没有匹配的操作符>> in std :: cin

问题描述

我有一个类员工

#include <iostream>
#include <string>
#include <fstream>
using namespace std;

class employee
{
    public:

            double operator + (employee);
            istream& operator>> (istream&);

            employee(int);
            double getSalary();

    private:

           double salary;

};

int main()
{
  employee A(400);
  employee B(800);

  employee C(220);

  cin>>C;

}

employee::employee(int salary)
{
    this->salary = salary;
}


double employee::operator + (employee e)
{
    double total;

    total = e.salary + this->salary;

    return total;
}


double employee::getSalary()
{
    return this->salary;
}

istream& employee::operator>> (istream& in)
{
    in>>this->salary;

    return in;

}

我试图重载输入操作符>>但是我收到以下错误

I am trying to overload the input operator >> to read in the employee object but i am getting the following error

我做错了什么？

编辑：我知道如何做

edit: I know how to do it through a friend function , i am now trying to learn how to do it through a member function

推荐答案

您不能。

对于二进制运算符@ 对象 A a 和 B b ，语法 a @ b 将调用或 运算符@（A，B） 或形式的成员函数的非成员函数形式为 A :: operator @（B）。没有其他。

For a binary operator@ and objects A a and B b, the syntax a @ b will call either a non-member function of the form operator@(A,B) or a member function of the form A::operator@(B). Nothing else.

所以要使 std :: cin>> C 工作，它必须是 std :: istream 的成员，但由于您不能修改 std :: istream 您不能实现 operator>> 作为成员函数。

So to make std::cin >> C work it must be as a member of std::istream, but since you can't modify std::istream you can't implement operator>> as a member function.

（除非你想变得奇怪和非常规，写 C 或 C>> std :: cin ，但如果你这样做，其他程序员会讨厌你混淆和非常规的。不要这样做。）

(Unless you want to be weird and unconventional and write C << std::cin or C >> std::cin, but if you do that other programmers will hate you for being confusing and unconventional. Do not do this.)

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