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。