截取中文字符串的函数

$s="[截取中文字符串的函数]";
function ch_left($s, $len){
if(strlen($s)>$len)
$s=substr($s, 0, $len);
$ch='['.chr(0x81)-chr(0xff).']';
if(preg_match("/$ch($ch{2})*$/", $s))
$s=substr($s,0,-1);
return $s;
}
echo ch_left($s,8);
?>