Multiple inheritance casting from base class to different derived class

c++ casting multiple-inheritance
Andrew picture Andrew · Sep 15, 2011 · Viewed 14k times · Source

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

iammilind picture iammilind · Sep 15, 2011

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

Related questions

C++ - downcasting a diamond shape inherited object without RTTI/dynamic_cast

I'm currently working on integrating a third-party package that uses lots of RTTI stuff on a non-RTTI platform (Android). Basically, I did my own RTTI implementation but I'm stuck on a problem. The issue is that a lot of classes …

Read More
Regular cast vs. static_cast vs. dynamic_cast

I've been writing C and C++ code for almost twenty years, but there's one aspect of these languages that I've never really understood. I've obviously used regular casts i.e. MyClass *m = (MyClass *)ptr; all over the place, but there …

Read More
When should static_cast, dynamic_cast, const_cast and reinterpret_cast be used?

What are the proper uses of: static_cast dynamic_cast const_cast reinterpret_cast C-style cast (type)value Function-style cast type(value) How does one decide which to use in which specific cases?

Read More