TP之msubstr()

function msubstr($str, $start=0, $length, $charset="utf-8", $suffix=true) {

        if(function_exists("mb_substr"))

            $slice = mb_substr($str, $start, $length, $charset);

        elseif(function_exists('iconv_substr')) {

            $slice = iconv_substr($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);

            $slice = join("",array_slice($match[0], $start, $length));

        }

        return $suffix ? $slice.'...' : $slice;

    }