在C ++中重载运算符时如何获取THIS

Question

I'm a student learning c++. today, I was making a operator overload function to use it in 'cout'. following is a class that contains name, coordinates, etc.

class Custom {
public:
    string name;
    int x;
    int y;

    Custom(string _name, int x, int y):name(_name){
        this->x = x;
        this->y = y;
    }
    int getDis() const {
        return static_cast<int>(sqrt(x*x+y*y));
    }
    friend ostream& operator << (ostream& os, const Custom& other);
};

ostream& operator << (ostream& os, const Custom& other){
    cout << this->name << " : " << getDis() << endl;; // error
    return os;
}

However, this code isn't working because of 'THIS' keyword that I was expecting it points to the object. I want to show the object's name and distance value. How can I solve it? I think it is similar with Java's toString method so that it will be able to get THIS.

Thanks in advance for your answer and sorry for poor english. If you don't understand my question don't hesitate to make a comment.

Answer 1

this is available only in member functions, but your operator<< is not a class member (declaring it as friend does not make it a member). It is a global function, as it should be. In a global function, just use the arguments you are passing in:

ostream& operator << (ostream& os, const Custom& other)
{
    os << other.name << " : " << other.getDis() << endl;
    return os;
}

Also note os replaced cout in the code above. Using cout was an error - the output operator should output to the provided stream, not to cout always.