C++输入输出操作符重载的深入分析

// OverloadCinCout.cpp : 定义控制台应用程序的入口点。
//
#include "stdafx.h"
#include "iostream"
#include "string"
using namespace std;
class Fruit
{
public:
 Fruit(const string &nst = "apple", const string &cst = "green"):name(nst),colour(cst){}
 ~Fruit(){}
 friend ostream& operator << (ostream& os, const Fruit& f);  //输入输出流重载，不是类的成员，
 friend istream& operator >> (istream& is, Fruit& f);       // 所以应该声明为类的友元函数
private:
    string name;
 string colour;
};
ostream& operator << (ostream& os, const Fruit& f)
{
 os << "The name is " << f.name << ". The colour is " << f.colour << endl;
 return os;
}
istream& operator >> (istream& is, Fruit& f)
{
 is >> f.name >> f.colour;
 if (!is)
 {
  cerr << "Wrong input!" << endl;
 }
 return is;
}
int _tmain(int argc, _TCHAR* argv[])
{
 Fruit apple;
 cout << "Input the name and colour of a kind of fruit." << endl;
 cin >> apple;     
 cout << apple;
 return 0;
}