c++ primer 第一章头文件

#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