Difference between a virtual function and a pure virtual function in C++

Following table shows the difference between Virtual and Pure Virtual Function:

Virtual Function	Pure Virtual Function
Virtual function has their definition in the class.	Pure virtual function has no definition.
Declaration: virtual funct_name(parameter_list) {. . . . .};	Declaration: virtual funct_name(parameter_list)=0;
It has no concept of derived class.	If a class contains at least one pure virtual function, then it is declared abstract.
If required, the base class can override a virtual function.	In case of pure virtual function derived class has to definitely override the pure virtual function.

virtual function

Example Code

 Live Demo

#include <iostream>
using namespace std;
class B {
   public:
      virtual void s() //virtual function {
         cout<<" In Base \n";
      }
};

class D: public B {
   public:
      void s() {
         cout<<"In Derived \n";
      }
};

int main(void) {
   D d; // An object of class D
   B *b= &d;// A pointer of type B* pointing to d
   b->s();// prints"D::s() called"
   return 0;
}

Output

In Derived

pure virtual function

Example Code

 Live Demo

#include<iostream>
using namespace std;
class B {
   public:
      virtual void s() = 0; // Pure Virtual Function
};

class D:public B {
   public:
      void s() {
         cout << " Virtual Function in Derived class\n";
      }
};

int main() {
   B *b;
   D dobj; // An object of class D
   b = &dobj;// A pointer of type B* pointing to dobj
   b->s();// prints"D::s() called"
}

Output

Virtual Function in Derived class