dynamics_cast<>

 #include <iostream>

 class A
 {
 public:
     A(){}
     ~A(){}
     virtual int data(){return ;}
 };
 class B:public A
 {
 public:
     B(){}
     ~B(){}
     int data(){return ;}
 };

 class C:public A
 {
 public:
     C(){}
     ~C(){}
     int data(){return ;}
 };

 class D:public C
 {
 public:
     D(){}
     ~D(){}
     int data(){return ;}
 };

 int main()
 {

     std::cout<<"dynamic_cast begin \n";
     A *a=new A;
     B *b=new B;
     C *c=new C;
     D *d=new D;

     if(dynamic_cast<B*> (a))   //this will fail  派生类不能指向基类
     {
         std::cout<<"A *a convert B class ok\n";
     }

     if(dynamic_cast<A*> (b))    // this will be ok   基类指向派生类 ok
     {
         std::cout<<"B *b convert A class ok\n";
     }

     if(dynamic_cast<C*> (a))     // 派生类不能指向基类
     {
         std::cout<<"A *a convert C class ok\n";
     }

     if(dynamic_cast<A*> (c))    //c派生类 所以可以被A指向
     {
         std::cout<<"A *a convert C class ok\n";
     }

     if(dynamic_cast<A*> (d))    //  A <- C <- D   基类可以指向派生类 ok
     {
         std::cout<<"D *d convert A class ok\n";
     }

     if(dynamic_cast<D*> (c))    // 派生类不能指向基类
     {
         std::cout<<"C *c convert D class ok\n";
     }

     if(dynamic_cast<C*> (d))    // C基类可以指向派生类D ok
     {
         std::cout<<"D *d convert C class ok\n";
     }

     if(dynamic_cast<D*> (d))    // ok
     {
         std::cout<<"d *d convert D class ok\n";
     }

     std::cin.get();
     return ;
 }