CODEWITHSUNDEEP
cpointerslinked-listpass-by-reference
ben lemasurier
ben lemasurier

Reputation: 2592

Linked Lists are turning my brain to mush. How should I be doing this?

I'm attempting to use linked lists as a way to buildup my knowledge of pointers in C. So, I wrote a small example but when I compile it I'm getting an error I can't seem to figure out:

In function 'append_node': 
error: request for member ‘next’ in something not a structure or union

What's the proper way to access (or pass) a structure by reference?

#include <stdio.h>
#include <stdlib.h>

struct node {
  int val;
  struct node *next;
};

static int append_node(int val, struct node **head) {
  struct node *new_node;

  new_node = (struct node *) malloc(sizeof(struct node));
  new_node->val  = val;
  new_node->next = NULL

  *(head)->next = new;

  return 0;
}

int main() {
  int i;
  struct node *head;
  struct node *curr;

  head = NULL;
  curr = (struct node *) malloc(sizeof(struct node));

  for(i = 1; i <= 10; i++) {
      append_node(i, &curr);
      head = curr;
  }

  curr = head;
  while(curr) {
      printf("%d\n", curr->val);
      curr = curr->next ;
  }

  return 0;
}

Any help would be great!

Upvotes: 4

Views: 226

Answers (3)

Jonathan Wood
Jonathan Wood

Reputation: 67223

Try this instead:

(*head)->next = new_node;

Turn **head to *head and then call members on it.

Upvotes: 1

codaddict
codaddict

Reputation: 455122

Two problems:

There is a missing ; at the end of 

new->next = NULL

and change 

*(head)->next = new;

to

(*head)->next = new;

Upvotes: 3

Mark Ransom
Mark Ransom

Reputation: 308206

Can I assume you're getting the error on this line?

  *(head)->next = new;

I think you need to make one trivial change:

  (*head)->next = new;

Since head is a pointer to a pointer, when you dereference it you get a pointer. The ->next operates on that pointer.

Upvotes: 3

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