C++之操作符重载

#include <iostream>
#include <string>

using namespace std;
//重载操作符
//定义的方式是operator*() 重载*运算符

class Sales_item
{
friend ostream &operator<<(ostream &out,const Sales_item &s);
friend istream &operator>>(istream &in,Sales_item &s);
friend bool operator==(const Sales_item &,const Sales_item &);
public:
    Sales_item(string &book,unsigned units,double price):
        isbn(book),
        units_sold(units),
        revenue(units*price){}
    Sales_item():
        units_sold(0),
        revenue(0.0){}
    //重载+=运算符 一般设置为成员函数 ，因为修改了当前对象
    Sales_item &operator+=(const Sales_item &);
public:
    double avg_price() const;
//    bool same_isbn(const Sales_item &rsh)
//    {
//        return isbn==rsh.isbn;
//    }
private:
    string isbn;
    unsigned units_sold;
    double revenue;
};
//计算书的平均价格
inline double Sales_item::avg_price() const
{
    if(units_sold)
    {
        return revenue/units_sold;
    }else{
        return 0;
    }
}
//重载==和!=运算符
inline bool operator==(const Sales_item &lsh,const Sales_item &rsh)
{
    return lsh.isbn==rsh.isbn && lsh.units_sold==rsh.units_sold && lsh.revenue==rsh.revenue;
}
bool operator!=(const Sales_item &lsh,const Sales_item &rsh)
{
    //让一个操作符调用另外一个操作符
    return !(lsh==rsh);
}
//重载+=操作符
Sales_item& Sales_item::operator+=(const Sales_item &s)
{
    this->units_sold+=s.units_sold;
    this->revenue+=s.revenue;
    return *this;
}
//重载加法操作符 一把不设置为成员函数
Sales_item operator+(const Sales_item &s1,const Sales_item &s2)
{
    //将第一个参数进行实现用于返回结果
    Sales_item ret(s1);
    ret+=s2;
    return ret;

}
//重载输出操作符
ostream &operator<<(ostream &out,const Sales_item &s)
{
    out<<s.isbn<<"--"<<s.units_sold<<"--"<<s.revenue;
    return out;
}
//重载输入操作符
istream &operator>>(istream &in,Sales_item &s)
{
    double price;
    in>>s.isbn>>s.units_sold>>price;
    //输入的时候进行错误检查 如果出错就创建一个新的订单
    if(in)
    {
        s.revenue=s.units_sold*price;
    }else{
        s=Sales_item();
    }

    return in;
}

int main()
{
    string s("1-001-2543");
//    Sales_item item1(s,25,2.50);
//    cout<<item1<<endl;
//    cin>>item1;
//    cout<<item1<<endl;
//    Sales_item item2(s,10,120.0);
//    Sales_item item3(s,20,200.0);
//    Sales_item ret=item2+item3;
//    cout<<ret<<endl;
//
//    Sales_item item4(s,20,200);
//    item4+=item4;
//    cout<<item4<<endl;
//    Sales_item a(s,10,120.0);
//    Sales_item b(s,10,120.0);
//    Sales_item c(s,20,110.0);
//    if(a==b)
//    {
//        cout<<"a和b是一个订单"<<endl;
//    }
//    if(a!=c)
//    {
//        cout<<"a和c不是一个订单"<<endl;
//    }


    return 0;
}