Is converting a reinterpret_cast'd derived class pointer to base class pointer undefined behavior?

Question

Have a look at is simple example:

struct Base { /* some virtual functions here */ };
struct A: Base { /* members, overridden virtual functions */ };
struct B: Ba         


        

Answer 1

Yes, It does have undefined behavior. The layout about suboject of Base in A and B is undefined. x may be not a real Base oject.