用图描述一下一个稍微复杂的链表数据结构

数据结构定义如下：

#define TASK_NAME 128
#define POL_NAME 128
#define SAVE_PATH 128
typedef struct
{
    unsigned int     pol_id;
    char          pol_name[POL_NAME];
    unsigned int    pol_type;//configfile scripts, crontab or file attribute
    char        save_path[SAVE_PATH];
}policy_t;

typedef struct _dev_task_t
{
    unsigned int index;//id for table t_task_result
    unsigned int host_id; //host id in t_dev
    unsigned int host_addr; //host address
    struct _dev_task_t * next;
}dev_task_t;

typedef struct _hosts_policy_t
{
    policy_t pol;
    dev_task_t * dev_list;
    struct _hosts_policy_t * next;
}hosts_policy_t;

typedef struct _task_t
{
    unsigned int task_id;
    char     task_name[TASK_NAME];
    time_t     borthday;
    hosts_policy_t * pol_list;
    struct _task_t * next;
}task_t;

用下图来表示:

初始化代码也比较复杂，从数据库中加载:

int    DbMonitor::load_host_policy (task_t* pt)
{
    int nRet = 0;
    task_t * pTask = pt;
    unsigned int old_pol_id = 0;
    //loop task list
    while (pTask)
    {
        char szSQL[800] = {0};
        pTask->pol_list = NULL;
        printf ("For task [%s]\n", pTask->task_name);
        cm_log.LogMessage (CONFIG_SERVER_LOG, "[%s:%d] for task [%s]\n", __FILE__, __LINE__, pTask->task_name);
        //load policy information for each task from table 't_task_result'
        sprintf (szSQL,
        "select t_task_result.Id, t_task_result.f_host_id, t_dev.dev_ip, t_task_result.f_pol_id, t_policy.name, t_policy.type, t_policy.savepath from t_task_result, t_dev, t_policy where t_task_result.f_task_id = %u and t_dev.Id = t_task_result.f_host_id and t_task_result.f_pol_id = t_policy.Id order by t_task_result.f_pol_id desc",
            pTask->task_id);
        cm_log.LogMessage (CONFIG_SERVER_LOG, "[%s:%d]try to run sql[%s]\n", __FILE__, __LINE__, szSQL);

        mysqlpp::Query query = m_pConnect->query(szSQL);
        if (mysqlpp::StoreQueryResult res = query.store())
        {
            cm_log.LogMessage(CONFIG_SERVER_LOG,
            "[%s:%d] success run sql[%s]\n", __FILE__, __LINE__, szSQL);
            //get each item
            mysqlpp::StoreQueryResult::const_iterator it;

            for (it = res.begin(); it != res.end(); ++it)
            {
                mysqlpp::Row row = *it;
                dev_task_t * new_dev = NULL;

                unsigned int tmp_id = atol(((string)row[3]).c_str());

                //new policy comes
                if (old_pol_id != tmp_id)
                {
                    hosts_policy_t * new_pol = new hosts_policy_t;
                    old_pol_id = tmp_id;

                    if (!new_pol)
                    {

                            cm_log.LogMessage(CONFIG_SERVER_LOG,
                        "[%s:%d] malloc new hosts_policy_t for task [%s] failed\n",
                            __FILE__, __LINE__, pTask->task_name);
                            return -1;

                    }

                    memset (new_pol, 0, sizeof(hosts_policy_t));
                    new_pol->next = NULL;
                    new_pol->pol.pol_id = tmp_id;
                    new_pol->pol.pol_type = atol(((string)row[5]).c_str());
                    sprintf (new_pol->pol.pol_name, "%s", ((string)row[4]).c_str() );
                    sprintf (new_pol->pol.save_path, "%s", ((string)row[6]).c_str() );
                    new_pol->dev_list = NULL;
                    if (!(pTask->pol_list))
                    {
                        pTask->pol_list = new_pol;
                    }else
                    {
                        new_pol->next = pTask->pol_list;
                        pTask->pol_list = new_pol;
                    }
                }

                //then add new node of device
                new_dev = new dev_task_t;
                if (!new_dev)
                {

                    cm_log.LogMessage(CONFIG_SERVER_LOG,
                    "[%s:%d] malloc new dev_task_t for task [%s]policy[%s] failed\n",
                    __FILE__, __LINE__, pTask->task_name, pTask->pol_list->pol.pol_name);
                    return -1;
                }
                memset (new_dev, 0, sizeof(dev_task_t));
                new_dev->next = NULL;

                new_dev->index = atol(((string)row[0]).c_str());
                new_dev->host_id = atol(((string)row[1]).c_str());
                new_dev->host_addr = atol(((string)row[2]).c_str());

                if (!pTask->pol_list->dev_list)
                {
                    pTask->pol_list->dev_list = new_dev;
                }else
                {
                    new_dev->next = pTask->pol_list->dev_list;
                    pTask->pol_list->dev_list = new_dev;
                }
                nRet++;
            }
        }//end of result list
        pTask = pTask->next;

    }
    return nRet;
}