14.2.1节练习

练习14.6：为你的Sales_data类定义输出运算符。

// ConsoleApplication1.cpp : 定义控制台应用程序的入口点。
#include "stdafx.h"
#include <iostream>
#include <vector>
#include <string>

using namespace std;

class Sales_data{
	friend std::istream &read(std::istream&, Sales_data&);
	friend std::istream &operator>>(istream &is, Sales_data&);
	friend std::ostream &operator<<(std::ostream& os, Sales_data& item);
public:
	Sales_data() = default;
	Sales_data(const std::string &s, unsigned n, double p) :bookNo(s), units_sold(n), revenue(p*n){}
	Sales_data(const std::string &s) :bookNo(s){}
	Sales_data(std::istream&);
	std::string isbn() const { return bookNo; }
private:
	double avg_price() const
	{
		return units_sold ? revenue / units_sold : 0;
	}
	std::string bookNo;
	unsigned units_sold = 0;
	double revenue = 0.0;
};
Sales_data::Sales_data(std::istream& is){
	read(is, *this);
}
istream &operator>>(std::istream& is, Sales_data& item){
	double price = 0;
	is >> item.bookNo >> item.units_sold >> price;
	item.revenue = price * item.units_sold;
	return is;
}
ostream &operator<<(std::ostream& os, Sales_data& item){
	os << item.bookNo << item.units_sold << item.revenue << endl;
	return os;
}
istream &read(istream &is, Sales_data &item){
	double price = 0;
	is >> item.bookNo >> item.units_sold >> price;
	item.revenue = price * item.units_sold;
	return is;
}

int _tmain(int argc, _TCHAR* argv[])
{
	Sales_data a;
	cin >> a;
	cout << a;
	return 0;
}

练习14.7：你在13.5节练习（第470页）中曾编写了一个string类，为它定义了一个输出运算符。