自己又寫了個截取中文字符串的函數

$s="[北京的金山上]";

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);

?>