    ds #H 0
.    ds #V .8m
.    ds #F .3m
.    ds #[ \f1
.    ds #] \fP
.if t \{\
.    ds #H ((1u-(\\\\n(.fu%2u))*.13m)
.    ds #V .6m
.    ds #F 0
.    ds #[ \&
.    ds #] \&
.    \" simple accents for nroff and troff
.if n \{\
.    ds ' \&
.    ds ` \&
.    ds ^ \&
.    ds , \&
.    ds ~ ~
.    ds /
.if t \{\
.    ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u"
.    ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u'
.    ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'^\h'|\\n:u'
.    ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u'
.    ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u'
.    ds / \\k:\h'-(\\n(.wu*8/10-\*(#H)'\z\(sl\h'|\\n:u'
.    \" troff and (daisy-wheel) nroff accents
.ds : \\k:\h'-(\\n(.wu*8/10-\*(#H+.1m+\*(#F)'\v'-\*(#V'\z.\h'.2m+\*(#F'.\h'|\\n:u'\v'\*(#V'
.ds 8 \h'\*(#H'\(*b\h'-\*(#H'
.ds o \\k:\h'-(\\n(.wu+\w'\(de'u-\*(#H)/2u'\v'-.3n'\*(#[\z\(de\v'.3n'\h'|\\n:u'\*(#]
.ds d- \h'\*(#H'\(pd\h'-\w'~'u'\v'-.25m'\f2\(hy\fP\v'.25m'\h'-\*(#H'
.ds D- D\\k:\h'-\w'D'u'\v'-.11m'\z\(hy\v'.11m'\h'|\\n:u'
.ds th \*(#[\v'.3m'\s+1I\s-1\v'-.3m'\h'-(\w'I'u*2/3)'\s-1o\s+1\*(#]
.ds Th \*(#[\s+2I\s-2\h'-\w'I'u*3/5'\v'-.3m'o\v'.3m'\*(#]
.ds ae a\h'-(\w'a'u*4/10)'e
.ds Ae A\h'-(\w'A'u*4/10)'E
.    \" corrections for vroff
.if v .ds ~ \\k:\h'-(\\n(.wu*9/10-\*(#H)'\s-2\u~\d\s+2\h'|\\n:u'
.if v .ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'\v'-.4m'^\v'.4m'\h'|\\n:u'
.    \" for low resolution devices (crt and lpr)
.if \n(.H>23 .if \n(.V>19 \
.    ds : e
.    ds 8 ss
.    ds o a
.    ds d- d\h'-1'\(ga
.    ds D- D\h'-1'\(hy
.    ds th \o'bp'
.    ds Th \o'LP'
.    ds ae ae
.    ds Ae AE
.rm #[ #] #H #V #F C
.\" ======================================================================
.IX Title "CPP 1"
.TH CPP 1 "gcc-3.1" "2002-06-19" "GNU"
cpp \- The C Preprocessor
cpp [\fB\-D\fR\fImacro\fR[=\fIdefn\fR]...] [\fB\-U\fR\fImacro\fR]
    [\fB\-I\fR\fIdir\fR...] [\fB\-W\fR\fIwarn\fR...]
    [\fB\-M\fR|\fB\-MM\fR] [\fB\-MG\fR] [\fB\-MF\fR \fIfilename\fR]
    [\fB\-MP\fR] [\fB\-MQ\fR \fItarget\fR...] [\fB\-MT\fR \fItarget\fR...]
    [\fB\-x\fR \fIlanguage\fR] [\fB\-std=\fR\fIstandard\fR]
    \fIinfile\fR \fIoutfile\fR
Only the most useful options are listed here; see below for the remainder.
The C preprocessor, often known as \fIcpp\fR, is a \fImacro processor\fR
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 \fImacros\fR, which are brief abbreviations for longer
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.  \fB\-traditional\fR
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 \s-1GNU\s0 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 \s-1GNU\s0 M4.
C preprocessors vary in some details.  This manual discusses the \s-1GNU\s0 C
preprocessor, which provides a small superset of the features of \s-1ISO\s0
Standard C.  In its default mode, the \s-1GNU\s0 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 \s-1ISO\s0 Standard C,
you should use the \fB\-std=c89\fR or \fB\-std=c99\fR options, depending
on which version of the standard you want.  To get all the mandatory
diagnostics, you must also use \fB\-pedantic\fR.  
.IX Header "OPTIONS"
The C preprocessor expects two file names as arguments, \fIinfile\fR and
\&\fIoutfile\fR.  The preprocessor reads \fIinfile\fR together with any
other files it specifies with \fB#include\fR.  All the output generated
by the combined input files is written in \fIoutfile\fR.
Either \fIinfile\fR or \fIoutfile\fR may be \fB-\fR, which as
\&\fIinfile\fR means to read from standard input and as \fIoutfile\fR
means to write to standard output.  Also, if either file is omitted, it
means the same as if \fB-\fR had been specified for that file.
Unless otherwise noted, or the option ends in \fB=\fR, all options
which take an argument may have that argument appear either immediately
after the option, or with a space between option and argument:
\&\fB\-Ifoo\fR and \fB\-I foo\fR have the same effect.
Many options have multi-letter names; therefore multiple single-letter
options may \fInot\fR be grouped: \fB\-dM\fR is very different from
\&\fB\-d\ \-M\fR.
.Ip "\fB\-D\fR \fIname\fR" 4
.IX Item "-D name"
Predefine \fIname\fR as a macro, with definition \f(CW\*(C`1\*(C'\fR.
.Ip "\fB\-D\fR \fIname\fR\fB=\fR\fIdefinition\fR" 4
.IX Item "-D name=definition"
Predefine \fIname\fR as a macro, with definition \fIdefinition\fR.
There are no restrictions on the contents of \fIdefinition\fR, but 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 \fBsh\fR and \fBcsh\fR,
\&\fB\-D'\fR\fIname\fR\fB(\fR\fIargs...\fR\fB)=\fR\fIdefinition\fR\fB'\fR works.
\&\fB\-D\fR and \fB\-U\fR options are processed in the order they
are given on the command line.  All \fB\-imacros\fR \fIfile\fR and
\&\fB\-include\fR \fIfile\fR options are processed after all
\&\fB\-D\fR and \fB\-U\fR options.
.Ip "\fB\-U\fR \fIname\fR" 4
.IX Item "-U name"
Cancel any previous definition of \fIname\fR, either built in or
provided with a \fB\-D\fR option.
.Ip "\fB\-undef\fR" 4
.IX Item "-undef"
Do not predefine any system-specific macros.  The common predefined
macros remain defined.
.Ip "\fB\-I\fR \fIdir\fR" 4
.IX Item "-I dir"
Add the directory \fIdir\fR to the list of directories to be searched
for header files.
Directories named by \fB\-I\fR are searched before the standard
system include directories.
It is dangerous to specify a standard system include directory in an
\&\fB\-I\fR option.  This defeats the special treatment of system
\&.  It can also defeat the repairs to buggy system headers which \s-1GCC\s0
makes when it is installed.
.Ip "\fB\-o\fR \fIfile\fR" 4
.IX Item "-o file"
Write output to \fIfile\fR.  This is the same as specifying \fIfile\fR
as the second non-option argument to \fBcpp\fR.  \fBgcc\fR has a
different interpretation of a second non-option argument, so you must
use \fB\-o\fR to specify the output file.
.Ip "\fB\-Wall\fR" 4
.IX Item "-Wall"
Turns on all optional warnings which are desirable for normal code.  At
present this is \fB\-Wcomment\fR and \fB\-Wtrigraphs\fR.  Note that
many of the preprocessor's warnings are on by default and have no
options to control them.
.Ip "\fB\-Wcomment\fR" 4
.IX Item "-Wcomment"
.PD 0
.Ip "\fB\-Wcomments\fR" 4
.IX Item "-Wcomments"
Warn whenever a comment-start sequence \fB/*\fR appears in a \fB/*\fR
comment, or whenever a backslash-newline appears in a \fB//\fR comment.
(Both forms have the same effect.)
.Ip "\fB\-Wtrigraphs\fR" 4
.IX Item "-Wtrigraphs"
Warn if any trigraphs are encountered.  This option used to take effect
only if \fB\-trigraphs\fR was also specified, but now works
independently.  Warnings are not given for trigraphs within comments, as
they do not affect the meaning of the program.
.Ip "\fB\-Wtraditional\fR" 4
.IX Item "-Wtraditional"
Warn about certain constructs that behave differently in traditional and
\&\s-1ISO\s0 C.  Also warn about \s-1ISO\s0 C constructs that have no traditional C
equivalent, and problematic constructs which should be avoided.
.Ip "\fB\-Wimport\fR" 4
.IX Item "-Wimport"
Warn the first time \fB#import\fR is used.
.Ip "\fB\-Wundef\fR" 4
.IX Item "-Wundef"
Warn whenever an identifier which is not a macro is encountered in an
\&\fB#if\fR directive, outside of \fBdefined\fR.  Such identifiers are
replaced with zero.
.Ip "\fB\-Werror\fR" 4
.IX Item "-Werror"
Make all warnings into hard errors.  Source code which triggers warnings
will be rejected.
.Ip "\fB\-Wsystem-headers\fR" 4
.IX Item "-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.
.Ip "\fB\-w\fR" 4
.IX Item "-w"
Suppress all warnings, including those which \s-1GNU\s0 \s-1CPP\s0 issues by default.
.Ip "\fB\-pedantic\fR" 4
.IX Item "-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
.Ip "\fB\-pedantic-errors\fR" 4
.IX Item "-pedantic-errors"
Issue all the mandatory diagnostics, and make all mandatory diagnostics
into errors.  This includes mandatory diagnostics that \s-1GCC\s0 issues
without \fB\-pedantic\fR but treats as warnings.
.Ip "\fB\-M\fR" 4
.IX Item "-M"
Instead of outputting the result of preprocessing, output a rule
suitable for \fBmake\fR describing the dependencies of the main
source file.  The preprocessor outputs one \fBmake\fR rule containing
the object file name for that source file, a colon, and the names of all
the included files, including those coming from \fB\-include\fR or
\&\fB\-imacros\fR command line options.
Unless specified explicitly (with \fB\-MT\fR or \fB\-MQ\fR), 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 \fB\e\fR\-newline.
The rule has no commands.
This option does not suppress the preprocessor's debug output, such as
\&\fB\-dM\fR.  To avoid mixing such debug output with the dependency
rules you should explicitly specify the dependency output file with
\&\fB\-MF\fR, or use an environment variable like
\&\fB\s-1DEPENDENCIES_OUTPUT\s0\fR.  Debug output
will still be sent to the regular output stream as normal.
Passing \fB\-M\fR to the driver implies \fB\-E\fR.
.Ip "\fB\-MM\fR" 4
.IX Item "-MM"
Like \fB\-M\fR 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
\&\fB#include\fR directive does not in itself determine whether that
header will appear in \fB\-MM\fR dependency output.  This is a
slight change in semantics from \s-1GCC\s0 versions 3.0 and earlier.
.Ip "\fB\-MF\fR \fIfile\fR" 4
.IX Item "-MF file"
When used with \fB\-M\fR or \fB\-MM\fR, specifies a
file to write the dependencies to.  If no \fB\-MF\fR switch is given
the preprocessor sends the rules to the same place it would have sent
preprocessed output.
When used with the driver options \fB\-MD\fR or \fB\-MMD\fR,
\&\fB\-MF\fR overrides the default dependency output file.
.Ip "\fB\-dependency-file\fR" 4
.IX Item "-dependency-file"
Like \fB\-MF\fR. (\s-1APPLE\s0 \s-1ONLY\s0)
.Ip "\fB\-MG\fR" 4
.IX Item "-MG"
When used with \fB\-M\fR or \fB\-MM\fR, \fB\-MG\fR says to treat missing
header files as generated files and assume they live in the same
directory as the source file.  It suppresses preprocessed output, as a
missing header file is ordinarily an error.
This feature is used in automatic updating of makefiles.
.Ip "\fB\-MP\fR" 4
.IX Item "-MP"
This option instructs \s-1CPP\s0 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 \fBmake\fR gives if you remove header
files without updating the \fIMakefile\fR to match.
This is typical output:
.Vb 1
\&        test.o: test.c test.h
.Vb 1
\&        test.h:
.Ip "\fB\-MT\fR \fItarget\fR" 4
.IX Item "-MT target"
Change the target of the rule emitted by dependency generation.  By
default \s-1CPP\s0 takes the name of the main input file, including any path,
deletes any file suffix such as \fB.c\fR, and appends the platform's
usual object suffix.  The result is the target.
An \fB\-MT\fR 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 \fB\-MT\fR, or use multiple \fB\-MT\fR options.
For example, \fB\-MT\ '$(objpfx)foo.o'\fR might give
.Vb 1
\&        $(objpfx)foo.o: foo.c
.Ip "\fB\-MQ\fR \fItarget\fR" 4
.IX Item "-MQ target"
Same as \fB\-MT\fR, but it quotes any characters which are special to
Make.  \fB\-MQ\ '$(objpfx)foo.o'\fR gives
.Vb 1
\&        $$(objpfx)foo.o: foo.c
The default target is automatically quoted, as if it were given with
.Ip "\fB\-MD\fR" 4
.IX Item "-MD"
\&\fB\-MD\fR is equivalent to \fB\-M \-MF\fR \fIfile\fR, except that
\&\fB\-E\fR is not implied.  The driver determines \fIfile\fR based on
whether an \fB\-o\fR option is given.  If it is, the driver uses its
argument but with a suffix of \fI.d\fR, otherwise it take the
basename of the input file and applies a \fI.d\fR suffix.
If \fB\-MD\fR is used in conjunction with \fB\-E\fR, any
\&\fB\-o\fR switch is understood to specify the dependency output file
(but \f(CW@pxref\fR{\-MF}), but if used without \fB\-E\fR, each \fB\-o\fR
is understood to specify a target object file.
Since \fB\-E\fR is not implied, \fB\-MD\fR can be used to generate
a dependency output file as a side-effect of the compilation process.
.Ip "\fB\-MMD\fR" 4
.IX Item "-MMD"
Like \fB\-MD\fR except mention only user header files, not system
\&\-header files.
.Ip "\fB\-x c\fR" 4
.IX Item "-x c"
.PD 0
.Ip "\fB\-x c++\fR" 4
.IX Item "-x c++"
.Ip "\fB\-x objective-c\fR" 4
.IX Item "-x objective-c"
.Ip "\fB\-x objective-c++\fR" 4
.IX Item "-x objective-c++"
.Ip "\fB\-x assembler-with-cpp\fR" 4
.IX Item "-x assembler-with-cpp"
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:
\&\fB.c\fR, \fB.cc\fR, \fB.m\fR, \fB.mm\fR, or \fB.S\fR.  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.
\&\fBNote:\fR Previous versions of cpp accepted a \fB\-lang\fR option
which selected both the language and the standards conformance level.
This option has been removed, because it conflicts with the \fB\-l\fR
.Ip "\fB\-std=\fR\fIstandard\fR" 4
.IX Item "-std=standard"
.PD 0
.Ip "\fB\-ansi\fR" 4
.IX Item "-ansi"
Specify the standard to which the code should conform.  Currently cpp
only knows about the standards for C; other language standards will be
added in the future.
may be one of:
.RS 4
.if n .Ip "\f(CW""""iso9899:1990""""\fR" 4
.el .Ip "\f(CWiso9899:1990\fR" 4
.IX Item "iso9899:1990"
.PD 0
.if n .Ip "\f(CW""""c89""""\fR" 4
.el .Ip "\f(CWc89\fR" 4
.IX Item "c89"
The \s-1ISO\s0 C standard from 1990.  \fBc89\fR is the customary shorthand for
this version of the standard.
The \fB\-ansi\fR option is equivalent to \fB\-std=c89\fR.
.if n .Ip "\f(CW""""iso9899:199409""""\fR" 4
.el .Ip "\f(CWiso9899:199409\fR" 4
.IX Item "iso9899:199409"
The 1990 C standard, as amended in 1994.
.if n .Ip "\f(CW""""iso9899:1999""""\fR" 4
.el .Ip "\f(CWiso9899:1999\fR" 4
.IX Item "iso9899:1999"
.PD 0
.if n .Ip "\f(CW""""c99""""\fR" 4
.el .Ip "\f(CWc99\fR" 4
.IX Item "c99"
.if n .Ip "\f(CW""""iso9899:199x""""\fR" 4
.el .Ip "\f(CWiso9899:199x\fR" 4
.IX Item "iso9899:199x"
.if n .Ip "\f(CW""""c9x""""\fR" 4
.el .Ip "\f(CWc9x\fR" 4
.IX Item "c9x"
The revised \s-1ISO\s0 C standard, published in December 1999.  Before
publication, this was known as C9X.
.if n .Ip "\f(CW""""gnu89""""\fR" 4
.el .Ip "\f(CWgnu89\fR" 4
.IX Item "gnu89"
The 1990 C standard plus \s-1GNU\s0 extensions.  This is the default.
.if n .Ip "\f(CW""""gnu99""""\fR" 4
.el .Ip "\f(CWgnu99\fR" 4
.IX Item "gnu99"
.PD 0
.if n .Ip "\f(CW""""gnu9x""""\fR" 4
.el .Ip "\f(CWgnu9x\fR" 4
.IX Item "gnu9x"
The 1999 C standard plus \s-1GNU\s0 extensions.
.RS 4
.Ip "\fB\-I-\fR" 4
.IX Item "-I-"
Split the include path.  Any directories specified with \fB\-I\fR
options before \fB\-I-\fR are searched only for headers requested with
\&\f(CW\*(C`#include\ "\f(CIfile\f(CW"\*(C'\fR; they are not searched for
\&\f(CW\*(C`#include\ <\f(CIfile\f(CW>\*(C'\fR.  If additional directories are
specified with \fB\-I\fR options after the \fB\-I-\fR, those
directories are searched for all \fB#include\fR directives.
In addition, \fB\-I-\fR inhibits the use of the directory of the current
file directory as the first search directory for \f(CW\*(C`#include\ "\f(CIfile\f(CW"\*(C'\fR.
.Ip "\fB\-nostdinc\fR" 4
.IX Item "-nostdinc"
Do not search the standard system directories for header files.
Only the directories you have specified with \fB\-I\fR options
(and the directory of the current file, if appropriate) are searched.
.Ip "\fB\-nostdinc++\fR" 4
.IX Item "-nostdinc++"
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.)
.Ip "\fB\-include\fR \fIfile\fR" 4
.IX Item "-include file"
Process \fIfile\fR as if \f(CW\*(C`#include "file"\*(C'\fR appeared as the first
line of the primary source file.  However, the first directory searched
for \fIfile\fR is the preprocessor's working directory \fIinstead of\fR
the directory containing the main source file.  If not found there, it
is searched for in the remainder of the \f(CW\*(C`#include "..."\*(C'\fR search
chain as normal.
If multiple \fB\-include\fR options are given, the files are included
in the order they appear on the command line.
.Ip "\fB\-imacros\fR \fIfile\fR" 4
.IX Item "-imacros file"
Exactly like \fB\-include\fR, except that any output produced by
scanning \fIfile\fR 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 \fB\-imacros\fR are processed before all files
specified by \fB\-include\fR.
.Ip "\fB\-idirafter\fR \fIdir\fR" 4
.IX Item "-idirafter dir"
Search \fIdir\fR for header files, but do it \fIafter\fR all
directories specified with \fB\-I\fR and the standard system directories
have been exhausted.  \fIdir\fR is treated as a system include directory.
.Ip "\fB\-iprefix\fR \fIprefix\fR" 4
.IX Item "-iprefix prefix"
Specify \fIprefix\fR as the prefix for subsequent \fB\-iwithprefix\fR
options.  If the prefix represents a directory, you should include the
final \fB/\fR.
.Ip "\fB\-iwithprefix\fR \fIdir\fR" 4
.IX Item "-iwithprefix dir"
.PD 0
.Ip "\fB\-iwithprefixbefore\fR \fIdir\fR" 4
.IX Item "-iwithprefixbefore dir"
Append \fIdir\fR to the prefix specified previously with
\&\fB\-iprefix\fR, and add the resulting directory to the include search
path.  \fB\-iwithprefixbefore\fR puts it in the same place \fB\-I\fR
would; \fB\-iwithprefix\fR puts it where \fB\-idirafter\fR would.
Use of these options is discouraged.
.Ip "\fB\-isystem\fR \fIdir\fR" 4
.IX Item "-isystem dir"
Search \fIdir\fR for header files, after all directories specified by
\&\fB\-I\fR 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.
.Ip "\fB\-fpreprocessed\fR" 4
.IX Item "-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 preprocessor still recognizes and removes comments, so that you can
pass a file preprocessed with \fB\-C\fR to the compiler without
problems.  In this mode the integrated preprocessor is little more than
a tokenizer for the front ends.
\&\fB\-fpreprocessed\fR is implicit if the input file has one of the
extensions \fB.i\fR, \fB.ii\fR or \fB.mi\fR.  These are the
extensions that \s-1GCC\s0 uses for preprocessed files created by
.Ip "\fB\-ftabstop=\fR\fIwidth\fR" 4
.IX Item "-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.
.Ip "\fB\-fno-show-column\fR" 4
.IX Item "-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 \fBdejagnu\fR.
.Ip "\fB\-A\fR \fIpredicate\fR\fB=\fR\fIanswer\fR" 4
.IX Item "-A predicate=answer"
Make an assertion with the predicate \fIpredicate\fR and answer
\&\fIanswer\fR.  This form is preferred to the older form \fB\-A\fR
\&\fIpredicate\fR\fB(\fR\fIanswer\fR\fB)\fR, which is still supported, because
it does not use shell special characters.
.Ip "\fB\-A -\fR\fIpredicate\fR\fB=\fR\fIanswer\fR" 4
.IX Item "-A -predicate=answer"
Cancel an assertion with the predicate \fIpredicate\fR and answer
.Ip "\fB\-A-\fR" 4
.IX Item "-A-"
Cancel all predefined assertions and all assertions preceding it on
the command line.  Also, undefine all predefined macros and all
macros preceding it on the command line.  (This is a historical wart and
may change in the future.)
.Ip "\fB\-dCHARS\fR" 4
.IX Item "-dCHARS"
\&\fI\s-1CHARS\s0\fR 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 \s-1GCC\s0, and so
are silently ignored.  If you specify characters whose behavior
conflicts, the result is undefined.
.RS 4
.Ip "\fBM\fR" 4
.IX Item "M"
Instead of the normal output, generate a list of \fB#define\fR
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 \fIfoo.h\fR, the command
.Vb 1
\&        touch foo.h; cpp -dM foo.h
will show all the predefined macros.
.Ip "\fBD\fR" 4
.IX Item "D"
Like \fBM\fR except in two respects: it does \fInot\fR include the
predefined macros, and it outputs \fIboth\fR the \fB#define\fR
directives and the result of preprocessing.  Both kinds of output go to
the standard output file.
.Ip "\fBN\fR" 4
.IX Item "N"
Like \fBD\fR, but emit only the macro names, not their expansions.
.Ip "\fBI\fR" 4
.IX Item "I"
Output \fB#include\fR directives in addition to the result of
.RS 4
.Ip "\fB\-P\fR" 4
.IX Item "-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
.Ip "\fB\-C\fR" 4
.IX Item "-C"
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 \fB\-C\fR; 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 \fB#\fR.
.Ip "\fB\-gcc\fR" 4
.IX Item "-gcc"
Define the macros _\|_GNUC_\|_, _\|_GNUC_MINOR_\|_ and
_\|_GNUC_PATCHLEVEL_\|_.  These are defined automatically when you use
\&\fBgcc \-E\fR; you can turn them off in that case with
.Ip "\fB\-traditional\fR" 4
.IX Item "-traditional"
Try to imitate the behavior of old-fashioned C, as opposed to \s-1ISO\s0
.Ip "\fB\-trigraphs\fR" 4
.IX Item "-trigraphs"
Process trigraph sequences.
.Ip "\fB\-remap\fR" 4
.IX Item "-remap"
Enable special code to work around file systems which only permit very
short file names, such as \s-1MS-DOS\s0.
.Ip "\fB\-$\fR" 4
.IX Item "-$"
Forbid the use of \fB$\fR in identifiers.  The C standard allows
implementations to define extra characters that can appear in
identifiers.  By default \s-1GNU\s0 \s-1CPP\s0 permits \fB$\fR, a common extension.
.Ip "\fB\-h\fR" 4
.IX Item "-h"
.PD 0
.Ip "\fB\*(--help\fR" 4
.IX Item "help"
.Ip "\fB\*(--target-help\fR" 4
.IX Item "target-help"
Print text describing all the command line options instead of
preprocessing anything.
.Ip "\fB\-v\fR" 4
.IX Item "-v"
Verbose mode.  Print out \s-1GNU\s0 \s-1CPP\s0's version number at the beginning of
execution, and report the final form of the include path.
.Ip "\fB\-H\fR" 4
.IX Item "-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
\&\fB#include\fR stack it is.
.Ip "\fB\-version\fR" 4
.IX Item "-version"
.PD 0
.Ip "\fB\*(--version\fR" 4
.IX Item "version"
Print out \s-1GNU\s0 \s-1CPP\s0's version number.  With one dash, proceed to
preprocess as normal.  With two dashes, exit immediately.
This section describes the environment variables that affect how \s-1CPP\s0
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
\&\fB\-I\fR, and control dependency output with options like
\&\fB\-M\fR.  These take precedence over
environment variables, which in turn take precedence over the
configuration of \s-1GCC\s0.
.Ip "\fB\s-1CPATH\s0\fR" 4
.IX Item "CPATH"
.PD 0
.Ip "\fB\s-1CPLUS_INCLUDE_PATH\s0\fR" 4
.Ip "\fB\s-1OBJC_INCLUDE_PATH\s0\fR" 4
Each variable's value is a list of directories separated by a special
character, much like \fB\s-1PATH\s0\fR, in which to look for header files.
The special character, \f(CW\*(C`PATH_SEPARATOR\*(C'\fR, is target-dependent and
determined at \s-1GCC\s0 build time.  For Windows-based targets it is a
semicolon, and for almost all other targets it is a colon.
\&\fB\s-1CPATH\s0\fR specifies a list of directories to be searched as if
specified with \fB\-I\fR, but after any paths given with \fB\-I\fR
options on the command line.  The 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 \fB\-isystem\fR, but after any
paths given with \fB\-isystem\fR options on the command line.
See also \f(CW@ref\fR{Search Path}.
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
The value of \fB\s-1DEPENDENCIES_OUTPUT\s0\fR 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
\&\fIfile\fR\fB \fR\fItarget\fR, in which case the rules are written to
file \fIfile\fR using \fItarget\fR as the target name.
In other words, this environment variable is equivalent to combining
the options \fB\-MM\fR and \fB\-MF\fR,
with an optional \fB\-MT\fR switch too.
This variable is the same as the environment variable
\&\fB\s-1DEPENDENCIES_OUTPUT\s0\fR, except that
system header files are not ignored, so it implies \fB\-M\fR rather
than \fB\-MM\fR.
.IX Header "SEE ALSO"
\&\fIgpl\fR\|(7), \fIgfdl\fR\|(7), \fIfsf-funding\fR\|(7),
\&\fIgcc\fR\|(1), \fIas\fR\|(1), \fIld\fR\|(1), and the Info entries for \fIcpp\fR, \fIgcc\fR, and
Copyright (c) 1987, 1989, 1991, 1992, 1993, 1994, 1995, 1996,
1997, 1998, 1999, 2000, 2001
Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the \s-1GNU\s0 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 \fIgfdl\fR\|(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 \s-1FSF\s0's Front-Cover Text is:
.Vb 1
\&     A GNU Manual
(b) The \s-1FSF\s0's Back-Cover Text is:
.Vb 3
\&     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.