使用未定义常量nd_mobile怎么办？

HYPHP详细调试页

错误信息: 使用未定义的常量 ND_MOBILE_V - 未定义的常量名: 'ND_MOBILE_V' (this will throw an Error in a future version of PHP)

发生错误文件: /storage/emulated/0/BDY_DOWNLOAD/吾乃zyx/bbs/Tmp/View_index_index_40e92011fb72922393de88dc8ba114aa.php

出错行数: 20

出现错误的地方

行数 代码内容

16: <meta name="viewport" content="width=device-width,initial-scale=1,user-scalable=no">

17: <link rel="alternate icon" type="image/png" href="<?php echo WWW;?>favicon.ico">

18: <link rel="apple-touch-icon-precomposed" href="<?php echo WWW;?>favicon.ico">

19: <!-- 引入样式 -->

20: <link rel="stylesheet" href="<?php echo WWW;?>View/nd_mobile/css/ydui.css?var=<?php echo ND_MOBILE_V;?>">

21: <link href="https://cdn.bootcss.com/Swiper/4.4.2/css/swiper.min.css" rel="stylesheet">

22: <link rel="stylesheet" href="<?php echo WWW;?>View/nd_mobile/css/style.css?var=<?php echo ND_MOBILE_V;?>">

23: <link rel="stylesheet" href="//at.alicdn.com/t/font_617807_ce25xljp8w.css">

24: <!-- 引入rem自适应类库 --