Linux C下链队列的实现

由于工作需求， 需要开发一个C版本的队列， 经过一天的开发测试， 原始版本已完成；

这也是我个人的第一篇博客， 希望将来能帮助更多后来开发者；

废话不多说， 直接进入主题。

队列是一种特殊的线性表，特殊之处在于它只允许在表的前端（front）进行删除操作，而在表的后端（rear）进行插入操作，

和栈一样，队列是一种操作受限制的线性表。进行插入操作的端称为队尾，进行删除操作的端称为队头。

队列的数据元素又称为队列元素。在队列中插入一个队列元素称为入队，从队列中删除一个队列元素成为出队。

因为队列只允许在一段插入，在另一端删除，所以只有最早进入队列的元素才能最先从队列中删除，

故队列又称为先进先出（FIFO—first in first out）线性表；

以上红字部分是借鉴于百度百科： 队列

关于实现：

队列的链式存储结构简称为链队列。它是限制仅在表头删除和表尾插入的单链表， 如下图：

如图所示， 我们会创建两个指针，front表示头指针， rear表示尾指针；

和线性表的单链表一样，为了操作方便，我们也给链队列添加一个头结点，并令头指针指向头结点；

链队列为空时， 头指针和尾指针均指向头结点；

这次主要是实现了几个功能：

init -->创建

insert-->插入

remove-->删除

deIninit-->销毁

插入讲解：

删除讲解：

以下是代码部分：

/*
beginning of the queue -- remove element
end tail of the queue -- insert element
*/
#include<stdio.h>
#include<stdlib.h>

#define true 1
#define false 0
 
typedef int QElemCommonType;
typedef int Status;
 
typedef struct historyQueueNode
{
    QElemCommonType  data;
    struct historyQueueNode  *next;
}SHistoryQueueNode,*pSHistoryQueueNode;
 
// this struct maintains a queue beginning pointer and end pointer
// the pointer will point to the node of queue.
typedef struct linkQueue
{
    pSHistoryQueueNode front;	// queue beginning pointer
    pSHistoryQueueNode rear;	// queue end pointer
 }SLinkQueue;
 
// method protype 
int initHistoryQueue(SLinkQueue *historyQueue);
int deInitHistoryQueue(SLinkQueue *historyQueue);
int clearHistoryQueue(SLinkQueue *historyQueue);
int insertHistoryQueue(SLinkQueue *historyQueue, QElemCommonType data);
int removeHistoryQueue(SLinkQueue *historyQueue, QElemCommonType *data);
int printHistoryQueue(SLinkQueue *historyQueue);
 
int initHistoryQueue(SLinkQueue *historyQueue)
{
	int result = false;

	do
	{
		// create a empty queue, the beginning and end queue will point to the head node.
		historyQueue-> front = historyQueue-> rear = (struct historyQueueNode *)malloc(sizeof(struct historyQueueNode));
		if(!historyQueue->front)
		{
			result = false;
			break;
		}
		historyQueue->front->next = NULL;

		//set return result to true;
		result = true;
	}while(0);

    return result;
}

// destory the queue, the queue is not exist;
// from the beginning of queue, destory each node;
// remove the head node, then the first, second node, untill remove it to end.
int deInitHistoryQueue(SLinkQueue *historyQueue)
{
    /*
    q->front will point to head node,
	q->front->next will point to the fisrt node.
    */
    while(historyQueue->front)
	{
        historyQueue->rear = historyQueue->front->next;
        free(historyQueue->front);

        historyQueue->front = historyQueue->rear;
    }

    return true;
}
 
int insertHistoryQueue(SLinkQueue *historyQueue, QElemCommonType data)
{
	int result = false;

	// insert element e
    pSHistoryQueueNode newNode = (struct historyQueueNode *)malloc(sizeof(struct historyQueueNode));
    if(!newNode)
	{
        result = false;
    }

	//set data to new node 
    newNode->data = data;
    newNode->next = NULL;

	//add the new data into link queue 
    historyQueue->rear->next = newNode;
    historyQueue->rear = newNode;

	result = true;

    return result;
}
 
int removeHistoryQueue(SLinkQueue *historyQueue, QElemCommonType *data)
{
	int result = false;

	do
	{
		//if queue is not empty, remove head element
		if(historyQueue->front == historyQueue->rear)
		{
		    result = false;
			break;
		}
	
		// get and remove the oldest node from the link queue.
		pSHistoryQueueNode oldNode =  historyQueue->front->next; //the head element
		historyQueue->front->next = oldNode->next; 

		*data = oldNode->data; 

		//if the element which will be removed is end element, the queue is empty.
		if(historyQueue->rear == oldNode) 
		{  
			historyQueue->rear = historyQueue->front;
		}
		//free 
		free(oldNode);

		result = true;
	}while(0);

	return result;
}

int printHistoryQueue(SLinkQueue *historyQueue)
{
 
    if(historyQueue->front==NULL)
	{
        printf("queue is not exist\n");
    }
	else if(historyQueue->front==historyQueue->rear)
	{
        printf("queue is empty\n");
    }
	else
	{
        //traverse link list queue.
        SHistoryQueueNode *temp;
        temp = historyQueue->front->next;
        while (temp)
        {
            printf("%d ",temp->data);
            temp = temp->next;
        }
        printf("\n");
    }
    return true;
}

int main()
{
    SLinkQueue q;
    int i,n;
    QElemCommonType e;

    printf("main: ====initHistoryQueue start====\n");
    initHistoryQueue(&q);
    printf("main: ====initHistoryQueue end====\n");

    printf("main: please input insert number n: ");
    scanf("%d",&n);

    for(i=0;i<n;i++)
	{
        insertHistoryQueue(&q,i);
    }

    printf("main: printHistoryQueue: \n");
    printHistoryQueue(&q);

    printf("main: removeHistoryQueue: \n");
    printf("main: please input remove number n: ");
    scanf("%d",&n);

	printf("main: remove number is ");
	for(i = 0; i < n; i++)
	{
		removeHistoryQueue(&q, &e);
		printf("%d ", e);
	}
	printf("\n");

    printf("main: printHistoryQueue: \n");
    printHistoryQueue(&q);

    printf("main: deInitHistoryQueue \n");
    deInitHistoryQueue(&q);

    printf("main: printHistoryQueue once again.\n");
    printHistoryQueue(&q);

    return 0;
}

测试结构如下：

duser@136.17.78.38:~/Desktop/testFunction/Queue$ gcc v2x_queue.c -o test
duser@136.17.78.38:~/Desktop/testFunction/Queue$ ./test 
main: ====initHistoryQueue start====
main: ====initHistoryQueue end====
main: please input insert number n: 100
main: printHistoryQueue: 
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 
50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 
main: removeHistoryQueue: 
main: please input remove number n: 50
main: remove number is 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 
40 41 42 43 44 45 46 47 48 49 
main: printHistoryQueue: 
50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 
main: deInitHistoryQueue 
main: printHistoryQueue once again.
queue is not exist
duser@136.17.78.38:~/Desktop/testFunction/Queue$ 

最后希望看的时候动起手来，画画图会更加容易理解；

代码中希望尽可能完善它； 另外请把int返回类型改成bool；

Best wishes!

Yannick Tong.