书店程序是《c++ primer》中重要的实例，涉及大部分重要知识点，但代码分散阅读不便，下面按照章节顺序总结
Sales_item.h
#ifndef SALESITEM_H // we're here only if SALESITEM_H has not yet been defined #define SALESITEM_H //#include "Version_test.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
- 定义了Sales_item类，其中涉及到运算符重载等知识在以后章节会涉及
item_io.cpp
#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; }
- 实现了从标准输入读入数据，存入一个Sales_item对象中，再将该对象的内容写回到标准输出
add_item.cpp
#include <iostream> #include "Sales_item.h" int main() { Sales_item item1, item2; std::cin >> item1 >> item2; //read a pair of transactions std::cout << item1 + item2 << std::endl; //print their sum return 0; }
- 实现了将两个Sales_item对象相加
add_item2.cpp
#include <iostream> #include "Sales_item.h" int main() { Sales_item item1, item2; std::cin >> item1 >> item2; // first check that item1 and item2 represent the same book if (item1.isbn() == item2.isbn()) { std::cout << item1 + item2 << std::endl; return 0; // indicate success } else { std::cerr << "Data must refer to same ISBN" << std::endl; return -1; // indicate failure } }
- 实现了先判断两个Sales_item对象是否具有相同的ISBN，再相加
avg_price.cpp
#include <iostream> #include "Sales_item.h" int main() { Sales_item total; // // read the first transaction and ensure that there are data to process if (std::cin >> total) { Sales_item trans; // variable to hold the running sum // read and process the remaining transactions while (std::cin >> trans) { // if we're still processing the same book if (total.isbn() == trans.isbn()) total += trans; // update the running total else { // print results for the previous book std::cout << total << std::endl; total = trans; // total now refers to the next book } } std::cout << total << std::endl; // print the last transaction } else { // no input! warn the user std::cerr << "No data?!" << std::endl; return -1; // indicate failure } return 0; }
- 实现了从一个文件中读取销售记录，生成每本书的销售报告，显示售出册数、总销售额和平均售价（假设每个ISBN书号的所有记录在文件中聚在一起保存）
- 将每个ISBN的所有数据合并存入变量total，用变量trans保存读取的每条记录，若total和trans指向相同的ISBN则更新total的值，否则打印total的值，并将其重置为刚读取的trans