cpp(1) CLIX cpp(1)
NAME
cpp - Runs the C language preprocessor
SYNOPSIS
LIBDIR/cpp [flag ... ] [ifile[ofile]]
FLAGS
-P Preprocesses the input without producing the line control
information used by the next pass of the C compiler.
-C Passes all comments (except those found on cpp directive
lines). By default, cpp strips C-style comments.
-Uname Removes any initial definition of name, where name is a
reserved symbol that is predefined by the particular
preprocessor. The following is the current list of these
possibly reserved symbols. On the AT&T, 3B2 and 3B5
Computers, unix, and one of u3b2 or u3b5 are defined.
operating system:
unix, dmert, gcos, ibm, os, tss
hardware:
interdata, pdp11, u370, u3b, u3b5, u3b2, u3b20d, vax
UNIX system variant:
RES, RT
lint: lint
-Dname
-Dname=def Defines name with value def as if by a #define directive. If
no =def is given, name is defined with value 1. The -D flag
has lower precedence than the -U flag. That is, if the same
name is used in both a -U flag and a -D flag, the name is
undefined regardless of the order of the flags.
-T Forces cpp to use only the first eight characters to
distinguish preprocessor symbols and is included for backward
compatibility.
-Idir Changes the algorithm for searching for #include files whose
names do not begin with / to look in dir before looking in
the directories on the standard list. Thus, #include files
whose names are enclosed in quotes (") are first searched for
in the directory of the file with the #include line, then in
directories named in -I flags, and last in directories on a
standard list. For #include files whose names are enclosed
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in angle brackets (<>), the directory of the file with the
#include line is not searched.
-Ydir Uses directory dir in place of the standard list of
directories when searching for #include files.
-H Displays, one per line on stderr, the pathnames of included
files.
DESCRIPTION
The C language preprocessor, cpp, is invoked as the first pass of any C
compilation by the cc command. The output of cpp is designed to be in a
form which is acceptable as input to the next pass of the C compiler. As
the C language evolves, cpp and the rest of the C compilation package is
modified to follow these changes. Therefore, the use of cpp other than
through the cc command is not suggested, since the functionality of cpp
may someday be moved elsewhere. See m4 for a general macro processor.
The command cpp optionally accepts two filenames as arguments. The ifile
and ofile are respectively the input and output for the preprocessor.
They default to stdin and stdout if not supplied.
Two special names are understood by cpp. The name __LINE__ is defined as
the current line number (as a decimal integer) as known by cpp, and
__FILE__ is defined as the current filename (as a C string) as known by
cpp. They can be used anywhere (including in macros) just as any other
defined name.
All cpp directive lines start with a pound sign (#) in column 1. Any
number of blanks and tabs is allowed between the # and the directive. The
directives are as follows:
#define name token-string
Replaces subsequent instances of name with token-string.
#define name(arg, ... ,arg) token-string
Replaces subsequent instances of name followed by a (, a list of
comma-separated sets of tokens, and a ) followed by token-string,
where each occurrence of an argument arg in the token-string is
replaced by the corresponding set of tokens in the comma-separated
list. When a macro with arguments is expanded, the arguments are
placed into the expanded token-string unchanged. After the entire
token-string has been expanded, cpp re-starts its scan for names to
expand at the beginning of the newly created token-string. Notice
that there can be no space between name and the (.
#undef name
Causes the definition of name (if any) to be forgotten from now on.
No additional tokens are permitted on the directive line after
name.
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#ident "string"
Put string into the .comment section of an object file.
#include "filename"
#include <filename>
Includes at this point the contents of filename (which is then run
through cpp). When the <filename> notation is used, filename is
only searched for in the standard places. See the -I and -Y flags
for more detail. No additional tokens are permitted on the
directive line after the final " or >.
#line integer-constant "filename"
Causes cpp to generate line control information for the next pass
of the C compiler. The integer-constant is the line number of the
next line and filename is the file from which it comes. If
"filename" is not given, the current filename is unchanged. No
additional tokens are permitted on the directive line after the
optional filename.
#endif Ends a section of lines begun by a test directive (#if, #ifdef, or
#ifndef). Each test directive must have a matching #endif. No
additional tokens are permitted on the directive line.
#ifdef name
The lines following will appear in the output if and only if name
has been the subject of a previous #define directive without being
the subject of an intervening #undef directive. No additional
tokens are permitted on the directive line after name.
#ifndef name:
The lines following will appear in the output if and only if name
has not been the subject of a previous #define directive. No
additional tokens are permitted on the directive line after name.
#if constant-expression
Lines following appear in the output if and only if the constant-
expression evaluates to nonzero. All binary nonassignment C
operators, the ?: operator, the unary -, !, and ~ operators are all
legal in constant-expression. The precedence of the operators is
the same as defined by the C language. There is also a unary
operator defined, which can be used in constant-expression in these
two forms: defined(name) or defined name. This allows the utility
of #ifdef and #ifndef in a #if directive. Only these operators,
integer constants, and names which are known by cpp should be used
in constant-expression. In particular, the sizeof operator is not
available.
To test whether either of two symbols, foo and fum, are defined,
use the following directive:
#if defined(foo) || defined(fum)
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#elif constant-expression
An arbitrary number of #elif directives is allowed between a #if,
#ifdef, or #ifndef directive and a #else or #endif directive. The
lines following the #elif directive will appear in the output if
and only if the preceding test directive evaluates to zero, all
intervening #elif directives evaluate to zero, and the constant-
expression evaluates to nonzero. If constant-expression evaluates
to nonzero, all succeeding #elif and #else directives will be
ignored. Any constant-expression allowed in a #if directive is
allowed in a #elif directive.
#else The lines following appear in the output if and only if the
preceding test directive evaluates to zero, and all intervening
#elif directives evaluate to zero. No additional tokens are
permitted on the directive line.
The test directives and the possible #else directives can be nested.
EXAMPLES
1. Processes a C file into its expanded form:
cpp myfile.c > myfile.cpp
2. Defines an identifier MY-ID to the preprocessor on the command line:
cpp -DMY_ID myfile.c > myfile.cpp
3. Changes the include file search path to first search the directory
/usr/src/myincludes:
cpp -I/usr/src/myincludes myfile.c > myfile.cpp
FILES
INCDIR Standard directory list for #include files. Usually
/usr/include.
LIBDIR Standard library files. Usually /lib.
NOTES
The unsupported W flag enables the #class directive. If it encounters a
#class directive, cpp exits with code 27 after finishing all other
processing. This flag provides support for ``C with classes''.
Because the standard directory for included files may be different in
different environments, this form of #include directive should be used
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rather than one with an absolute path:
#include <file.h>
If an absolute path such as
#include /usr/include/file.h
is used, cpp warns about the use of the absolute pathname.
DIAGNOSTICS
The error messages produced by cpp are intended to be self-explanatory.
The line number and filename where the error occurred are displayed along
with the diagnostic.
EXIT VALUES
The cpp command returns a value of 27 if it encounters a #class directive.
RELATED INFORMATION
Commands: acc(1), cc(1), lint(1), m4(1)
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