定义

• 特点：先进先出（FIFO）
• 队尾：入队操作
• 队头：出队操作

.h文件

typedef int datatype;

typedef struct node
{
    datatype data;
    struct node *next;
}listnode, *linklist;

typedef struct _linkqueue {
    linklist front;
    linklist rear;
}linkqueue;

linkqueue* queue_create();
int enqueue(linkqueue *lq, datatype x);
datatype dequeue(linkqueue *lq);
int queue_empty(linkqueue *lq);
int queue_clear(linkqueue *lq);
linkqueue* queue_free(linkqueue *lq);

.c文件

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

linkqueue* queue_create()
{
    linkqueue *lq = (linkqueue *)malloc(sizeof(linkqueue));
    if(lq == NULL){
        printf("malloc linkqueue fail\n");
        return NULL;
    }

    lq->front = lq->rear = (linklist)malloc(sizeof(listnode));
    if(lq->front == NULL){
        printf("malloc listnode fail\n");
         return NULL;
    }

    lq->front->data = 0;
    lq->front->next = NULL;

    return lq;
}
int enqueue(linkqueue *lq, datatype x){
    if(lq == NULL){
    printf("lq is NULL\n");
    return -1;
    }

    linklist p= (linklist)malloc(sizeof(listnode));
    if(p == NULL){
    printf("malloc node fail\n");
        return -1;
    }
    p->data = x;
    p->next = NULL;
    lq->rear->next = p;//连接
    lq->rear = p;//移位

    return 0;
}
datatype dequeue(linkqueue *lq){
    linklist p;
    datatype temp;
    if (lq == NULL){
        printf("lq is NULL\n");
        return 0;
    }
    if (lq->front == lq->rear){
        printf("lq is empty\n");
        return 0;
    }
    p = lq->front;
    lq->front= p->next;
    temp = lq->front->data;
    free(p);
    p = NULL;
    
    return temp;
}
int queue_empty(linkqueue *lq){
    if (lq == NULL){
        printf("lq is NULL\n");
        return -1;
    }

    if (lq->front == lq->rear){
        printf("linkqueue is empty\n");
        return -1;
    }
    return 0;
}

int queue_clear(linkqueue *lq){
    linklist p;  
    if (lq == NULL){
        printf("lq is NULL\n");
        return 0;
    }
    
    while (!(lq->front == lq->rear))
    {
        p = lq->front;
        lq->front = p->next;
        printf("clear:%d\n",p->data);
        free(p);
        p = NULL;
    }
    return 0;
}
linkqueue* queue_free(linkqueue *lq){
    linklist p;
    if (lq == NULL){
        printf("lq is NULL\n");
        return 0;
    }
    p = lq->front;
    while (lq->front)
    {
        lq->front = p->next;
        printf("free:%d\n",p->data);
        free(p);
        p = lq->front;
    }
    free(lq);
    lq = NULL;

    return lq;
}

main函数

#include <stdio.h>
#include <stdlib.h>
#include "linkqueue.h"
static int test();
int main()
{
    printf("Mian start:\n");
    test();
    return 0;
}

static int test(){

    linkqueue *lq;
    lq = queue_create();
    if(lq == NULL){
        return -1;
    }

    enqueue(lq,9);
    enqueue(lq,19);
    enqueue(lq,29);
    enqueue(lq,39);
    enqueue(lq,49);
    
    queue_clear(lq);
    while (!queue_empty(lq))
    {
        printf("dequeue:%d\n",dequeue(lq));
    }
    lq = queue_free(lq);
    return 0;
}

结果：