Why vptr is not static?

Question

Every class which contains one or more virtual function has a Vtable associated with it. A void pointer called vptr points to that vtable. Every object of that class contains that vptr which points to the same Vtable. Then why isn't vptr static ? Instead of associating the vptr with the object, why not associate it with the class ?

Answer 1

The virtual table (which is, by the way, an implementation mechanism not mentioned in the C++ standard) is used to identify the dynamic type of an object at runtime. Therefore, the object itself must hold a pointer to it. If it was static, then only the static type could be identified by it and it would be useless.

If you are thinking of somehow using typeid() internally to identify the dynamic type and then call the static pointer with it, be aware that typeid() only returns the dynamic type for objects belonging to types with virtual functions; otherwise it just returns the static type (§ 5.2.8 in the current C++ standard). Yes, this means that it works the other way around: typeid() typically uses the virtual pointer to identify the dynamic type.