C++:运算符重载 - cout和cin - ostream函数,不能被引用 - 它是一个已删除的函数

Question

我重载了一个cout和cin opeartor,当我尝试使用它时,它给了我一个像这样的错误:

1 IntelliSense: function "std::basic_ostream<_Elem, _Traits>::basic_ostream(const     std::basic_ostream<_Elem, _Traits>::_Myt &) 
[with _Elem=char, _Traits=std::char_traits<char>]" 
(declared at line 84 of "C:\Program   Files (x86)\Microsoft Visual Studio 12.0\VC\include\ostream") cannot be referenced -- it is a deleted function    

这是我班级的头文件:

#pragma once
#include <iostream>

class Point2D
{
private:
    int m_X;
    int m_Y;
public:
    Point2D(): m_X(0), m_Y(0)
    {
    }

    Point2D(int x, int y): m_X(x), m_Y(y)
    {
    }

    friend std::ostream& operator<< (std::ostream out, const Point2D &point)
    {
        out << "(" << point.m_X << "," << point.m_Y << ")" << std::endl;

        return out;
    }

    friend std::istream& operator>> (std::istream in, Point2D &point) 
    {
        in >> point.m_X;
        in >> point.m_Y;

        return in;
    }

    int getX() const { return m_X; }
    int getY() const { return m_Y; }

    ~Point2D();
};

所以,基本上,它只是一个可以返回并设置X和Y坐标的类.我覆盖<<和>>操作员使事情变得更容易.

但是当我尝试在主函数中使用它时,如下所示:

#include "stdafx.h"

#include <iostream>
#include "Point2D.h"

using namespace std;

int main(int argc, char * argv[])
{
    Point2D point(7, 7);

    cout << point;  //there's an error here.


    return 0;
}

这一行似乎有错误:

cout << point; 

我究竟做错了什么？

Answer 1

错误消息显示ostream无法复制.

friend std::ostream& operator<< (std::ostream out, const Point2D &point)
{
    ...

std::ostream out是值传递:当operator <<调用时,编译器会尝试复制参数.但是,std::ostream无法复制,因此编译失败.

你应该使用参考.

friend std::ostream& operator<< (std::ostream &out, const Point2D &point)
{
    ...

friend std::istream& operator>> (std::istream &in, Point2D &point) 
{
    ...

(即使你使用的是一些提供复制的类,你也不应该使用pass-by-val.复制一些对象是如此昂贵;)