Error: Reference to non-static member function must be called (2)

Question

I have a piece of code like this

class A {
public:

typedef int (A::*AFn)(int);
std::map<std::string, AFn> fm_;

A() {
    fm_.insert("fn1", fn);
}

int fn(int a) {
    return a;
}

};

I get a compile time error saying error: reference to non-static member function must be called fm_.insert("fn1", fn);

Why does this happen and how do I correct it?

Answer 1

Since fn is a non-static member function, a lone fn is not a valid expression. The only thing you can do with non-qualified fn in this context is call it: fn(something). This is what the compiler is telling you.

If you want to obtain a pointer to member function A::fn, you have to explcitly use operator & and supply a qualified member name: &A::fn.