Why can't we declare a variable of type void?

Question

I\'m looking for a formal explanation of that fact in the Standard. I\'ve found what 3.9.1/9 says and trying to give an explanation used that section.

S

Answer 1

void is an incomplete type - you can only declare pointers to them and use them in function signatures. Obviously, extern Foo f; is permitted because struct Foo can be defined in another compilation unit (and if it's not the error will be detected by the linker), but void can't ever be "defined" (and the compiler knows this, of course) so void's quite special in this case.