#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, 561friend 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 beforeprivate:    std::string bookNo;      // implicitly initialized to the empty string    unsigned units_sold;    double revenue;};// used in chapter 10inlinebool compareIsbn(const Sales_item &lhs, const Sales_item &rhs) { return lhs.isbn() == rhs.isbn(); }// nonmember binary operator: must declare a parameter for each operandSales_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 ISBNSales_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 ISBNSales_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 << " bookNo "<< s.isbn() << " soldNum " << s.units_sold << " totalSoldMoney "        << s.revenue << " price " << s.avg_price();    return out;}double Sales_item::avg_price() const{    if (units_sold)         return revenue/units_sold;     else         return 0;}#endif复制代码
      
     

下面开始编写代码：

    hello.cc

#include 
     
      #include "Sales_item.h"int main(){   Sales_item totalBook;//统计对象   if(std::cin>>totalBook){//第一次读取的值赋值给totalBook	   Sales_item  currBook;//当前对象	   while(std::cin>>currBook)//从第二次开始，读取的值赋给currBook	   {		   if(totalBook.isbn()==currBook.isbn())//上一次读取的对象与当前读取的对象书本编号相等，就叠加		   {			   totalBook += currBook;		   }else{//否则就打印上次书本统计的结果，接着又把当前读取的对象赋值给统计对象			   std::cout<
      
       <
      
     

逻辑类似于上一个，就不一一分析了。

接下来就是编译阶段

1：生成可执行程序

在window下会生成book.exe可执行程序

ps：上述的所有文件都在统一目录下，这点很重要，不然会报错

2：读取销售记录文件以及程序输出到文件中