Doubly Linked list C

queue.c

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

#ifndef QUEUE_H

#define INPUT_BUFFER_SIZE 100

#define OP_QUEUE_ENQUEUE	0
#define OP_QUEUE_DEQUEUE	1
#define OP_QUEUE_END		2

typedef struct node_t {
	int             value;
	struct node_t  *next;
	struct node_t  *previous;
}               node_t;

typedef struct {
	int             count;
	struct node_t  *front;
	struct node_t  *rear;
}               queue_t;

void            queue_init(queue_t *);
int             queue_is_empty(queue_t *);
void            queue_enqueue(queue_t *, int);
int             queue_dequeue(queue_t *);
void            queue_free(queue_t *);

#endif

void
queue_init(queue_t * pque)
{
	assert(pque != NULL);

	/* init queue data structure */
	pque->count = 0;
	pque->front = NULL;
	pque->rear = NULL;
}

void
queue_enqueue(queue_t * pque, int item)
{
	node_t         *new;
	assert(pque != NULL);

	/*
	 * allocate memory and exit if we can't allocate anymore memory.
	 * Cleanup before we exit the program though
	 */
	if ((new = malloc(sizeof(node_t))) == NULL) {
		fprintf(stderr, "Memory allocation for queue_enqueue failed! "
			"Aborting data entry !\n");
		queue_free(pque);
		exit(EXIT_FAILURE);
	}
	new->value = item;
	new->previous = NULL;
	new->next = pque->front;

	/* empty queue */
	if (pque->front != NULL) {
		pque->front->previous = new;
	}
	if (pque->rear == NULL) {
		pque->rear = new;
	}
	/* add new item to the front */
	pque->front = new;
	pque->count++;
}

int
queue_dequeue(queue_t * pque)
{
	node_t         *last;
	int             val;

	assert(pque != NULL);
	assert(pque->count > 0);

	/* remove last item and make 2nd last = rear */
	last = pque->rear;
	pque->rear = last->previous;
	if (pque->rear)
		pque->rear->next = NULL;
	val = last->value;
	free(last);		/* free memory used by item */

	pque->count--;

	return val;
}

int
queue_is_empty(queue_t * pque)
{
	assert(pque != NULL);

	if (pque->count == 0)
		return 1;

	return 0;
}

void
queue_free(queue_t * pque)
{
	node_t         *del;

	assert(pque != NULL);

	/*
	 * remove and delete items from the back of the list till there is no
	 * item left
	 */
	while (!queue_is_empty(pque)) {
		del = pque->rear;
		pque->rear = del->previous;
		pque->count--;
		free(del);
	}
	pque->front = NULL;
	pque->rear = NULL;
}