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Why doesn't this remove the last node in a linked list?

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Join Date: Aug 2004

Posts: 6

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paynekiller paynekiller is offline

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Why doesn't this remove the last node in a linked list?

Aug 9th, 2004

I've got a singly linked list, and the following code is supposed to delete all nodes that are ranked as "Trainee", it deletes them all, but if the last node is a "Trainee", it will not delete it, why is that?

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void LinkedList::removeLowest()
{
	Soldier * ptrDelete;
	ptrCurrent = ptrHead;
	while(ptrCurrent != NULL)
	{
		if(!strcmp(ptrCurrent->getRank(), "Trainee"))
		{
			ptrCurrent->Show();
			ptrDelete = ptrCurrent;
			ptrCurrent = ptrCurrent->ptrNext;
			delete ptrDelete;
		}
		else
		{
			ptrCurrent = ptrCurrent->ptrNext;
		}
	}
 
	cout << "\nTrainees Sacked!";
void LinkedList::removeLowest()
{
	Soldier * ptrDelete;
	ptrCurrent = ptrHead;
	while(ptrCurrent != NULL)
	{
		if(!strcmp(ptrCurrent->getRank(), "Trainee"))
		{
			ptrCurrent->Show();
			ptrDelete = ptrCurrent;
			ptrCurrent = ptrCurrent->ptrNext;
			delete ptrDelete;
		}
		else
		{
			ptrCurrent = ptrCurrent->ptrNext;
		}
	}

	cout << "\nTrainees Sacked!";

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Join Date: Jun 2004

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Chainsaw

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Re: Why doesn't this remove the last node in a linked list?

Aug 9th, 2004

Because you don't update ptrHead. If you delete the last node, ptrHead should become NULL.

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Join Date: Aug 2004

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paynekiller paynekiller is offline

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Re: Why doesn't this remove the last node in a linked list?

Aug 10th, 2004

but ptrHead just points to the first node in the list, setting it to NULL would delete that node

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Join Date: Jun 2004

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Reputation: Chainsaw is an unknown quantity at this point

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Chainsaw

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Re: Why doesn't this remove the last node in a linked list?

Aug 10th, 2004

Sorry, I misunderstood; I thought you meant Last as in "last remaining".

You have a list like this:

head-->first-->second-->third-->last

and you want to delete second because she is a trainee.

your code does this:

ptrCurrent points to second
show second
set ptrCurrent to point to third
delete second

Unless the destructor does some work on the entire list, you have this list:

head-->first-->[deleted second]-->third-->last

1) Does the destructor move first's next pointer to point to third (second's next)?

2) If you delete 'first', who updates the head pointer to point to first's next pointer?

3) If you delete 'last' does third get updated to point to null (last's next)? (note this would work fine if (1) works fine, I think)