如何在转换为基数 class 后让 C++ 调用重写方法

Question

I have a class A with method Hello:我有一个 class A 方法你好：

class A {
 public:
  void Hello(){
     std::cout << "Hi from class A!" << std::endl;
  }
};

I then have a class B that inherits class A and has its own Hello method:然后我有一个 class B 继承了 class A 并且有自己的 Hello 方法：

class B : public A {
 public:
  void Hello(){
     std::cout << "Hi from class B!" << std::endl;
  }
};

I create a new object of class B, and later cast it to be of type class A.我创建了一个新的 class B 的 object，然后将其转换为 class A 类型。

B myB;
A myA = static_cast<A>(myB);

How do I make it so myA.Hello();我该怎么做myA.Hello(); prints "Hi from class B?"?打印“你好，来自 class B？”？

Answer 1

You should use reference and can call Hello()您应该使用参考并可以调用 Hello()

    B myB;
    A& myA = static_cast<A&>(myB);
    myA.Hello();

oupput:输出：

Hi from class A!

If you add "virtual" to Hello() of class A,如果将“虚拟”添加到 class A 的 Hello()，

virtual void Hello() {

you can get output below.您可以在下面获得 output。

Hi from class B!