Why does a member function needs '&' (e.g. in std::bind)?

Question

When I was playing with std::bind from the C++11 -standard I recognized the following would be allowed by the compiler:

class Foo
{
public:
  void F();
  int G(int, int);
};

void Foo::F()
{
  auto f = bind(&Foo::G, this, _1, _2);
  cout << f(1,2) << endl;
}

int Foo::G(int a, int b)
{
  cout << a << ',' << b << endl;
  return 666;
}

But if I eliminated the '&' in front of the Foo::G in the bind -line, I would get some compiler errors (using MinGW 4.7).

Why is Foo::G not valid as a pointer to a member function, although H and &H would both work for "usual" functions?

LG ntor

Answer 1

& is required to take address of a member function, some compilers will allow you to omit the same but it is non-standard and at times confusing.

you can read about member function pointers in here: http://www.codeproject.com/Articles/7150/Member-Function-Pointers-and-the-Fastest-Possible

Answer 2

I take it that one of the reasons could have been consistency. Recall that within a class, you can say

MyClassOrOneOfItsBases::memberFunction();

It compiles fine, since the qualified name names the member function, instead of forming a pointer to member.