解释一下最终的输出答案

Question

#include <iostream.h>

class A

{

public:

A()

{ cout<<"A constructor called!"<<endl; }

void f(){ cout<<"f() is called in A!"<<endl; }

};

class B :public A

{

public:

B(){ cout<<"B constructor called!"<<endl; }

 virtual void f(){ cout<<"f() is called in B!"<<endl; }

};

class C:public B

{

public:

C(){cout<<"C constructor called!"<<endl;}

void f(){cout<<"f() is called in C!"<<endl;}      

};

void main()

{

 A * pa;

 B * pb;

 pa = pb = new C;

 pa->f();

 pb->f();

}

Answer 1

pa->f()输出f() is called in A!pb->f()输出f() is called in C!这里是C++多态的例子。多态就是对于有虚函数的父类对象来说（这里是B* pb)，对象实际指向的类型不由声明决定，而是由赋值决定的，所以pb = new C以后，实际pb指向的是C类型，所以调用pb->f()的时候，实际调用的是C的f()函数。而A没有虚函数（或纯虚函数），所以pa = new C并不会触发pa的多态，也就是pa还是A类型，所以调用pa->f()的时候，实际调用的是A的f()函数。