朋友与类，但不能访问私人成员 [英] friend with class but can't access private members

问题描述

朋友的功能应该能够访问类私有成员吗？
那么我在这里做错了什么？我已经包括我的.h文件与操作符<<我打算和这个班交朋友。

Friend functions should be able to access a class private members right? So what have I done wrong here? I've included my .h file with the operator<< I intent to befriend with the class.

#include <iostream>

using namespace std;
class fun
{
private:
    int a;
    int b;
    int c;


public:
    fun(int a, int b);
    void my_swap();
    int a_func();
    void print();

    friend ostream& operator<<(ostream& out, const fun& fun);
};

ostream& operator<<(ostream& out, fun& fun)
{
    out << "a= " << fun.a << ", b= " << fun.b << std::endl;

    return out;
}

推荐答案

/ p>

In here...

ostream& operator<<(ostream& out, fun& fun)
{
    out << "a= " << fun.a << ", b= " << fun.b << std::endl;

    return out;
}

您需要

ostream& operator<<(ostream& out, const fun& fun)
{
    out << "a= " << fun.a << ", b= " << fun.b << std::endl;

    return out;
}

（我已经被烧伤了很多次;定义的运算符重载与声明不完全匹配，因此它被认为是一个不同的函数。）

(I've been bitten on the bum by this numerous times; the definition of your operator overload doesn't quite match the declaration, so it is thought to be a different function.)

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