（1）queue.h
/*****************************************************************************
* *
* ------------------------------- queue.h -------------------------------- *
* *
*****************************************************************************/
#ifndef QUEUE_H
#define QUEUE_H
#include <stdlib.h>
#include "list.h"
#include "queue.h"
/*****************************************************************************
* *
* Implement queues as linked lists. *
* *
*****************************************************************************/
typedef List Queue;
/*****************************************************************************
* *
* --------------------------- Public Interface --------------------------- *
* *
*****************************************************************************/
#define queue_init list_init
#define queue_destroy list_destroy
int queue_enqueue(Queue *queue, const void *data);
int queue_dequeue(Queue *queue, void **data);
#define queue_peek(queue) ((queue)->head == NULL ? NULL : (queue)->head->data)
#define queue_size list_size
/*****************************************************************************
* *
* ------------------------------- queue.c -------------------------------- *
* *
*****************************************************************************/
/*****************************************************************************
* *
* ----------------------------- queue_enqueue ---------------------------- *
* *
*****************************************************************************/
int queue_enqueue(Queue *queue, const void *data) {
/*****************************************************************************
* *
* Enqueue the data. *
* *
*****************************************************************************/
return list_ins_next(queue, list_tail(queue), data);
}
/*****************************************************************************
* *
* ----------------------------- queue_dequeue ---------------------------- *
* *
*****************************************************************************/
int queue_dequeue(Queue *queue, void **data) {
/*****************************************************************************
* *
* Dequeue the data. *
* *
*****************************************************************************/
return list_rem_next(queue, NULL, data);
}
#endif
（2）ex-2.c
/*****************************************************************************
* *
* ex-1.c *
* ====== *
* *
* Description: Illustrates using a queue (see Chapter 6). *
* *
*****************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include "list.h"
#include "queue.h"
/*****************************************************************************
* *
* ------------------------------ print_queue ----------------------------- *
* *
*****************************************************************************/
static void print_queue(const Queue *queue) {
ListElmt *element;
int *data,
size,
i;
/*****************************************************************************
* *
* Display the queue. *
* *
*****************************************************************************/
fprintf(stdout, "Queue size is %d\n", size = queue_size(queue));
i = 0;
element = list_head(queue);
while (i < size) {
data = list_data(element);
fprintf(stdout, "queue[%03d]=%03d\n", i, *data);
element = list_next(element);
i++;
}
return;
}
/*****************************************************************************
* *
* --------------------------------- main --------------------------------- *
* *
*****************************************************************************/
int main(int argc, char **argv) {
Queue queue;
int *data,
i;
/*****************************************************************************
* *
* Initialize the queue. *
* *
*****************************************************************************/
queue_init(&queue, free);
/*****************************************************************************
* *
* Perform some queue operations. *
* *
*****************************************************************************/
fprintf(stdout, "Enqueuing 10 elements\n");
for (i = 0; i < 10; i++) {
if ((data = (int *)malloc(sizeof(int))) == NULL)
return 1;
*data = i + 1;
if (queue_enqueue(&queue, data) != 0)
return 1;
}
print_queue(&queue);
fprintf(stdout, "Dequeuing 5 elements\n");
for (i = 0; i < 5; i++) {
if (queue_dequeue(&queue, (void **)&data) == 0)
free(data);
else
return 1;
}
print_queue(&queue);
fprintf(stdout, "Enqueuing 100 and 200\n");
if ((data = (int *)malloc(sizeof(int))) == NULL)
return 1;
*data = 100;
if (queue_enqueue(&queue, data) != 0)
return 1;
if ((data = (int *)malloc(sizeof(int))) == NULL)
return 1;
*data = 200;
if (queue_enqueue(&queue, data) != 0)
return 1;
print_queue(&queue);
if ((data = queue_peek(&queue)) != NULL)
fprintf(stdout, "Peeking at the head element...Value=%03d\n", *data);
else
fprintf(stdout, "Peeking at the head element...Value=NULL\n");
print_queue(&queue);
fprintf(stdout, "Dequeuing all elements\n");
while (queue_size(&queue) > 0) {
if (queue_dequeue(&queue, (void **)&data) == 0)
free(data);
}
if ((data = queue_peek(&queue)) != NULL)
fprintf(stdout, "Peeking at an empty queue...Value=%03d\n", *data);
else
fprintf(stdout, "Peeking at an empty queue...Value=NULL\n");
/*****************************************************************************
* *
* Destroy the queue. *
* *
*****************************************************************************/
fprintf(stdout, "Destroying the queue\n");
queue_destroy(&queue);
return 0;
}