2019-02-22
Multiple inheritance casting from base class to different derived class
stackoverflow
Question

Let's assume there is such class hierarchy:

class A //base class

class B //interface

class C : public A, public B

Then C object is created:

A *object = new C();

Is it possible to cast object to B ?

Important: I assume I don't know that object is C. I just know that it implements interface B

Answer
1

No. This is not possible (direct casting from A* to B*).

Because the address of A and B are at different locations in class C. So the cast will be always unsafe and possibly you might land up in unexpected behavior. Demo.

The casting should always go through class C. e.g.

A* pa = new C();
B* pb = static_cast<C*>(pa);
                   ^^^^ go through class C

Demo

Multiple inheritance casting from base class to different derived class
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