引言

鏈表和數(shù)組是兩種不同的數(shù)據(jù)存儲方式。鏈表是一種物理存儲單元上非連續(xù)、非順序的存儲結構，數(shù)據(jù)元素的邏輯順序是通過鏈表中的指針鏈接次序實現(xiàn)的。數(shù)組是把具有相同類型的若干元素按有序的形式組織起來的一種形式，數(shù)組中的各元素的存儲是有先后順序的，它們在內存中按照這個先后順序連續(xù)存放在一起。本文將對這兩種存儲方式的優(yōu)缺點做一個大致的介紹，并詳細介紹鏈表在操作系統(tǒng)中定義和使用的方式。

一、鏈表和數(shù)組

鏈表是鏈式的存儲結構，數(shù)組是順序的存儲結構，其在內存存儲上的不同形式決定了其各自的特點。

鏈表通過指針來鏈接元素，鏈表中的結點順序關系由指針來體現(xiàn)；數(shù)組將元素按次序依次存儲，元素順序關系由元素在數(shù)組中的位置（下標）確定。

鏈表節(jié)點的存儲單元在程序執(zhí)行時動態(tài)向系統(tǒng)申請，鏈表的結點個數(shù)可按需要增減；數(shù)組元素的存儲單元在數(shù)組定義時分配，其元素個數(shù)是固定的，對于不是固定長度的列表，用可能最大長度的數(shù)組來描述。

鏈表插入刪除元素不需要移動元素，且較為容易實現(xiàn)長度擴充，但是尋找某個元素較為困難；數(shù)組尋找某個元素較為簡單，但插入與刪除比較復雜。

總體來說，鏈表使用指針將一系列數(shù)據(jù)節(jié)點鏈接成數(shù)據(jù)鏈，相對于數(shù)組，它具有良好的動態(tài)性，建立鏈表時不需要提前知道數(shù)據(jù)量，可以隨時分配空間，可以高效地在鏈表中的任意位置插入或者刪除數(shù)據(jù)。操作系統(tǒng)中存在著大量的基礎數(shù)據(jù)結構鏈表和鏈表項，理解鏈表對理解操作系統(tǒng)至關重要。

二、單向鏈表和雙向鏈表

通常鏈表數(shù)據(jù)結構包含兩部分，一部分是數(shù)據(jù)域，用于存儲數(shù)據(jù)；另外一部分是指針域，用于建立與其它節(jié)點的關系。鏈表項中可以包含一個指向下一個鏈表項的指針而不包含指向上一個鏈表的指針，也可以兩者都包含，前者稱為單向鏈表，后者為雙向鏈表。

OneOS 物聯(lián)網(wǎng)操作系統(tǒng)中提供的鏈表不包含數(shù)據(jù)域，使用時不是在鏈表結構中包含數(shù)據(jù)，而是在用戶的數(shù)據(jù)結構中包含鏈表節(jié)點，操作系統(tǒng)中提供了雙向鏈表及單向鏈表的一些比較通用的操作接口。

2.1 單向鏈表

OneOS 操作系統(tǒng)中的單向鏈表包含一個節(jié)點指針，這個節(jié)點指針指向下一個節(jié)點。OneOS 操作系統(tǒng)中的單向鏈表是一個非循環(huán)鏈表，單向鏈表本身首尾并非相連，單向鏈表中的最后一個節(jié)點指向 OS_NULL（循環(huán)鏈表單向鏈表中的最后一個節(jié)點指向單向鏈表中的第一個節(jié)點），其示意圖如下所示。

OneOS 操作系統(tǒng)中單向鏈表節(jié)點的結構體如下所示。

struct os_slist_node
{
    struct os_slist_node *next;     /* Point to next node */
};

2.2 雙向鏈表

OneOS 操作系統(tǒng)中的雙向鏈表包含了兩個結點指針，一個節(jié)點指針指向下一個節(jié)點，另一個節(jié)點指針指向上一個節(jié)點。OneOS 操作系統(tǒng)中的雙向鏈表是一個循環(huán)鏈表，雙向鏈表本身首尾相連，雙向鏈表最后一個節(jié)點的指向下一個節(jié)點的節(jié)點指針指向第一個節(jié)點，第一個節(jié)點的指向上一個節(jié)點的節(jié)點指針指向最后一個節(jié)點，其示意圖如下所示。

OneOS 操作系統(tǒng)中雙向鏈表節(jié)點的結構體如下所示。

struct os_list_node
{
    struct os_list_node *next;      /* Point to next node */
    struct os_list_node *prev;      /* point to previous node */
};

三、應用示例

單向鏈表應用示例

#include #include #include #include #include #include #include 
#define TEST_TAG        "TEST"
#define STUDENT_NUM     10#define TEST_NAME_MAX   16
char *name[STUDENT_NUM] = {"xiaoming", "xiaohua", "xiaoqiang", "xiaoli", "xiaofang", "zhangsan", "lisi", "wangwu", "zhaoliu", "qianqi"};uint32_t score[STUDENT_NUM] = {70, 83, 68, 80, 88, 86, 78, 92, 55, 82};
struct student_score
{
    os_slist_node_t list_node;
    char name[TEST_NAME_MAX];
    uint32_t id;
    uint32_t score;
};typedef struct student_score student_score_t;
void single_list_sample(void)
{
    uint32_t i = 0;
    os_slist_node_t list_head = OS_SLIST_INIT(list_head);
    student_score_t *data;
    os_slist_node_t *node_temp;
    os_slist_node_t *node;

    LOG_W(TEST_TAG, "single_list_sample insert data");
    for (i = 0; i < STUDENT_NUM; i++)
    {
        data = os_malloc(sizeof(student_score_t));
        data->id = i;
        memset(data->name, 0, TEST_NAME_MAX);
        strncpy(data->name, name[i], TEST_NAME_MAX);
        data->score = score[i];
        if (i < STUDENT_NUM/2)
        {
            LOG_W(TEST_TAG, "insert tail -- id:%d score:%d name:%s", data->id, data->score, data->name);
            os_slist_add_tail(&list_head, &data->list_node);
        }
        else
        {
            LOG_W(TEST_TAG, "insert front-- id:%d score:%d name:%s", data->id, data->score, data->name);
            os_slist_add(&list_head, &data->list_node);
        }
    }

    LOG_W(TEST_TAG, "single_list_sample show result");
    os_slist_for_each(node, &list_head)
    {
        data = os_slist_entry(node, student_score_t, list_node);
        LOG_W(TEST_TAG, "id:%d score:%d name:%s", data->id, data->score, data->name);
    }

    LOG_W(TEST_TAG, "single_list_sample list_len is:%d", os_slist_len(&list_head));
    LOG_W(TEST_TAG, "single_list_sample delete the score less than 60");
    os_slist_for_each_safe(node, node_temp, &list_head)
    {
        data = os_slist_entry(node, student_score_t, list_node);
        if (data->score < 60)
        {
            LOG_W(TEST_TAG, "delete -- id:%d score:%d name:%s", data->id, data->score, data->name);
            os_slist_del(&list_head, &data->list_node);
            os_free(data);
        }
    }

    LOG_W(TEST_TAG, "single_list_sample list_len is:%d", os_slist_len(&list_head));
    LOG_W(TEST_TAG, "single_list_sample show result, and then delete");
    os_slist_for_each_safe(node, node_temp, &list_head)
    {
        data = os_slist_entry(node, student_score_t, list_node);
        LOG_W(TEST_TAG, "delete -- id:%d score:%d name:%s", data->id, data->score, data->name);
        os_slist_del(&list_head, &data->list_node);
        os_free(data);
    }

    LOG_W(TEST_TAG, "single_list_sample list_len is:%d", os_slist_len(&list_head));
}

SH_CMD_EXPORT(test_single_list, single_list_sample, "test single list");

sh>test_single_list
W/TEST: single_list_sample insert data
W/TEST: insert tail -- id:0 score:70 name:xiaoming
W/TEST: insert tail -- id:1 score:83 name:xiaohua
W/TEST: insert tail -- id:2 score:68 name:xiaoqiang
W/TEST: insert tail -- id:3 score:80 name:xiaoli
W/TEST: insert tail -- id:4 score:88 name:xiaofang
W/TEST: insert front-- id:5 score:86 name:zhangsan
W/TEST: insert front-- id:6 score:78 name:lisi
W/TEST: insert front-- id:7 score:92 name:wangwu
W/TEST: insert front-- id:8 score:55 name:zhaoliu
W/TEST: insert front-- id:9 score:82 name:qianqi
W/TEST: single_list_sample show result
W/TEST: id:9 score:82 name:qianqi
W/TEST: id:8 score:55 name:zhaoliu
W/TEST: id:7 score:92 name:wangwu
W/TEST: id:6 score:78 name:lisi
W/TEST: id:5 score:86 name:zhangsan
W/TEST: id:0 score:70 name:xiaoming
W/TEST: id:1 score:83 name:xiaohua
W/TEST: id:2 score:68 name:xiaoqiang
W/TEST: id:3 score:80 name:xiaoli
W/TEST: id:4 score:88 name:xiaofang
W/TEST: single_list_sample list_len is:10
W/TEST: single_list_sample delete the score less than 60
W/TEST: delete -- id:8 score:55 name:zhaoliu
W/TEST: single_list_sample list_len is:9
W/TEST: single_list_sample show result, and then delete
W/TEST: delete -- id:9 score:82 name:qianqi
W/TEST: delete -- id:7 score:92 name:wangwu
W/TEST: delete -- id:6 score:78 name:lisi
W/TEST: delete -- id:5 score:86 name:zhangsan
W/TEST: delete -- id:0 score:70 name:xiaoming
W/TEST: delete -- id:1 score:83 name:xiaohua
W/TEST: delete -- id:2 score:68 name:xiaoqiang
W/TEST: delete -- id:3 score:80 name:xiaoli
W/TEST: delete -- id:4 score:88 name:xiaofang
W/TEST: single_list_sample list_len is:0

#include #include #include #include #include #include #include 
#define TEST_TAG        "TEST"
#define STUDENT_NUM     10#define TEST_NAME_MAX   16
char *name[STUDENT_NUM] = {"xiaoming", "xiaohua", "xiaoqiang", "xiaoli", "xiaofang", "zhangsan", "lisi", "wangwu", "zhaoliu", "qianqi"};uint32_t score[STUDENT_NUM] = {70, 83, 68, 80, 88, 86, 78, 92, 55, 82};
struct student_score
{
    os_list_node_t list_node;
    char name[TEST_NAME_MAX];
    uint32_t id;
    uint32_t score;
};typedef struct student_score student_score_t;
void list_sample(void)
{
    uint32_t i = 0;
    os_list_node_t list_head = OS_LIST_INIT(list_head);
    student_score_t *data;
    student_score_t *data_temp;
    os_list_node_t *node;
    os_list_node_t *node_temp;

    LOG_W(TEST_TAG, "list_sample insert data");
    for (i = 0; i < STUDENT_NUM; i++)
    {
        data = os_malloc(sizeof(student_score_t));
        data->id = i;
        memset(data->name, 0, TEST_NAME_MAX);
        strncpy(data->name, name[i], TEST_NAME_MAX);
        data->score = score[i];
        if (i < STUDENT_NUM/2)
        {
            LOG_W(TEST_TAG, "insert tail -- id:%d score:%d name:%s", data->id, data->score, data->name);
            os_list_add_tail(&list_head, &data->list_node);
        }
        else
        {
            LOG_W(TEST_TAG, "insert front-- id:%d score:%d name:%s", data->id, data->score, data->name);
            os_list_add(&list_head, &data->list_node);
        }
    }

    LOG_W(TEST_TAG, "list_sample show result");
    os_list_for_each_entry(data, &list_head, student_score_t, list_node)
    {
        LOG_W(TEST_TAG, "id:%d score:%d name:%s", data->id, data->score, data->name);
    }

    LOG_W(TEST_TAG, "list_sample list_len is:%d", os_list_len(&list_head));
    LOG_W(TEST_TAG, "list_sample delete the score less than 60");
    os_list_for_each_entry_safe(data, data_temp, &list_head, student_score_t, list_node)
    {
        if (data->score < 60)
        {
            LOG_W(TEST_TAG, "delete -- id:%d score:%d name:%s", data->id, data->score, data->name);
            os_list_del(&data->list_node);
            os_free(data);
        }
    }

    LOG_W(TEST_TAG, "list_sample list_len is:%d", os_list_len(&list_head));
    LOG_W(TEST_TAG, "list_sample show result, and then delete");
    os_list_for_each_safe(node, node_temp, &list_head)
    {
        data = os_list_entry(node, student_score_t, list_node);
        LOG_W(TEST_TAG, "delete -- id:%d score:%d name:%s", data->id, data->score, data->name);
        os_list_del(&data->list_node);
        os_free(data);
    }

    LOG_W(TEST_TAG, "list_sample list_len is:%d", os_list_len(&list_head));
}

SH_CMD_EXPORT(test_list, list_sample, "test list");

sh>test_list
W/TEST: list_sample insert data
W/TEST: insert tail -- id:0 score:70 name:xiaoming
W/TEST: insert tail -- id:1 score:83 name:xiaohua
W/TEST: insert tail -- id:2 score:68 name:xiaoqiang
W/TEST: insert tail -- id:3 score:80 name:xiaoli
W/TEST: insert tail -- id:4 score:88 name:xiaofang
W/TEST: insert front-- id:5 score:86 name:zhangsan
W/TEST: insert front-- id:6 score:78 name:lisi
W/TEST: insert front-- id:7 score:92 name:wangwu
W/TEST: insert front-- id:8 score:55 name:zhaoliu
W/TEST: insert front-- id:9 score:82 name:qianqi
W/TEST: list_sample show result
W/TEST: id:9 score:82 name:qianqi
W/TEST: id:8 score:55 name:zhaoliu
W/TEST: id:7 score:92 name:wangwu
W/TEST: id:6 score:78 name:lisi
W/TEST: id:5 score:86 name:zhangsan
W/TEST: id:0 score:70 name:xiaoming
W/TEST: id:1 score:83 name:xiaohua
W/TEST: id:2 score:68 name:xiaoqiang
W/TEST: id:3 score:80 name:xiaoli
W/TEST: id:4 score:88 name:xiaofang
W/TEST: list_sample list_len is:10
W/TEST: list_sample delete the score less than 60
W/TEST: delete -- id:8 score:55 name:zhaoliu
W/TEST: list_sample list_len is:9
W/TEST: list_sample show result, and then delete
W/TEST: delete -- id:9 score:82 name:qianqi
W/TEST: delete -- id:7 score:92 name:wangwu
W/TEST: delete -- id:6 score:78 name:lisi
W/TEST: delete -- id:5 score:86 name:zhangsan
W/TEST: delete -- id:0 score:70 name:xiaoming
W/TEST: delete -- id:1 score:83 name:xiaohua
W/TEST: delete -- id:2 score:68 name:xiaoqiang
W/TEST: delete -- id:3 score:80 name:xiaoli
W/TEST: delete -- id:4 score:88 name:xiaofang
W/TEST: list_sample list_len is:0