2012-02-12



This is how you can effectively create a  single-linked  list  by
*appending* entries:

     node *head = NULL, *elem;
     char *str;

     while (str = getnextstr()) {
             elem = getelem(str);
             if (!head) {
                     head = elem;
                     elem->next = elem;
             } else {
                     elem->next = head->next;
                     head->next = elem;
                     head = elem;
             }
     }
     head = elem->next;
     elem->next = NULL;

The clue is to store the pointer to the beginning of the list al-
ways  in  the last entry's next pointer. Note that you cannot use
the list until you've done the finishing (last two lines).  Thus,
this  technique  can only be used if you finish building the list
completely before you start accessing  it.   Also,  there  `elem'
needs to be set *inside* the loop, not in the condition.

You see, this is a special-case optimization. You won't see  this
one  often and that's good. It likely causes errors: People won't
recognize it quickly.  The identifiers `head' changes its meaning
between  ``tail''  and  ``head''.   The limiting conditions might
change, possibly making the algorithm unusable.

It's good to have seen such an  implementation  to  recognize  it
when  you  came  across it, but please dont implement it yourself
this way. At least not without an explaining  comment  (only  bad
algorithm  choices  need this).  If you want to append to single-
linked lists, then use a separate `tail' pointer.



http://marmaro.de/lue/        markus schnalke <meillo@marmaro.de>