When is static cast safe when you are using multiple inheritance?

Question

I found myself in a situation where I know what type something is. The Type is one of three (or more) levels of inheritance. I call factory which returns B* how

Answer 1

A cross-cast:

struct Base1 { virtual void f1(); };
struct Base2 { virtual void f2(); };
struct Derived : Base1, Base2 {};

Base1* b1 = new Derived();
Base2* b2 = dynamic_cast(b1);

requires use of dynamic_cast, it cannot be done with static_cast (static_cast should have caused a compile-time error). dynamic_cast will also fail if either base class is not polymorphic (the presence of virtual functions is NOT optional).

See this explanation on MSDN