87.重载流式运算符以及外部函数重载运算符

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
using namespace std;

class box
{
private:
    int x;
    int y;
    int z;
    

public:
    box() :x(10), y(20), z(30)
    {

    }

    friend box operator +(const box &box1, const box &box2);
    friend box operator +(const box &box1, int num);
    friend ostream & operator << (ostream &, const box &box1);
    friend istream &operator >> (istream &, box &box1);

    void show()
    {
        cout << x << y << z << endl;
    }

};

//外部重载,没有this指针隐含对象
box operator +(const box &box1, const box &box2)
{
    box tmp;
    tmp.x = box1.x + box2.x;
    tmp.y = box1.y + box2.y;
    tmp.z = box1.z + box2.z;
    return tmp;
}


box operator +(const box &box1, int num)
{
    box tmp;
    tmp.x = box1.x + num;
    return tmp;
}


//重载流运算符,输入一个引用,返回一个引用
ostream & operator << (ostream &,const box &box1)
{
    return cout << box1.x << box1.y << box1.z << endl;
}

istream &operator >> (istream &, box &box1)
{
    return cin >> box1.x >> box1.y >> box1.z ;
}

void main()
{
    box box1;
    box box2;
    box box3 = box1 + box2;
    box box4 = box1 + 20;
    /*box4.show();*/
    cin >> box1;
    cout << box1;
    cin.get();
}