Question

In C++ you can create a “function type” with for example:

void main() {
 int a();
}

And a has the type “int ()”, but is it possible to use it? I can’t even pass ‘a’ as a template argument (but I can pass “int ()” as one)

Answer 1

You are not declaring a “function type”. You are declaring a function. This is the same thing that you normally do in file scope, but in this case you do it in local scope

int main() {
   int a(); /* declare function `a` */
   ...
   int i = a(); /* call function `a` */
}

int a() { /* define function `a` */
  /* whatever */
}

And yes, you can pass it as a template argument. It has to be a non-type argument, of course

template <int A()> void foo() { 
  A(); /* call the function specified by the template argument */
}

int main() {
   int a(); /* declare function `a` */
   foo<a>(); /* pass it as a template argument */
}