一个简单的c++程序

    #include <iostream>      using namespace std;      class vehicle      {      protected:      int wheels;      int weight;      public:      virtual void display(){cout<<wheels<<weight<<endl;}      vehicle(){wheels = 1;weight = 2;}      ~vehicle(){cout<<"释放12";}      };            class car:public vehicle      {      private:      int passenger_load;      public:      virtual void display(){cout<<passenger_load<<endl;}      car():vehicle(){passenger_load=3;}      ~car(){cout<<"释放3";}      };            class truck:public vehicle      {      private:      int passenger_load;      int payload;      public:      //      truck():vehicle(){passenger_load =4;payload = 5;}       void display(){cout<<passenger_load<<payload<<endl;}      ~truck(){cout<<"释放45";}      };            int main()      {      vehicle *p;      vehicle a1;      car a;      truck b;      p =&a1;      p->display();      p=&a;      p->display();      p=&b;      p->display();      //system("pause");      return 0;      }  

运行结果为：