[ksherlock]

I didn't believe it would work but it does. It boils down to

    sizeof(int) == sizeof(void)

vs

    sizeof(int) == sizeof(int)

As a non-standard extension, in gcc (and thus clang and icc for compatibility, it seems) void has a size of 1. In a conforming compiler, it's an error.

[AstralStorm]

Not quite.

Gcc it didn't fold it during preprocessing for a fully constant expression, which is allowed. In which case always sizeof(void) is a valid answer. Which is a compile error.

That is at least what C99 draft seems to say.

I'll check C11 draft next. Edit: same.