标签：Chapter std const rhs Sales c++ item operator primer
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
标签：Chapter,std,const,rhs,Sales,c++,item,operator,primer 来源： https://www.cnblogs.com/cxc1357/p/12169098.html
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