虚函数的使用

虚函数使用的条件：

继承，virtual指定函数，父类指针或引用指向子类对象的地址

其中父类的析构函数需要为virtual，保证了内存的正确释放。

/*
	设计一个汽车类vehicle，它有一个两个参数的构造函数，车轮数量wheels和车重量weights，
	小汽车car类继承汽车类，其成员变量为passengers；开车类truck，成员变量：passengers和负载payload
*/

#include<iostream>
using namespace std;

class vehicle
{
private:
	int wheels;
protected:
	int weights;//子类可以使用
public:
	vehicle(int wheels, int weights) :wheels(wheels), weights(weights)
	{
		cout << "This is vehicle" << endl;
	}
	virtual ~vehicle()
	{
		cout << "This is desconstruct vehicle" << endl;
	}
	virtual void show()const;
	
};
void vehicle::show() const 
{
	cout << "vehicle has " << wheels << "wheels and the weights of vehicle is " << weights << endl;
}
class car :public vehicle
{
private:
	int passengers;
public:
	car(int passengers, int weights, int wheels) :passengers(passengers), vehicle(wheels,weights)
	{
		cout << "This is car" << endl;
	}
	~car()
	{
		cout << "This is car desconstruction" << endl;
	}
	void show() const
	{
		vehicle::show();
		cout << "car can take  " << passengers << " passengers"<< endl;
	}
};


class truck :public vehicle
{
private:
	int passengers;
	int payload;
public:
	truck(int passengers, int payload, int wheels,int weights) :passengers(passengers), payload(payload), vehicle(wheels, weights)
	{
		cout << "This is  truck" << endl;
	}
	~truck()
	{
		cout << "This is desconstruction truck" << endl;
	}
	void show() const
	{
		vehicle::show();
		cout << "truck can take " << passengers << "passengers,and the payload is " << payload << endl;
	}


};
int main()
{
	vehicle *v = NULL;
	car c(5,1000,4);
	truck t(3,5000,4,2000);
	v = &c;
	v->show();

	v = &t;
	v->show();
	return 0;
}