运营商LT;＆LT;和运算符＆gt;＆gt;重载函数

Question

在我的班级定义中我有以下朋友功能：

      friend  ostream& operator << (ostream& out, const Person& p1);

      friend istream& operator >> (ostream& out Person& p1);

在我的实施文件中：

       ostream& operator << (ostream& out, const Person& p1)
      {
       out<< p1.age; //this is a private variable
      }

      istream& operator << (istream& in, Person& p1)
      {
       in >> p1.age; //this is a private variable
      }

但是当我编译它时，我得到一个错误，上面写着“ostream”并没有说出类型朋友ostream＆amp;运算符（ostream＆amp; out，const Person＆amp; p1）..同样适用于istream。由于这些是朋友功能，他们可以访问私有变量，即年龄，所以问题是什么？

Answer 1

首先，你的函数应该返回一些东西，所以：

ostream& operator << (ostream& out, const Person& p1)
  {
   return out<< p1.age; //this is a private variable
  }

和

istream& operator << (istream& in, Person& p1)
  {
   return in >> p1.age; //this is a private variable
  }

你应该记得添加include <iostream>标题。和using namespace std;

并且最重要的是一个错字

friend istream& operator >> (istream& out Person& p1);