overloading the << operator in c++

Question

hey, i got something that i cannot understand ,there are two types of solutions for overloading this operator 1 is including the friend at the start of the method and the other 1 goes without the friend. i would very much like if some1 explain whats the difference between them advantages / disadvantages. for example overloading the operator << in class rational:

class Rational:
{
    private: int m_t,m_b;
    ...
    friend ostream& operator<<(ostream& out,const Rational& r) // option 1
    { return out << r.m_t << "/" <<r.m_b;}  // continue of option 1

    ostream& operator<<(ostream& out,const Rational& r){return r.print();} // option 2
    virtual ostream& print(ostream& out) const // continue of option 2
    { //
      return out<<m_t << "/" << m_b;
    } //
};

i was told that the second option isnt correct , if some1 can correct me about it i would much appriciate it. thanks in advance.

Answer 1

operator<< (for ostream) needs to be a free function (since the left-hand argument is a stream, not your class).

The friend keyword makes it a free function (a free function that has access to the private members).

However, if this functionality can be implemented in terms of the public interface, it is better to do so and just use a non-friend free function.

class Rational:
{
    private: int m_t,m_b;
    public:
    ...
    virtual ostream& print(ostream& out) const
    { 
      return out<<m_t << "/" << m_b;
    } 
};

ostream& operator<<(ostream& out,const Rational& r)
{
    return r.print(out);
}