为什么 DateTime 方法差异在 PHP（时区相关）中表现不同？答案

【问题标题】：Why do DateTime method diff behave differently in PHP (timezone related)?为什么 DateTime 方法差异在 PHP（时区相关）中表现不同？
【发布时间】：2020-06-16 10:09:29
【问题描述】：

我希望了解为什么不能信任这个简单的 DateTime 操作 (2020-07-01)->diff(2020-07-31)。

<?php

$timeZones = ['GMT', 'Europe/Paris', 'America/Denver', 'Asia/Qatar', 'Australia/Sydney'];

echo('Doing (2020-07-01)->diff(2020-07-31)' . "\n\n");

foreach ($timeZones as $timeZone) {

    date_default_timezone_set($timeZone);

    $startDate = new \DateTime('2020-07-01');

    $calcDateA = (new \DateTime('2020-07-01'))->modify('+1 month -1 day');
    $calcDateB = (new \DateTime('2020-07-01'))->modify('+30 days');
    $calcDateC = new \DateTime('2020-07-31');

    $diffA = $startDate->diff($calcDateA);
    $diffB = $startDate->diff($calcDateB);
    $diffC = $startDate->diff($calcDateC);

    echo("Using $timeZone\n");

    echo('days (A): ' . $diffA->d . "\n");
    echo('months (A): ' . $diffA->m . "\n");

    echo('days (B): ' . $diffB->d . "\n");
    echo('months (B): ' . $diffB->m . "\n");

    echo('days (C): ' . $diffC->d . "\n");
    echo('months (C): ' . $diffC->m . "\n\n");
}

此代码在任何 PHP 版本中执行时，都会输出以下内容：

Doing (2020-07-01)->diff(2020-07-31)

Using GMT

days (A): 30
months (A): 0

days (B): 30
months (B): 0

days (C): 30
months (C): 0

Using Europe/Paris

days (A): 0
months (A): 1

days (B): 0
months (B): 1

days (C): 0
months (C): 1

Using America/Denver

days (A): 30
months (A): 0

days (B): 30
months (B): 0

days (C): 30
months (C): 0

Using Asia/Qatar

days (A): 0
months (A): 1

days (B): 0
months (B): 1

days (C): 0
months (C): 1

Using Australia/Sydney

days (A): 0
months (A): 1

days (B): 0
months (B): 1

days (C): 0
months (C): 1

我感觉内部计算是使用 UTC 进行的，有人忘记补偿时区。任何人都可以确认？

谢谢。

【问题讨论】：

标签： php datetime timezone

【解决方案1】：

简短回答：是的，这是一个错误。

我已经简化了您的测试用例，使其更加明显：

$timeZones = ['GMT', 'Europe/Paris'];
foreach ($timeZones as $timeZone) {
    date_default_timezone_set($timeZone);
    $startDate = new \DateTime('2020-07-01');
    $calcDateA = (new \DateTime('2020-07-01'))->modify('+1 month -1 day');
    $diffA = $startDate->diff($calcDateA);
    echo("Using $timeZone\n");
    echo $startDate->format('r'), "\n";
    echo $calcDateA->format('r'), "\n";
    echo $diffA->format('Days: %d / Months: %m'), "\n\n";
}

Using GMT
Wed, 01 Jul 2020 00:00:00 +0000
Fri, 31 Jul 2020 00:00:00 +0000
Days: 30 / Months: 0

Using Europe/Paris
Wed, 01 Jul 2020 00:00:00 +0200
Fri, 31 Jul 2020 00:00:00 +0200
Days: 0 / Months: 1

我的猜测是，正如您所建议的，计算是在 UTC 中完成的：

$utc = new DateTimeZone('UTC');
foreach ($timeZones as $timeZone) {
    date_default_timezone_set($timeZone);
    $startDate = new \DateTime('2020-07-01');
    $startDate->setTimezone($utc);
    $calcDateA = (new \DateTime('2020-07-01'))->modify('+1 month -1 day');
    $calcDateA->setTimezone($utc);
    $diffA = $startDate->diff($calcDateA);
    echo("Using $timeZone\n");
    echo $startDate->format('r'), "\n";
    echo $calcDateA->format('r'), "\n";
    echo $diffA->format('Days: %d / Months: %m'), "\n\n";
}

这会导致某些上下文丢失：

Using GMT
Wed, 01 Jul 2020 00:00:00 +0000
Fri, 31 Jul 2020 00:00:00 +0000
Days: 30 / Months: 0

Using Europe/Paris
Tue, 30 Jun 2020 22:00:00 +0000
Thu, 30 Jul 2020 22:00:00 +0000
Days: 0 / Months: 1

PHP 错误跟踪器中有几张票。在one of them 中，一位贡献者解释道：

这与 DST 转换无关（仅一次）。但发生的事情是 PHP首先将其转换为UTC时间，最后进行比较 2016-12-31 23:00 到 2017-09-30 22:00 - 然后算法得到更加混乱和混乱。

这段代码很复杂，很遗憾需要重写。它会花点时间。

【讨论】：