问使用代码块的C++类

EN

#include <iostream>
#include "Sales_item.h"
int main()
{
    Sales_item book;
    //read ISBN, number of copies sold, and sales price
    std::cin>>book;
    //write ISBN, number of copies sold, total revenue, and average price
    std::cout<<book<<std:endl;
    return 0;
}

Sales_item.h.h  

#ifndef SALES_ITEM_H_H
#define SALES_ITEM_H_H


class Sales_item.h
{
    public:
        Sales_item.h();
        virtual ~Sales_item.h();
    protected:
    private:
};

#endif // SALES_ITEM_H_H

Sales_item.h.cpp

#include "Sales_item.h.h"

Sales_item.h::Sales_item.h()
{
    //ctor
}

Sales_item.h::~Sales_item.h()
{
    //dtor
}

/* This file defines the Sales_item class used in chapter 1.
* The code used in this file will be explained in
* Chapter 7 (Classes) and Chapter 14 (Overloaded Operators)
* Readers shouldn't try to understand the code in this file
* until they have read those chapters.
*/

#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
    Sales_item(): units_sold(0), revenue(0.0) { }
    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
    unsigned units_sold;
    double revenue;
};