第33课 双向循环链表的实现

Posted 2020-09-27 浅墨浓香

1. DTLib中双向链表的设计思路

 

（1）数据结点之间在逻辑上构成双向循环，这有别于Linux内核链表的实现。

（2）头结点仅用于结点的定位，而Linux内核链表是将头结点作为循环的一部分。

2. 实现思路

 

（1）通过模板定义DualCircleList类，继承自DualLinkList类

（2）在DualCircleList内部使用Linux内核链表进行实现（另类实现）

（3）使用struct list_head定义DualCircleList的头结点

（4）特殊处理：循环遍历时忽略头结点

3. 实现要点

（1）通过list_head进行目标结点定位（position(i)）

（2）通过list_entry将list_head指针转换为目标结点指针

（3）通过list_for_each实现int find(const T& e)函数

（4）遍历函数中的next和prev需要考虑跳过头结点

【编程实验】基于Linux内核链表的双向循环链表

//LinuxList.h

#ifndef _LINUX_LIST_H
#define _LINUX_LIST_H

//#include <linux/types.h>
//#include <linux/stddef.h>
//#include <linux/poison.h>
//#include <linux/prefetch.h>

/*
 * Simple doubly linked list implementation.
 *
 * Some of the internal functions ("__xxx") are useful when
 * manipulating whole lists rather than single entries, as
 * sometimes we already know the next/prev entries and we can
 * generate better code by using them directly rather than
 * using the generic single-entry routines.
 */

#ifndef offsetof
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
#endif

#ifndef container_of
#define container_of(ptr, type, member) ((type *)((char *)ptr - offsetof(type,member)))
#endif

#define prefetch(x)  ((void)x)
#define LIST_POISON1  (NULL)
#define LIST_POISON2  (NULL)

struct list_head{
    struct list_head *next, *prev;
};

struct hlist_node{
    struct hlist_node *next, **pprev;
};

struct hlist_head{
    struct hlist_node *first;
};

#define LIST_HEAD_INIT(name) { &(name), &(name) }

#define LIST_HEAD(name) \\
    struct list_head name = LIST_HEAD_INIT(name)

static void INIT_LIST_HEAD(struct list_head *list)
{
    list->next = list;
    list->prev = list;
}

/*
 * Insert a new entry between two known consecutive entries.
 *
 * This is only for internal list manipulation where we know
 * the prev/next entries already!
 */
#ifndef CONFIG_DEBUG_LIST
static void __list_add(struct list_head *node,
                  struct list_head *prev,
                  struct list_head *next)
{
    next->prev = node;
    node->next = next;
    node->prev = prev;
    prev->next = node;
}
#else
extern void __list_add(struct list_head *node,
                  struct list_head *prev,
                  struct list_head *next);
#endif

/**
 * list_add - add a new entry
 * @node: new entry to be added
 * @head: list head to add it after
 *
 * Insert a new entry after the specified head.
 * This is good for implementing stacks.
 */
static void list_add(struct list_head *node, struct list_head *head)
{
    __list_add(node, head, head->next);
}


/**
 * list_add_tail - add a new entry
 * @node: new entry to be added
 * @head: list head to add it before
 *
 * Insert a new entry before the specified head.
 * This is useful for implementing queues.
 */
static void list_add_tail(struct list_head *node, struct list_head *head)
{
    __list_add(node, head->prev, head);
}

/*
 * Delete a list entry by making the prev/next entries
 * point to each other.
 *
 * This is only for internal list manipulation where we know
 * the prev/next entries already!
 */
static void __list_del(struct list_head * prev, struct list_head * next)
{
    next->prev = prev;
    prev->next = next;
}

/**
 * list_del - deletes entry from list.
 * @entry: the element to delete from the list.
 * Note: list_empty() on entry does not return true after this, the entry is
 * in an undefined state.
 */
#ifndef CONFIG_DEBUG_LIST
static void __list_del_entry(struct list_head *entry)
{
    __list_del(entry->prev, entry->next);
}

static void list_del(struct list_head *entry)
{
    __list_del(entry->prev, entry->next);
    entry->next = LIST_POISON1;
    entry->prev = LIST_POISON2;
}
#else
extern void __list_del_entry(struct list_head *entry);
extern void list_del(struct list_head *entry);
#endif

/**
 * list_replace - replace old entry by new one
 * @old : the element to be replaced
 * @node : the new element to insert
 *
 * If @old was empty, it will be overwritten.
 */
static void list_replace(struct list_head *old,
                struct list_head *node)
{
    node->next = old->next;
    node->next->prev = node;
    node->prev = old->prev;
    node->prev->next = node;
}

static void list_replace_init(struct list_head *old,
                    struct list_head *node)
{
    list_replace(old, node);
    INIT_LIST_HEAD(old);
}

/**
 * list_del_init - deletes entry from list and reinitialize it.
 * @entry: the element to delete from the list.
 */
static void list_del_init(struct list_head *entry)
{
    __list_del_entry(entry);
    INIT_LIST_HEAD(entry);
}

/**
 * list_move - delete from one list and add as another\'s head
 * @list: the entry to move
 * @head: the head that will precede our entry
 */
static void list_move(struct list_head *list, struct list_head *head)
{
    __list_del_entry(list);
    list_add(list, head);
}

/**
 * list_move_tail - delete from one list and add as another\'s tail
 * @list: the entry to move
 * @head: the head that will follow our entry
 */
static void list_move_tail(struct list_head *list,
                  struct list_head *head)
{
    __list_del_entry(list);
    list_add_tail(list, head);
}

/**
 * list_is_last - tests whether @list is the last entry in list @head
 * @list: the entry to test
 * @head: the head of the list
 */
static int list_is_last(const struct list_head *list,
                const struct list_head *head)
{
    return list->next == head;
}

/**
 * list_empty - tests whether a list is empty
 * @head: the list to test.
 */
static int list_empty(const struct list_head *head)
{
    return head->next == head;
}

/**
 * list_empty_careful - tests whether a list is empty and not being modified
 * @head: the list to test
 *
 * Description:
 * tests whether a list is empty _and_ checks that no other CPU might be
 * in the process of modifying either member (next or prev)
 *
 * NOTE: using list_empty_careful() without synchronization
 * can only be safe if the only activity that can happen
 * to the list entry is list_del_init(). Eg. it cannot be used
 * if another CPU could re-list_add() it.
 */
static int list_empty_careful(const struct list_head *head)
{
    struct list_head *next = head->next;
    return (next == head) && (next == head->prev);
}

/**
 * list_rotate_left - rotate the list to the left
 * @head: the head of the list
 */
static void list_rotate_left(struct list_head *head)
{
    struct list_head *first;

    if (!list_empty(head)) {
        first = head->next;
        list_move_tail(first, head);
    }
}

/**
 * list_is_singular - tests whether a list has just one entry.
 * @head: the list to test.
 */
static int list_is_singular(const struct list_head *head)
{
    return !list_empty(head) && (head->next == head->prev);
}

static void __list_cut_position(struct list_head *list,
        struct list_head *head, struct list_head *entry)
{
    struct list_head *new_first = entry->next;
    list->next = head->next;
    list->next->prev = list;
    list->prev = entry;
    entry->next = list;
    head->next = new_first;
    new_first->prev = head;
}

/**
 * list_cut_position - cut a list into two
 * @list: a new list to add all removed entries
 * @head: a list with entries
 * @entry: an entry within head, could be the head itself
 *    and if so we won\'t cut the list
 *
 * This helper moves the initial part of @head, up to and
 * including @entry, from @head to @list. You should
 * pass on @entry an element you know is on @head. @list
 * should be an empty list or a list you do not care about
 * losing its data.
 *
 */
static void list_cut_position(struct list_head *list,
        struct list_head *head, struct list_head *entry)
{
    if (list_empty(head))
        return;
    if (list_is_singular(head) &&
        (head->next != entry && head != entry))
        return;
    if (entry == head)
        INIT_LIST_HEAD(list);
    else
        __list_cut_position(list, head, entry);
}

static void __list_splice(const struct list_head *list,
                 struct list_head *prev,
                 struct list_head *next)
{
    struct list_head *first = list->next;
    struct list_head *last = list->prev;

    first->prev = prev;
    prev->next = first;

    last->next = next;
    next->prev = last;
}

/**
 * list_splice - join two lists, this is designed for stacks
 * @list: the new list to add.
 * @head: the place to add it in the first list.
 */
static void list_splice(const struct list_head *list,
                struct list_head *head)
{
    if (!list_empty(list))
        __list_splice(list, head, head->next);
}

/**
 * list_splice_tail - join two lists, each list being a queue
 * @list: the new list to add.
 * @head: the place to add it in the first list.
 */
static void list_splice_tail(struct list_head *list,
                struct list_head *head)
{
    if (!list_empty(list))
        __list_splice(list, head->prev, head);
}

/**
 * list_splice_init - join two lists and reinitialise the emptied list.
 * @list: the new list to add.
 * @head: the place to add it in the first list.
 *
 * The list at @list is reinitialised
 */
static void list_splice_init(struct list_head *list,
                    struct list_head *head)
{
    if (!list_empty(list)) {
        __list_splice(list, head, head->next);
        INIT_LIST_HEAD(list);
    }
}

/**
 * list_splice_tail_init - join two lists and reinitialise the emptied list
 * @list: the new list to add.
 * @head: the place to add it in the first list.
 *
 * Each of the lists is a queue.
 * The list at @list is reinitialised
 */
static void list_splice_tail_init(struct list_head *list,
                     struct list_head *head)
{
    if (!list_empty(list)) {
        __list_splice(list, head->prev, head);
        INIT_LIST_HEAD(list);
    }
}

/**
 * list_entry - get the struct for this entry
 * @ptr:    the &struct list_head pointer.
 * @type:    the type of the struct this is embedded in.
 * @member:    the name of the list_struct within the struct.
 */
#define list_entry(ptr, type, member) \\
    container_of(ptr, type, member)

/**
 * list_first_entry - get the first element from a list
 * @ptr:    the list head to take the element from.
 * @type:    the type of the struct this is embedded in.
 * @member:    the name of the list_struct within the struct.
 *
 * Note, that list is expected to be not empty.
 */
#define list_first_entry(ptr, type, member) \\
    list_entry((ptr)->next, type, member)

/**
 * list_for_each    -    iterate over a list
 * @pos:    the &struct list_head to use as a loop cursor.
 * @head:    the head for your list.
 */
#define list_for_each(pos, head) \\
    for (pos = (head)->next; prefetch(pos->next), pos != (head); \\
            pos = pos->next)

/**
 * __list_for_each    -    iterate over a list
 * @pos:    the &struct list_head to use as a loop cursor.
 * @head:    the head for your list.
 *
 * This variant differs from list_for_each() in that it\'s the
 * simplest possible list iteration code, no prefetching is done.
 * Use this for code that knows the list to be very short (empty
 * or 1 entry) most of the time.
 */
#define __list_for_each(pos, head) \\
    for (pos = (head)->next; pos != (head); pos = pos->next)

/**
 * list_for_each_prev    -    iterate over a list backwards
 * @pos:    the &struct list_head to use as a loop cursor.
 * @head:    the head for your list.
 */
#define list_for_each_prev(pos, head) \\
    for (pos = (head)->prev; prefetch(pos->prev), pos != (head); \\
            pos = pos->prev)

/**
 * list_for_each_safe - iterate over a list safe against removal of list entry
 * @pos:    the &struct list_head to use as a loop cursor.
 * @n:        another &struct list_head to use as temporary storage
 * @head:    the head for your list.
 */
#define list_for_each_safe(pos, n, head) \\
    for (pos = (head)->next, n = pos->next; pos != (head); \\
        pos = n, n = pos->next)

/**
 * list_for_each_prev_safe - iterate over a list backwards safe against removal of list entry
 * @pos:    the &struct list_head to use as a loop cursor.
 * @n:        another &struct list_head to use as temporary storage
 * @head:    the head for your list.
 */
#define list_for_each_prev_safe(pos, n, head) \\
    for (pos = (head)->prev, n = pos->prev; \\
         prefetch(pos->prev), pos != (head); \\
         pos = n, n = pos->prev)

/**
 * list_for_each_entry    -    iterate over list of given type
 * @pos:    the type * to use as a loop cursor.
 * @head:    the head for your list.
 * @member:    the name of the list_struct within the struct.
 */
#define list_for_each_entry(pos, head, member)                \\
    for (pos = list_entry((head)->next, typeof(*pos), member);    \\
         prefetch(pos->member.next), &pos->member != (head);     \\
         pos = list_entry(pos->member.next, typeof(*pos), member))

/**
 * list_for_each_entry_reverse - iterate backwards over list of given type.
 * @pos:    the type * to use as a loop cursor.
 * @head:    the head for your list.
 * @member:    the name of the list_struct within the struct.
 */
#define list_for_each_entry_reverse(pos, head, member)            \\
    for (pos = list_entry((head)->prev, typeof(*pos), member);    \\
         prefetch(pos->member.prev), &pos->member != (head);     \\
         pos = list_entry(pos->member.prev, typeof(*pos), member))

/**
 * list_prepare_entry - prepare a pos entry for use in list_for_each_entry_continue()
 * @pos:    the type * to use as a start point
 * @head:    the head of the list
 * @member:    the name of the list_struct within the struct.
 *
 * Prepares a pos entry for use as a start point in list_for_each_entry_continue().
 */
#define list_prepare_entry(pos, head, member) \\
    ((pos) ? : list_entry(head, typeof(*pos), member))

/**
 * list_for_each_entry_continue - continue iteration over list of given type
 * @pos:    the type * to use as a loop cursor.
 * @head:    the head for your list.
 * @member:    the name of the list_struct within the struct.
 *
 * Continue to iterate over list of given type, continuing after
 * the current position.
 */
#define list_for_each_entry_continue(pos, head, member)         \\
    for (pos = list_entry(pos->member.next, typeof(*pos), member);    \\
         prefetch(pos->member.next), &pos->member != (head);    \\
         pos = list_entry(pos->member.next, typeof(*pos), member))

/**
 * list_for_each_entry_continue_reverse - iterate backwards from the given point
 * @pos:    the type * to use as a loop cursor.
 * @head:    the head for your list.
 * @member:    the name of the list_struct within the struct.
 *
 * Start to iterate over list of given type backwards, continuing after
 * the current position.
 */
#define list_for_each_entry_continue_reverse(pos, head, member)        \\
    for (pos = list_entry(pos->member.prev, typeof(*pos), member);    \\
         prefetch(pos->member.prev), &pos->member != (head);    \\
         pos = list_entry(pos->member.prev, typeof(*pos), member))

/**
 * list_for_each_entry_from - iterate over list of given type from the current point
 * @pos:    the type * to use as a loop cursor.
 * @head:    the head for your list.
 * @member:    the name of the list_struct within the struct.
 *
 * Iterate over list of given type, continuing from current position.
 */
#define list_for_each_entry_from(pos, head, member)             \\
    for (; prefetch(pos->member.next), &pos->member != (head);    \\
         pos = list_entry(pos->member.next, typeof(*pos), member))

/**
 * list_for_each_entry_safe - iterate over list of given type safe against removal of list entry
 * @pos:    the type * to use as a loop cursor.
 * @n:        another type * to use as temporary storage
 * @head:    the head for your list.
 * @member:    the name of the list_struct within the struct.
 */
#define list_for_each_entry_safe(pos, n, head, member)            \\
    for (pos = list_entry((head)->next, typeof(*pos), member),    \\
        n = list_entry(pos->member.next, typeof(*pos), member);    \\
         &pos->member != (head);                     \\
         pos = n, n = list_entry(n->member.next, typeof(*n), member))

/**
 * list_for_each_entry_safe_continue - continue list iteration safe against removal
 * @pos:    the type * to use as a loop cursor.
 * @n:        another type * to use as temporary storage
 * @head:    the head for your list.
 * @member:    the name of the list_struct within the struct.
 *
 * Iterate over list of given type, continuing after current point,
 * safe against removal of list entry.
 */
#define list_for_each_entry_safe_continue(pos, n, head, member)         \\
    for (pos = list_entry(pos->member.next, typeof(*pos), member),         \\
        n = list_entry(pos->member.next, typeof(*pos), member);        \\
         &pos->member != (head);                        \\
         pos = n, n = list_entry(n->member.next, typeof(*n), member))

/**
 * list_for_each_entry_safe_from - iterate over list from current point safe against removal
 * @pos:    the type * to use as a loop cursor.
 * @n:        another type * to use as temporary storage
 * @head:    the head for your list.
 * @member:    the name of the list_struct within the struct.
 *
 * Iterate over list of given type from current point, safe against
 * removal of list entry.
 */
#define list_for_each_entry_safe_from(pos, n, head, member)             \\
    for (n = list_entry(pos->member.next, typeof(*pos), member);        \\
         &pos->member != (head);                        \\
         pos = n, n = list_entry(n->member.next, typeof(*n), member))

/**
 * list_for_each_entry_safe_reverse - iterate backwards over list safe against removal
 * @pos:    the type * to use as a loop cursor.
 * @n:        another type * to use as temporary storage
 * @head:    the head for your list.
 * @member:    the name of the list_struct within the struct.
 *
 * Iterate backwards over list of given type, safe against removal
 * of list entry.
 */
#define list_for_each_entry_safe_reverse(pos, n, head, member)        \\
    for (pos = list_entry((head)->prev, typeof(*pos), member),    \\
        n = list_entry(pos->member.prev, typeof(*pos), member);    \\
         &pos->member != (head);                     \\
         pos = n, n = list_entry(n->member.prev, typeof(*n), member))

/**
 * list_safe_reset_next - reset a stale list_for_each_entry_safe loop
 * @pos:    the loop cursor used in the list_for_each_entry_safe loop
 * @n:        temporary storage used in list_for_each_entry_safe
 * @member:    the name of the list_struct within the struct.
 *
 * list_safe_reset_next is not safe to use in general if the list may be
 * modified concurrently (eg. the lock is dropped in the loop body). An
 * exception to this is if the cursor element (pos) is pinned in the list,
 * and list_safe_reset_next is called after re-taking the lock and before
 * completing the current iteration of the loop body.
 */
#define list_safe_reset_next(pos, n, member)                \\
    n = list_entry(pos->member.next, typeof(*pos), member)

/*
 * Double linked lists with a single pointer list head.
 * Mostly useful for hash tables where the two pointer list head is
 * too wasteful.
 * You lose the ability to access the tail in O(1).
 */

#define HLIST_HEAD_INIT { .first = NULL }
#define HLIST_HEAD(name) struct hlist_head name = {  .first = NULL }
#define INIT_HLIST_HEAD(ptr) ((ptr)->first = NULL)
static void INIT_HLIST_NODE(struct hlist_node *h)
{
    h->next = NULL;
    h->pprev = NULL;
}

static int hlist_unhashed(const struct hlist_node *h)
{
    return !h->pprev;
}

static int hlist_empty(const struct hlist_head *h)
{
    return !h->first;
}

static void __hlist_del(struct hlist_node *n)
{
    struct hlist_node *next = n->next;
    struct hlist_node **pprev = n->pprev;
    *pprev = next;
    if (next)
        next->pprev = pprev;
}

static void hlist_del(struct hlist_node *n)
{
    __hlist_del(n);
    n->next = LIST_POISON1;
    n->pprev = LIST_POISON2;
}

static void hlist_del_init(struct hlist_node *n)
{
    if (!hlist_unhashed(n)) {
        __hlist_del(n);
        INIT_HLIST_NODE(n);
    }
}

static void hlist_add_head(struct hlist_node *n, struct hlist_head *h)
{
    struct hlist_node *first = h->first;
    n->next = first;
    if (first)
        first->pprev = &n->next;
    h->first = n;
    n->pprev = &h->first;
}

/* next must be != NULL */
static void hlist_add_before(struct hlist_node *n,
                    struct hlist_node *next)
{
    n->pprev = next->pprev;
    n->next = next;
    next->pprev = &n->next;
    *(n->pprev) = n;
}

static void hlist_add_after(struct hlist_node *n,
                    struct hlist_node *next)
{
    next->next = n->next;
    n->next = next;
    next->pprev = &n->next;

    if(next->next)
        next->next->pprev  = &next->next;
}

/* after that we\'ll appear to be on some hlist and hlist_del will work */
static void hlist_add_fake(struct hlist_node *n)
{
    n->pprev = &n->next;
}

/*
 * Move a list from one list head to another. Fixup the pprev
 * reference of the first entry if it exists.
 */
static void hlist_move_list(struct hlist_head *old,
                   struct hlist_head *node)
{
    node->first = old->first;
    if (node->first)
        node->first->pprev = &node->first;
    old->first = NULL;
}

#define hlist_entry(ptr, type, member) container_of(ptr,type,member)

#define hlist_for_each(pos, head) \\
    for (pos = (head)->first; pos && ({ prefetch(pos->next); 1; }); \\
         pos = pos->next)

#define hlist_for_each_safe(pos, n, head) \\
    for (pos = (head)->first; pos && ({ n = pos->next; 1; }); \\
         pos = n)

/**
 * hlist_for_each_entry    - iterate over list of given type
 * @tpos:    the type * to use as a loop cursor.
 * @pos:    the &struct hlist_node to use as a loop cursor.
 * @head:    the head for your list.
 * @member:    the name of the hlist_node within the struct.
 */
#define hlist_for_each_entry(tpos, pos, head, member)             \\
    for (pos = (head)->first;                     \\
         pos && ({ prefetch(pos->next); 1;}) &&             \\
        ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \\
         pos = pos->next)

/**
 * hlist_for_each_entry_continue - iterate over a hlist continuing after current point
 * @tpos:    the type * to use as a loop cursor.
 * @pos:    the &struct hlist_node to use as a loop cursor.
 * @member:    the name of the hlist_node within the struct.
 */
#define hlist_for_each_entry_continue(tpos, pos, member)         \\
    for (pos = (pos)->next;                         \\
         pos && ({ prefetch(pos->next); 1;}) &&             \\
        ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \\
         pos = pos->next)

/**
 * hlist_for_each_entry_from - iterate over a hlist continuing from current point
 * @tpos:    the type * to use as a loop cursor.
 * @pos:    the &struct hlist_node to use as a loop cursor.
 * @member:    the name of the hlist_node within the struct.
 */
#define hlist_for_each_entry_from(tpos, pos, member)             \\
    for (; pos && ({ prefetch(pos->next); 1;}) &&             \\
        ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \\
         pos = pos->next)

/**
 * hlist_for_each_entry_safe - iterate over list of given type safe against removal of list entry
 * @tpos:    the type * to use as a loop cursor.
 * @pos:    the &struct hlist_node to use as a loop cursor.
 * @n:        another &struct hlist_node to use as temporary storage
 * @head:    the head for your list.
 * @member:    the name of the hlist_node within the struct.
 */
#define hlist_for_each_entry_safe(tpos, pos, n, head, member)          \\
    for (pos = (head)->first;                     \\
         pos && ({ n = pos->next; 1; }) &&                  \\
        ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \\
         pos = n)

#endif

View Code

//DualCircleList.h

#ifndef _DUALCIRCLELIST_H_
#define _DUALCIRCLELIST_H_

#include "LinuxList.h"
#include "DualLinkList.h"

namespace DTLib
{

template <typename T>
class DualCircleList : protected DualLinkList<T>
{
protected:
    //自定义链表结点类型
    struct Node : public Object
    {
        list_head head;
        T value;
    };


    list_head* m_current;
    int m_step;

    list_head m_header;

    list_head* position(int index) const
    {
        //const对象不能对成员变量取地址，需去掉const限定
        list_head* ret = const_cast<list_head*>(&m_header);

        for(int i=0; i<index; i++){
            ret = ret->next;
        }

        return ret;
    }

    int mod(int value)
    {
        return (this->m_length==0) ? 0: (value % this->m_length);
    }

public:

    DualCircleList()
    {
        this->m_length = 0;
        m_current = NULL;
        m_step = 1;

        //初始化Linux内核链表，形成循环链表
        INIT_LIST_HEAD(&this->m_header);
    }

    bool insert(const T& elem)
    {
        return insert(this->m_length, elem);
    }

    bool insert(int index, const T& elem)
    {
        bool ret = (0<=index);

        if (ret){
            index = index % (this->m_length + 1);

            Node* node = new Node();
            if(node != NULL){
                node->value = elem;

                list_add_tail(&node->head, position(index)->next);

                this->m_length++;

            }else{
                THROW_EXCEPTION(NotEnoughMemoryException, "No memory to insert new element...");
            }
        }

        return ret;
    }

    bool remove(int index)
    {
        bool ret = true;

        index = mod(index);

        ret = ((0<=index) && (index<this->m_length));

        if(ret){
            list_head* toDel = position(index)->next;

            if(m_current == toDel){
                m_current = toDel->next;
            }

            list_del(toDel);

            this->m_length--;

            delete list_entry(toDel, Node, head);
        }

        return ret;
    }

    bool set(int index, const T& elem) //O(n)
    {
        bool ret = true;

        index = mod(index);

        ret = (0 <= index) && (index < this->m_length);

        《链表》之带头双向循环链表

 C语言实现双向非循环链表的逆序打印
 C语言实现双向非循环链表的节点插入
 C语言实现双向非循环链表的清空
 数据结构开发(11)：双向循环链表的实现
 双向循环链表