php 中文切割字符串长度

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