Are inner classes in C++ automatically friends?

Question

If I define an inner class in C++, is it automatically a friend of the class that contains it? For example, is this legal:

class Outer {
public:
    class Inner {
    public:
        void mutateOuter(Outer& o);
    };

private:
    int value;
};

void Outer::Inner::mutateOuter(Outer& o) {
    o.value ++; // Legal?  Or not?
}

I ask because on some compilers I've tried (VS2003) this code won't work, but I've heard at least anecdotally that it does work on some compilers. I can't find a relevant section in the C++ spec about this, and if anyone can cite something specific that would say that it is or is not legal that would be great.

Answer 1

After having asked more or less the same question here myself, I wanted to share the (apparently) updated answer for C++11:

Quoted from https://stackoverflow.com/a/14759027/1984137:

standard $11.7.1

"A nested class is a member and as such has the same access rights as any other member. The members of an enclosing class have no special access to members of a nested class; the usual access rules shall be obeyed"

and the usual access rules specify that:

"A member of a class can also access all the names to which the class has access..."

specific examples has been given in the standard:

class E {
    int x;
    class B { };

    class I {
        B b; // OK: E::I can access E::B
        int y;
        void f(E* p, int i) {
            p->x = i; // OK: E::I can access E::x
        }
    };
}