PHP UTF8 字符截取

// 字数截取函数
function csubstr($string, $start = 0,$sublen=12, $code = 'UTF-8',$ellipsis='...'){
 if($code == 'UTF-8'){
   $pa = "/[\x01-\x7f]|[\xc2-\xdf][\x80-\xbf]|\xe0[\xa0-\xbf][\x80-\xbf]|[\xe1-\xef][\x80-\xbf][\x80-\xbf]|\xf0[\x90-\xbf][\x80-\xbf][\x80-\xbf]|[\xf1-\xf7][\x80-\xbf][\x80-\xbf][\x80-\xbf]/";
   preg_match_all($pa, $string, $t_string);

   if(count($t_string[0]) - $start > $sublen) return join('', array_slice($t_string[0], $start, $sublen)).$ellipsis;
   return join('', array_slice($t_string[0], $start, $sublen));
 }else{
   $start = $start*2;
   $sublen = $sublen*2;
   $strlen = strlen($string);
   $tmpstr = '';
   for($i=0; $i<$strlen; $i++){
     if($i>=$start && $i<($start+$sublen)){
       if(ord(substr($string, $i, 1))>129) $tmpstr.= substr($string, $i, 2);
       else $tmpstr.= substr($string, $i, 1);
     }
     if(ord(substr($string, $i, 1))>129) $i++;
   }
   if(strlen($tmpstr)<$strlen ) $tmpstr.= $ellipsis;
   return $tmpstr;
 }
}