Bug #70126 [Sus->Nab]: Wrong calculation of the difference between two dates

Edit report at https://bugs.php.net/bug.php?id=70126&edit=1 ID: 70126 Updated by: derick@php.net Reported by: php at tul dot io Summary: Wrong calculation of the difference between two dates -Status: Suspended +Status: Not a bug Type: Bug Package: Date/time related Operating System: any PHP Version: 7.0.0beta2 Assigned To: derick Block user comment: N Private report: N New Comment: Sorry, but your problem does not imply a bug in PHP itself. For a list of more appropriate places to ask for help using PHP, please visit http://www.php.net/support.php as this bug system is not the appropriate forum for asking support questions. Due to the volume of reports we can not explain in detail here why your report is not a bug. The support channels will be able to provide an explanation for you. Thank you for your interest in PHP. The actual result is the correct result. What "diff" returns you is a way how to get from $date1 to the argument in the ->diff() method through the use of the string "+{$m} month {$d} days" as an argument to ->modify(). To go from 2015/01/31 to 2015/03/01, it can't be 1 month and 1 day, because that would do the following: 2015/01/31 +1 +1 2015/02/32 which rolls over to: 2015/03/04 Which is clearly not the right answer: <?php echo (new DateTimeImmutable("2015-01-31"))->modify("+1 month 1 day")->format("Y-m-d"), "\n"; ?> // 2015-03-04 The only value that works is 0 months, 29 days: <?php echo (new DateTimeImmutable("2015-01-31"))->modify("+0 month 29 days")->format("Y-m-d"), "\n"; ?> // 2015-03-01 Previous Comments: ------------------------------------------------------------------------ [2015-07-24 10:33:19] derick@php.net timelib development lives at http://github.com/derickr/timelib - the one in PHP is a bundled version. Timelib does right now not have a test harnass for diffs, although there is a tester for it: https://github.com/derickr/timelib/blob/master/tests/tester-diff.c Once it's fixed (and tested) in timelib, I'm happy to resync it back to PHP. ------------------------------------------------------------------------ [2015-07-24 09:50:38] php at tul dot io Description: ------------ DateTime::diff() reports the wrong number of days and months when not in an inverted order (start date < end date). To reproduce, the two dates used as input have to be even number of months apart and the day of the start date has to be greater than the day of the end date (e.g. 2015-01-31 to 2015-03-01). Test script: --------------- <?php $date1 = new DateTime('2015/01/31'); $date2 = new DateTime('2015/03/01'); print_r($date1->diff($date2)); print_r($date2->diff($date1)); Expected result: ---------------- DateInterval Object ( [y] => 0 [m] => 1 [d] => 1 [h] => 0 [i] => 0 [s] => 0 [weekday] => 0 [weekday_behavior] => 0 [first_last_day_of] => 0 [invert] => 0 [days] => 29 [special_type] => 0 [special_amount] => 0 [have_weekday_relative] => 0 [have_special_relative] => 0 ) DateInterval Object ( [y] => 0 [m] => 1 [d] => 1 [h] => 0 [i] => 0 [s] => 0 [weekday] => 0 [weekday_behavior] => 0 [first_last_day_of] => 0 [invert] => 1 [days] => 29 [special_type] => 0 [special_amount] => 0 [have_weekday_relative] => 0 [have_special_relative] => 0 ) Actual result: -------------- DateInterval Object ( [y] => 0 [m] => 0 [d] => 29 [h] => 0 [i] => 0 [s] => 0 [weekday] => 0 [weekday_behavior] => 0 [first_last_day_of] => 0 [invert] => 0 [days] => 29 [special_type] => 0 [special_amount] => 0 [have_weekday_relative] => 0 [have_special_relative] => 0 ) DateInterval Object ( [y] => 0 [m] => 1 [d] => 1 [h] => 0 [i] => 0 [s] => 0 [weekday] => 0 [weekday_behavior] => 0 [first_last_day_of] => 0 [invert] => 1 [days] => 29 [special_type] => 0 [special_amount] => 0 [have_weekday_relative] => 0 [have_special_relative] => 0 ) ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=70126&edit=1