What Is RTTI For?

Suppose you have a hierarchy of classes descended from a common base class. You can set a base-class pointer to point to an object of any of the classes in this hierarchy. Next, you call a function that, after processing some information, selects one of these classes, creates an object of that type, and returns its address, which gets assigned to a base-class pointer. How can you tell what kind of object it points to?

Before answering this question, you need to think about why you would want to know the type. Perhaps you want to invoke the correct version of a class method. If that’s the case, you don’t really need to know the object type, as long as that function is a virtual function possessed by all members of the class hierarchy. But it could be that a derived object has an uninherited method. In that case, only some objects could use the method. Or maybe, for debugging purposes, you would like to keep track of which kinds of objects were generated. For these last two cases, RTTI provides an answer.