Bug #65730 [Opn->Nab]: DateTime::format('W') returns wrong week number

Edit report at https://bugs.php.net/bug.php?id=65730&edit=1 ID: 65730 Updated by: rasmus@php.net Reported by: glavic at gmail dot com Summary: DateTime::format('W') returns wrong week number -Status: Open +Status: Not a bug Type: Bug Package: Date/time related Operating System: ALL PHP Version: Irrelevant Block user comment: N Private report: N New Comment: PHP uses the ISO 8601 standard for day, month and week numbers. This is pretty clearly documented and if you read ISO 8601 it states that the first week of the year is "the week with the year's first Thursday in it" and since ISO 8601 weeks start on Mondays, it is quite normal for the first ISO week to contain days from a previous year. If they didn't then it would be impossible to consistently start weeks on Mondays since Jan.1 is not always a Monday. If you apply the ISO 8601 definition to the dates in question here you will find PHP is quite correct here. Previous Comments: ------------------------------------------------------------------------ [2013-09-21 11:04:29] glavic at gmail dot com Description: ------------ DateTime::format('W') returns wrong week number when date is 2013-12-30 or 2013-12-31. Test script: --------------- <?php $dt = new DateTime; for ($w = 52; $w <= 54; $w++) { $dt->setISODate(2013, $w); print_r($dt); echo $dt->format('Y W') . "\n\n"; } # see this script running on all php versions http://3v4l.org/9aua5 Expected result: ---------------- DateTime Object ( [date] => 2013-12-23 11:02:12 [timezone_type] => 3 [timezone] => UTC ) 2013 52 DateTime Object ( [date] => 2013-12-30 11:02:12 [timezone_type] => 3 [timezone] => UTC ) 2014 01 # or 2013 53, but surely not 2013 01 !!! DateTime Object ( [date] => 2014-01-06 11:02:12 [timezone_type] => 3 [timezone] => UTC ) 2014 02 Actual result: -------------- DateTime Object ( [date] => 2013-12-23 11:02:12 [timezone_type] => 3 [timezone] => UTC ) 2013 52 DateTime Object ( [date] => 2013-12-30 11:02:12 [timezone_type] => 3 [timezone] => UTC ) 2013 01 DateTime Object ( [date] => 2014-01-06 11:02:12 [timezone_type] => 3 [timezone] => UTC ) 2014 02 ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=65730&edit=1