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(-);
     }
 }

 /*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 = ; i < ; i++)
     {
         create_node(&new_node);
         new_node->data = i + ;
         insert_node_tail(head, new_node);
     }
     output_link(head);

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

     release_link(&head);

     output_link(head);
     return ;
 }

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。