php: setting a timezone by UTC offset

Question

Using javascript I know that my users timezone is UTC +3.

Now I want to create DateTime object with this knowledge:

$usersNow = new DateTime('now', new DateTimeZone("+3")); 

I receive as a respsonse:

'Unknown or bad timezone (+2)' 

What am I doing wrong? How can I fix?

Answer 1

how about this...

$original = new DateTime("now", new DateTimeZone('UTC')); $timezoneName = timezone_name_from_abbr("", 3*3600, false); $modified = $original->setTimezone(new DateTimezone($timezoneName)); 

Answer 2

You said:

Using javascript I know that my users timezone is UTC +3.

You probably ran something like this:

var offset = new Date().getTimezoneOffset(); 

This returns the current offset from UTC in minutes, with positive values falling west of UTC. It does not return a time zone!

A time zone is not an offset. A time zone has an offset. It can have multiple different offsets. Often there are two offsets, one for standard time and one for daylight saving time. A single numeric value cannot represent this alone.

• Example of a time zone: "America/New_York"
  • Corresponding standard offset: UTC-5
  • Corresponding daylight offset: UTC-4

Besides the two offsets, also wrapped up in that time zone are the dates and times for transitioning between the two offsets so you know when they apply. There's also a historical record of how the offsets and transitions may have changed over time.

See also "Time Zone != Offset" in the timezone tag wiki.

In your example case, you probably received a value of -180 from javascript, representing a current offset of UTC+3. But that's just the offset for that particular point in time! If you follow minaz's answer, you will get a time zone that makes the assumption that UTC+3 is always the correct offset. That would work if the real time zone is something like "Africa/Nairobi" which has never used anything except UTC+3. But for all you know your user could be in "Europe/Istanbul", which uses UTC+3 in the summer and UTC+2 in the winter.