cast classes to common ancestor

[deadguysfrom]

Ive got two classes in the same class hierarchy, and I want to find
their common ancestor. Any idea how to do this?

class A {};
class B : public A {};
class C : public B {};
class D : public B {};

I have pointers to C and D, I want pointers to B.

thanks

[Ian Collins]

de**********@gmail.com wrote:

Ive got two classes in the same class hierarchy, and I want to find
their common ancestor. Any idea how to do this?

class A {};
class B : public A {};
class C : public B {};
class D : public B {};

I have pointers to C and D, I want pointers to B.

int main()
{
D* d = new D;

B* b = d;
}

--
Ian Collins.

[Kai-Uwe Bux]

Alf P. Steinbach wrote:

* de**********@gmail.com:

>Ive got two classes in the same class hierarchy, and I want to find
their common ancestor. Any idea how to do this?

class A {};
class B : public A {};
class C : public B {};
class D : public B {};

I have pointers to C and D, I want pointers to B.

See the reply by Ian Collins else-thread.

If your enquiry is of a more academic, theoretical nature:

You can check whether the classes /have/ a common ancestor by using
static_cast, possibly combined with SFINAE.

Since it sounded like a nice template exercise, I just tried to do that,
i.e., I tried to whip up a template

template < typename A, typename B >
class have_common_base {

// some SFINAE magic

public:

static bool const value =
// some more magic

};

so that have_common_base<A,B>::value would be true if and only if A and B
are derived from some common base class.

I failed, and your hint didn't quite cut it for me :-(

How would you do it?

[snip]
Best

Kai-Uwe Bux