php中截取中文字符串csubstr

    /* 
    * 中文截取，支持gb2312,gbk,utf-8,big5 
    * 
    * @param string $str 要截取的字串 
    * @param int $start 截取起始位置 
    * @param int $length 截取长度 
    * @param string $charset utf-8|gb2312|gbk|big5 编码 
    * @param $suffix 是否加尾缀 
    */
    public function csubstr($str, $start = 0, $length, $charset = "utf-8", $suffix = true)
    {
        if (function_exists("mb_substr")) {
            if (mb_strlen($str, $charset) <= $length) return $str;            $slice = mb_substr($str, $start, $length, $charset);        } else {            $re['utf-8'] = "/[x01-x7f]|[xc2-xdf][x80-xbf]|[xe0-xef][x80-xbf]{2}|[xf0-xff][x80-xbf]{3}/";            $re['gb2312'] = "/[x01-x7f]|[xb0-xf7][xa0-xfe]/";            $re['gbk'] = "/[x01-x7f]|[x81-xfe][x40-xfe]/";            $re['big5'] = "/[x01-x7f]|[x81-xfe]([x40-x7e]|xa1-xfe])/";            preg_match_all($re[$charset], $str, $match);                        if (count($match[0]) <= $length) return $str;            $slice = join("", array_slice($match[0], $start, $length));        }        if ($suffix) return $slice . "…";        return $slice;    }