Simple Doubly-Linked List question.

[gp364481]

Hey guys,
my list is NULL in the beginning.
do I have to make a special case for when inserting the first element of the doubly linked list? I am having trouble with pointing to the previous element when adding the first element.

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

/*prototypes*/
int push(struct node**, int);
int printList(struct node*);

/*doubly linked-list structure*/
struct node {
	int data;
	struct node* nextPtr;
	struct node* previousPtr;
	struct node* childPtr; /*will point to another list*/
};

/*main*/
int main(void){
	struct node* head = NULL;
	int m = 5;

	push(&head, m);
	printList(head);
	
	free(head);       /*hehe, ya I know*/
	return 0;
}
int push(struct node** head, int data){
	struct node* current = *head;
	struct node* newNode;
	if( !(newNode = malloc(sizeof(struct node))) )
		return -1;

	newNode->data = data;
	newNode->nextPtr = *head;
	newNode->previousPtr = NULL;

	/* I tried (*head)->previousPtr = newNode here but the program crashes. 
	 *I think its because *head is NULL here*/

	*head = newNode;

	return 0;
}
int printList(struct node* head){
	while(head != NULL){
		printf("%d ", head->data);
		head = head->nextPtr;
	}
	printf("\n");
	return 0;
}

So yeah, my question is do I need to make a special case for inserting the first element in a doubly linked list, or is there a way around it?
Thanks!

PS -- I havent done all the error handling etc yet. I usually do that at the end.

[Bayint Naung]

This tutorial is a good read.
Yes, you'll need a special case. But there're other ways also(such as dummy head,etc).

[MK27]

The "special case" could be as simple as testing if head == NULL. If it does, then you create the head -- obviously, head->prev should then be NULL.

[gp364481]

Cool, thank you.
I've been at it for a while and I am overcomplicating things.

Thanks again.

[Bayint Naung]

	free(head);       /*hehe, ya I know*/

Actually you don't know it might be leaking memory if there's more than one element in list.

[gp364481]

	free(head);       /*hehe, ya I know*/

Actually you don't know it might be leaking memory if there's more than one element in list.

wait do i have to do "walk" through the linked list and free each node individually?

	while(head){
		temp = head;
		head = head->nextPtr;
		free(temp);
	}

Like that ?

[iMalc]

Yep, that'll free it all up nicely.

[chris.r]

One of my professors taught me a trick that will save you MANY MANY headaches developing data structures.
The FIRST thing you should do is map out the special cases in your code:

if (a) { }
else if (b) { }
else if (c) { }
else { }

The next step is to tackle the easy cases.
Finally, you should develop the most complicated case.
Most people dive into inserting/deleting by writing the complicated case then thinking why the H**L it doesn't work half of the time.