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：

注意：

1、

析构函数一定要有函数体，即后面要有大括号｛｝

~truck()；这样写不行，必须要有实现。

2、从运行结果可以看出，派生类析构函数的调用顺序：

派生类→派生类中的基类→派生类→派生类中的基类→基类析构函数

3、这里display（）是虚函数，实现运行时多态。派生类中的2个display（）前virtual关键字可加可不加。