PHP function to intercept Chinese characters (utf-8 format)

/**
@UTF-8 Chinese character truncation program
@http://bbs.it-home.org
*/
$str = "321 This is a test string";
$str1 = "()()";
echo subUTF8str ($str,0,3)."";
echo subUTF8str($str,0,4)."";
echo subUTF8str($str1,0,4)."< br>";
echo subUTF8str($str1,0,10)."";
function subUTF8str($str,$start=0,$length=80){
$cur_len = 0; //The string length understood by humans
$all_len = strlen($str); //The string length understood by machines
if($length > $all_len)
{
return $str;
}
for($i = 0;$i < $all_len;)
{
if($cur_len == $start)
{
break;
}
if (ord($str[$i]) > 127 )
{
$i += 3;
}else{
$i += 1;
}
$cur_len ++;
}
$start_pos = $i;
$temp_pos = $cur_len;
for(;$ cur_len - $temp_pos < $length;)
{
if($i >= $all_len)
break;
if (ord($str[$i]) > 127)
{
$i += 3 ;
}else{
$i += 1;
}
$cur_len ++;
}
$end_pos = $i;
return substr($str,$start_pos,$end_pos);
}
?>