error: ‘void A::ohai()’ is inaccessible

 struct A { void ohai() {} };

             ^

main.cpp:20:11: error: within this context

  B().ohai();

       ^

main.cpp:8:17: error: ‘void A::ohai()’ is inaccessible

 struct A { void ohai() {} };

             ^

main.cpp:22:11: error: within this context

  D().ohai();

​

struct A { void ohai() {} };

​

struct B: protected A {};

​

struct C: private A { friend int main();};

​

struct D: B { void test() { ohai();} };

​

struct E: C { void test() { ohai();} };

​

int main() {

    A().ohai();

    B().ohai();

    C().ohai();

    D().ohai();    

    return 0;

}

​