<?php

 $filename = "filename.txt";

 $handle = fopen($filename, "r");//读取二进制文件时，需要将第二个参数设置成'rb'

 //通过filesize获得文件大小，将整个文件一下子读到一个字符串中

 $contents = fread($handle, filesize ($filename));

 $e=mb_detect_encoding($contents, array('UTF-8', 'CP936'));

 switch($e){

     case 'UTF-8':

             break;

     case 'CP936':$contents=iconv("GB2312", "UTF-8", $contents);

            break;

 }

 fclose($handle);

 ?>