Pure Virtual Functions and Abstract Classes in C++ (original) (raw)

Last Updated : 15 Oct, 2025

A pure virtual function is a virtual function with no implementation in the base class, declared using = 0. A class with at least one pure virtual function is an abstract class that cannot be instantiated and serves as a blueprint for derived classes, which must provide their own implementation.

• A class with at least one pure virtual function becomes an abstract class and Objects of abstract classes cannot be created directly.
• Abstract classes are used to define interfaces and ensure common structure among derived classes.
• Useful in polymorphism where different classes share the same interface but have different behaviors.
• A pure virtual function forces derived classes to override it.
• virtual void draw() = 0; declares a pure virtual function, forcing derived classes to provide their own implementation. C++ `

#include using namespace std;

class Shape { public: virtual void draw() = 0; // Pure virtual function };

class Circle : public Shape { public: void draw() override { cout << "Drawing Circle\n"; } };

int main() {

// Error in the below line : Cannot create 
// object of abstract class
// Shape s;      

// Pointer to abstract class
Shape* s = new Circle(); 

// Output: Drawing Circle
s->draw();    

delete s;

}

`

**Explanation: This example shows an abstract class Shape with a pure virtual function draw(). Circle overrides draw(), and using a Shape pointer to a Circle demonstrates polymorphism, outputting Drawing Circle.