PHP DateTime::createFromFormat returning the wrong

Question

When trying to run createFromFormat using the Pacific/Auckland timezone and the format string 'F-Y'. The date returned is the first of October even though I have supplied it with 'September-2019'.

I have tried running it on PHP 7.3.9 and 7.2.22 in CLI and FPM, and online in a PHP sandbox.

<?php
echo DateTime::createFromFormat('F-Y', 'September-2019')                                                           
    ->setTimezone(new DateTimeZone('Pacific/Auckland'))
    ->format('Y-m-d');
// 2019-10-01

echo DateTime::createFromFormat('F-Y', 'September-2019')
    ->format('Y-m-d');
// 2019-09-01

In both of these examples the returned date should have been 2019-09-01. This wasn't happening yesterday.

Answer 1

The reason for this behaviour is that when you don't specify the missing parts of a date/time input to DateTime::createFromFormat, it uses the values from the current local date and time. In Auckland, that is October 31st and so it tries to make a date out of September 31 2019, which comes out as October 1 2019. To avoid this problem, use a ! at the start of the format string; this will instead substitute values from January 1 1970, 00:00:00 (the Unix Epoch) as required for those that are not specified in the time value:

echo DateTime::createFromFormat('!F-Y', 'September-2019')
    ->setTimeZone(new DateTimeZone('Pacific/Auckland'))
    ->format('Y-m-d');

Output:

2019-09-01

Demo on 3v4l.org

Answer 2

What about this my friend:

date_default_timezone_set('Pacific/Auckland');

$date = DateTime::createFromFormat('F-Y', 'September-2019');

$new_date_format = $date->format('Y-m-01');

echo $new_date_format;