说明：  C语言中可复用的链表结构，可以不必关心用户数据结构完成链表的增删该查及排序、保存等操作，提供枚举器枚举链表数据
(reusable linked list structure in C language.you don't have to worry about the user data structure, complete the additions and deletions of the list, check and sort, save, and so on, and provide enumerator to enumerate the list data.)