dynamics_cast<>

#include <iostream>

class A
{
public:
    A(){}
    ~A(){}
    virtual int data(){return 1;}
};
class B:public A
{
public:
    B(){}
    ~B(){}
    int data(){return 2;}
};

class C:public A
{
public:
    C(){}
    ~C(){}
    int data(){return 3;}
};

class D:public C
{
public:
    D(){}
    ~D(){}
    int data(){return 4;}
};

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 0;
}