队列的简单操作

      队列，是先进先出（FIFO）的线性表。在具体应用中通常用链表或者数组来实现。队列只允许在后端（称为rear）进行插入操作，在前端（称为front）进行删除操作。
queue.h

#ifndef _QUEUE_H
#define _QUEUE_H
#define Type int

#ifdef _MSC_VER

#define bool int
#define true 1
#define false 0

#else

#include <stdbool.h>
#include <stdint.h>

#endif

struct queue;

struct queue *init_queue();
void destory_queue(struct queue *q);
void clear_queue(struct queue *q);

bool en_queue(struct queue *q, Type data);
bool de_queue(struct queue *q);

Type gethead(struct queue *q);

bool queue_empty(struct queue *q);
int queue_size(struct queue *q);

void print_queue(struct queue *q);

#endif

queue.c

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

struct queue_node {
    Type data;
    struct queue_node  *next;
};

struct queue {
    struct queue_node *front;
    struct queue_node *rear;
};

struct queue *init_queue()
{
    struct queue *q = (struct queue *)malloc(sizeof(struct queue));
    if (q == NULL)
        return NULL;
    q->front = q->rear = (struct queue_node *)malloc(sizeof(struct queue_node));
    if (q->front == NULL)
        return NULL;
    q->front->next = NULL;
    return q;
}

void destory_queue(struct queue *q)
{
    assert(q != NULL);
    while (q->front != NULL) {/*also free head node*/
        q->rear = q->front->next;
        free (q->front);
        q->front = q->rear;
    }
    free(q);
    q = NULL;
}

void clear_queue(struct queue *q)
{
    assert(q != NULL);
    struct queue_node *h, *p;
    h = q->front->next;
    q->rear = q->front;
    q->front->next = NULL;
    while (h != NULL) {
        p = h;
        h = h->next;
        free(p);
    }
}

bool en_queue(struct queue *q, Type data)
{
    assert(q != NULL);
    struct queue_node *p = (struct queue_node *)malloc(sizeof(struct queue_node));
    if (p == NULL)
        return false;
    p->data = data;
    p->next = NULL;
    q->rear->next = p;
    q->rear = p;
    return true;
}

bool de_queue(struct queue *q)
{
    assert(q != NULL);
    if (q->front == q->rear)
        return false;
    struct queue_node *p = q->front->next;
    q->front->next = p->next;
    if (q->rear == p)
        q->rear = q->front;/*null*/
    free(p);
    return true;
}

bool queue_empty(struct queue *q)
{
    assert(q != NULL);
    if (q->front->next == NULL)
        return true;
    else
        return false;
}

int queue_size(struct queue *q)
{
    struct queue_node *p = q->front;
    int i = 0;
    while (p != q->rear) {
        i++;
        p = p->next;
    }
    return i;
}

Type gethead(struct queue *q)
{
    assert(q != NULL);
    if (q->front != q->rear)
        return q->front->next->data;
    else
        return 0;
}

void print_queue(struct queue *q)
{
    assert(q != NULL);
    struct queue_node *p = q->front;
    while (p->next != NULL) {
        p = p->next;
        printf("%d ", p->data);
    }
}

主函数

#include <stdio.h>
#include "queue.h"

int main()
{
    struct queue *q = init_queue();
    en_queue(q, 2);
    en_queue(q, 1);
    en_queue(q, 3);
    en_queue(q, 5);
    de_queue(q);
    print_queue(q);
    destory_queue(q);
    return 0;
}