MAN page from Trustix cpp-2.95.3-1tr.i586.rpm
Section: GNU Tools (1)
cccp, cpp - The GNU C-Compatible Compiler Preprocessor.
- [-$][-Apredicate[(value)]][-C][-Dname[=definition]][-dD][-dM][-I directory][-H][-I-][-imacros file][-include file][-idirafter dir][-iprefix prefix][-iwithprefix dir][-lang-c][-lang-c++][-lang-objc][-lang-objc++][-lint][-M [-MG]][-MM [-MG]][-MD file ][-MMD file ][-nostdinc][-nostdinc++][-P][-pedantic][-pedantic-errors][-traditional][-trigraphs][-Uname][-undef][-Wtrigraphs][-Wcomment][-Wall][-Wtraditional]
The C preprocessor is a macro processor
that is used automatically bythe C compiler to transform your program before actual compilation. It iscalled a macro processor because it allows you to define macros
,which are brief abbreviations for longer constructs.
The C preprocessor provides four separate facilities that you can use asyou see fit:
- Inclusion of header files. These are files of declarations that can besubstituted into your program.
- Macro expansion. You can define macros, which are abbreviationsfor arbitrary fragments of C code, and then the C preprocessor willreplace the macros with their definitions throughout the program.
- Conditional compilation. Using special preprocessing directives, youcan include or exclude parts of the program according to variousconditions.
- Line control. If you use a program to combine or rearrange source files intoan intermediate file which is then compiled, you can use line controlto inform the compiler of where each source line originally came from.
C preprocessors vary in some details. For a full explanation of theGNU C preprocessor, see theinfofile `cpp.info', or the manualThe C Preprocessor. Both of these are built from the same documentation source file, `cpp.texinfo'. The GNU Cpreprocessor provides a superset of the features of ANSI Standard C.
ANSI Standard C requires the rejection of many harmless constructs commonlyused by today's C programs. Such incompatibility would be inconvenient forusers, so the GNU C preprocessor is configured to accept these constructsby default. Strictly speaking, to get ANSI Standard C, you must use theoptions `-trigraphs', `-undef' and `-pedantic', but inpractice the consequences of having strict ANSI Standard C make itundesirable to do this.
Most often when you use the C preprocessor you will not have to invoke itexplicitly: the C compiler will do so automatically. However, thepreprocessor is sometimes useful individually.
When you call the preprocessor individually, either name(cpp or cccp) will do---they are completely synonymous.
The C preprocessor expects two file names as arguments, infile andoutfile. The preprocessor reads infile together with any otherfiles it specifies with `#include'. All the output generated by thecombined input files is written in outfile.
Either infile or outfile may be `-', which as infilemeans to read from standard input and as outfile means to write tostandard output. Also, if outfile or both file names are omitted,the standard output and standard input are used for the omitted file names.
Here is a table of command options accepted by the C preprocessor. These options can also be given when compiling a C program; they arepassed along automatically to the preprocessor when it is invoked bythe compiler.
- Inhibit generation of `#'-lines with line-number information inthe output from the preprocessor. This might beuseful when running the preprocessor on something that is not C codeand will be sent to a program which might be confused by the`#'-lines.
- Do not discard comments: pass them through to the output file.Comments appearing in arguments of a macro call will be copied to theoutput before the expansion of the macro call.
- Try to imitate the behavior of old-fashioned C, as opposed to ANSI C.
- Process ANSI standard trigraph sequences. These are three-charactersequences, all starting with `??', that are defined by ANSI C tostand for single characters. For example, `??/' stands for`\',so `'??/n'' is a character constant for a newline.Strictly speaking, the GNU C preprocessor does not support allprograms in ANSI Standard C unless `-trigraphs' is used, but ifyou ever notice the difference it will be with relief.
You don't want to know any more about trigraphs.
- Issue warnings required by the ANSI C standard in certain cases suchas when text other than a comment follows `#else' or `#endif'.
- Like `-pedantic', except that errors are produced rather thanwarnings.
- Warn if any trigraphs are encountered (assuming they are enabled).
- Warn whenever a comment-start sequence `/*' appears in a comment.(Both forms have the same effect).
- Requests both `-Wtrigraphs' and `-Wcomment' (but not`-Wtraditional').
- Warn about certain constructs that behave differently in traditional andANSI C.
- -I directory
- Add the directory directory to the end of the list ofdirectories to be searched for header files.This can be used to override a system header file, substituting yourown version, since these directories are searched before the systemheader file directories. If you use more than one `-I' option,the directories are scanned in left-to-right order; the standardsystem directories come after.
- Any directories specified with `-I' options before the `-I-'option are searched only for the case of `#include file"';they are not searched for `#include <file>'.
If additional directories are specified with `-I' options afterthe `-I-', these directories are searched for all `#include'directives.
In addition, the `-I-' option inhibits the use of the currentdirectory as the first search directory for `#include file"'.Therefore, the current directory is searched only if it is requestedexplicitly with `-I.'. Specifying both `-I-' and `-I.'allows you to control precisely which directories are searched beforethe current one and which are searched after.
- Do not search the standard system directories for header files.Only the directories you have specified with `-I' options(and the current directory, if appropriate) are searched.
- Do not search for header files in the C++ specific standarddirectories, but do still search the other standard directories.(This option is used when building libg++.)
- -D name
- Predefine name as a macro, with definition `1'.
- -D name=definition
- Predefine name as a macro, with definition definition.There are no restrictions on the contents of definition, but ifyou are invoking the preprocessor from a shell or shell-like programyou may need to use the shell's quoting syntax to protect characterssuch as spaces that have a meaning in the shell syntax. If you use more thanone `-D' for the samename, the rightmost definition takes effect.
- -U name
- Do not predefine name. If both `-U' and `-D' arespecified for one name, the `-U' beats the `-D' and the nameis not predefined.
- Do not predefine any nonstandard macros.
- -A name(value)
- Assert (in the same way as the #assert directive)the predicate name with tokenlist value. Remember to escape or quote the parentheses onshell command lines.
You can use `-A-' to disable all predefined assertions; it alsoundefines all predefined macros.
- Instead of outputting the result of preprocessing, output a list of`#define' directives for all the macros defined during theexecution of the preprocessor, including predefined macros. This givesyou a way of finding out what is predefined in your version of thepreprocessor; assuming you have no file `foo.h', the command
touch foo.h; cpp -dM foo.h
will show the values of any predefined macros.
- Like `-dM' except in two respects: it does not include thepredefined macros, and it outputs both the `#define'directives and the result of preprocessing. Both kinds of output go tothe standard output file.
- -M [-MG]
- Instead of outputting the result of preprocessing, output a rulesuitable for make describing the dependencies of the mainsource file. The preprocessor outputs one make rule containingthe object file name for that source file, a colon, and the names ofall the included files. If there are many included files then therule is split into several lines using `\\'-newline.
`-MG' says to treat missing header files as generated files and assume they live in the same directory as the source file. It must be specified in addition to `-M'.
This feature is used in automatic updating of makefiles.
- -MM [-MG]
- Like `-M' but mention only the files included with `#include"file"'. System header files included with `#include<file>' are omitted.
- -MD file
- Like `-M' but the dependency information is written to `file'. This is in addition to compiling the file asspecified---`-MD' does not inhibit ordinary compilation the way`-M' does.
When invoking gcc, do not specify the `file' argument. Gcc will create file names made by replacing `.c' with `.d' at the end of the input file names.
In Mach, you can use the utility md to merge multiple filesinto a single dependency file suitable for using with the `make'command.
- -MMD file
- Like `-MD' except mention only user header files, not systemheader files.
- Print the name of each header file used, in addition to other normalactivities.
- -imacros file
- Process file as input, discarding the resulting output, beforeprocessing the regular input file. Because the output generated fromfile is discarded, the only effect of `-imacros file' is tomake the macros defined in file available for use in the maininput. The preprocessor evaluates any `-D' and `-U' optionson the command line before processing `-imacros file' .
- -include file
- Process fileas input, and include all the resulting output,before processing the regular input file.
- -idirafter dir
- Add the directory dir to the second include path. The directorieson the second include path are searched when a header file is not foundin any of the directories in the main include path (the one that`-I' adds to).
- -iprefix prefix
- Specify prefix as the prefix for subsequent `-iwithprefix'options.
- -iwithprefix dir
- Add a directory to the second include path. The directory's name ismade by concatenating prefix and dir, where prefixwas specified previously with `-iprefix'.
- Specify the source language. `-lang-c++' makes the preprocessorhandle C++ comment syntax, and includes extra default includedirectories for C++, and `-lang-objc' enables the Objective C`#import' directive. `-lang-c' explicitly turns off both ofthese extensions, and `-lang-objc++' enables both.
These options are generated by the compiler driver gcc, but notpassed from the `gcc' command line.
- Look for commands to the program checker lint embedded incomments, and emit them preceded by `#pragma lint'. For example,the comment `/* NOTREACHED */' becomes `#pragma lintNOTREACHED'.
This option is available only when you call cpp directly;gcc will not pass it from its command line.
- Forbid the use of `$' in identifiers. This was formerly required for strict conformanceto the C Standard before the standard was corrected.
This option is available only when you call cpp directly;gcc will not pass it from its command line.
;The C Preprocessor
, Richard M. Stallman.gcc
'entry in info
;Using and Porting GNU CC (for version 2.0)
, Richard M. Stallman.
Copyright (c) 1991, 1992, 1993 Free Software Foundation, Inc.
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- SEE ALSO
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