class A{public: virtual void a() { cout << "A" << endl; } virtual void a2();}; class B : public A{public: void a() { cout << "B" << endl; } virtual void a2();}; A a, * pA; B b, * pB;pA = &a;pB = &b; pA->a();pB->a();pA = & b;pA->a();