Re: Problem with list

From:
Old Wolf <oldwolf@inspire.net.nz>
Newsgroups:
comp.lang.c++
Date:
23 May 2007 17:20:36 -0700
Message-ID:
<1179966036.812586.304740@d30g2000prg.googlegroups.com>
On May 24, 10:34 am, Gaijinco <gaiji...@gmail.com> wrote:

    void insert(T data)
    {
       Node* p = new Node(data);

       if(p!=(Node*)NULL)
       {
          if(nodes==0)
              head = p;
          else if(head->data > data)
             p->setNext(head);


I think you're missing a "head = p" here,
after this statement you have not actually
added p to the list.

          else
          {
            bool done=false;
            Node* q = head;

            while(head!=(Node*)NULL && !done)
              if(head->getNext()->getData() < data)


Here's your problem: when you only have one
node in the list, head->getNext() is NULL,
so you have just dereferenced a null pointer.
I think you meant the loop condition to be:

  while (head->getNext() != NULL && !done)

Note that your "(Node*)NULL" casts are useless
and obfuscatory; remove them.

                         done = true;
                      else
                         head = head->getNext();

                   if(done)
                      q->setNext(p);
                   else
                      p->setNext(q);
                }


This loop trashes 'head' . It no longer points
to the head of the list after this.

                ++nodes;
             }


I think this is correct (untested though),
note that i think you had the comparison
the wrong way around too:
{
  Node* q;

/* go through until data is less than next entry */
  for (q = head; q->getNext() != NULL; q = q->getNext() )
    if ( data < q->getNext()->getData() )
      break;

/* insert p after the spot we stopped (note that
   this code still works if we stopped on the final node) */
  p->setNext( q->getNext() );
  q->setNext( p );
}

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