C++虚拟函数问题3-yiteyi-C++库

以下程序的输出

null

                     #include<iostream>                   
                     using                               namespace                               std;                   
                             
                     class                               Base                   
                     {                   
                     public                               :                   
                                         virtual                               void                               show() { cout<<                               " In Base "                               ; }                   
                     };                   
                             
                     class                               Derived:                               public                               Base                   
                     {                   
                     public                               :                   
                                         void                               show() { cout<<                               "In Derived "                               ; }                   
                     };                   
                             
                     int                               main(                               void                               )                   
                     {                   
                                         Base *bp, b;                   
                                         Derived d;                   
                                         bp = &d;                   
                                         bp->show();                   
                                         bp = &b;                   
                                         bp->show();                   
                                         return                               0;                   
                     }                   