php日期转时间戳,指定日期转换成时间戳

$sql=”select * from message Where DATE_FORMAT(FROM_UNIXTIME(chattime),'%Y-%m-%d') = DATE_FORMAT(NOW(),'%Y-%m-%d') order by id desc”;

class SaonekController extends Controller {

 public function indexAction(){
/*时间戳转换成日期不用说了
但是日期要转成时间戳的话就要用到strtotime()
*/
         $time = time();//时间戳
   $nowtime = date('Y-m-d H:i:s',$time);//生成带格式的日期
   $oldtime = '2010-11-10 22:19:21';
         $catime = strtotime($oldtime);//日期转换为时间戳
   $nowtimes = date('Y-m-d H:i:s',$catime);//时间戳又转回日期了
   echo  $nowtimes;
 }
}

?>

$y=date("Y",time());
$m=date("m",time());
$d=date("d",time());
$start_time = mktime(9, 0, 0, $m, $d ,$y);
$end_time = mktime(19, 0, 0, $m, $d ,$y);
$time = time();
if($time >= $start_time && $time <= $end_time)
{
// do something....
}
?>

# on 2/8/2010
date('m/d/y', strtotime('first day')); # 02/01/10
date('m/d/y', strtotime('last day')); # 02/28/10
date('m/d/y', strtotime('last day next month')); # 03/31/10
date('m/d/y', strtotime('last day last month')); # 01/31/10
date('m/d/y', strtotime('2009-12 last day')); # 12/31/09 - this doesn't work if you reverse the order of the year and month
date('m/d/y', strtotime('2009-03 last day')); # 03/31/09
date('m/d/y', strtotime('2009-03')); # 03/01/09
date('m/d/y', strtotime('last day of march 2009')); # 03/31/09
date('m/d/y', strtotime('last day of march')); # 03/31/10
?>