inheratance and object pointer

[tiffini]

Hi,

I have an interesting question about an object pointer.
If you have

Class A <---- Class B <--- Class C <- Class D
/
/
Class F <----- Class E <---

So A and F are base classes and B and E derive from them respectively and C derives from Both E and B. Then D derives from C.
int method foo(B * ptr pB)
{
D *pD= (D*)pB;

pD->methodgooOnCla ssF();

}

int main ()
{
D instaD;
// ...
// set and do stuff with foo.

foo ( (B*) &instaD);
}
So Now the question:
The object being passed around even though it is passed around by it's base class does not lose anything. It is still an object that contains the classes a-f correct? This is correct so long as a copy is not attempted, right?

Thanks in Advance

[=?iso-8859-1?q?Erik_Wikstr=F6m?=]

On Feb 26, 6:41 am, tiffini <tiff...@val13x r8.orgwrote:

Hi,

I have an interesting question about an object pointer.

If you have

Class A <---- Class B <--- Class C <- Class D
/
/
Class F <----- Class E <---

So A and F are base classes and B and E derive from them respectively andC derives from Both E and B. Then D derives from C.

int method foo(B * ptr pB)
{
D *pD= (D*)pB;

pD->methodgooOnCla ssF();

}

int main ()
{
D instaD;
// ...
// set and do stuff with foo.

foo ( (B*) &instaD);

}

So Now the question:
The object being passed around even though it is passed around by it's base class does not lose anything. It is still an object that contains the classes a-f correct? This is correct so long as a copy is not attempted, right?

Yes, since you are not passing around the object, but only a pointer
to the object, nothing will to the actual object until you modify it.
And even then it will still be an object of class D.

If you make a copy then that copy will be of the type you declare it
to be, never more, never less. So if you have

int main()
{
D d;
C c(d);
}

Then C will be of type C and you can not use it as if it were of type
D (though you can still use it where an object of type A, B, E, and F
is expected).

--
Erik Wikström