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问题:

Server Environment

Redhat Enterprise Linux
PHP 5.3.5

Problem

Let's say I have a UTC date and time such as 2011-04-27 02:45 and I want to convert it to my local time, which is America/New_York.

Three questions:

1.) My code below might solve the problem, would you agree?

<?php

date_default_timezone_set('America/New_York');  // Set timezone.

$utc_ts = strtotime("2011-04-27 02:45");  // UTC Unix timestamp.

// Timezone offset in seconds. The offset for timezones west of UTC is always negative,
// and for those east of UTC is always positive.
$offset = date("Z");

$local_ts = $utc_ts + $offset;  // Local Unix timestamp. Add because $offset is negative.

$local_time = date("Y-m-d g:i A", $local_ts);  // Local time as yyyy-mm-dd h:m am/pm.

echo $local_time;  // 2011-04-26 10:45 PM

?>

2.) But, does the value of $offset automatically adjust for Daylight Savings Time (DST) ?
3.) If not, how should I tweak my code to automatically adjust for DST ?

Thank you :-)

回答1:

This will do what you want using PHPs native DateTime and DateTimeZone classes:

$utc_date = DateTime::createFromFormat(
                'Y-m-d G:i', 
                '2011-04-27 02:45', 
                new DateTimeZone('UTC')
);

$nyc_date = $utc_date;
$nyc_date->setTimeZone(new DateTimeZone('America/New_York'));

echo $nyc_date->format('Y-m-d g:i A'); // output: 2011-04-26 10:45 PM

See DateTime::createFromFormat man page for more information.

After some experimentation between time zones that do and do not currently have DST I have discovered that this will take DST into account. The same conversion using my method above renders the same resulting time.

回答2:

I know this is an old post, but there is another line you need to add to get the correct time.

Before converting to local time, you need to set the default time zone to UTC like this (if it is the time zone of the time you are providing):

function GmtTimeToLocalTime($time) {
    date_default_timezone_set('UTC');
    $new_date = new DateTime($time);
    $new_date->setTimeZone(new DateTimeZone('America/New_York'));
    return $new_date->format("Y-m-d h:i:s");
}

回答3:

date_default_timezone_set('America/New_York');  // Set timezone.
$utc_ts = strtotime("2011-04-27 02:45");  // UTC Unix timestamp.

Just after this executing this, $utc_ts contains the local time. PHP handles the DST itself.

=H=

回答4:

I'll improve on Hasin Hayder's answer

date_default_timezone_set('America/New_York');  // Set timezone.
$utc_ts = strtotime("2011-04-27 02:45 UTC");  // UTC Unix timestamp.
echo date('Y-m-d H:i:s a T', $utc_ts);

It should output