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 ([class.access]) shall be obeyed.
[Example 1: class E {int x;
class B {};
class I {
B b; / OK, E::I can access E::Bint y;
void f(E* p, int i){
p->x = i; / OK, E::I can access E::x}};
int g(I* p){return p->y; / error: I::y is private}};
— end example]