#ifdef WIN32 #elif WIN64 #endif

Question

I have come across some example code that goes like this:

#ifdef WIN32
   ...
#elif WIN64
   ...
#endif

In an #ifdef block, is it actually legal to use #elif to mean #elif defined?

Answer 1

No, it shouldn't be. That's not to say that some obscure C compiler wouldn't accept it as such, but it isn't part of the C standard.

Normally, for something like this you would use either #elifdef FOO (which I've never actually seen in production code) or #elif defined(FOO) (like you mentioned).

This code appears to be working in a odd way; it's rather first checking if WIN32 is defined, then checking if WIN64 is nonzero.