我这个有错误吗？为啥放到thread_list.inc.htm里，不管用呢，判断函数放到哪个文件里这里才能正常调用？

<!--uuuuuuuuuuu--->

<?php

// check if wap

function check_wap(){

    // 先检查是否为wap代理，准确度高

    if(stristr($_SERVER['HTTP_VIA'],"wap")){

            return true;

        }

        // 检查浏览器是否接受 WML.

        elseif(strpos(strtoupper($_SERVER['HTTP_ACCEPT']),"VND.WAP.WML") > 0){

        return true;

   }

   //检查USER_AGENT

   elseif(preg_match('/(blackberry|configuration\/cldc|hp |hp-|htc |htc_|htc-|iemobile|kindle|midp|mmp|motorola|mobile|nokia|opera mini|opera |Googlebot-Mobile|YahooSeeker\/M1A1-R2D2|android|iphone|ipod|mobi|palm|palmos|pocket|portalmmm|ppc;|smartphone|sonyericsson|sqh|spv|symbian|treo|up.browser|up.link|vodafone|windows ce|xda |xda_)/i', $_SERVER['HTTP_USER_AGENT'])){

        return true;           

    }

    else{

        return false;  

   }

}

$agent = check_wap();

?>

<!--uuuuuuuuuuu--->

<a href="<?php echo url("thread-$_thread[tid]");?>">

<!--uuuuuuuuuuu--->

<?php if($agent){ 

echo xn_substr( $_thread [ 'subject' ], 0, 20);

<?php } ?> </a> <?php 

else

{

echo $_thread['subject'];

<?php } ?></a><!--<?php echo $_thread['subject'];?></a>标题截取-->