数据结构：双向链表

#ifndef DOUBLYLINKEDLIST_H
#define DOUBLYLINKEDLIST_H

typedef struct node *link;
struct node
{
	unsigned char item;
	link prev, next;
};

link make_node(unsigned char item);
void free_node(link p);
link search(unsigned char key);
void insert(link p);
void delete(link p);
void traverse(void (*visit)(link));
void destroy(void);
void enqueue(link p);
link dequeue(void);

#endif

#include <stdlib.h>
#include "doublylinkedlist.h"

struct node tailsentinel;
struct node headsentinel = {0, NULL, &tailsentinel};
struct node tailsentinel = {0, &headsentinel, NULL};

static link head = &headsentinel;
static link tail = &tailsentinel;

link make_node(unsigned char item)//创建结点
{
	link p = malloc(sizeof *p);
	p->item = item;
	p->prev = p->next = NULL;
	return p;
}

void free_node(link p)//释放结点
{
	free(p);
}

link search(unsigned char key)//查询
{
	link p;
	for (p = head->next; p != tail; p = p->next)
	{
		if (p->item == key)
			return p;
	}

	return NULL;
}

void insert(link p)//插入结点
{
	p->next = head->next;
	head->next->prev = p;
	head->next = p;
	p->prev = head;
}

void delete(link p)//删除结点
{
	p->prev->next = p->next;
	p->next->prev = p->prev;
}

void traverse(void (*visit)(link))//遍历链表
{
	link p;
	for (p = head->next; p != tail; p = p->next)
	{
		visit(p);
	}
}

void destroy(void)//销毁链表
{
	link q, p = head->next;
	head->next = tail;
	tail->prev = head;

	while (p != tail)
	{
		q = p;
		p = p->next;
		free_node(q);
	}
}

void enqueue(link p)//入队
{
	insert(p);
}

link dequeue(void)//出队
{
	if (tail->prev == head)
	{
		return NULL;
	}
	else
	{
		link p = tail->prev;
		delete(p);
		return p;
	}
}

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

void print_item(link p)
{
	printf("%d\n", p->item);
}

int main(void)
{
	link p = make_node(10);
	insert(p);
	p = make_node(5);
	insert(p);
	p = make_node(90);
	insert(p);
	p = search(5);
	delete(p);
	free_node(p);
	traverse(print_item);
	destroy();

	p = make_node(100);
	enqueue(p);
	p = make_node(200);
	enqueue(p);
	p = make_node(250);
	enqueue(p);
	while (p = dequeue())
	 {
		print_item(p);
		free_node(p);
	}

	return 0;
}