There is a pitfall with the summertime in the timezone Europe/Berlin.
Beginning Summer-Timer
=======================
The hour between 2020-03-29 02:00:00 and 2020-03-29 03:00:00 is missing in the Timezone 'Europe/Berlin'.
Explanation to the code below
----------------------------------
The DateInterval of 20700 minutes point to 2020-03-29 03:00:00.
The DateInterval of 20701 minutes points to the not existing '2020-03-29 02:59:00', which is resolved to '2020-03-29 03:59:59' by rounding up.
The DateInterval-object of 20761 minutes calculate the existing '2020-03-29 01:59:00'. The hour between 2:00 - 3:00 does not exist in the euopean summertime for the date 2020-03-29. The missing hour will be additionally calculated in the substraction. This explain the result '2020-03-29 00:59:00'. It seems, that the addition of the DateInterval-object does not recalculate the missing hour for some (?) reasons.
<?php
$test = [];
$check = date_create_from_format('Y-m-d H:i:s', '2020-04-12 12:00:00', new DateTimeZone('Europe/Berlin'));
for ($i = 0; $i < 30000; $i++) {
$expectEaster = clone $check;
$interval = new DateInterval('PT' . $i . 'M');
$expectEaster->sub($interval);
$dummy = clone $expectEaster;
$expectEaster->add($interval);
if (!in_array($expectEaster->format('Y-m-d H:i:s'), $test)) {
$test[$i] = $expectEaster->format('Y-m-d H:i:s');
echo($i . ' near summertime start ' . $expectEaster->format('Y-m-d H:i:s') . '[' . $dummy->format('Y-m-d H:i:s') . ']' . "\n");
}
}
// 0 near summertime start 2020-04-12 12:00:00[2020-04-12 12:00:00]
// 20701 near summertime start 2020-04-12 13:00:00[2020-03-29 03:59:00]
// 20761 near summertime start 2020-04-12 11:00:00[2020-03-29 00:59:00]
?>
Ending Summer Timer
====================
The european summertime defines the existence of two hours with the notation 2020-10-25 02:00:00 - 2020-10-25 03:00:00 (a) and 2020-10-25 02:00:00 - 2020-10-25 03:00:00 (b).
It seems, that the dateTime-object handles the additional hour on an simple internal way. It seems, that you can't differ between this two hours (a) and (b) with the DateTime-object in a simple way.
<?php
$check = date_create_from_format('Y-m-d H:i:s', '2020-10-25 06:00:00', new DateTimeZone('Europe/Berlin'));
for ($i = 0; $i < 361; $i = $i + 60) {
$expectEaster = clone $check;
$interval = new DateInterval('PT' . $i . 'M');
$expectEaster->sub($interval);
$dummy = clone $expectEaster;
$expectEaster->add($interval);
$test[$i] = $expectEaster->format('Y-m-d H:i:s');
echo($i . ' near summertime end ' . $expectEaster->format('Y-m-d H:i:s') .
'[' . $dummy->format('Y-m-d H:i:s') . ' / ' . $dummy->getTimestamp() . ']' .
"\n");
}
// 0 near summertime end 2020-10-25 06:00:00[2020-10-25 06:00:00 / 1603602000]
// 60 near summertime end 2020-10-25 06:00:00[2020-10-25 05:00:00 / 1603598400]
// 120 near summertime end 2020-10-25 06:00:00[2020-10-25 04:00:00 / 1603594800]
// 180 near summertime end 2020-10-25 06:00:00[2020-10-25 03:00:00 / 1603591200]
// 240 near summertime end 2020-10-25 06:00:00[2020-10-25 02:00:00 / 1603587600]
// 300 near summertime end 2020-10-25 06:00:00[2020-10-25 02:00:00 / 1603587600]
// 360 near summertime end 2020-10-25 06:00:00[2020-10-25 01:00:00 / 1603580400] }
?>
日付/時刻 の算術
以下の例は、DST(夏時間) への移行や、 異なった日を持つ月に関する 日付/時刻 の算術の罠をいくつか紹介します。
例1 DateTimeImmutable::add/sub は、経過時間を含む区間を足してしまう
DST (夏時間) への移行タイミングをまたいで 24時間を足してしまうと、 (ほとんどのタイムゾーンでは) 23/25時間を足しているように見える
<?php
$dt = new DateTimeImmutable("2015-11-01 00:00:00", new DateTimeZone("America/New_York"));
echo "Start: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
$dt = $dt->add(new DateInterval("PT3H"));
echo "End: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
?>上の例の出力は以下となります。
Start: 2015-11-01 00:00:00 -04:00 End: 2015-11-01 02:00:00 -05:00
例2 DateTimeImmutable::modify と strtotime を使い、個々のコンポーネントの値をインクリメント/デクリメントする
DST (夏時間) の移行のタイミングをまたいで24時間を足すと、日付/時刻 文字列に正確に24時間足されることになります (開始時刻と終了時刻が同じ移行ポイントにない場合) point).
<?php
$dt = new DateTimeImmutable("2015-11-01 00:00:00", new DateTimeZone("America/New_York"));
echo "Start: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
$dt = $dt->modify("+24 hours");
echo "End: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
?>上の例の出力は以下となります。
Start: 2015-11-01 00:00:00 -04:00 End: 2015-11-02 00:00:00 -05:00
例3 時刻を引き算すると、日付がオーバー/アンダーフローする可能性がある
1月31日 + 1ヶ月 のような計算をすると、(うるう年のときは) 3月2日、 または (通常の年は) 3月3日になります。
<?php
echo "Normal year:\n"; // February has 28 days
$dt = new DateTimeImmutable("2015-01-31 00:00:00", new DateTimeZone("America/New_York"));
echo "Start: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
$dt = $dt->modify("+1 month");
echo "End: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
echo "Leap year:\n"; // February has 29 days
$dt = new DateTimeImmutable("2016-01-31 00:00:00", new DateTimeZone("America/New_York"));
echo "Start: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
$dt = $dt->modify("+1 month");
echo "End: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
?>上の例の出力は以下となります。
Normal year: Start: 2015-01-31 00:00:00 -05:00 End: 2015-03-03 00:00:00 -05:00 Leap year: Start: 2016-01-31 00:00:00 -05:00 End: 2016-03-02 00:00:00 -05:00
次の月の最後の日を得るために(つまり、オーバーフローを避けるため)、
last day of フォーマットも利用できます。
<?php
echo "Normal year:\n"; // February has 28 days
$dt = new DateTimeImmutable("2015-01-31 00:00:00", new DateTimeZone("America/New_York"));
echo "Start: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
$dt = $dt->modify("last day of next month");
echo "End: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
echo "Leap year:\n"; // February has 29 days
$dt = new DateTimeImmutable("2016-01-31 00:00:00", new DateTimeZone("America/New_York"));
echo "Start: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
$dt = $dt->modify("last day of next month");
echo "End: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
?>上の例の出力は以下となります。
Normal year: Start: 2015-01-31 00:00:00 -05:00 End: 2015-02-28 00:00:00 -05:00 Leap year: Start: 2016-01-31 00:00:00 -05:00 End: 2016-02-29 00:00:00 -05:00
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