$content = file_get_contents($url);
   $encode =  mb_detect_encoding($content,'CP936,UTF-8') ;
   //如果是CP936，就是gbk编码，如果是UTF-8, 就是utf-8编码
   if ($encode =='CP936') {
      //再调用转换成utf-8编码的函数,最终确保是utf-8
      $content = mb_convert_encoding ($content, 'UTF-8' ,'GBK');
   }
   echo $content;