A pure virtual member function is a member function that the base class forces derived classes to provide. Normally these member functions have no implementation. Pure virtual functions are equated to zero.
internally it tells the compiler to reserve a slot for a function in the VTABLE but not to put an address in the particular slot. Thus the VTABLE is incomplete.
Pure virtual function is a virtual function which has no defination in base class but must be redefined in derieved class or else compile time error will be generated by the compiler.
any class which is having atleast on pure virtual function is termed as an abstract base class (ABC) which cannot be instanciated but we can have a reference or pointer to that class.
for eg :
class myclass { public: virtual void display() 0; //pure virtual function with no defination here... };
class der : public myclass { public: /*must be redefined in derieved class */ void display() { cout << blah blah........ << n ; } };
Pure virtual function is the virtual functions which member functions does not have any definitions(implementation) just it equates( ) to 0. With Pure virtual function the base class becomes "Abstract class". The abstract class does not instantiate/ create objects. But it's pointers can be assigned with Derived class objects. The pure virtual member functions must be overriden in derived classes.
Hope it helps you in understanding Thanks Niranjan ambati
