php gets the number of days in the month at the specified time

php gets the number of days in the month at the specified time

 $days = cal_days_in_month(CAL_GREGORIAN, 4, 2011);
 echo "Return the number of days in 2011-4".$days."";
 $days = date( 't', strtotime("2011-4-1"));
 echo "Return the number of days in 2011-4".$days."";
 $days = date("t");
 echo "The number of days in the current month".$days."";
?>