Basic Polimorphism question

Yep.  Inheritance is the "is-a" relationship.  

aa "is a" A.
bb "is a" A, since a B "is a" A.

Anything that' s a subclass of A can be used where an A is expected.

Incidentally, that's not even polymorphism, that's just straight inheritance.

Yes, of course you can:

class A
{
};

class B : public A
{
};

class C: public B
{

};

class D
{
public:
void someFunction(A *a);

};

void D::someFunction(A* a)
{

}

int main ()
{

A *aa = new A( );
B *bb = new B( );
C *cc = new C( );

D d;
d.someFunction(aa);

d.someFunction(bb);
d.someFunction(cc);

return 0;
}

C:\tmp\cc>cl baspoly.cpp
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 12.00.8804 for 80x86
Copyright (C) Microsoft Corp 1984-1998. All rights reserved.

baspoly.cpp
Microsoft (R) Incremental Linker Version 6.00.8447
Copyright (C) Microsoft Corp 1992-1998. All rights reserved.

/out:baspoly.exe
baspoly.obj

But, keep in mind that you only will be able to access the 'A' aspect of teh object passed in, everything else would require a typecast.

Again, the same problem.  If one of the object is multiple inherited...   Sorry, I was thinking the multiple inheritiance shouldn't matter and simpilified the problem.  So, I guess, I cannot do this with multiple inheritance...

class A{};
class B: public A{};
class X:public A{};
class C: public B, public X{};