You can also use pycparser[0]. It is fully compatible C99, but be careful it doesn't support gnu extensions (like attributes, #indent, asm() ...). You can however work around most of them by -D defining them to empty macro in the argument.
As long as we’re on this tangent, here’s the challenge I’m facing with automated analysis of student code: from foo.c make bar.c which is identical to foo.c except that comments have been turned into spaces. I think this is annoyingly non-trivial.