virtual class 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

Syntax for Pure Virtual Function is ?

Editor — Mon, 12 Jul 2021 22:58:10 +0000

Syntax for Pure Virtual Function is ?

A. virtual void show()==0

B. void virtual show()==0

C. virtual void show()=0

D. void virtual show()=0

Answer : B. virtual void show()==0

Explanation :

In C++, A pure virtual function or abstract function is a virtual function for which we don’t have implementation, we only declare it. A pure virtual function is declared by assigning 0 in declaration.

Syntax

// An abstract class 
class Sample
{    
    // Data members of class 
public: 
    // Pure Virtual Function 
    virtual void show() = 0; 
    
   /* Other members */
};

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.

What is pure virtual function in C++ ?

Editor — Mon, 12 Jul 2021 22:24:30 +0000

What is pure virtual function in C++ ?

- A virtual function will become pure virtual function when you append “=0” at the end of declaration of virtual function.
- Pure virtual function doesn’t have body or implementation. We must implement all pure virtual functions in derived class.

Pure virtual function is also known as abstract function.
A class with at least one pure virtual function or abstract function is called abstract class. We can’t create an object of abstract class. Member functions of abstract class will be invoked by derived class object.

Sample Code

#include
       #include

       class BaseClass       //Abstract class
       {

              public:
               virtual void Display1()=0;     //Pure virtual function or abstract function
               virtual void Display2()=0;     //Pure virtual function or abstract function

               void Method3()
               {
                      cout<<"\n\tMethod3() is Base Class";
               }

       };

       class DerivedClass : public BaseClass
       {

              public:
               void Method1()
               {
                      cout<<"\n\tMethod1() is Derived Class";
               }

               void Method2()
               {
                      cout<<"\n\tMethod2() is Derived Class";
               }

       };

       void main()
       {

              DerivedClass D;

              D.Method1();            // This will invoke Method1() Derived Class
              D.Method2();            // This will invoke Method2() Derived Class
              D.Method3();            // This will invoke Method3() Base Class

       }

Output

Method1() is Derived Class
Method2() is Derived Class 
Method3() is Base Class