Double pointers and linked lists.

I'm creating an a* algorithm implementation using two double linked lists.

p_node is the node being copied. ppDest is the tail node and ppDestlist_h is the head node.

I'm not entirely sure about my double pointers and I might just be making a schoolboy error here. I only learnt about their use yesterday, and have converted my code to use it instead of returning pointers to the nodes.

Code:

---

int addtolist(p_node *node, p_node **ppDest, p_node *ppDestlist_h)
{

  if(( node == NULL ))
  {
      printf("Node pointer is null!\n");
      return 1;
  }

  /*edit* /
  ppDest = &(*ppDestlist_h);
 
  /*double pointers here are used to keep going forward until null is hit*/
  /* if null is hit immediately then copy the node right away*/
  while(*ppDest != NULL)
  { ppDest = &(*ppDest)->next;}
 
  memcpy(&(*ppDest), &node, sizeof(p_node));
 
  printf("node inside func: %d Current:  \n", (*ppDest)->x);
 
  /*now I set the next value of the node to NULL*/
 
  (*ppDest)->next = NULL;
 
  return;
 
}

---

This seems like it should work, but doesnt want to.

has anyone got any pointers? (ouch that was bad)

thanks,

-Simo

It took me some time to read this horrible code...

Code:

---

memcpy(&(*ppDest), &node, sizeof(p_node));

---

&(*ppDest) is just ppDest - pointer to pointer
&node - is pointer to pointer as well
so
*ppDest = node; should be enough...

instead of it you are trying to copy other the pointer the whole p_node structure of bytes (from location that does not contains enogh info) overwriting all memory after ppDest ...

It does not seems as it should work...

Quote:

---

Originally Posted by vart

It took me some time to read this horrible code...

Code:

---

memcpy(&(*ppDest), &node, sizeof(p_node));

---

&(*ppDest) is just ppDest - pointer to pointer
&node - is pointer to pointer as well
so
*ppDest = node; should be enough...

instead of it you are trying to copy other the pointer the whole p_node structure of bytes (from location that does not contains enogh info) overwriting all memory after ppDest ...

It does not seems as it should work...

---

heh yeah you were right. I really had no idea what I was doing using memcpy. I rewrote it today and just copied the data over and It worked on the first compile. heh.

Thanks