友好“>>"有自己的课 [英] Friending '>>' with own class

问题描述

我有一个以下课程，我与cout作了朋友，现在我正尝试与cin做朋友，但是我遇到了一个错误...有人可以帮助我，或者告诉我我做了什么错了吗?

I have the following class, which I friended with cout and now I'm trying to friend it with cin but I get an error... Could anyone help me, or tell me what I've done wrong?

错误:

c:\ mingw \ bin ../lib/gcc/mingw32/4.6.1/include/c ++/bits/stl_algo.h:2215:4:错误:将'const RAngle'传递为'this'参数int RAngle :: operator<(RAngle)'丢弃限定词[-fpermissive]

c:\mingw\bin../lib/gcc/mingw32/4.6.1/include/c++/bits/stl_algo.h:2215:4: error: passing 'const RAngle' as 'this' argument of 'int RAngle::operator<(RAngle)' discards qualifiers [-fpermissive]

类RAngle:

class RAngle
{
    private:
        int *x,*y,*l;
    public:
        int solution,prec;
        RAngle(){
            this->x = 0;
            this->y = 0;
            this->l = 0;
        }

        RAngle(int i,int j,int k){
            this->x = &i;
            this->y = &j;
            this->l = &k;
        }

    friend istream& operator >>( istream& is, RAngle &ra)
    {
        is >> ra->x;
        is >> ra->y;
        is >> ra->l;

        return is ;
    }
}

推荐答案

没有足够的代码来回答您的问题.但是从错误中我会告诉你，您的int RAngle::operator<(RAngle)没有定义为const方法，而是在只有const的地方使用它.

There is not enough code to answer your question. But from error I would say you, that your int RAngle::operator<(RAngle) is not defined as const method and you use it somewhere, where you have only const.

此外，使operator<或其他比较运算符返回int不太可行，因为这可能会引起误解.此类运算符应返回bool.

Also, it's not very good practive to make operator< or other comparison operators return int, because this may lead to misunderstanding. Such operators should return bool.

所以，会有这样的东西bool RAngle::operator<(const RAngle& other) const { /*...*/ }.在此处和此处.

So, there sould be something like this bool RAngle::operator<(const RAngle& other) const { /*...*/ }. This topic is covered here and here.

更新该代码是完全陌生的.为什么使用指向int的指针?为什么将某些数据设为私有?构造函数RAngle(int i,int j,int k)将无法正常工作.

Update This code is completely strange. Why use pointers to int? Why make some data private? Constructor RAngle(int i,int j,int k) will not work as you suppose.

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