Multi-pass C preprocessor [closed]

Question

Is it remotely sane to apply the C preprocessor to the same codebase multiple times (specifically, twice in sequence?)

For instance, having declarations such as the following:

##define DECLARE(FILE) # define DECLARATIONS \
                       #   include FILE \
                       # undef DECLARATIONS

Have you ever seen such an idiom before? If so, what codebase? Can you link it? What sort of patterns would be followed to compile a project doing something like this? Can the CPP as it stands be made to do this, or do I need to write a meta-preprocessor to “hide” the single-hash declarations while processing the double-hash declarations, and so on?

Answer 1

I think when you need multiple CPP passes, you might want to consider m4 or some other sophisticated macro system/code generator. I think it will be hard to do what you want, and since you are going to be changing your build process for this anyway, look at other templating or macro systems.

Answer 2

Oh wow, why would you want to do this? I am sure GCC could be coerced into doing something like this with some clever make tricks (use the -E flag for GCC) but I can't imagine anyone being able to maintain it later.