带头结点的循环单链表C语言

/*****************************************************
Author：Simon_Kly    Version:0.1    Date: 20170520
Description：循环单链表
Mail:degaullekong@gmail.com
Funcion List: 
*****************************************************/

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

typedef struct node
{
    int data;
    struct node *next;
}Node, *Link;

/*判断malloc是否成功执行*/
void is_malloc_ok(Link node)
{
    if(node == NULL)
    {
        printf("malloc error!\n");
        exit(-1);
    }
}

/*创建单链表*/
void create_link(Link * head)
{
    *head = (Link)malloc(sizeof(Node));
    is_malloc_ok(*head);
    (*head)->next = *head;
}

/*创建节点*/
void create_node(Link * new_node)
{
    *new_node = (Link)malloc(sizeof(Node));
    is_malloc_ok(*new_node);
    (*new_node)->next = NULL;
}

/*插入节点尾插法*/
void insert_node_tail(Link head, Link new_node)
{
    Link p = NULL;

    p = head;

    while (p->next != head)
    {
        p = p->next;
    }
    new_node->next = head;
    p->next = new_node;
}

/*插入节点头插*/
void insert_node_head(Link head, Link new_node)
{
    new_node->next = head->next;
    head->next = new_node;
}

/*输出链表*/
void output_link(Link head)
{
    Link p = NULL;

    if (head == NULL)
    {
        printf("link is not exist!\n");
        return ;
    }
    else if(head->next == head)
    {
        printf("link is empty!\n");
        return ;
    }

    p = head->next;

    while (p != head)
    {
        printf("%d\n", p->data);
        p = p->next;
    }
}

/*置为空链*/
void make_link_empty(Link *head)
{
    Link p = NULL;

    p = (*head)->next;

    while (*head != (*head)->next)
    {
        (*head)->next = (*head)->next->next;
        free(p);
        p = (*head)->next;
    }
}

/*销毁链*/
void release_link(Link * head)
{
    make_link_empty(head);
    free(*head);
    *head = NULL;
}

int main()
{
    int i;
    Link head = NULL;
    Link new_node = NULL;
    
    output_link(head);
    create_link(&head);
    output_link(head);
    for (i = 0; i < 10; i++)
    {
        create_node(&new_node);
        new_node->data = i + 1;
        insert_node_tail(head, new_node);
    }
    output_link(head);

    create_node(&new_node);
    new_node->data = 20;
    insert_node_head(head, new_node);
    output_link(head);

    release_link(&head);

    output_link(head);
    return 0;
}

循环单链表的于单链表唯一的不同：在对链表中添加或者删除节点时一定要保持链表的头尾连接，在遍历时不能再以NULL为循环结束判断条件，应该使用头和尾相等来判断整个链表结束。