Using macro with string fails on VC 2015

Question

Why does this fail to compile?

char programDate[] = \"(\"__DATE__\")\";

But this compiles fine (see space):

char programDat         


        

Answer 1

Since C++11, user-defined literals exist and are part of preprocessing. The grammar is:

preprocessing-token:
    user-defined-string-literal
    // other stuff...

user-defined-string-literal:
    string_literal ud-suffix

ud-suffix:
    identifier

So "("__DATE__ matches preprocessing-token, but "(" __DATE__ doesn't (that is two separate preprocessing tokens).

Macro replacement happens after tokenization. Since there is no token __DATE__ in your first example, there is no replacement.