获取当天00:00:00时间值秒数

 //获取今天00:00:00的UNIX时间值
    time_t cur_time;
    cur_time = time(NULL); //
    struct tm *time_tm;
    time_tm = localtime(&cur_time);
    time_tm->tm_hour=0;
    time_tm->tm_min=0;
    time_tm->tm_sec=0;
    //printf("%d\n",(unsigned int)mktime(time_tm));
    uint32_t today_begin = mktime(time_tm);