C++：使用成员 function 的二元运算符重载

Question

I've searched stackoverflow a bit and found some topics similar to what I am doing. However, I just do not understand yet the probably very simple errors I made.

Can you please help me out? As you can see I make really basic mistakes.

The function is for practice purposes only. I want to have a class for points with x , y coordinates in double data type, these are privates.

To practice operator overloading/member function based operator access to privates, I wrote the following code.

In the end, I just want to print out the results of the addition of each of the coordinates x and y of two points.

What are the mistakes that I am making?

Thank you in advance for any hints.

#include <stdio.h>
#include <iostream>

class point{
    
    public:
        // this operator adds a point "p2" to the point of class "point"
        // OVERLOADING BINARY + USING A MEMBER FUNCTION:
        point operator+(point p){ // n is the 2nd number in the addition
            return point(x+p.x, y+p.y); // equals (this->x+p2.x, ...)
        }
        
    // private numbers 
    private:
        //declaration and initialization of x and y:
        double x=1.1,y=2.2;
};

int main()
{
    // Create two new points:
    point *p1 = new point ();
    point *p2 = new point ();
    
    cout << "The result of the addition is: " << (*p1+*p2);
    
    return 0;
}

Currently the error I get is:

In member function ‘point point::operator+(point)’: main.cpp:16:38:
error: no matching function for call to ‘point::point(double, double)’
return point(x+p.x, y+p.y); // equals (this->x+p2.x, ...)

Answer 1

Like churill pointed out, you missed implementing two things:

First you need to implement a constructor for your point class that takes 2 doubles:

point(double x, double y)
  : x(x), y(y)
{}

The above constructor is using initializer lists and does the same as this:

point(double x, double y) {
    this.x = x;
    this.y = y;
}

and don't forget to implement the default constructor again since otherwise C++ will not find it anymore and your code will fail to compile

point() {}

Second You need to overwrite the "<<" operator which will allow you to cout your point object:

friend ostream& operator<<(ostream& os, const point& p) {
    os << "(" << p.x << ',' << p.y << ')'; // will output (x,y)
    return os;
}

if you put all the above in your point class as public it should compile without a problem