Why use double pointer when inserting node to the head (linkedlist)?

Asked Apr 03 '19 at 06:09

Active Apr 03 '19 at 06:12

Viewed 80 times

int list_insert_head(node **phead, int data){
  node *newnode = malloc(sizeof(node));
  if(newnode == 0)
    return 0; /*memory allocation failed*/
  newnode -> data = data;
  newnode -> next = *phead;
  *phead = newnode; /* what is this?*/
  return 1;

}

So I'm not quite sure why you have to pass in double pointer **phead, and only use a single pointer *phead inside the function. I assume you use double pointer b/c you're manipulating actual head, which itself is a single pointer. Inside the function by the way, if you were going to do this,

*phead = newnode;

why don't you just pass in *phead in the function parameter?

Thank you.

asked Apr 03 '19 at 06:09

raven39

2

If you don't use a double pointer you'll be asking *this* question https://stackoverflow.com/questions/766893/how-do-i-modify-a-pointer-that-has-been-passed-into-a-function-in-c – StoryTeller - Unslander Monica Apr 03 '19 at 06:10
1

The question is not a duplicate *per se*, but the answer would be. ;-) So I closed the question as such. – DevSolar Apr 03 '19 at 06:12
2

@DevSolar - I edited another posts into the dupe list. All bases should be covered now. – StoryTeller - Unslander Monica Apr 03 '19 at 06:13
1

If you haven't already, please see what happens when a double pointer is not used. That should give some idea. – J...S Apr 03 '19 at 06:14

Why use double pointer when inserting node to the head (linkedlist)?

0 Answers0