operator<< overloading ostream

Question

In order to use cout as such : std::cout << myObject, why do I have to pass an ostream object? I thought that was an implicit parameter.

ostream &o         


        

Answer 1

Only if it is a member function of the class that would otherwise be the first argument. Thus, it would be:

class ostream {
    ...
    ostream &operator << (const myClass &o);
    ...
};

Since ostream was written long before your class, you see the problem of getting your class in there. Thus, we must implement the operator as a freestanding function:

(return type) operator << ( (left hand side), (right hand side) );

When operators are implemented as member-functions of classes, the left hand side is this, and the argument becomes the right hand side. (For binary operators - unary operators work similarly.)