cpp.1

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.TH cpp 1 RISC
.SH Name
cpp \- the C language preprocessor
.SH Syntax
.NXR "cpp command"
.B /lib/cpp [
.I option ...
.B ]
.B [
.I ifile
.B [
.I ofile
.B ] ]
.SH Description
The
.PN cpp\^
command
is the C language preprocessor which is invoked as the
first pass of any C compilation using the
.MS cc 1
command.  Thus, the output of
.PN cpp\^
is designed to be in a form acceptable as input
to the next pass of the C compiler.
.PP
The preferred way to invoke
.PN cpp\^ ,
however, is through the
.MS cc 1
command.  See
.MS m4 1
for a general macro processor.
.SH Arguments
The
.PN cpp\^
command optionally accepts two file names as arguments.
The
.I ifile\^
and
.I ofile\^ 
are, respectively, the input and output
for the preprocessor.  They default to standard input
and standard output if no argument is supplied.
.SH Options
.TP 20
.B \-B
Strips C++-style comments (begin with \fB//\fP and end with newline).
.TP
.B \-C
Passes along all comments, except those found on
.PN cpp
directive lines.
By default,
.PN cpp\^
strips C-style comments.  
.TP
.B \-M
Generates dependency lists suitable for use with
.MS make 1
instead of the normal output.
.TP
.B \-P
Preprocesses the input without producing the line control
information used by the next pass of the C compiler.
.TP
.B \-R
Permits recursion when a macro is expanded.
.TP
.BI \-U name
Removes any initial definition of
.IR name ,
where
.I name\^
is a reserved symbol
that is predefined by the preprocessor.
The symbols predefined by this implementation are bsd4_2, ultrix, unix,
mips, host_mips, and MIPSEL.
.PD
.TP
.BI \-D name
.PD 0
.TP
.BI \-D name=def
Defines
.I name\^
as if by a
.B #define
directive.  If no
.I =def\^
is given,
.I name\^
is defined as 1.
The
.B \-D
option has lower precedence than the
.B \-U
option.
That is, if the same name is used in both a
.B \-U
option and a
.B \-D
option, the name remains undefined regardless of the order of the options.
.PD
.TP
.BI \-I dir
Changes the algorithm for searching for 
.B #include
files
whose names do not begin with a slash ( \fB/\fP )
to look in
.I dir\^
before looking in the directories on the standard list.
Thus, 
.B #include
files whose names are enclosed in quotes ( \fB"\|"\fP )
will be searched for
first in the directory of the
file with the
.B #include
line,
then in directories named in 
.B \-I
options,
and, finally, in directories on a standard list.
For
.B #include
files whose names are enclosed in angle brackets
.BR ( <> ),
the directory of the
file with the
.B #include
line is not searched.
.SH Directives
.PP
All
.PN cpp\^
directives start with lines that begin with a pound sign
.BR ( # ).
Any number of blanks and tabs are allowed between the
pound signs
and the directive.
The following is a list of the directives:
.TP 20
\fB#define \fIname\fB(\fIarg\fB, ...,\fIarg\fB )\fI token-string\fR
Replaces subsequent instances of
.I name
and the following set of tokens that is enclosed in parentheses
by
.IR token-string .
Each occurrence of an
.I arg
in the
.I token-string
is replaced by the corresponding set of tokens in the comma-separated list.
Note that spaces between
.I name
and the left parenthesis
.BR ( ( )
are not allowed.
When a macro with arguments is expanded, the arguments are placed 
unchanged into the expanded
.I token-string .
After the entire
.I token-string
has been expanded,
.PN cpp
re-starts its scan for names to expand at the beginning of the newly
created
.IR token-string .
.TP
.BI #undef " name"
Causes the definition of
.I name
(if any) to be forgotten.
.TP
\fB#include\fI "filename"
.PD 0
.TP
.BI #include " " < filename >
Includes the contents of
.I filename ,
which will then be run through
.PN cpp .
When the
.BI < filename >
notation is used,
.I filename
is searched for in the standard places.
See the
.B \-I
option above for more detail.
.PD
.TP
\fB#line\fI integer-constant "filename"
Causes
.PN cpp
to generate line control information for the next pass of the
C compiler.
.I Integer-constant
is the line number of the next line
and
.I filename
is the file that it comes from.
If \fI"filename"\fR is not given, the current file name is unchanged.
.TP
.B #endif
.br
Ends a section of lines begun by a test directive
.RB ( #if ,
.BR #ifdef ,
or
.BR #ifndef ).
Each test directive must have a matching
.BR #endif .
.TP
.BI #ifdef " name"
Defines text that will appear in the output if 
.I name
has been the subject of a previous
.B #define
without being the subject of an intervening
.BR #undef .
.TP
.BI #ifndef " name"
Defines text that will not appear in the output if 
.I name
has been the subject of a previous
.B #define
without being the subject of an intervening
.BR #undef .
.TP
.BI #if " constant-expression"
Defines text that will appear in the output if 
.I constant-expression 
is not zero.
All binary non-assignment C operators, which include the
.B ?: ,
en dash
.BR (\(mi ) ,
exclamation mark
.BR (!) ,
and tilde
.B (~)
are legal in
.IR constant-expression .
The precedence of the operators is the same as defined by the C language.
There is also a unary operator
.BR defined ,
which can be used in
.I constant-expression
in these two forms:
.BI defined " " ( " name " )
or
.BI defined " name" .
This allows the utility of
.BR #ifdef " and " #ifndef
in a
.B #if
directive.
Only these operators, integer constants, and names which
are known by
.PN cpp
should be used in
.IR constant-expression .
In particular, the
.B sizeof
operator is not available.
.TP
.B #else
Reverses the notion of the test directive which
matches this directive.  So if lines prior to
this directive are ignored, the following lines
will appear in the output.
The reverse is also true.
.TP
.BI #elif " constant-expression"
Defines text that will appear in the output if the preceding
test directive and all intervening
.B #elif
directives equalled zero and the
.I constant-expression
did not equal zero.
The rules for
.I constant-expression
are the same as for the
.B #if
directive.
.PP
The test directives and the possible
.B #else
and
.B #elif
directives can be nested.
.PP
In addition to these directives, the System V
.B #ident
directive is recognized and ignored.
.PP
Two special names are understood by
.PN cpp :
.B _\^\^_\s-1LINE\s+1_\^\^_
is defined as the current line number (as a decimal integer) 
and
.B _\^\^_\s-1FILE\s+1_\^\^_
is defined as the current file name (as a C string).
They can be used in any situations where you would use
other defined names, including in macros.
.SH Diagnostics
The error messages produced by
.PN cpp\^
are self-explanatory.  The line number and filename
where the error occurred are printed along with the diagnostic.
.SH Files
.TP 1.5i
/usr/include
standard directory for
.B #include
files
.SH See Also
cc(1), m4(1)