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

Question

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\

Answer 1

The problem with virtual inheritance is that the base class address is not necessarily the same as the derived address. Thus, even reinterpret_cast or void* casts will not help.

One way to solve this without using dynamic_cast is to compute the offset between both pointer type (the exact type and ref type) in order to modify the object address accordingly during the cast.

 template 
 E& force_exact(const T& ref)
 {
   static const E* exact_obj;
   static const T& exact_obj_ref = *exact_obj;
   static const ptrdiff_t exact_offset =
     (const char*)(void*)(&exact_obj_ref)
     - (const char*)(void*)(exact_obj);
   return *(E*)((char*)(&ref) - exact_offset);
 }