C++ Primer 第五版第一章Sales_item.h源码

#ifndef SALESITEM_H  
// we're here only if SALESITEM_H has not yet been defined   
#define SALESITEM_H  
  
  
// Definition of Sales_item class and related functions goes here  
#include   
#include   
  
class Sales_item {  
    // these declarations are explained section 7.2.1, p. 270   
    // and in chapter 14, pages 557, 558, 561  
    friend std::istream& operator>>(std::istream&, Sales_item&);  
    friend std::ostream& operator<<(std::ostream&, const Sales_item&);  
    friend bool operator<(const Sales_item&, const Sales_item&);  
    friend bool  
        operator==(const Sales_item&, const Sales_item&);  
public:  
    // constructors are explained in section 7.1.4, pages 262 - 265  
    // default constructor needed to initialize members of built-in type  
#if defined(IN_CLASS_INITS) && defined(DEFAULT_FCNS)  
    Sales_item() = default;  
#else  
    Sales_item() : units_sold(0), revenue(0.0) { }  
#endif  
    Sales_item(const std::string &book) :  
        bookNo(book), units_sold(0), revenue(0.0) { }  
    Sales_item(std::istream &is) { is >> *this; }  
public:  
    // operations on Sales_item objects  
    // member binary operator: left-hand operand bound to implicit this pointer  
    Sales_item& operator+=(const Sales_item&);  
  
    // operations on Sales_item objects  
    std::string isbn() const { return bookNo; }  
    double avg_price() const;  
    // private members as before  
private:  
    std::string bookNo;      // implicitly initialized to the empty string  
#ifdef IN_CLASS_INITS  
    unsigned units_sold = 0; // explicitly initialized  
    double revenue = 0.0;  
#else  
    unsigned units_sold;  
    double revenue;  
#endif  
};  
  
// used in chapter 10  
inline  
bool compareIsbn(const Sales_item &lhs, const Sales_item &rhs)  
{  
    return lhs.isbn() == rhs.isbn();  
}  
  
// nonmember binary operator: must declare a parameter for each operand  
Sales_item operator+(const Sales_item&, const Sales_item&);  
  
inline bool  
operator==(const Sales_item &lhs, const Sales_item &rhs)  
{  
    // must be made a friend of Sales_item  
    return lhs.units_sold == rhs.units_sold &&  
        lhs.revenue == rhs.revenue &&  
        lhs.isbn() == rhs.isbn();  
}  
  
inline bool  
operator!=(const Sales_item &lhs, const Sales_item &rhs)  
{  
    return !(lhs == rhs); // != defined in terms of operator==  
}  
  
// assumes that both objects refer to the same ISBN  
Sales_item& Sales_item::operator+=(const Sales_item& rhs)  
{  
    units_sold += rhs.units_sold;  
    revenue += rhs.revenue;  
    return *this;  
}  
  
// assumes that both objects refer to the same ISBN  
Sales_item  
operator+(const Sales_item& lhs, const Sales_item& rhs)  
{  
    Sales_item ret(lhs);  // copy (|lhs|) into a local object that we'll return  
    ret += rhs;           // add in the contents of (|rhs|)   
    return ret;           // return (|ret|) by value  
}  
  
std::istream&  
operator>>(std::istream& in, Sales_item& s)  
{  
    double price;  
    in >> s.bookNo >> s.units_sold >> price;  
    // check that the inputs succeeded  
    if (in)  
        s.revenue = s.units_sold * price;  
    else  
        s = Sales_item();  // input failed: reset object to default state  
    return in;  
}  
  
std::ostream&  
operator<<(std::ostream& out, const Sales_item& s)  
{  
    out << s.isbn() << " " << s.units_sold << " "  
        << s.revenue << " " << s.avg_price();  
    return out;  
}  
  
double Sales_item::avg_price() const  
{  
    if (units_sold)  
        return revenue / units_sold;  
    else  
        return 0;  
}  
#endif