unidirectional linked list pointer problem Post: 302594180

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Top Forums Programming unidirectional linked list pointer problem Post 302594180 by DreamWarrior on Monday 30th of January 2012 05:59:27 PM

01-30-2012

Registered User

I'm not sure what you want the "dlist_position" to be, but what you're doing in that insert won't work at all. How you have it coded right now is very likely to crash when executing newPosition->next = p->next as the first time it's called p is NULL (likely; possibly some random value depending on compiler/optimizations, etc) and you can not execute p->next through the NULL pointer.

I would assume you want "dlist_position" to be a node in the list (maybe consider calling it dlist_node?). If that's the case, you'll have to special case when you want the new data to be inserted as the first position in the list.

I suggest allowing dlist_insert to special case when p == NULL, handling it correctly by linking the new position to the head of l. Then the very first call:

Code:

p = dlist_insert(list, p, element[0]);

becomes:

Code:

p = dlist_insert(list, NULL, element[0]);

Having no idea what the structure for dlist is, however, we can't help any more.

edit: also, dlist_position newPosition=malloc(sizeof(element)); looks odd -- I can only hope that dlist_position is just typedef'd as a pointer to an element...but, again, not enough code to tell.

Last edited by DreamWarrior; 01-30-2012 at 07:06 PM..

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list

list(3) 						    InterNetNews Documentation							   list(3)

NAME

       list - list routines

SYNOPSIS

       #include <inn/list.h>

       struct node {
	   struct node *succ;
	   struct node *pred; };

       struct list {
	   struct node *head;
	   struct node *tail;
	   struct node *tailpred; };

       void list_new(struct list *list);

       struct node *list_addhead(struct list *list, struct node *node);

       struct node *list_addtail(struct list *list, struct node *node);

       struct node *list_head(struct list *list);

       struct node *list_tail(struct list *list);

       struct node *list_succ(struct node *node);

       struct node *list_pred(struct node *node);

       struct node *list_remhead(struct list *list);

       struct node *list_remtail(struct list *list);

       struct node *list_remove(struct node *node);

       struct node *list_insert(struct list *list, struct node *node, struct node *pred);

       bool list_isempty(struct list *list);

DESCRIPTION

       list_new initialises the list header list so as to create an empty list.

       list_addhead adds node to the head of list, returning the node just added.

       list_addtail adds node to the tail of list, returning the node just added.

       list_head returns a pointer to the the node at the head of list or NULL if the list is empty.

       list_tail returns a pointer to the the node at the tail of list or NULL if the list is empty.

       list_succ returns the next (successor) node on the list after node or NULL if node was the final node.

       list_pred returns the previous (predecessor) node on the list before node or NULL if node was the first node.

       list_remhead removes the first node from list and returns it to the caller. If the list is empty NULL is returned.

       list_remtail removes the last node from list and returns it to the caller. If the list is empty NULL is returned.

       list_remove removes node from the list it is on and returns it to the caller.

       list_insert inserts node onto list after the node pred. If pred is NULL then node is added to the head of list.

HISTORY

       Written by Alex Kiernan <alex.kiernan@thus.net> for InterNetNews 2.4.0.

       $Id: list.pod 7851 2008-05-26 19:33:08Z iulius $

INN 2.5.2							    2009-05-21								   list(3)