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Can derived class use friend function of the basis class?

Answer 1

+1 A:

The compiler is comparing them as objects of class Basis. Since you can always implicitly convert from a derived class to a base class, the compiler is able to pass them to the Basis overload of operator !=. Of course, this comparison can only use fields declared in Basis, so if you want the comparison to be more specific by using members of Derived, you'll have to define a separate operator != overload.

The friendship declaration isn't relevant when it comes to calling operator !=; all it does is allow operator != to access private members declared in Basis.

Nick Meyer 2010-07-23 14:19:53

@Nick Meyer: if I write if( derived != basis ) will it work?

Chan 2010-07-23 14:26:23

@Chan, yes, any combination of objects of type `Basis` or a derived class could be compared with your `operator !=` overload, with the caveat that the overload only uses the parts inherited from `Basis`. This is a consequence of the basic OO 'is-a' inheritance relationship. (http://en.wikipedia.org/wiki/Inheritance_(object-oriented_programming))

Nick Meyer 2010-07-23 14:31:57

The best thanks a lot

Chan 2010-07-23 14:38:48

Answer 2

A:

It sounds like your friend function only compares the Basis parts of Derived. So, it works after a fashion, but ignores any data in Derived.

Pontus Gagge 2010-07-23 14:20:00

Answer 3

A:

Because your Derived class inherits everything that your Basis class has, which in this case is an operator overload for !=, your Derived objects (derived1 and derived2) also have them defined.

danyim 2010-07-23 14:22:00

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Can derived class use friend function of the basis class?

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