operator overloading for streams

Hi,

This one's not so important but, nice to have. I've been playing with the operator overloading for some simple classes and it's quite nice. I found some examples of overloading << which don't work for me though.

I use this in the header file:

Code:

ostream& operator <<(ostream&, const Point2D&);

// the actual operator

ostream & Point2D::operator <<(ostream &os, const & Point2D point) {
	return os << point.x << "," << point.y << endl;
}

I get some compiler error complaining about too many parameters. Although every example I've seen takes two parameters. I get actually get it to compile with only the ostream parameter but it doesn't do anything for me...

It should not be a member function of Point2D. In general it could either be a member of ostream (the left hand argument) or a non-member function. Since you aren't allowed to change ostream yourself, you must make it a non-member function.

The examples you've seen don't implement it as a class member...

Code:

ostream & operator <<(ostream &os, const & Point2D point) {
	return os << point.x << "," << point.y << endl;
}

It's kinda hard to explain... but...

• When you implement a binary operator as a class member, it assumes that *this is the left side operand, and the paramater is the right hand operand. So, there's no room for a second operand.
• operator<< is a binary operator

Look at all your examples, implementing operator<< as a class member only really makes sense if you are making an ostream.

Hope that makes sense.

That actually makes sense, thanks for the explanation. It works great now.