重载运算符=错误

Question

I am trying to use overloading concept to equate 3 objects c1 , c2 , c3 . But it is giving me an error

error: no match for 'operator=' in 'c3 = c2. circle::operator=(((circle&)(& c1)))'

What's the reason behind it how do I rectify it??

#include<iostream>
using namespace std;

class circle
{
  private:
    int radius;
    float x,y;
  public:
    circle()
    {}
    circle(int rr,float xx,float yy)
    {
      radius=rr;
      x=xx;
      y=yy;
    }
    circle& operator=(const circle& c)
    {
     cout<<endl<<"assignment operator invoked";  
     radius=c.radius;
     x=c.x;
     y=c.y;
     return *this;
     }
    void showdata()
    {
      cout<<endl<<"\n radius="<<radius;
      cout<<endl<<"x coordinate="<<x;
      cout<<endl<<"y coordinate="<<y<<endl;
    }
};
int main()
{
  circle c1 (10,2.5,2.5);
  circle c2,c3;
  c3=c2=c1;
  c1.showdata();
  c2.showdata();
  c3.showdata();
  return 0;
} 

so this overloaded operator will be called two times.. First for c2=c1 and then for c3=c2 but how will compiler compare it with overloaded operator definition??

Answer 1

In order to chain operator= calls, you must make sure that it returns a reference

circle& operator=(const circle& c)
{
   cout<<endl<<"assignment operator invoked";  
   radius=c.radius;
   x=c.x;
   y=c.y;
   return *this;
}

c1=c2=c3 is parsed as c1 = (c2 = c3) . If operator = doesn't return a reference, c2 = c3 is an rvalue, and it cannot bind to the reference argument of c1.operator = (In case if the argument is a reference to const, it can bind to rvalues, but that doesn't mean you shouldn't return a reference).

Also note that it makes sense to take the parameter by const reference, because you don't want to change the argument that you assign.

Also remember the rule of three , that is, if you really need to do any of the following:

• overload operator =

• explicitly provide a copy constructor

• explicitly provide a destructor

then you probably want to do the other two too. In your particular case, you don't seem to need to overload operator = at all.