Queue C language concepts and basic operations

Queue: only data insertion operation end, special linear table delete data operation at the other end, having a FIFO queue FIFO (First In First Out)

Queues: one end of the insertion operation is referred to as the tail

Dequeue: delete operation is referred to as a head-end

Queue structure can also achieve the arrays and lists, linked lists some of the structure to achieve better, because using the array structure, the data array of the queue head, efficiency will be relatively low

Function declarations

#pragma once


typedef int QDataType;

// 链式结构：表示队列 
typedef struct QListNode
{
	struct QListNode* _pNext;
	QDataType _data;
}QNode;

// 队列的结构 
typedef struct Queue
{
	QNode* _front;
	QNode* _rear;
}Queue;

// 初始化队列 
void QueueInit(Queue* q);

// 队尾入队列 
void QueuePush(Queue* q, QDataType data);

// 队头出队列 
void QueuePop(Queue* q);

// 获取队列头部元素 
QDataType QueueFront(Queue* q);

// 获取队列队尾元素 
QDataType QueueBack(Queue* q);

// 获取队列中有效元素个数 
int QueueSize(Queue* q);

// 检测队列是否为空，如果为空返回非零结果，如果非空返回0 
int QueueEmpty(Queue* q);

// 销毁队列 
void QueueDestroy(Queue* q);

Function definition

#include <stdio.h>
#include <assert.h>
#include "Queue.h"

// 初始化队列 
void QueueInit(Queue* q)
{
	assert(q);

	q->_front = NULL;
	q->_rear = q->_front;
	/*q->_front = (QNode *)malloc(sizeof(QNode));
	if (q->_front == NULL || q->_rear == NULL)
	{
		return;
	}
		
	q->_front->_pNext = NULL;
	q->_front->_data = 0;
	q->_rear = q->_front;*/	//头节点与尾节点相等时队列为空
}

// 队尾入队列 
void QueuePush(Queue* q, QDataType data)
{
	assert(q);

	QNode *qnode = (QNode *)malloc(sizeof(QNode));
	qnode->_pNext = NULL;
	qnode->_data = data;

	if (q->_front == NULL)
	{
		q->_front = q->_rear = qnode;
		return;
	}
	q->_rear->_pNext = qnode;
	q->_rear = qnode;
}

// 队头出队列 
void QueuePop(Queue* q)
{
	assert(q);

	if (q->_front == q->_rear)
	{
		printf("队列为空，出队列失败！\n");
		return;
	}

	QNode *cur = q->_front;
	if (cur)
	{
		q->_front = cur->_pNext;
		free(cur);
	}
}

// 获取队列头部元素 
QDataType QueueFront(Queue* q)
{
	assert(q);

	if (q->_front == q->_rear)
	{
		printf("队列为空，获取队列头部元素失败！\n");
		return;
	}
	return q->_front->_data;
}

// 获取队列队尾元素 
QDataType QueueBack(Queue* q)
{
	assert(q);

	if (q->_front == q->_rear)
	{
		printf("队列为空，获取队尾元素失败！\n");
		return;
	}
	return q->_rear->_data;
}

// 获取队列中有效元素个数 
int QueueSize(Queue* q)
{
	assert(q);

	int count = 0;
	QNode *cur = q->_front;

	while (cur != NULL)
	{
		++count;
		cur = cur->_pNext;
	}
	return count;
}

// 检测队列是否为空，如果为空返回非零结果，如果非空返回0 
int QueueEmpty(Queue* q)
{
	assert(q);
	if (q->_front == q->_rear)
	{
		return 1;
	}
	return 0;
}

// 销毁队列 
void QueueDestroy(Queue* q)
{
	assert(q);
	QNode *cur = q->_front->_pNext;
	while (cur->_pNext != q->_rear)
	{
		QNode *next = cur->_pNext;
		free(cur);
		cur = next;
	}
	q->_front = q->_rear;
}

//打印
void Pri(Queue* q)
{
	assert(q);

	//队列为空
	if (q->_front == q->_rear)
	{
		return;
	}

	QNode *cur = q->_front;
	while (cur != NULL)
	{
		printf("%d ", cur->_data);
		cur = cur->_pNext;
	}
	printf("\n");
}

test

int main()
{
	QNode q;

	//初始化队列
	QueueInit(&q);

	//队尾入队列
	QueuePush(&q, 1);
	QueuePush(&q, 2);
	QueuePush(&q, 3);
	QueuePush(&q, 4);
	QueuePush(&q, 5);
	// 1 2 3 4 5
	printf("入队列后：\n");
	Pri(&q);

	//队头出队列
	QueuePop(&q);
	// 1 2 3 4
	printf("出队列后：\n");
	Pri(&q);

	// 获取队列头部元素 
	printf("队列头部元素为：%d\n", QueueFront(&q));
	printf("\n");

	// 获取队列队尾元素 
	printf("队列队尾元素为：%d\n", QueueBack(&q));
	printf("\n");

	// 获取队列中有效元素个数 
	printf("队列中有效元素个数为：%d\n", QueueSize(&q));
	printf("\n");

	// 检测队列是否为空，如果为空返回非零结果，如果不为空返回0 
	int ret = QueueEmpty(&q);
	if (ret == 0)
	{
		printf("此队列不为空\n");
	}
	else
		printf("此队列为空\n");
	printf("\n");

	// 销毁队列 
	QueueDestroy(&q);

	ret = QueueEmpty(&q);
	if (ret == 0)
	{
		printf("此队列不为空\n");
	}
	else
		printf("此队列为空\n");
	printf("\n");


	return 0;
}