MOOC清华《面向对象程序设计》第3章：流运算符重载实验

#include <iostream>using namespace std;class Test{int id;public:Test(int i): id(i) {cout << "obj_" << id << " created\n";}friend istream& operator>> (istream& in, Test& dst);//dst = destinationfriend ostream& operator<< (ostream& out, const Test& src);//src = source};istream& operator>> (istream& in, Test& dst){in >> dst.id;return in;}ostream& operator<< (ostream& out, const Test& src){out << src.id << endl;return out;}int main(){Test obj(1);  cout << obj;cin >> obj;   cout << obj;return 0;}

程序运行到第二行就停住了，第三行光标闪动提示输入，第三行输入2，回车，第四行显示2，程序结束。