Destructor

[rachitagrawal]

I am bit confused with the use of destructor. Please can someone clarify my doubt?

Compiler automatically creates a destructor, if it is not explicitely written in the code. Then why should we write it, when it is being automatically done by the compiler?

Thanks in advance.

[helios]

Because the default destructor is too simplistic.
Suppose you have a class:

class A{
	int a;
	std::string b;
	B c;
};

The default destructor will call the destructors of A::b and A::c. And that's fine, but if the class looks like this:

class A{
	int a;
	std::string *b;
	B *c;
};

the default destructor doesn't follow pointers, so if *A::b and *A::c were created by A, a memory leak will be created.
In this case, you should write you own destructor that does follow pointers (or not):

A::~A(){
	delete b;
	delete c;
}

[rachitagrawal]

Thanks for the reply. That gave me a better understanding. :)

[rachitagrawal]

I have one more question. If I have two clases of this sort. Will the automatically generated destructor destroy the Node object.

What I mean is automatically generated desctructor destroy the user defined class objects?

class Node
{
int key;
};

class A{
int a;
Node b;
B c;
};

[helios]

Since A::b is a Node, and not a pointer to a Node, it will be destructed with the rest of the object by the default destructor.

[rachitagrawal]

If i have a linked list. Can you please explain how will i write destructor for the list class and node class?

Thanks

[helios]

The node should only free its own data. Its an error for a node to try to free its neighbors.
The list object should free whatever node it has access to until there are no more nodes in the list.