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.\"
.IX Title "Filter::cpp 3pm"
.TH Filter::cpp 3pm "2019-02-10" "perl v5.28.1" "User Contributed Perl Documentation"
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.SH "NAME"
Filter::cpp \- cpp source filter
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&    use Filter::cpp ;
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This source filter pipes the current source file through the C
pre-processor (cpp) if it is available.
.PP
As with all source filters its scope is limited to the current source
file only. Every file you want to be processed by the filter must have a
.PP
.Vb 1
\&    use Filter::cpp ;
.Ve
.PP
near the top.
.PP
Here is an example script which uses the filter:
.PP
.Vb 1
\&    use Filter::cpp ;
\&
\&    #define FRED 1
\&    $a = 2 + FRED ;
\&    print "a = $a\en" ;
\&    #ifdef FRED
\&    print "Hello FRED\en" ;
\&    #else
\&    print "Where is FRED\en" ;
\&    #endif
.Ve
.PP
And here is what it will output:
.PP
.Vb 2
\&    a = 3
\&    Hello FRED
.Ve
.PP
This example below, provided by Michael G Schwern, shows a clever way
to get Perl to use a C pre-processor macro when the Filter::cpp module
is available, or to use a Perl sub when it is not.
.PP
.Vb 2
\&    # use Filter::cpp if we can.
\&    BEGIN { eval \*(Aquse Filter::cpp\*(Aq }
\&
\&    sub PRINT {
\&        my($string) = shift;
\&
\&    #define PRINT($string) \e
\&        (print $string."\en")
\&    }
\&     
\&    PRINT("Mu");
.Ve
.PP
Look at Michael's Tie::VecArray module for a practical use.
.SH "AUTHOR"
.IX Header "AUTHOR"
Paul Marquess
.SH "DATE"
.IX Header "DATE"
11th December 1995.