The Art of Assembly Language, 2nd Edition

12.13 Runtime Type Information

When working with an object variable (as opposed to a pointer to an object), the type of that object is obvious: It's the variable's declared type. Therefore, at both compile time and runtime the program knows the type of the object. When working with pointers to objects you cannot, in the general case, determine the type of an object a pointer references. However, at runtime it is possible to determine the object's actual type. This section discusses how to detect the underlying object's type and how to use this information.

If you have a pointer to an object and that pointer's type is some base class, at runtime the pointer could point at an object of the base class or any derived type. At compile time it is not ...