截取字符串 支持多编码字符串截取php函数

function cutstr($str, $start=0, $length, $charset="utf-8", $suffix="")
{
    if(function_exists("mb_substr")){
        return mb_substr($str, $start, $length, $charset).$suffix;
     }
     elseif(function_exists('iconv_substr')){
         return iconv_substr($str,$start,$length,$charset).$suffix;
     }
     $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 $slice.$suffix;
}