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C++primer书店程序

#include <iostream>
#include <string>
#include <cassert>
#include <algorithm>
#include <vector>
using namespace std;

class Sales_data
{
    friend std::istream& operator>>(std::istream&, Sales_data&);
    friend std::ostream& operator<<(std::ostream&, const Sales_data&);
    friend Sales_data operator+(const Sales_data&,const Sales_data&);//非成员函数(对称性)
    friend bool operator==(const Sales_data&,const Sales_data&);
    friend bool operator!=(const Sales_data&,const Sales_data&);
    
public:
    Sales_data():units_sold(0),revenue(0.0){}
    Sales_data(const std::string &s):bookNo(s),units_sold(0),revenue(0.0){}
    Sales_data(const std::string &s,unsigned n,double p):bookNo(s),units_sold(n),revenue(n*p){}
    Sales_data(std::istream &is);

    Sales_data& operator+=(const Sales_data&);//成员函数(复合赋值通常是成员函数)
    std::string isbn()const{return bookNo;}

    Sales_data& operator=(const std::string &s);
private:
    inline double avg_price()const;//inline
private:
    std::string bookNo; //isbn
    unsigned units_sold;//销售量
    double revenue;     //总价
};

inline double Sales_data::avg_price() const
{
    return units_sold ?

revenue/units_sold : 0; } Sales_data::Sales_data(std::istream &is) { is>>*this; } std::istream& operator>>(std::istream& is,Sales_data& item) { double price=0.0; is>>item.bookNo>>item.units_sold>>price; if(is)//检測流的状态,输入易错且改写对象数据 item.revenue=item.units_sold*price; else item=Sales_data(); return is; } std::ostream& operator<<(std::ostream& os, const Sales_data& item) { os<<item.isbn()<<" "<<item.units_sold<<" " <<item.revenue<<" "<<item.avg_price(); return os; } Sales_data operator+(const Sales_data& item1,const Sales_data& item2) { Sales_data s(item1); s+=item2;//调用复合赋值 return s; } Sales_data& Sales_data::operator+=(const Sales_data& rhs) { units_sold+=rhs.units_sold; revenue+=rhs.revenue; return *this; } bool operator==(const Sales_data& lhs,const Sales_data& rhs) { return lhs.bookNo==rhs.bookNo && lhs.units_sold==rhs.units_sold && lhs.revenue==rhs.revenue; } bool operator!=(const Sales_data& lhs,const Sales_data& rhs) { return !(lhs==rhs); } Sales_data& Sales_data::operator=(const std::string &s) { *this=Sales_data(s); return *this; }


C++primer书店程序