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Question

I want to preprocess C++ header files keeping all macros verbatim in the output text.

For that, I need a C preprocessor-like program that performs these tasks:

• store in memory macros from #define directives;
• recursively follow #include directives;
• evaluate conditions in #if and #ifdef directives;
• suppress the code in inactive portions of #if .. #else .. #endif blocks;
• (optionally) remove /* .. */ and // comments;
• remove all remaining directives lines.

But the macros must not be replaced in the output. Or alternatively, the preprocessor may take in argument a list of macro names that shall not be replaced.

This may sound weird, but I have a good reason for that. I have a series of Perl scripts able to analyze preprocessed C++ class headers. And I use some macros to tell them for example which methods to export.

I haven't found a preprocessor program able to perform what I need, so I wrote a Perl script. The latter actually works, but is slow and non standard. I am looking for a better alternative.

Answer 1

Use gcc -E to run the preprocessor manually. This will expand all the macros but that's not a problem.

What you want is special macros for the time when you need the output for your Perl scripts. Try this:

#ifdef PERL_PREPROCESSING
# define EXPORT(...) PERL_EXPORT
#else
# define EXPORT(...) ...normal C code...
#endif

So the idea is that you call gcc -E -DPERL_PREPROCESSING to switch some of the macros to produce output that your perl scripts can locate. The macros will be expanded as usual.

[EDIT] If you don't want to pollute your sources with Perl-specific macros, use this trick: Create a folder which contains the header file with the Perl versions of the macros and include this folder before every other folder with -I . gcc will then ignore the standard header file.

Answer 2

If you are using *nix you can use the grep command to find all the #defines in the directory

grep -R . '#define'

For the preprocessing required, use gcc -E.