笔试面试 class A { public: A() { num++; } virtual void print() { std::cout << num; } private: int num = { 0 }; }; class B : public A { public: virtual void print() { std::cout << num; } private: int num = { 0 }; }; int main() { A* a = new B(); a->print(); }以上输出结果是什么?