Virtual Destructors

Virtual Destructors

• Destructor is basically used to de‒allocate the memory allocated for the objects. Thus use of destructor is to clean up the memory allocated for the class members. The destructor is denoted using ~ symbol.

• When a class is derived from a base class then on calling the destructor, it does not destruct the memory of derived class. This problem can be fixed up by making the base class destructor virtual.

• Following program illustrates this idea

#include<iostream>

using namespace std;

class Base

{

public:

Base()

{

   cout<<"\n Calling Base class Constructor";

}

~Base()

{

   cout<<"\n Calling Base class Destructor";

}

};

class Derived:public Base

{

public:

Derived()

{

   cout<<"\n Calling Derived class Constructor";

}

~Derived()

{

   cout<<"\n Calling Derived class Destructor";

}

};

int main()

{

   Base *obj=new Derived(); //object creation

   delete obj;

   return 0.

}

Output

Calling Base class Constructor

Calling Derived class Constructor

Calling Base class Destructor

Now change the above program as

#include<iostream>

using namespace std;

class Base

}

public:

Base()

{

   cout<<"\n Calling Base class Constructor";

}

virtual~Base()                   //Note that this is virtual constructor

{

   cout<<"\n Calling Base class Destructor";

}

};

class Derived.public Base

{

public:

Derived()

{

   cout<<"\n Calling Derived class Constructor";

}

~ Derived()

{

   cout<<"\n Calling Derived class Destructor";

}

};

int main()

{

   Base *obj=new Derived(); //object creation

   delete obj;

   return 0;

}

Output

Calling Base class Constructor

Calling Derived class Constructor

Calling Derived class Destructor

Calling Base class Destructor

Review Question

1. Explain virtual destructor with example.