What is the meaning of "virtual" inheritance? I saw the following code, and I don't understand what is the meaning of the word "virtual" in the following context:
class A {};
class B : public virtual A;
Thanks!
+1
A:
Virtual inherutance is used to solve the DDD problem (Dreadful Diamond on Derivation).
Look at the following example, where you have two classes that inherit from the same base class:
class Base
{
public:
virtual void Ambig();
};
class C : public Base
{
public:
...
};
class D : public Base
{
public:
...
};
Now, you want to create a new class that inherits both from C and D classes (which both have inherited the Base::Ambig() function):
class Wrong : public C, public D
{
public:
...
};
While you define the "Wrong" class above, you actually created the DDD (Diamond Derivation problem), because you can't call:
Wrong wrong; wrong.Ambig();
//This is ambiguous function because it defined twice: Wrong::C::Base::Ambig() and Wrong::D::Base::Ambig()
In order to prevent this kind of problem, you should use the virtual inheritance, which will know to refer to the right Ambig() function.
so - define:
class c : public virtual Base
class D : public virtual Base
class Right : public C, public D
Ohad
2009-01-07 11:40:15
A:
Isn't it as simple as "virtualness is inherited"? I.e., if you inherit a class with a virtual function - the function will still be virtual in it's subclass irrespective of the subclass definition?
Henrik Hartz
2009-01-07 13:00:08