C++ Primer 第五版第一章Sales_item.h源码

た入场券 2022-05-31 23:38 166阅读 0赞

#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 <iostream>  
    #include <string>  
      
    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