php 拆分utf-8格式的字符串

    function utf8_str_split($str, $split_len = 1)
    {
        if (!preg_match('/^[0-9]+$/', $split_len) || $split_len < 1)
            return FALSE;

        $len = mb_strlen($str, 'UTF-8');
        if ($len <= $split_len)
            return array($str);

        preg_match_all('/.{'.$split_len.'}|[^x00]{1,'.$split_len.'}$/us', $str, $ar);

        return $ar[0];
    }

$ceshi = '中国加油';
$this->utf8_str_split($ceshi );