/**
+----------------------------------------------------------
* 字符串截取，支持中文和其他编码
+----------------------------------------------------------
* @param string $source 需要转换的字符串
* @param string $start 开始位置
* @param string $length 截取长度
* @param string $charset 编码格式
* @param string $suffix 截断显示字符后缀
+----------------------------------------------------------
* @return string
+----------------------------------------------------------
*/
function xs_substr($source, $start=0, $length, $charset="utf-8", $suffix="")
{
	if(function_exists("mb_substr"))        //采用PHP自带的mb_substr截取字符串
	{
		$string = mb_substr($source, $start, $length, $charset).$suffix;
	}
	elseif(function_exists('iconv_substr')) //采用PHP自带的iconv_substr截取字符串
	{
		$string = iconv_substr($source,$start,$length,$charset).$suffix;
	}
	else
	{
		$pattern['utf-8']   = "/[x01-x7f]|[xc2-xdf][x80-xbf]|[xe0-xef][x80-xbf]{2}|[xf0-xff][x80-xbf]{3}/";
		$pattern['gb2312'] = "/[x01-x7f]|[xb0-xf7][xa0-xfe]/";
		$pattern['gbk']    = "/[x01-x7f]|[x81-xfe][x40-xfe]/";
		$pattern['big5']   = "/[x01-x7f]|[x81-xfe]([x40-x7e]|xa1-xfe])/";
		preg_match_all($pattern[$charset], $source, $match);
		$slice = join("",array_slice($match[0], $start, $length));
		 
		$string = $slice.$suffix;
	}
	return $string;
}