How does Thinkphp distinguish the mobile terminal and PC terminal through an entry file?

<?php
// 检测PHP环境
if(version_compare(PHP_VERSION,&#39;5.3.0&#39;,&#39;<&#39;)) die(&#39;require PHP > 5.3.0 !&#39;);
// 开启调试模式 建议开发阶段开启 部署阶段注释或者设为false
define(&#39;APP_DEBUG&#39;,True);
define(&#39;MULTI_MODULE&#39;, false);
// 获取当前文件所在的目录
define(&#39;DKSITE_TSDIR&#39;, dirname(__FILE__));
// 定义应用目录
define(&#39;APP_PATH&#39;,DKSITE_TSDIR.&#39;/Application/&#39;);
//
function is_mobile(){ 
  $user_agent = $_SERVER[&#39;HTTP_USER_AGENT&#39;];
  $mobile_agents = Array("240x320","acer","acoon","acs-","abacho","ahong","airness","alcatel","amoi","android","anywhereyougo.com","applewebkit/525","applewebkit/532","asus","audio","au-mic","avantogo","becker","benq","bilbo","bird","blackberry","blazer","bleu","cdm-","compal","coolpad","danger","dbtel","dopod","elaine","eric","etouch","fly ","fly_","fly-","go.web","goodaccess","gradiente","grundig","haier","hedy","hitachi","htc","huawei","hutchison","inno","ipad","ipaq","ipod","jbrowser","kddi","kgt","kwc","lenovo","lg ","lg2","lg3","lg4","lg5","lg7","lg8","lg9","lg-","lge-","lge9","longcos","maemo","mercator","meridian","micromax","midp","mini","mitsu","mmm","mmp","mobi","mot-","moto","nec-","netfront","newgen","nexian","nf-browser","nintendo","nitro","nokia","nook","novarra","obigo","palm","panasonic","pantech","philips","phone","pg-","playstation","pocket","pt-","qc-","qtek","rover","sagem","sama","samu","sanyo","samsung","sch-","scooter","sec-","sendo","sgh-","sharp","siemens","sie-","softbank","sony","spice","sprint","spv","symbian","tablet","talkabout","tcl-","teleca","telit","tianyu","tim-","toshiba","tsm","up.browser","utec","utstar","verykool","virgin","vk-","voda","voxtel","vx","wap","wellco","wig browser","wii","windows ce","wireless","xda","xde","zte"); 
  $is_mobile = false; 
  foreach ($mobile_agents as $device) {//这里把值遍历一遍，用于查找是否有上述字符串出现过 
    if (stristr($user_agent, $device)) { //stristr 查找访客端信息是否在上述数组中，不存在即为PC端。 
      $is_mobile = true; 
      break; 
    } 
  } 
  return $is_mobile; 
}
//判断
if(is_mobile()){
 echo &#39;您当前是在：手机端&#39;; 
  // 手机端模块
 define(&#39;BIND_MODULE&#39;,&#39;Mobile&#39;);
}else{ 
 echo &#39;您当前是在：pc端&#39;;
  // pc端前台模块
 define(&#39;BIND_MODULE&#39;,&#39;Home&#39;);      
} 
// 引入ThinkPHP入口文件
require dirname(__FILE__).&#39;/ThinkPHP/ThinkPHP.php&#39;;