Assignment operator overloading

Question

I was trying to overload assignment operator. Given

Point p1(1,2,3);
Point p2(1,2,3);
Point p3 = p1 + p2;
Point p4 = 22;
cout<< p4;

Here is my full code:

#include<iostream>
#include <bits/stdc++.h>


using namespace std;

class Point{
private:
    int m_x, m_y, m_z;
public:
    Point(int x=0, int y = 0, int z = 0):m_x(x), m_y(y), m_z(z)
    {
    }
    friend Point operator+(Point &p1, Point &p2);
    friend ostream& operator<<(ostream &out, Point &p);
    Point operator=(int val);

};

Point operator+(Point &p1, Point &p2){
    return Point(p1.m_x+p2.m_x , p1.m_y+ p2.m_y , p1.m_z+p2.m_z);
}

ostream& operator<<(ostream &out, Point &p){
    out<<"output: "<<p.m_x<<" "<<p.m_y<<" "<< p.m_z<<'\n';
    return out;
}
Point Point::operator=(int val){
    return Point(val, val, val);
}

int main(){
Point p1(1,2,3);
Point p2(1,2,3);
Point p3 = p1 + p2;
Point p4 = 22;
cout<< p4;

}

I can't insert the value 22 or any value in m_x, m_y ,m_z. How can I solve the line:

Point p4 = 22;

It is running perfectly fine on gccV7 , Please tell which compiler and version you are using and what is error you are getting. — Arun Pal
– Arun Pal, Commented Feb 21, 2019 at 9:14
I think his desired output is 22 22 22 whereas he's getting 22 0 0, at least that's what I'm getting. — Blaze
– Blaze, Commented Feb 21, 2019 at 9:17
^ if that is true, add a constructor Point(int x): m_x(x), m_y(x), m_z(x) {} — M.M
– M.M, Commented Feb 21, 2019 at 9:19

super · Accepted Answer · 2019-02-21 09:26:59Z

2

The are 2 different problems here.

Point p4 = 22;

This is not an assignment, it's actually a call to a constructor. Since you declared your constructor that takes 3 ints with default values, it can be called with 1, 2 or 3 values.

So it's equivalent of doing either of these two

Point p4(22, 0, 0);
Point p4(22);

If you want to use the assignment operator you need to write

Point p4;
p4 = 22;

But here we run in to the second problem, your assignment operator creates a new Point and returns it by value. What you want to do is modify the existing one.

Point& Point::operator=(int val){ // Return by reference
    m_x = m_y = m_z = val;
    return *this;
}

answered Feb 21, 2019 at 9:26

super

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Comments

Aris · Accepted Answer · 2019-02-21 10:03:59Z

And you don't need to make the + operation a friend function.

using namespace std;

class Point {

public:
    Point() {}
    Point(int x , int y , int z ) :m_x(x), m_y(y), m_z(z)
    {
    }
    Point& operator+(const Point &p1);
    friend ostream& operator<<(ostream &out, Point &p);
    Point& operator=(int val);
private:
    int m_x, m_y, m_z;
};

Point& Point::operator+(const Point& p1)
{
    Point temp;

    temp.m_x = this->m_x + p1.m_x;
    temp.m_y = this->m_y + p1.m_y;
    temp.m_z = this->m_z + p1.m_z;

    return temp;

}

ostream& operator<<(ostream &out, Point &p) {
    out << "output: " << p.m_x << " " << p.m_y << " " << p.m_z << '\n';
    return out;
}
Point& Point::operator=(int val) { // Return by reference
    m_x = m_y = m_z = val;
    return *this;
}
int main() {
    Point p1(1, 2, 3);
    Point p2(1, 2, 3);
    Point p3 = p1 + p2;
    Point p4;
    p4 = 22;
    cout << p4;

}

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