Operator overloading of operator= using friend function

Question

#include<iostream>
using namespace std;
class a
{
    int x;
    int y;
    public:
    void get_xy(int x,int y)
    {
        this->x=x;
        this->y=y;  
    }   
    friend int operator=(a,a);
};
int operator=(a a5,a a6)
{
    if(a5.x==a6.x&&a5.y==a6.y)
    {
        return(1);
    }
    else
    {
        return 0;
    }
}

int main()
{
    a a1,a2;
    a1.get_xy(5,4);
    a2.get_xy(5,4);
    if(a1=a2)
    {
        cout<<"y"<<endl;
    }
    else
    {
        cout<<"n"<<endl;
    }

    return 0;
}

I am trying to overload the assignment operator= by means of using a friend function and stuck with error in attached screen shot. However when I overload it with a member function it works as expected. The code is posted above.

The assignment operator can't be made a non-member function, it must *always* be a member function. See the table in [this operator overloading reference](http://en.cppreference.com/w/cpp/language/operators). — Some programmer dude, Mar 06 '16 at 10:17
Please reconsider your use of bad practices [`using namespace std;`](http://stackoverflow.com/q/1452721/1171191) and [`endl`](http://chris-sharpe.blogspot.co.uk/2016/02/why-you-shouldnt-use-stdendl.html). — BoBTFish, Mar 06 '16 at 10:22
Overloading `operator=` to mean `==` would be **extremely** confusing for everyone else. Also your `get_xy` looks very much like a `set_xy` function, or better could be a constructor for `a`. — Bo Persson, Mar 06 '16 at 11:14

score 0 · Accepted Answer · answered Mar 15 '16 at 16:04

C++11 13.5.3/1:

An assignment operator shall be implemented by a non-static member function with exactly one parameter...

So the standard just flatly prohibits overloading operator= as a non-member.

And as a side note: Don't overload assignment to mean comparison, it will confuse all future maintainers.

Operator overloading of operator= using friend function

1 Answers1