Why doesn't the C++ compiler complain when I use functions without parentheses?

Question

I was looking at some code a friend sent me, and he said: "It compiles, but doesn't work". I saw that he used the functions without the parentheses, something like this:

void foo(){
  cout<< "Hello world\n";
}

int main(){
  foo; //function without parentheses
  return 0;
}

The first I said was "use parentheses, you have to". And then I tested that code - it does compile, but when executed doesn't work (no "Hello world" shown).

So, why does it compile (no warning at all from the compiler GCC 4.7), but doesn't work?

Answer 1

It surely warns if you set the warning level high enough.

A function name evaluates to the address of the function, and is a legal expression. Usually it is saved in a function pointer,

void (*fptr)() = foo;

but that is not required.