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C++ compiler creates a hidden class member called virtual-pointer or in short vptr when there are one or more virtual functions. This vptr is a pointer that points to a table of function pointers. This table is also created by compiler and called virtual function table or vtable. Each row of the vtable is a function pointer pointing to a corresponding virtual function.

To accomplish late binding, the compiler creates this vtable table for each class that contains virtual functions and for the class derived from it. The compiler places the addresses of the virtual functions for that particular class in ‘vtable’.

When virtual function call is made through a base-class pointer, the compiler quietly inserts code to fetch the VPTR and look up the function address in the VTABLE, thus calling the right function and causing late/dynamic binding to take place.

class base 
  virtual void funct1(void);
  virtual void funct2(void);
base b;

b.vptr = address of b.vtable
b.vtable[0]= &base::funct1()
b.vtable[1]= &base::funct2()

b.vptr ->Vtable[0] ->base::funct1()
Vtable[1] ->base::funct2()

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