PHP wrong unix timestamp

Question

find some problem when i was try to count days between two dates.
For fast debug my code i use http://sandbox.onlinephpfunctions.com/ with PHP version 7.4.0

Problem:

$date = new DateTime( '2018-02-28' );
$date2 = new DateTime( '2018-03-12' );
$diff = $date2->getTimestamp() - $date->getTimestamp();
var_dump($diff/(60*60*24)); //float(11.958333333333)

As you see - i set dates and calculated unixtimestamp-diff between dates.
Then i try find date when diff between two dates != 86400.

$date = new DateTime( '2020-03-08' );
$date2 = new DateTime( '2020-03-09' );
$diff = $date2->getTimestamp() - $date->getTimestamp();
var_dump($diff/(60*60*24)); //float(0.95833333333333)

Then i find all days from 2010 year:

$secInDay = 60 * 60 * 24;
$start_date = strtotime('2010-01-01');
$end_date = strtotime('2021-01-01');

while($start_date<$end_date) {
    $next_date = strtotime('+1 day', $start_date);
    $diff = ($next_date - $start_date) / $secInDay;
    if ($diff !== 1) {
        var_dump(date('d.m.Y', $start_date) . ' -> ' . date('d.m.Y', $next_date));
    }
    $start_date = strtotime('+1 day', $start_date);
}

Result:
string(24) "14.03.2010 -> 15.03.2010"
string(24) "07.11.2010 -> 08.11.2010"
string(24) "13.03.2011 -> 14.03.2011"
string(24) "06.11.2011 -> 07.11.2011"
string(24) "11.03.2012 -> 12.03.2012"
string(24) "04.11.2012 -> 05.11.2012"
string(24) "10.03.2013 -> 11.03.2013"
string(24) "03.11.2013 -> 04.11.2013"
string(24) "09.03.2014 -> 10.03.2014"
string(24) "02.11.2014 -> 03.11.2014"
string(24) "08.03.2015 -> 09.03.2015"
string(24) "01.11.2015 -> 02.11.2015"
string(24) "13.03.2016 -> 14.03.2016"
string(24) "06.11.2016 -> 07.11.2016"
string(24) "12.03.2017 -> 13.03.2017"
string(24) "05.11.2017 -> 06.11.2017"
string(24) "11.03.2018 -> 12.03.2018"
string(24) "04.11.2018 -> 05.11.2018"
string(24) "10.03.2019 -> 11.03.2019"
string(24) "03.11.2019 -> 04.11.2019"
string(24) "08.03.2020 -> 09.03.2020"
string(24) "01.11.2020 -> 02.11.2020"

So my main question - why PHP get wrong unix-timestamp for current dates?

Your algorithm finds the days for the changeover from winter/summer time and summer/winter time for the current time zone. These days have 23 or 25 hours. — jspit
– jspit, Commented Feb 28, 2020 at 11:16
Please highlight which exact results are not calculated as expected, and explain the difference. Also explain which timezone you use — Nico Haase
– Nico Haase, Commented Feb 28, 2020 at 11:26

jspit · Accepted Answer · 2020-02-28 11:39:40Z

1

Your algorithm finds the days for the changeover from winter/summer time and summer/winter time for the current time zone. These days have not 24 hours.

Russia no longer knows summer time. With

date_default_timezone_set('Europe/Moscow');

in the first line you get the result for your region. Try it self.

Update:

You get correct results with DateTime-Objects:

date_default_timezone_set('Europe/Moscow');

$diff = date_create('28.03.2010')->diff(date_create('29.03.2010'))->days;
echo $diff;  //1

edited Feb 28, 2020 at 11:39

answered Feb 28, 2020 at 11:28

jspit

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1 Comment

Igor Novikov Over a year ago

Thanks! Don't think about winter/summer time!

user10485200 · Accepted Answer · 2020-02-28 10:49:36Z

0

You can change the default UTC with this function:

date_default_timezone_set('America/Los_Angeles');

https://www.php.net/manual/en/function.date-default-timezone-set.php

Or directly edit your INI configuration file from your web server. https://www.php.net/manual/en/datetime.configuration.php#ini.date.timezone

answered Feb 28, 2020 at 10:49

user10485200

1 Comment

Wiimm Over a year ago

Editing the INI configuration is not a good idea: If 2 authors need 2 different time zones for 2 different websites at the same server, and both are edit the INI file, then one website doesn't work like expected. Using date_default_timezone_set() at a central place of the website (e.g. standard library) is clearly the better choice.

RiggsFolly · Accepted Answer · 2020-02-28 11:22:17Z

If you use the DateTime class like this and calculate the interval the leap year is catered for

function days_between( $start, $end )
{
    // Put the 2 dates into DateTime objects
    $start = new DateTime($start);
    $end  = new DateTime($end);
    // Create a DateInterval object using diff() method
    $interval = $end->diff($start);
    // Format the result as an integer, representing number of days
    return $interval->format('%a');
}

#not leap year
echo days_between('2019-02-27', '2019-02-27') . PHP_EOL;    // 0
echo days_between('2019-02-27', '2019-02-28') . PHP_EOL;    // 1
echo days_between('2019-02-27', '2019-02-29') . PHP_EOL;    // 2 (there is no 29th
echo days_between('2019-02-27', '2019-03-01') . PHP_EOL;    // 2
echo PHP_EOL;

#Leap Year
echo days_between('2020-02-27', '2020-02-27') . PHP_EOL;    // 0
echo days_between('2020-02-27', '2020-02-28') . PHP_EOL;    // 1
echo days_between('2020-02-27', '2020-02-29') . PHP_EOL;    // 2
echo days_between('2020-02-27', '2020-03-01') . PHP_EOL;    // 3

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