When does the vptr (pointing to vtable) get initialized for a polymorphic class?

This is not about "When VTABLE is created?". Rather, when the VPTR should be initialized? Is it at the beginning/end of the constructor or before/after the constructor?

A::A () : i(0), j(0)  -->> here ?
{
  -->> here ?
  //...
  -->> here ?
}