CareerCup

address of virtual function &, you will get the offset of the function in the vtbl, and compiler will use that to access the virtual function

Virtual function: function meant to be overridden in the derived class.
Each class maitains a virtual function table containing the address of the virtual functions. When the object of a class is made a virtual pointer is created that points to the virtual table. So when a function is called the vpointer looks up the vtable which contains the virtual function address and calls the correct function

The compiler doesn't know. That's the whole point. Other than that, the above descriptions of the VTBL are more-or-less correct.