cpp/CPrimerPlus6E/Ch17/queue.c

/* queue.c -- the Queue type implementation*/
#include <stdio.h>
#include <stdlib.h>
#include "queue.h"

/* local functions */
static void CopyToNode(Item item, Node * pn);
static void CopyToItem(Node * pn, Item * pi);

void InitializeQueue(Queue * pq)
{
    pq->front = pq->rear = NULL;
    pq->items = 0;
}

bool QueueIsFull(const Queue * pq)
{
    return pq->items == MAXQUEUE;
}

bool QueueIsEmpty(const Queue * pq)
{
    return pq->items == 0;
}

int QueueItemCount(const Queue * pq)
{
    return pq->items;
}

bool EnQueue(Item item, Queue * pq)
{
    Node * pnew;
    
    if (QueueIsFull(pq))
        return false;
    pnew = (Node *) malloc( sizeof(Node));
    if (pnew == NULL)
    {
        fprintf(stderr,"Unable to allocate memory!\n");
        exit(1);
    }
    CopyToNode(item, pnew);
    pnew->next = NULL;
    if (QueueIsEmpty(pq))
        pq->front = pnew;           /* item goes to front     */
    else
        pq->rear->next = pnew;      /* link at end of queue   */
    pq->rear = pnew;                /* record location of end */
    pq->items++;                    /* one more item in queue */
    
    return true;
}

bool DeQueue(Item * pitem, Queue * pq)
{
    Node * pt;
    
    if (QueueIsEmpty(pq))
        return false;
    CopyToItem(pq->front, pitem);
    pt = pq->front;
    pq->front = pq->front->next;
    free(pt);
    pq->items--;
    if (pq->items == 0)
        pq->rear = NULL;
    
    return true;
}

/* empty the queue                */
void EmptyTheQueue(Queue * pq)
{
    Item dummy;
    while (!QueueIsEmpty(pq))
        DeQueue(&dummy, pq);
}

/* Local functions                 */

static void CopyToNode(Item item, Node * pn)
{
    pn->item = item;
}

static void CopyToItem(Node * pn, Item * pi)
{
    *pi = pn->item;
}