C++ looks like it ought to be OK to parse, but turns out to be completely evil. (flamebait mode on) Bit like the rest of the language really. (flamebait apologia: I spend most of my time coding C++; sometimes I even enjoy it...)
Just lexing C++ is a major project, because of the 'phases of translation', the preprocessor, the preprocessor tokens, etc., and then trying to make it fast.
