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Virtual Destructor is used to release the derived class objects in a proper order....



Consider an Example:



Code: Cpp



#include<iostream.h>



class Base

{

public:

Base()

{

cout<<"Base class constructor"<<endl;

}

virtual void show()

{

cout<<"Base class Inside show function"<<endl;

}

void display()

{

cout<<"Display method"<<endl;

}

~Base ()

{

cout<<"Base class Destructor"<<endl;

}

};

class Derived : public Base

{



public:

Derived()

{

cout<<"Derived class constructor"<<endl;

}

void show()

{

cout<<"Inside derived show function"<<endl;

}

void display()

{

cout<<"Inside derived display function"<<endl;

}

~Derived()

{

cout<<"Derived class destructor"<<endl;

}

};



void main()

{

Base *b=new Derived;

b->show();

b->display();

delete b;

}





Output for the above program is:-



Code:



Base class constructor

Derived class constructor

Inside derived show function

Display function

Base class Destructor



Consider a line



Base *b=new Derived;



Pointer object created for base class (Base class constructor and
Derived class constructor automatically called during object creation
phase)...



Consider a line



delete b;



In the above line base class object b destructs automatically (without destructing derived class



To avoid it if we have a concept called virtual destructor .



Example:



Code: Cpp

#include<iostream.h>

class Base

{

public:

Base()

{

cout<<"Base class constructor"<<endl;

}

virtual void show()

{

cout<<"Base class Inside show function"<<endl;

}

void display()

{

cout<<"Display method"<<endl;



}

virtual ~Base ( )//virtual destructor See the virtual keyword

{

cout<<"Base class Destructor"<<endl;

}

};



class Derived : public Base

{

public:

Derived()

{

cout<<"Derived class constructor"<<endl;

}

void show()

{

cout<<"Inside derived show function"<<endl;

}

void display()

{

cout<<"Inside derived display function"<<endl;

}

~Derived()

{

cout<<"Derived class destructor"<<endl;

}

};



void main()

{

Base *b=new Derived;

b->show();

b->display();//if a method is not at all virtual only base class function called

delete b;

}





Output is :-

Base class constructor

Derived class constructor

Inside derived show function

Display function

Derived class destructor

Base class Destructor







In the above program , Object destructs in a proper order(b'coz base class destructor is made as virtual......)



V-Table:



Normally v_table(virtual table ) is created for each and every class
.The v-table normally contains the addresses of the virtual functions
and the pointer to point the function(called as v-pointer). Whenever
Virtual function is called , v-table decides to the function
address..........



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