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Explain the purpose of the virtual keyword and virtual functions in C++.

Steilla Mitchel27704-Aug-2023

Explain the purpose of the 'virtual' keyword and virtual functions in C++.

visual c++ c++  keywords 
Updated on 06-Aug-2023
Steilla Mitchel

Steilla Mitchel

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I completed my post-graduation in 2013 in the engineering field. Engineering is the application of science and math to solve problems. Engineers figure out how things work and find practical uses for scientific discoveries. Scientists and inventors often get the credit for innovations that advance the human condition, but it is engineers who are instrumental in making those innovations available to the world. I love pet animals such as dogs, cats, etc.

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2 Answers

Aryan Kumar

Aryan Kumar

06-Aug-2023

The virtual keyword in C++ is used to declare a virtual function. A virtual function is a member function in a base class that can be redefined in a derived class. When you refer to a derived class object using a pointer or a reference to the base class, you can call a virtual function for that object and execute the derived class's version of the function.

Virtual functions are used to achieve polymorphism in C++. Polymorphism is the ability of an object to take on different forms. In the context of C++, polymorphism allows you to have a base class pointer that can point to objects of different derived classes. When you call a virtual function on a base class pointer, the compiler will determine the actual function to call at runtime, based on the type of the object that the pointer is pointing to.

For example, consider the following code:

C++

class Animal {
public:
  virtual void speak() {
    cout << "I am an animal!" << endl;
  }
};

class Dog : public Animal {
public:
  void speak() {
    cout << "Woof!" << endl;
  }
};

class Cat : public Animal {
public:
  void speak() {
    cout << "Meow!" << endl;
  }
};

int main() {
  Animal* animal = new Dog();
  animal->speak(); // "Woof!"

  animal = new Cat();
  animal->speak(); // "Meow!"

  return 0;
}

In this code, we have a base class called Animal, and two derived classes called Dog and Cat. The speak() function is declared as virtual in the Animal class. This means that it can be redefined in the derived classes.

In the main() function, we create a pointer to the Animal class. We then assign it to a Dog object and a Cat object. When we call the speak() function on the pointer, the compiler will determine the actual function to call at runtime, based on the type of the object that the pointer is pointing to.

In the first case, the pointer is pointing to a Dog object, so the Dog version of the speak() function will be called. In the second case, the pointer is pointing to a Cat object, so the Cat version of the speak() function will be called.

Virtual functions are a powerful tool that can be used to achieve polymorphism in C++. They allow you to have a base class pointer that can point to objects of different derived classes, and to call the correct function for each object at runtime.

Gulshan Negi

Gulshan Negi

05-Aug-2023

Well, in simple line In C++ programming language, virtual keyword is used in OOP (object-oriented programming) to declare and define the virtual functions.  

Code Reference: 

class Base {
public:
   virtual void someFunction() {
       // Function implementation in the base class
   }
};
 

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