Number of virtual pointer in a class

well if you ask for a pointer to the vtable of a polymorphic class then a class with a virtual method will have a single vtable and this vtable is shared by all objects of this class.
Each object instance of this class will have its own pointer to that vtable , typically called a virtual pointer or vptr. The compiler implicitly generates code to initialize the vptr in the constructor. So, thers is 1 virtual pointer per object instance.