date_default_timezone_set

(PHP 5 >= 5.1.0)

date_default_timezone_set — Sets the default timezone used by all date/time functions in a script

Description

bool date_default_timezone_set ( string $timezone_identifier )

date_default_timezone_set() sets the default timezone used by all date/time functions.

Note: Since PHP 5.1.0 (when the date/time functions were rewritten), every call to a date/time function will generate a E_NOTICE if the timezone isn't valid, and/or a E_WARNING message if using the system settings or the TZ environment variable.

Instead of using this function to set the default timezone in your script, you can also use the INI setting date.timezone to set the default timezone.

Parameters

timezone_identifier: The timezone identifier, like UTC or Europe/Lisbon. The list of valid identifiers is available in the List of Supported Timezones.

Return Values

This function returns FALSE if the timezone_identifier isn't valid, or TRUE otherwise.

Examples

Example #1 Getting the default timezone


<?php
date_default_timezone_set('America/Los_Angeles');

$script_tz = date_default_timezone_get();

if (strcmp($script_tz, ini_get('date.timezone'))){
    echo 'Script timezone differs from ini-set timezone.';
} else {
    echo 'Script timezone and ini-set timezone match.';
}
?>

Changelog

Version	Description
5.3.0	Now throws `E_WARNING` rather then `E_STRICT`.
5.1.2	The function started to validate the `timezone_identifier` parameter.


It's really a hassle that there is no way to set the timezone offset. I attempted to use the code that searched for the correct timezone name by offset from below. I found it didn't work reliably since various cities may have different rules about time DST etc. My solution is to actually search the array and do a test to insure the offset is what I expect it to be. It seems very kludgey (if thats a word) but it works. 





<?php


function setTimezoneByOffset($offset) 


    {


      $testTimestamp = time();


        date_default_timezone_set('UTC');


        $testLocaltime = localtime($testTimestamp,true);


        $testHour = $testLocaltime['tm_hour'];        





      


    $abbrarray = timezone_abbreviations_list();


    foreach ($abbrarray as $abbr) 


    {


        //echo $abbr."<br>";


      foreach ($abbr as $city) 


      {


                date_default_timezone_set($city['timezone_id']);


                $testLocaltime     = localtime($testTimestamp,true);


                $hour                     = $testLocaltime['tm_hour'];        


                $testOffset =  $hour - $testHour;


                if($testOffset == $offset)


                {


                    return true;


                }


      }


    }


    return false;


    }


?>

Christopher Kramer
09-Jan-2010 04:52


I experienced that using this function highly increases performance of functions like getdate() or date() using PHP 5.2.6 on Windows.

I experienced similar results on Linux servers with PHP 5.2.6 and 5.2.10, although the difference was not that significant on these servers: The PHP 5.2.10 server did run with date_default_timezone_set ("only") twice as fast as without. The 5.2.6 server did 5 times faster with date_default_timezone_set. As you can see below, the 5.2.6-Windows machine did a LOT faster.

Of course these machines have completely different hardware and can not really be compared, but all show improved performance.



I checked PHP 4.4.9 on Windows (without date_default_timezone_set of course) and noticed that its as fast as PHP 5.2.6 with date_default_timezone_set.



The following script shows this:



<?php



# uncomment to see difference

# date_default_timezone_set(date_default_timezone_get());



function getmicrotime()

 {

 list($usec, $sec) = explode(' ',microtime());

 return ($sec.substr($usec,1,7));

 }

 

$start=mktime(0,0,0,1,1,2005);

$end=mktime(0,0,0,1,1,2020);

$nr=50000;

 

$start_time=getmicrotime();

for($i=0;$i<$nr;$i++) {

# $value=getdate(rand($start,$end));

  date("H:i:s d.m.Y",rand($start,$end));

}

$end_time=getmicrotime();



echo "Time: ".($end_time-$start_time);



// With date_default_timezone_set(): "Time: 0.379343986511"

// Without date_default_timezone_set(): "Time: 7.4971370697"



?>



Note that the timezone is not changed, it is only set again. I really wonder why this makes such a big performance difference, but its good to know.

ted dot chou12 at gmail dot com
03-Dec-2008 08:13


Timezone using other approaches:

<?php $datetime = strtotime($originaldatetime) + $time;

$datetime = date('M d, Y h:i A', $datetime);?>



$time obtained from table below:

-25200|International Date Line (West) GMT-12|

-21600|Midway Island, Samoa GMT-11|

-18000|Hawaii, Honolulu GMT-10|

-14400|Alaska GMT-9|

-10800|Pacific Standard Time, US, Canada GMT-8|

-7200|British Columbia N.E., Santa Fe, Mountain Time GMT-7|

-3600|Central America, Chicago, Guatamala, Mexico City GMT-6|

0|US, Canada, Bogota, Boston, New York GMT-5|

+3600|Canada, Santiago, Atlantic Standard Time GMT-4|

+7200|Brazilia, Buenos Aires, Georgetown, Greenland GMT-3|

+10800|Mid-Atlantic GMT-2|

+14400|Azores, Cape Verde Is., Western Africa Time GMT-1|

+18000|London, Iceland, Ireland, Morocco, Portugal GMT|

+21600|Amsterdam, Berlin, Bern, Madrid, Paris, Rome, GMT+1|

+25200|Athens, Cairo, Cape Town, Finland, Greece, Israel GMT+2|

+28800|Ankara, Aden, Baghdad, Beruit, Kuwait, Moscow GMT+3|

+32400|Abu Dhabi, Baku, Kabul, Tehran, Tbilisi, Volgograd GMT+4|

+36000|Calcutta, Colombo, Islamabad, Madras, New Dehli GMT+5|

+39600|Almaty, Dhakar, Kathmandu, Colombo, Sri Lanka GMT+6|

+43200|Bangkok, Hanoi, Jakarta, Phnom Penh, Australia GMT+7|

+46800|Taipei, Beijing, Hong Kong, Singapore, GMT+8|

+50400|Seoul, Tokyo, Central Australia GMT+9|

+54000|Brisbane, Canberra, Guam, Melbourne, Sydney, GMT+10|

+57600|Magadan, New Caledonia, Solomon Is. GMT+11|

+61200|Auckland, Fiji, Kamchatka, Marshall, Wellington, GMT+12|

jason at jasonpriem dot com
12-Nov-2008 05:29


While it's easy to change timezones based on names or abbreviations, I haven't found any straightforward way of doing so using an offset integer.  This situation comes up if you're using AJAX to get information about a user's timezone; javascript's getTimezoneOffset() method just sends you an offset number. So, here's my clunky solution: an adaptation of chris' function at http://us.php.net/manual/en/function.timezone-name-from-abbr.php.





<?php


    function set_tz_by_offset($offset) {


        $offset = $offset*60*60;


        $abbrarray = timezone_abbreviations_list();


        foreach ($abbrarray as $abbr) {


            //echo $abbr."<br>";


                foreach ($abbr as $city) {


                    //echo $city['offset']." $offset<br>";


                        if ($city['offset'] == $offset) { // remember to multiply $offset by -1 if you're getting it from js


                               date_default_timezone_set($city['timezone_id']);


                               return true;


                        }


                }


        }


    date_default_timezone_set("ust");


       return false;


       }





set_tz_by_offset(-1);





?>





[EDIT BY thiago AT php DOT net: This code has contributions from iateadonut at gmail dot com]

Anonymous
28-Sep-2008 07:34


If you have problems with errors, why the default is not set use this on the top of the script:



<?php

if(function_exists("date_default_timezone_set") and function_exists("date_default_timezone_get"))

@date_default_timezone_set(@date_default_timezone_get());

?>

Rob Kaper
15-Jul-2008 10:46


If you want users to choose their own timezones, here's some code that gets all available timezones but only uses one city for each possible value:



<?php



$timezones = DateTimeZone::listAbbreviations();



$cities = array();

foreach( $timezones as $key => $zones )

{

    foreach( $zones as $id => $zone )

    {

        /**

         * Only get timezones explicitely not part of "Others".

         * @see http://www.php.net/manual/en/timezones.others.php

         */

        if ( preg_match( '/^(America|Antartica|Arctic|Asia|Atlantic|Europe|Indian|Pacific)\//', $zone['timezone_id'] ) )

            $cities[$zone['timezone_id']][] = $key;

    }

}



// For each city, have a comma separated list of all possible timezones for that city.

foreach( $cities as $key => $value )

    $cities[$key] = join( ', ', $value);



// Only keep one city (the first and also most important) for each set of possibilities. 

$cities = array_unique( $cities );



// Sort by area/city name.

ksort( $cities );



?>

PeerGoal.com
12-Feb-2007 01:21


The problem:



date() [function.date]: It is not safe to rely on the system's timezone settings. Please use the date.timezone setting, the TZ environment variable or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/Los_Angeles' for 'PST/-8.0/no DST' instead



Of course this is a problem that recently surfaced since PHP5. Quick fix is to set your time zone, add this line to your php code:



date_default_timezone_set("America/Los_Angeles");

davidn at datalinktech dot com dot au
22-Dec-2006 02:27


Note that there may be some unexpected side-effects that result from using either set_default_timezone() or the putenv("TZ=...") workalike for earlier PHP versions.  ANY date formatted and output either by PHP or its apache host process will be unconditionally expressed in that timezone.





[red. That is only true for the putenv() hack - Derick]





This does indeed include the web server's logs and other output files and reports which by default usually do not include any indication of timezone. This has a further side-effect on log processing and analysis, obviously.

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date_diff

date_default_timezone_get

Last updated: Fri, 12 Mar 2010