如何在函数中判断传递的对象指向的是哪个类

Three classes A, B and C are shown below:

class A {public:virtual ~A() {};};class B: public A {};class C: public B {};

You are to implement a function string verify(A *), such that it returns "grandpa" if the passed-in argument points to a class A object, and "father" for a class B object , "son" for a class C object.

Your submitted source code should include the whole implementation of the function verify, but without any class defined above.
No main() function should be included.

主程序：

#include <iostream>  #include <string>   using namespace std;     class A {  public:       virtual ~A() {};   };   class B: public A {};    class C: public B {};       #include "source"      int main()   {       A a;       B b;       C c;       cout<<verify(&a)<<endl;       cout<<verify(&b)<<endl;       cout<<verify(&c)<<endl;          return 0;   } 

答案程序 "source":

string verify(A *p){  if (dynamic_cast<C*>(p))     return "son";  else if (dynamic_cast<B*>(p))     return "father";  else     return "grandpa";}