Question

I found something interesting. The error message says it all. What is the reason behind not allowing parentheses while taking the address of a non-static member function? I compiled it on gcc 4.3.4.

#include <iostream>

class myfoo{
    public:
     int foo(int number){
         return (number*10);
     }
};

int main (int argc, char * const argv[]) {

    int (myfoo::*fPtr)(int) = NULL;

    fPtr = &(myfoo::foo);  // main.cpp:14

    return 0;

}

Error: main.cpp:14: error: ISO C++ forbids taking the address of an unqualified or parenthesized non-static member function to form a pointer to member function. Say ‘&myfoo::foo’

Answer 1

From the error message, it looks like you’re not allowed to take the address of a parenthesized expression. It’s suggesting that you rewrite

fPtr = &(myfoo::foo);  // main.cpp:14

to

fPtr = &myfoo::foo;

This is due to a portion of the spec (§5.3.1/3) that reads

A pointer to member is only formed when an explicit & is used and its operand is a qualified-id not enclosed in parentheses […]

(my emphasis). I’m not sure why this is a rule (and I didn’t actually know this until now), but this seems to be what the compiler is complaining about.

Hope this helps!