Sales_item.h

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这个是《C++primer》书中介绍和使用的Sales_item.h类

经本人测试可以使用。

头文件内容如下：

#ifndef SALESITEM_H#define SALESITEM_H#include <iostream>#include <string>  class Sales_item{public:    Sales_item(const std::string &book):isbn(book),units_sold(0),revenue(0.0){}    Sales_item(std::istream &is){ is >> *this;}    friend std::istream& operator>>(std::istream &,Sales_item &);    friend std::ostream& operator<<(std::ostream &,const Sales_item &);public:    Sales_item & operator+=(const Sales_item&);public:    double avg_price() const;bool same_isbn(const Sales_item &rhs)const{    return isbn == rhs.isbn;}Sales_item():units_sold(0),revenue(0.0){}public:    std::string isbn;    unsigned units_sold;    double revenue;}; using std::istream;using std::ostream;Sales_item operator+(const Sales_item &,const Sales_item &);inline bool operator==(const Sales_item &lhs,const Sales_item &rhs){    return lhs.units_sold == rhs.units_sold && lhs.revenue == rhs.revenue && lhs.same_isbn(rhs);}inline bool operator!=(const Sales_item &lhs,const Sales_item &rhs){    return !(lhs == rhs);} inline Sales_item & Sales_item::operator +=(const Sales_item &rhs){    units_sold += rhs.units_sold;    revenue += rhs.revenue;    return *this;}inline Sales_item operator+(const Sales_item &lhs,const Sales_item &rhs){    Sales_item ret(lhs);    ret += rhs;    return ret;}inline istream& operator>>(istream &in,Sales_item &s){    double price;    in >> s.isbn >> s.units_sold >> price;    if(in)         s.revenue = s.units_sold * price;    else    s = Sales_item();    return in;}inline ostream& operator<<(ostream &out,const Sales_item &s){    out << s.isbn << "t" <<s.units_sold << "t" << s.revenue << "t" << s.avg_price();    return out;}inline double Sales_item::avg_price() const{    if(units_sold)        return revenue/units_sold;    else    return 0;}#endif