//定义 插入:s->prior = p->prior;p->prior->next = s;s->next = p;p->prior = s;//第一句必须在第四句之前完成，否则*p的前驱结点就丢掉了。 删除:p->prior->next = p->next;p->next->prior = p->prior;free(p);//绕过p
