Parsing Source Code

I need to parse the source code of different files, each written in a different language, and I would like to do this with C.

To do this, I thought about using yacc/ lex, but I find them very difficult to understand, possibly due to the complete lack of decent documentation (either this or they are really cryptic).

So my questions are: where can I find good documentation for yacc/ lex, preferably introducing a textbook style? Or is there a better way to do this in C? Maybe there is something else that I could use instead of yacc/ lex, maybe even written in another language?