Virtual Function in C++ - Wikitechy

What are Virtual functions in C++ ?

webmaster — Fri, 19 Aug 2022 12:34:29 +0000

Virtual function is a member function which is re-defined by a derived class and declared within a base class.
When you refer to a derived class object using a reference or pointer to the base class, you can call a virtual function for that object and execute the derived class’s version of the function.
It ensures that the correct function is called for an object, regardless of the type of reference used for function call.
It is mainly used to achieve Run-time polymorphism.
In base class functions are declared with a virtual. At run time the resolving of function call is done.

Sample Code

using namespace std;
 
class base {
public:
    virtual void print()
    {
        cout << "print base class\n";
    }
 
    void show()
    {
        cout << "show base class\n";
    }
};
 
class derived : public base {
public:
    void print()
    {
        cout << "print derived class\n";
    }
 
    void show()
    {
        cout << "show derived class\n";
    }
};
 
int main()
{
    base *bptr;
    derived d;
    bptr = &d;
 
    // Virtual function, binded at runtime
    bptr->print();
 
    // Non-virtual function, binded at compile time
    bptr->show();
   
    return 0;
}

Output

Which type of inheritance needs a virtual function ?

Editor — Fri, 27 Aug 2021 00:47:53 +0000

Which type of inheritance needs a virtual function ?

A. Multi level inheritance

B. Multiple inheritance

C. Hybrid inheritance

D. All of the above

Answer : D. All of the above

Find the wrong statement about Abstract Class ?

Editor — Mon, 12 Jul 2021 22:54:00 +0000

Find the wrong statement about Abstract Class ?

A. We can’t create its objects

B. We can’t create pointers to an abstract class

C. It contains at least one pure virtual function

D. We can create references to an abstract class

Answer : B. We can’t create pointers to an abstract class

Explanation :

Abstract Class is a class which contains atleast one Pure Virtual function.
An abstract class is a class that is designed to be specifically used as a base class.
It is used to provide an Interface for its sub classes.
Classes inheriting an Abstract Class must provide definition to the pure virtual function, otherwise they will also become abstract class.
You declare a pure virtual function by using a pure specifier (= 0) in the declaration of a virtual member function in the class declaration.

Example

class AB {
public:
  virtual void f() = 0;
};

C++ supports run time polymorphism with the help of virtual functions, which is called ______ binding

Editor — Mon, 12 Jul 2021 22:49:38 +0000

C++ supports run time polymorphism with the help of virtual functions, which is called ______ binding.

A. Dynamic

B. Run time

C. Early binding

D. Static

Answer : A. Dynamic

Explanation :

Dynamic binding (dynamic dispatch) means that a block of code executed with reference to a procedure call is determined at run time.

A virtual function that has no definition within the base class is called ?

Editor — Mon, 12 Jul 2021 22:45:35 +0000

A virtual function that has no definition within the base class is called ?

A. Pure virtual function

B. Pure static function

C. Pure Const function

D. Virtual Function

Answer : A. Pure virtual function

Which of the following statements about virtual base classes is correct ?

Editor — Mon, 12 Jul 2021 22:41:41 +0000

Which of the following statements about virtual base classes is correct ?

A. It is used to provide multiple inheritance .

B. It is used to avoid multiple copies of base class in derived class .

C. It is used to allow multiple copies of base class in a derived class.

D. It allows private members of the base class to be inherited in the derived class.

Answer : B. It is used to avoid multiple copies of base class in derived class .

Explanation

When two or more objects are derived from a common base class, we can prevent multiple copies of the base class being present in an object derived from those objects by declaring the base class as virtual when it is being inherited such a base class is known as virtual base class.
Virtual base classes, used in virtual inheritance, is a way of preventing multiple “instances” of a given class appearing in an inheritance hierarchy when using multiple inheritance.