It also depends on what functionality you want your parser to support. In theory, parsing just means "accept or reject". In practice, you need to do something like build a tree, and there are many different possible tree representations depending on what you want to do.

Clang aims to support very general transformation of C++ with their parser and AST. I was shocked to learn that Clang's AST has 60K lines of header files! That's not including the code, and it's not templates! That's class definitions!!! (wc -l include/clang/AST/*.h)