/**
 *  参数说明
 *  $string  欲截取的字符串
 *  $sublen  截取的长度
 *  $start   从第几个字节截取，默认为0
 *  $code    字符编码，默认UTF-8
 */

function cut_str($string, $sublen, $start = 0, $code = 'UTF-8') {

    if ($code == 'UTF-8') {

        $pa = "/[\x01-\x7f]|[\xc2-\xdf][\x80-\xbf]|\xe0[\xa0-\xbf][\x80-\xbf]|[\xe1-\xef][\x80-\xbf][\x80-\xbf]|\xf0[\x90-\xbf][\x80-\xbf][\x80-\xbf]|[\xf1-\xf7][\x80-\xbf][\x80-\xbf][\x80-\xbf]/";

        preg_match_all($pa, $string, $t_string);

        if (count($t_string[0]) - $start > $sublen) return join('', array_slice($t_string[0], $start, $sublen)) . ".....";

        return join('', array_slice($t_string[0], $start, $sublen));

    } else {

        $start = $start * 2;

        $sublen = $sublen * 2;

        $strlen = strlen($string);

        $tmpstr = '';

        for ($i = 0; $i < $strlen; $i++) {

            if ($i >= $start && $i < ($start + $sublen)) {

                if (ord(substr($string, $i, 1)) > 129) {

                    $tmpstr.= substr($string, $i, 2);

                } else {

                    $tmpstr.= substr($string, $i, 1);

                }

            }

            if (ord(substr($string, $i, 1)) > 129) $i++;

        }

        if (strlen($tmpstr) < $strlen) $tmpstr.= "";

        return $tmpstr;

    }

}

$str="哈哈，帅哥在此！";

echo cut_str($str, 30, 0, 'gb2312');  // gb2312字符编码

echo cut_str($str,30,0)  //utf-8字符编码