#include <iostream>
using namespace std;
struct A {
 
    //protected:
 
    struct C { static void f() { cout << "A::C::f" <<endl; } };
 
};
 
struct B: A {
    C c1;            // the only C known here is A::C
    struct C { static void f() { cout << "B::C::f" <<endl; }};
    C c2;            // but here the closes C known is B::C
    A::C c3;         // and here I can be explicit about the C I want
    using D=A::C;    // and here another way to be explicit:
    D c4; 
};
 
int main() {
	B::C x;
	B::A::C y;
	A a =  B();
    decltype(a)::C::f();
 
    B  b; 
    decltype(b.c1)::C::f();
    decltype(b.c2)::C::f();
    decltype(b.c3)::C::f();
    decltype(b.c4)::C::f();
	return 0;
}

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