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PHP Worldwide Times Using DateTime Objects

Posted on 2014-02-20
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Hello Experts!

Another quick question for you PHP experts out there.  I know I can use DateTimeZone::listIdentifiers() to obtain a list of all the time zones available to PHP, and I can use DateTimeZone::getTransitions() to obtain neat info for each time zone like offsets, daylight savings time, etc.

My question is that once I have the offset for each time zone, is there a way to display the current time for each time zone, such as
America/Los Angeles (9:03 AM PST)

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?

Any help would be greatly appreciated.  I just need the code that will actually calculate the correct time based on the provided offset or time zone.  Bonus points to the most elegant solution!
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Question by:OmniUnlimited
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by:Ray Paseur
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This and much more is shown in the article here (look for the code snippet with "Timezones Around the Globe"):
http://www.experts-exchange.com/Web_Development/Web_Languages-Standards/PHP/A_201-Handling-date-and-time-in-PHP-and-MySQL.html

See date_default_timezone_set().  Easy!
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by:OmniUnlimited
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Hi Ray!

I knew I could count on you for a great answer.  Unfortunately, this question is really meant to help me understand (teach me, if you will) how I can work with times from different time zones WITHOUT changing the default time zone for the server using the DateTime classes (DateTime, DateTimeImmutable, DateTimeInterface, DateTimeZone, etc.)  Are you familiar with the use of the PHP DateTime classes after PHP v.5.2?
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by:Ray Paseur
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Yes, I am familiar with DateTime objects.  Just curious - why would you not want to change the default timezone?  You can get it and set it pretty easily.

If you want to give me some examples of things you would like to do, I'll be glad to show you some demonstration scripts.
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by:OmniUnlimited
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The site has a bunch of asynchronous stuff going on, some of which are dependent upon the system time.  I don't want a system wide resetting of the time zone to mess these up.

I am just looking for the shortest, cleanest solution to display the proper time next to its respective time zone.  As I mentioned earlier, I can iterate through the array supplied by the DateTimeZone::listIdentifiers() method to get each time zone, then I can use the DateTimeZone::getTransitions() method to get the neat information like offset, daylight savings time, time zone abbreviation, etc.  Having this information available (offset, name of time zone), I want a statement that can display the actual time for this time zone.

I hope this makes sense.
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by:Dave Baldwin
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Changing the "default time zone" changes it for your Page, not for the server.  You can change it as often as you want.  Linux servers are normally set to use GMT or whatever it's called now.

https://php.net/manual/en/timezones.others.php
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by:OmniUnlimited
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@DaveBaldwin:  Yeah, I was wondering about that.  The PHP manual states that date_default_timezone_set sets the default timezone used by all date/time functions in a script.  Obviously, this would include all included scripts, am I not right?  Would this affect scripts that are called from that script via AJAX?
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by:Dave Baldwin
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Would this affect scripts that are called from that script via AJAX?
That doesn't actually make any sense.  You have to remember the separation of code.  PHP runs on the server and sends the page to the browser and then it's Done.  Any scripts contacted thru AJAX are 'new' in the sense that they are loaded when the AJAX call is made.  They don't 'know' anything about the original PHP script that was used to load the page.  If you need a 'default timezone' in the script called by AJAX, it has to be set in that script.  It does not in any case carry over from the PHP script that was used to load the page in the first place.
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by:OmniUnlimited
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@DaveBaldwin: :P You know I've been working long hours, and I guess I am not thinking very clearly this morning.  You are absolutely right.  The asynchronous scripts would not be affected by a change in the default time zone settings.

I still would be curious to see the solution using DateTime objects, however.
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by:Dave Baldwin
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I still would be curious to see the solution using DateTime objects, however.
I have no idea what that means.  If you look at this page, you will see that most Date/Time functions are actually aliases of the Date/Time classes.

http://us3.php.net/manual/en/book.datetime.php

And in this page, it says that you will get a 'notice' if the 'default timezone' has not been set before the functions are used.

http://us3.php.net/manual/en/function.date-default-timezone-set.php

And this page shows the two different 'styles':

http://us3.php.net/manual/en/datetime.settimezone.php
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Accepted Solution

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Julian Hansen earned 500 total points
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How about this
<?php
// GET OUR OFFSET FROM GMT (OR UCT)

$datetime = new DateTime();
$offset = $datetime->getOffset();

// GET THE CURRENT TIME 

$theTime = time();

// GET LIST OF TZ's AND LOOP THROUGH THEM

$times = DateTimeZone::listIdentifiers();
foreach($times as $t) {

  // CREATE A NEW DateTimeZone OBJECT WITH THE CURRENT IDENTIFIER
  
  $tz = new DateTimeZone($t);
  
  // GET THE TRANSITIONS FOR THE CURRENT TIME - WILL RETURN A 
  //SINGLE ELEMENT ARRAY
  
  $trans = $tz->getTransitions($theTime, $theTime);
  
  // WORK OUT THE TIME FOR THE LOCATION BY TAKING THE CURRENT 
  // TIME (UCT) AND ADDING THE OFFSET FOR THE LOCATION AND 
  // SUBTRACTING OUR LOCAL OFFSET
  
  $time = strtotime($trans[0]['time']) + $trans[0]['offset'] - $offset;
  
  // FINALLY OUTPUT THE RESULT
  
  echo "$t (" . date('h:i:s a', $time) . ")<br/>";
}
?>

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by:OmniUnlimited
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That's perfect!  Thanks.
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by:Julian Hansen
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You are welcome - thanks for the poitnts.
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