operator overloading using friend function

If i have a class:

Code:

class Rational{
..
..
Rational operator+(Rational &rat);
friend Rational operator+(Rational rat1, Rational rat2);
...
...
};

Rational operator+(Rational rat1, Rational rat2);

int main()
{
Rational r1(2,3),r2(4,5);
....
...
r1=r1+r2;
...
}

-------------------------------
I know in this case the member function of class Rational will be invoked. But how do i invoke the non-member friend function which is in the global area. Am i supposed to do this:

r1=operator+(r1,r2);

?

 

Normally, you would have operator += as the member function
(returning a reference), and operator + as the non member function
(implemented in terms of the member +=). And no need for the non-member
function to be a friend.

Code:

class Rational
{
public:
  Rational & operator += (const Rational & rat)
  {
   // code then
   return *this;
  }
};

Rational operator + (Rational rat1, const Rational & rat2)
{
     return rat1+=rat2;
}

// or 
Rational operator + (const Rational & rat1, const Rational & rat2)
{
   Rational tmp = rat1;
   return tmp+=rat2;
}