In C++, Pure virtual method or pure virtual function is a virtual function in which virtual function does not contain a definition inside the function declaration. A pure virtual function/method is declared by assigning a function equal to 0 in declaration.

In pure virtual function/method, notation =0 is used to indicate that the virtual function is a pure virtual function/method, and that the function/method has no body or definition.

Syntax:-

class Someclassname 
         {
             public:
             virtual void purevirtual() = 0;  // a pure virtual function

              // note that there is no function body        
          };

A pure virtual function/method is implemented by class which are derived from a Abstract class.Following example to demonstrate the same.

#include<iostream.h>
#include<conio.h>

class BaseA
{
int x;
public:
    virtual void fun() = 0;
    int getX() { return x; }
};

// This class ingerits from Base and implements fun()

class DerivedB: public BaseA
{
   int y;
public:
    void fun() 
       { 
         cout << "fun() called"; 
       }
    };

int main()
{
   DerivedB d;
   d.fun();
   return 0;
}

Output:

fun() called