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# Basic Polimorphism question

Posted on 2006-11-10
Medium Priority
241 Views
Hi Experts,

I have the following

class A
{
};

class B : public A
{
};

class C: public B
{

}

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

};

Can I do the following??

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

someFunction(bb);
someFunction(cc);
0
Question by:ambuli
• 2
• 2

LVL 19

Expert Comment

ID: 17919777
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.
0

LVL 86

Expert Comment

ID: 17919788
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

baspoly.cpp
Microsoft (R) Incremental Linker Version 6.00.8447

/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.
0

Author Comment

ID: 17919880
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{};
0

LVL 19

Accepted Solution

VoteyDisciple earned 1000 total points
ID: 17919887
All those things still qualify as an instance of A.

Multiple inheritance just means that a C there can pass anywhere you need a B (which can pass anywhere you need an A) and it can also pass anywhere you need an X (which, completely unrelated, can also be used anywher eyou need an A).

If class X had no parent, you could still pass a C* to a function that wanted an A*.
0

LVL 86

Assisted Solution

jkr earned 1000 total points
ID: 17919897
As with your other Q, there is no problem unless something else is fundamentally going wrong.
0

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