Changing current user timezone based on server UTC offset and user UTC offset

Question

im writing a twitter web service in php. When a user signs in, i receive this node:

<utc_offset>-18000</utc_offset>

I have to change the script's timezone so that it adapts to the user's real timezone. The only php function i have found for this is: date_default_timezone_set($timezone_identifier) but it won't let me use -18000 as a the $timezone_identifier parameter.

So, how can i change the current user timezone based on two values: Server UTC offset and User UTC offset

BTW, this is how i'm getting the server UTC offset value:

$this_tz_str = date_default_timezone_get();
$this_tz = new DateTimeZone($this_tz_str);
$now = new DateTime("now", $this_tz);
$offset = $this_tz->getOffset($now);

Any ideas? Thanks!

-18000 is offset not identifier for time zone. For valid timezone identifiers [visit this link](http://php.net/manual/en/timezones.php). — Wh1T3h4Ck5, Apr 12 '11 at 18:20
i'll use your $usertime instead of time() to calculate dates :) — Andres SK, Apr 12 '11 at 20:47

Wh1T3h4Ck5 · Accepted Answer · 2011-04-12T18:54:49.843

To get current server time

date_default_timezone_set(date_default_timezone_get());
echo date('Y-m-d H:i:s', time());

Output for Europe/Paris (my server settings; UTC+2)

2011-04-12 20:39:43

To get user's time by offset

$user_offset = '-18000';
date_default_timezone_set('UTC');
$diff = "$user_offset seconds";
if ((substr($diff,0,1) != '+') && (substr($diff,0,1) != '-')) $diff = '+' . $diff;
$usertime = strtotime($diff, time());
echo date('Y-m-d H:i:s', $usertime);

Output UTC-5 (Ecuador -> Quito time NO DST), php timezone identifier 'America/Guayaquil'.

2011-04-12 13:39:43

PHP.net manual:

Timezone offset in seconds. The offset for timezones west of UTC is always negative, and for those east of UTC is always positive. (-43200 through 50400)

thanks for the code, worked great! nice detail on finding out where my timezone was hehe. — Andres SK, Apr 12 '11 at 19:00

score 1 · Answer 2 · answered Apr 12 '11 at 18:21

1

The date_default_timezone... functions expect a string giving something like "Africa/Luanda" or whatever.

I suggest programmatically searching through the timezone database for a matching offset. If I recall correctly, those are in minutes from UTC, so you should divide the offset you are given by 60.

answered Apr 12 '11 at 18:21

wallyk

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offset is given in seconds... if you divide 18000 by 60 it's 300 hours difference... just not possible UTC-300 :) – Wh1T3h4Ck5 Apr 12 '11 at 18:27
18000 would be 300 minutes or 5 hours. – wallyk Apr 12 '11 at 18:33
Yes, so you should divide offset by 3600 to get UTC difference in hours UTC-5, right? – Wh1T3h4Ck5 Apr 12 '11 at 18:42

Changing current user timezone based on server UTC offset and user UTC offset

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