The preprocessor, which means whatever the editor sees might have a complete different meaning. There are people that make all sorts of dirty tricks with the C and C++ preprocessor.

C++'s grammar is not context free, so you really need a compiler frontend to make sure the refactored code isn't broken.

I'm not a C++ programmer, but I'd imagine it having to do with turing-complete metaprogramming.

(lack of) context free grammar.