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@c Copyright (c) 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008,

@c 2010, Free Software Foundation, Inc.

@c This is part of the CPP and GCC manuals.

@c For copying conditions, see the file gcc.texi.

@c ---------------------------------------------------------------------

@c Options affecting the preprocessor

@c ---------------------------------------------------------------------

@c If this file is included with the flag ``cppmanual'' set, it is

@c formatted for inclusion in the CPP manual; otherwise the main GCC manual.

@table @gcctabopt

@item -D @var{name}

@opindex D

Predefine @var{name} as a macro, with definition @code{1}.

@item -D @var{name}=@var{definition}

The contents of @var{definition} are tokenized and processed as if

they appeared during translation phase three in a @samp{#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 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 @command{sh} and @command{csh},

@option{-D'@var{name}(@var{args@dots{}})=@var{definition}'} works.

@option{-D} and @option{-U} options are processed in the order they

are given on the command line.  All @option{-imacros @var{file}} and

@option{-include @var{file}} options are processed after all

@option{-D} and @option{-U} options.

@item -U @var{name}

@opindex U

Cancel any previous definition of @var{name}, either built in or

provided with a @option{-D} option.

@item -undef

@opindex undef

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

standard predefined macros remain defined.

@ifset cppmanual

@xref{Standard Predefined Macros}.

@end ifset

@item -I @var{dir}

@opindex I

Add the directory @var{dir} to the list of directories to be searched

for header files.

@ifset cppmanual

@xref{Search Path}.

@end ifset

Directories named by @option{-I} are searched before the standard

system include directories.  If the directory @var{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

@ifset cppmanual

(@pxref{System Headers})

@end ifset

.

If @var{dir} begins with @code{=}, then the @code{=} will be replaced

by the sysroot prefix; see @option{--sysroot} and @option{-isysroot}.

@item -o @var{file}

@opindex o

Write output to @var{file}.  This is the same as specifying @var{file}

as the second non-option argument to @command{cpp}.  @command{gcc} has a

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

use @option{-o} to specify the output file.

@item -Wall

@opindex Wall

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

At present this is @option{-Wcomment}, @option{-Wtrigraphs},

@option{-Wmultichar} and a warning about integer promotion causing a

change of sign in @code{#if} expressions.  Note that many of the

preprocessor's warnings are on by default and have no options to

control them.

@item -Wcomment

@itemx -Wcomments

@opindex Wcomment

@opindex Wcomments

Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}

comment, or whenever a backslash-newline appears in a @samp{//} comment.

(Both forms have the same effect.)

@item -Wtrigraphs

@opindex Wtrigraphs

@anchor{Wtrigraphs}

Most trigraphs in comments cannot affect the meaning of the program.

However, a trigraph that would form an escaped newline (@samp{??/} 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 @option{-Wall}.  If @option{-Wall} is not

given, this option is still enabled unless trigraphs are enabled.  To

get trigraph conversion without warnings, but get the other

@option{-Wall} warnings, use @samp{-trigraphs -Wall -Wno-trigraphs}.

@item -Wtraditional

@opindex 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.

@ifset cppmanual

@xref{Traditional Mode}.

@end ifset

@item -Wundef

@opindex Wundef

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

@samp{#if} directive, outside of @samp{defined}.  Such identifiers are

replaced with zero.

@item -Wunused-macros

@opindex Wunused-macros

Warn about macros defined in the main file that are unused.  A macro

is @dfn{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.

@emph{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:

@smallexample

#if defined the_macro_causing_the_warning

#endif

@end smallexample

@item -Wendif-labels

@opindex Wendif-labels

Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.

This usually happens in code of the form

@smallexample

#if FOO

@dots{}

#else FOO

@dots{}

#endif FOO

@end smallexample

@noindent

The second and third @code{FOO} should be in comments, but often are not

in older programs.  This warning is on by default.

@item -Werror

@opindex Werror

Make all warnings into hard errors.  Source code which triggers warnings

will be rejected.

@item -Wsystem-headers

@opindex 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.

@item -w

@opindex w

Suppress all warnings, including those which GNU CPP issues by default.

@item -pedantic

@opindex 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.

@item -pedantic-errors

@opindex pedantic-errors

Issue all the mandatory diagnostics, and make all mandatory diagnostics

into errors.  This includes mandatory diagnostics that GCC issues

without @samp{-pedantic} but treats as warnings.

@item -M

@opindex M

@cindex @command{make}

@cindex dependencies, @command{make}

Instead of outputting the result of preprocessing, output a rule

suitable for @command{make} describing the dependencies of the main

source file.  The preprocessor outputs one @command{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 @option{-include} or

@option{-imacros} command line options.

Unless specified explicitly (with @option{-MT} or @option{-MQ}), the

object file name consists of the name of the source file with any

suffix replaced with object file suffix and with any leading directory

parts removed.  If there are many included files then the rule is

split into several lines using @samp{\}-newline.  The rule has no

commands.

This option does not suppress the preprocessor's debug output, such as

@option{-dM}.  To avoid mixing such debug output with the dependency

rules you should explicitly specify the dependency output file with

@option{-MF}, or use an environment variable like

@env{DEPENDENCIES_OUTPUT} (@pxref{Environment Variables}).  Debug output

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

Passing @option{-M} to the driver implies @option{-E}, and suppresses

warnings with an implicit @option{-w}.

@item -MM

@opindex MM

Like @option{-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

@samp{#include} directive does not in itself determine whether that

header will appear in @option{-MM} dependency output.  This is a

slight change in semantics from GCC versions 3.0 and earlier.

@anchor{dashMF}

@item -MF @var{file}

@opindex MF

When used with @option{-M} or @option{-MM}, specifies a

file to write the dependencies to.  If no @option{-MF} switch is given

the preprocessor sends the rules to the same place it would have sent

preprocessed output.

When used with the driver options @option{-MD} or @option{-MMD},

@option{-MF} overrides the default dependency output file.

@item -MG

@opindex MG

In conjunction with an option such as @option{-M} requesting

dependency generation, @option{-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

@code{#include} directive without prepending any path.  @option{-MG}

also suppresses preprocessed output, as a missing header file renders

this useless.

This feature is used in automatic updating of makefiles.

@item -MP

@opindex 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 @command{make} gives if you remove header

files without updating the @file{Makefile} to match.

This is typical output:

@smallexample

test.o: test.c test.h

test.h:

@end smallexample

@item -MT @var{target}

@opindex MT

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 @samp{.c}, and

appends the platform's usual object suffix.  The result is the target.

An @option{-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 @option{-MT}, or use multiple @option{-MT} options.

For example, @option{@w{-MT '$(objpfx)foo.o'}} might give

@smallexample

$(objpfx)foo.o: foo.c

@end smallexample

@item -MQ @var{target}

@opindex MQ

Same as @option{-MT}, but it quotes any characters which are special to

Make.  @option{@w{-MQ '$(objpfx)foo.o'}} gives

@smallexample

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

@end smallexample

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

@option{-MQ}.

@item -MD

@opindex MD

@option{-MD} is equivalent to @option{-M -MF @var{file}}, except that

@option{-E} is not implied.  The driver determines @var{file} based on

whether an @option{-o} option is given.  If it is, the driver uses its

argument but with a suffix of @file{.d}, otherwise it takes the name

of the input file, removes any directory components and suffix, and

applies a @file{.d} suffix.

If @option{-MD} is used in conjunction with @option{-E}, any

@option{-o} switch is understood to specify the dependency output file

(@pxref{dashMF,,-MF}), but if used without @option{-E}, each @option{-o}

is understood to specify a target object file.

Since @option{-E} is not implied, @option{-MD} can be used to generate

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

@item -MMD

@opindex MMD

Like @option{-MD} except mention only user header files, not system

header files.

@ifclear cppmanual

@item -fpch-deps

@opindex fpch-deps

When using precompiled headers (@pxref{Precompiled Headers}), this flag

will cause the dependency-output flags to also list the files from the

precompiled header's dependencies.  If not specified only the

precompiled header would be listed and not the files that were used to

create it because those files are not consulted when a precompiled

header is used.

@item -fpch-preprocess

@opindex fpch-preprocess

This option allows use of a precompiled header (@pxref{Precompiled

Headers}) together with @option{-E}.  It inserts a special @code{#pragma},

@code{#pragma GCC pch_preprocess "@var{filename}"} in the output to mark

the place where the precompiled header was found, and its @var{filename}.

When @option{-fpreprocessed} is in use, GCC recognizes this @code{#pragma}

and loads the PCH@.

This option is off by default, because the resulting preprocessed output

is only really suitable as input to GCC@.  It is switched on by

@option{-save-temps}.

You should not write this @code{#pragma} in your own code, but it is

safe to edit the filename if the PCH file is available in a different

location.  The filename may be absolute or it may be relative to GCC's

current directory.

@end ifclear

@item -x c

@itemx -x c++

@itemx -x objective-c

@itemx -x assembler-with-cpp

@opindex x

Specify the source language: C, 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:

@samp{.c}, @samp{.cc}, @samp{.m}, or @samp{.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.

@emph{Note:} Previous versions of cpp accepted a @option{-lang} option

which selected both the language and the standards conformance level.

This option has been removed, because it conflicts with the @option{-l}

option.

@item -std=@var{standard}

@itemx -ansi

@opindex ansi

@opindex std=

Specify the standard to which the code should conform.  Currently CPP

knows about C and C++ standards; others may be added in the future.

@var{standard}

may be one of:

@table @code

@item c90

@itemx c89

@itemx iso9899:1990

The ISO C standard from 1990.  @samp{c90} is the customary shorthand for

this version of the standard.

The @option{-ansi} option is equivalent to @option{-std=c90}.

@item iso9899:199409

The 1990 C standard, as amended in 1994.

@item iso9899:1999

@itemx c99

@itemx iso9899:199x

@itemx c9x

The revised ISO C standard, published in December 1999.  Before

publication, this was known as C9X@.

@item iso9899:2011

@itemx c11

@itemx c1x

The revised ISO C standard, published in December 2011.  Before

publication, this was known as C1X@.

@item gnu90

@itemx gnu89

The 1990 C standard plus GNU extensions.  This is the default.

@item gnu99

@itemx gnu9x

The 1999 C standard plus GNU extensions.

@item gnu11

@itemx gnu1x

The 2011 C standard plus GNU extensions.

@item c++98

The 1998 ISO C++ standard plus amendments.

@item gnu++98

The same as @option{-std=c++98} plus GNU extensions.  This is the

default for C++ code.

@end table

@item -I-

@opindex I-

Split the include path.  Any directories specified with @option{-I}

options before @option{-I-} are searched only for headers requested with

@code{@w{#include "@var{file}"}}; they are not searched for

@code{@w{#include <@var{file}>}}.  If additional directories are

specified with @option{-I} options after the @option{-I-}, those

directories are searched for all @samp{#include} directives.

In addition, @option{-I-} inhibits the use of the directory of the current

file directory as the first search directory for @code{@w{#include

"@var{file}"}}.

@ifset cppmanual

@xref{Search Path}.

@end ifset

This option has been deprecated.

@item -nostdinc

@opindex nostdinc

Do not search the standard system directories for header files.

Only the directories you have specified with @option{-I} options

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

@item -nostdinc++

@opindex 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.)

@item -include @var{file}

@opindex include

Process @var{file} as if @code{#include "file"} appeared as the first

line of the primary source file.  However, the first directory searched

for @var{file} is the preprocessor's working directory @emph{instead of}

the directory containing the main source file.  If not found there, it

is searched for in the remainder of the @code{#include "@dots{}"} search

chain as normal.

If multiple @option{-include} options are given, the files are included

in the order they appear on the command line.

@item -imacros @var{file}

@opindex imacros

Exactly like @option{-include}, except that any output produced by

scanning @var{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 @option{-imacros} are processed before all files

specified by @option{-include}.

@item -idirafter @var{dir}

@opindex idirafter

Search @var{dir} for header files, but do it @emph{after} all

directories specified with @option{-I} and the standard system directories

have been exhausted.  @var{dir} is treated as a system include directory.

If @var{dir} begins with @code{=}, then the @code{=} will be replaced

by the sysroot prefix; see @option{--sysroot} and @option{-isysroot}.

@item -iprefix @var{prefix}

@opindex iprefix

Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix}

options.  If the prefix represents a directory, you should include the

final @samp{/}.

@item -iwithprefix @var{dir}

@itemx -iwithprefixbefore @var{dir}

@opindex iwithprefix

@opindex iwithprefixbefore

Append @var{dir} to the prefix specified previously with

@option{-iprefix}, and add the resulting directory to the include search

path.  @option{-iwithprefixbefore} puts it in the same place @option{-I}

would; @option{-iwithprefix} puts it where @option{-idirafter} would.

@item -isysroot @var{dir}

@opindex isysroot

This option is like the @option{--sysroot} option, but applies only to

header files (except for Darwin targets, where it applies to both header

files and libraries).  See the @option{--sysroot} option for more

information.

@item -imultilib @var{dir}

@opindex imultilib

Use @var{dir} as a subdirectory of the directory containing

target-specific C++ headers.

@item -isystem @var{dir}

@opindex isystem

Search @var{dir} for header files, after all directories specified by

@option{-I} 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.

@ifset cppmanual

@xref{System Headers}.

@end ifset

If @var{dir} begins with @code{=}, then the @code{=} will be replaced

by the sysroot prefix; see @option{--sysroot} and @option{-isysroot}.

@item -iquote @var{dir}

@opindex iquote

Search @var{dir} only for header files requested with

@code{@w{#include "@var{file}"}}; they are not searched for

@code{@w{#include <@var{file}>}}, before all directories specified by

@option{-I} and before the standard system directories.

@ifset cppmanual

@xref{Search Path}.

@end ifset

If @var{dir} begins with @code{=}, then the @code{=} will be replaced

by the sysroot prefix; see @option{--sysroot} and @option{-isysroot}.

@item -fdirectives-only

@opindex fdirectives-only

When preprocessing, handle directives, but do not expand macros.

The option's behavior depends on the @option{-E} and @option{-fpreprocessed}

options.

With @option{-E}, preprocessing is limited to the handling of directives

such as @code{#define}, @code{#ifdef}, and @code{#error}.  Other

preprocessor operations, such as macro expansion and trigraph

conversion are not performed.  In addition, the @option{-dD} option is

implicitly enabled.

With @option{-fpreprocessed}, predefinition of command line and most

builtin macros is disabled.  Macros such as @code{__LINE__}, which are

contextually dependent, are handled normally.  This enables compilation of

files previously preprocessed with @code{-E -fdirectives-only}.

With both @option{-E} and @option{-fpreprocessed}, the rules for

@option{-fpreprocessed} take precedence.  This enables full preprocessing of

files previously preprocessed with @code{-E -fdirectives-only}.

@item -fdollars-in-identifiers

@opindex fdollars-in-identifiers

@anchor{fdollars-in-identifiers}

Accept @samp{$} in identifiers.

@ifset cppmanual

@xref{Identifier characters}.

@end ifset

@item -fextended-identifiers

@opindex fextended-identifiers

Accept universal character names in identifiers.  This option is

experimental; in a future version of GCC, it will be enabled by

default for C99 and C++.

@item -fpreprocessed

@opindex 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 @option{-C} to the compiler without

problems.  In this mode the integrated preprocessor is little more than

a tokenizer for the front ends.

@option{-fpreprocessed} is implicit if the input file has one of the

extensions @samp{.i}, @samp{.ii} or @samp{.mi}.  These are the

extensions that GCC uses for preprocessed files created by

@option{-save-temps}.

@item -ftabstop=@var{width}

@opindex ftabstop

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.

@item -fdebug-cpp

@opindex fdebug-cpp

This option is only useful for debugging GCC.  When used with

@option{-E}, dumps debugging information about location maps.  Every

token in the output is preceded by the dump of the map its location

belongs to.  The dump of the map holding the location of a token would

be:

@smallexample

@{@samp{P}:@file{/file/path};@samp{F}:@file{/includer/path};@samp{L}:@var{line_num};@samp{C}:@var{col_num};@samp{S}:@var{system_header_p};@samp{M}:@var{map_address};@samp{E}:@var{macro_expansion_p},@samp{loc}:@var{location}@}

@end smallexample

When used without @option{-E}, this option has no effect.

@item -ftrack-macro-expansion@r{[}=@var{level}@r{]}

@opindex ftrack-macro-expansion

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 @var{level} parameter can be used to choose the level of

precision of token location tracking thus decreasing the memory

consumption if necessary. Value @samp{0} of @var{level} de-activates

this option just as if no @option{-ftrack-macro-expansion} was present

on the command line. Value @samp{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 @samp{2} tracks

tokens locations completely. This value is the most memory hungry.

When this option is given no argument, the default parameter value is

@samp{2}.

@item -fexec-charset=@var{charset}

@opindex fexec-charset

@cindex character set, execution

Set the execution character set, used for string and character

constants.  The default is UTF-8.  @var{charset} can be any encoding

supported by the system's @code{iconv} library routine.

@item -fwide-exec-charset=@var{charset}

@opindex fwide-exec-charset

@cindex character set, wide execution

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 @code{wchar_t}.  As with

@option{-fexec-charset}, @var{charset} can be any encoding supported

by the system's @code{iconv} library routine; however, you will have

problems with encodings that do not fit exactly in @code{wchar_t}.

@item -finput-charset=@var{charset}

@opindex finput-charset

@cindex character set, input

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.  @var{charset} can be any encoding

supported by the system's @code{iconv} library routine.

@item -fworking-directory

@opindex fworking-directory

@opindex fno-working-directory

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 @option{-fno-working-directory}.  If the @option{-P} flag is

present in the command line, this option has no effect, since no

@code{#line} directives are emitted whatsoever.

@item -fno-show-column

@opindex 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 @command{dejagnu}.

@item -A @var{predicate}=@var{answer}

@opindex A

Make an assertion with the predicate @var{predicate} and answer

@var{answer}.  This form is preferred to the older form @option{-A

@var{predicate}(@var{answer})}, which is still supported, because

it does not use shell special characters.

@ifset cppmanual

@xref{Obsolete Features}.

@end ifset

@item -A -@var{predicate}=@var{answer}

Cancel an assertion with the predicate @var{predicate} and answer

@var{answer}.

@item -dCHARS

@var{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.

@table @samp

@item M

@opindex dM

Instead of the normal output, generate a list of @samp{#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 @file{foo.h}, the command

@smallexample

touch foo.h; cpp -dM foo.h

@end smallexample

@noindent

will show all the predefined macros.

If you use @option{-dM} without the @option{-E} option, @option{-dM} is

interpreted as a synonym for @option{-fdump-rtl-mach}.

@xref{Debugging Options, , ,gcc}.

@item D

@opindex dD

Like @samp{M} except in two respects: it does @emph{not} include the

predefined macros, and it outputs @emph{both} the @samp{#define}

directives and the result of preprocessing.  Both kinds of output go to

the standard output file.

@item N

@opindex dN

Like @samp{D}, but emit only the macro names, not their expansions.

@item I

@opindex dI

Output @samp{#include} directives in addition to the result of

preprocessing.

@item U

@opindex dU

Like @samp{D} 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

@samp{#undef} directives are also output for macros tested but

undefined at the time.

@end table

@item -P

@opindex 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.

@ifset cppmanual

@xref{Preprocessor Output}.

@end ifset

@item -C

@opindex 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 @option{-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 line, since the first token on the line is no longer a @samp{#}.

@item -CC

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

like @option{-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 @option{-C} option, the

@option{-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 @option{-CC} option is generally used to support lint comments.

@item -traditional-cpp

@opindex traditional-cpp

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

opposed to ISO C preprocessors.

@ifset cppmanual

@xref{Traditional Mode}.

@end ifset

@item -trigraphs

@opindex trigraphs

Process trigraph sequences.

@ifset cppmanual

@xref{Initial processing}.

@end ifset

@ifclear cppmanual

These are three-character sequences, all starting with @samp{??}, that

are defined by ISO C to stand for single characters.  For example,

@samp{??/} stands for @samp{\}, so @samp{'??/n'} is a character

constant for a newline.  By default, GCC ignores trigraphs, but in

standard-conforming modes it converts them.  See the @option{-std} and

@option{-ansi} options.

The nine trigraphs and their replacements are

@smallexample

Trigraph:       ??(  ??)  ??<  ??>  ??=  ??/  ??'  ??!  ??-

Replacement:      [    ]    @{    @}    #    \    ^    |    ~

@end smallexample

@end ifclear

@item -remap

@opindex remap

Enable special code to work around file systems which only permit very

short file names, such as MS-DOS@.

@itemx --help

@itemx --target-help

@opindex help

@opindex target-help

Print text describing all the command line options instead of

preprocessing anything.

@item -v

@opindex v

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

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

@item -H

@opindex 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

@samp{#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 @samp{...x} and a valid one with @samp{...!} .

@item -version

@itemx --version

@opindex version

Print out GNU CPP's version number.  With one dash, proceed to

preprocess as normal.  With two dashes, exit immediately.

@end table