Typically a cast of a pointer to another type does not change the value. However, in some cases, C++ changes the pointer to the instance of the class to support multiple inheritance. Most C++ programmers are unaware of this side effect of multiple inheritance. Suppose we have a C++ class CA:

 class CA : public IX, public IY { ... }

Since CA inherits IX and IY, we can use a pointer to the CA wherever you can use a pointer to the IX or IY. A pointer to the CA can be passed into a function that takes a pointer to the IX or IY, and the function will work correctly. For example:

void foo(IX* pIX); 
void bar(IY* pIY); 
 
int main() { 
    CA* pA = new CA; 
     foo(pA); 
     bar(pA); 
     delete pA; 
     return 0; 
} 

foo requires a pointer to a pointer to the virtual functions table of class IX, and the bar requires a pointer to a pointer to the virtual functions table of class IY. The contents of virtual functions tables of classes IX and IY, of course, is different. We can not transfer vtbl pointer of class IX into the bar function and expect that the function works. Thus, the compiler can not pass the same pointer into the foo and bar functions; it should modify the pointer to the CA class so that it points to the appropriate pointer of virtual functions table.