php格式化日期

function ShowDate($flag=0, $timestr=NULL)
{
	// 获取周几
	$warr = array(
	"0" => 星期日,
	"1" => 星期一,
	"2" => 星期二,
	"3" => 星期三,
	"4" => 星期四,
	"5" => 星期五,
	"6" => 星期六
	);
	$i = date("w", $timeStamp);
	
	// 设置北京时间并获取时间戳
	date_default_timezone_set('PRC');
	$timeStamp = NULL;
	if ($timestr)
		$timeStamp = strtotime($timestr);
	else
		$timeStamp = time();

	// 设置时间显示格式
	$ret1 = date("Y年m月d日 H:m:s", $timeStamp) . " " . $warr[$i];
	$ret2 = date("Y-m-d H:m:s", $timeStamp) . " " . $warr[$i];
	$ret3 = date("y/m/d", $timeStamp);
	$ret = $ret1; // 默认返回第一种
	
	if ($flag == 2)
		$ret = $ret2;
	else if ($flag == 3)
		$ret = $ret3;
		
	return $ret;
}