Partially preprocess a C or C++ source file?

Question

Is there a way to partially pre-process a C or C++ source file? By "partially preprocess" I mean expanding some but not all of the #include directives. For example, I would like to expand #includes pointing to my project headers, but not #includes pointing to other libraries' headers.

I tried to do this by running gcc -E with only the -I flags for my project headers and not the -I flags for the libraries, but that doesn't work because gcc gives an error when it encounters an #include it cannot expand.

EDIT: I do not really care about the preprocessor's behaviour with respect to macro expansion.

Answer 1

The C preprocessor isn't smart enough to do this on its own. If you're only interested in #include, you should just roll your own tool (in, say, Perl) to process the source files, expanding #include lines that interest you and ignoring the rest.

This script prefixes uninteresting header lines with // Ignored:

#!/usr/bin/perl

use warnings;
use strict;

my @uninteresting = qw(iostream vector map);
my $uninteresting = join '|', @uninteresting;

while (<>) {
    s%(#include <(?:$uninteresting)>)%// Ignored $1%;
    print;
}

Now you can do:

cat sourcefile.cpp | perl ignore-meh.pl | g++ -E

And if you want to get really fancy:

#!/usr/bin/perl

use warnings;
use strict;

while (<>) {
    s%// Ignored (#include <[^>]+>)%$1%;
    print;
}

Now you can do:

cat sourcefile.cpp | perl ignore-meh.pl | g++ -E | perl restore-meh.pl