date_default_timezone_set

Christopher Kramer (2013-03-09 21:39:40)

Regarding my post 3 years before:
The performance impact seems to be caused by the fact that a log message is written if you do not set a timezone. And writing a log message to disk can take significantly longer than actually calculating date() or getdate() - esp. on systems with slow IO like the Windows machine I used 3 years ago.
PHP 4 did not produce any log messages, and therefore was as fast as PHP5 with a timezone set.
So if you run date() or getdate() a lot of times, this will cause a lot of log messages to be written to disk (if you did not disable them in your php.ini settings), which will take its time.
So either use this function or set the ini-setting "date.timezone" to make things faster.
(And have a look into your logfiles! Solving all those warnings will not only save you disk space but will also speed up your web application.)

Pierre Gourlaouen (2012-07-06 08:45:52)

A simple method for conversation between two time zone.

<?php
$date = new DateTime("2012-07-05 16:43:21", new DateTimeZone('Europe/Paris'));

date_default_timezone_set('America/New_York');

echo date("Y-m-d h:iA", $date->format('U'));

// 2012-07-05 10:43AM
?>

Stephan Rudlof (2012-05-25 02:26:55)

Problem with the table above: timezone offset from Javascript contains summertime offset, but php wants to have geographic timezone without summertime derivation (seems to compute it itself).
Here is an alternative, which works for me (summertime in Germany):
<?php
  /* May fail for timezones not 'Etc/GMT*' (if they are summertime). */
  $zonelist = array('Etc/GMT+12' => -12.00, 'Etc/GMT+11' => -11.00, 'Etc/GMT+10' => -10.00, 'Etc/GMT+9' => -9.00, 'Etc/GMT+8' => -8.00, 'Etc/GMT+7' => -7.00, 'Etc/GMT+6' => -6.00, 'Etc/GMT+5' => -5.00, 'America/Caracas' => -4.30, 'Etc/GMT+4' => -4.00, 'America/St_Johns' => -3.30, 'Etc/GMT+3' => -3.00, 'Etc/GMT+2' => -2.00, 'Etc/GMT+1' => -1.00, 'Etc/GMT' => 0, 'Etc/GMT-1' => 1.00, 'Etc/GMT-2' => 2.00, 'Etc/GMT-3' => 3.00, 'Asia/Tehran' => 3.30, 'Etc/GMT-4' => 4.00, 'Etc/GMT-5' => 5.00, 'Asia/Kolkata' => 5.30, 'Asia/Katmandu' => 5.45, 'Etc/GMT-6' => 6.00, 'Asia/Rangoon' => 6.30, 'Etc/GMT-7' => 7.00, 'Etc/GMT-8' => 8.00, 'Etc/GMT-9' => 9.00, 'Australia/Darwin' => 9.30, 'Etc/GMT-10' => 10.00, 'Etc/GMT-11' => 11.00, 'Etc/GMT-12' => 12.00, 'Etc/GMT-13' => 13.00);
?>

daneiracleous at gmail dot com (2012-01-28 08:11:24)

If you want to set the default timezone to the user's local timezone, you have to combine PHP and JavaScript. Here's how to do it:

<?php
session_start();
if(!isset($_SESSION['timezone']))
{
    if(!isset($_REQUEST['offset']))
    {
    ?>
    <script>
    var d = new Date()
    var offset= -d.getTimezoneOffset()/60;
    location.href = "<?php echo $_SERVER['PHP_SELF']; ?>?offset="+offset;
    </script>
    <?php    
    }
    else
    {
        $zonelist = array('Kwajalein' => -12.00, 'Pacific/Midway' => -11.00, 'Pacific/Honolulu' => -10.00, 'America/Anchorage' => -9.00, 'America/Los_Angeles' => -8.00, 'America/Denver' => -7.00, 'America/Tegucigalpa' => -6.00, 'America/New_York' => -5.00, 'America/Caracas' => -4.30, 'America/Halifax' => -4.00, 'America/St_Johns' => -3.30, 'America/Argentina/Buenos_Aires' => -3.00, 'America/Sao_Paulo' => -3.00, 'Atlantic/South_Georgia' => -2.00, 'Atlantic/Azores' => -1.00, 'Europe/Dublin' => 0, 'Europe/Belgrade' => 1.00, 'Europe/Minsk' => 2.00, 'Asia/Kuwait' => 3.00, 'Asia/Tehran' => 3.30, 'Asia/Muscat' => 4.00, 'Asia/Yekaterinburg' => 5.00, 'Asia/Kolkata' => 5.30, 'Asia/Katmandu' => 5.45, 'Asia/Dhaka' => 6.00, 'Asia/Rangoon' => 6.30, 'Asia/Krasnoyarsk' => 7.00, 'Asia/Brunei' => 8.00, 'Asia/Seoul' => 9.00, 'Australia/Darwin' => 9.30, 'Australia/Canberra' => 10.00, 'Asia/Magadan' => 11.00, 'Pacific/Fiji' => 12.00, 'Pacific/Tongatapu' => 13.00);
        $index = array_keys($zonelist, $_REQUEST['offset']);
        $_SESSION['timezone'] = $index[0];
    }
}
date_default_timezone_set($_SESSION['timezone']);

//rest of your code goes here
?>

power2all at gmail dot com (2011-02-01 08:30:24)

After poundering and knocking my head on the table, I finally got a proper fix for Windows and PHP timezone handling.

Since Windows applies the DST to ActiveTimeBias in the registry, you only need this to apply.
The only problem is, that it cant use the timezone_set command.

You can request a response back in any date-format you wish, or use the default one given in the function itself.

<?php

// Return proper time
function time_zone_fix($timeGiven = "H:i:s")
{
    $shell = new COM("WScript.Shell") or die("Requires Windows Scripting Host");
    $time_bias = -($shell->RegRead("HKEY_LOCAL_MACHINE\\SYSTEM\\
CurrentControlSet\\Control\\TimeZoneInformation\\
ActiveTimeBias")) / 60;
    $timestamp_bias = 60 * 60 * $time_bias;
    echo $time_bias . "<br />";
    return gmdate($timeGiven, strtotime($timestamp_bias . " seconds"));
}
?>

Anonymous (2010-11-20 13:58:56)

People complaining that there's no way to set the offset - you are wrong. You can easily set the offset from GMT (see "Other" in available zones). And since all zones are offset from GMT it's just easy math with + or - to get that. So if you i.e. want the offset not from GMT but your timezone, then compute offset of your zone from GMT (say if you in Berlin its +1 now (mind summer time!)) and then offset for your target zone (i.e NYC is -5) then sum abs! of these values and set the sign of bigger (abs) value -> total offset from your european zone to NYC is then abs(-5)+abs(1) = 6 and set "-" as NYC zone absolute value is bigger. So whatever time is in Berlin, in NYC it's 6hrs earlier. But it's better to do two step calculation and calculate always from GMT

steve at pozzie dot net (2010-10-11 01:35:20)

Most of the scripts here depend on PHP identifying the correct zone when one is not set, but that does not always happen. 

For example PHP 5.3.3 gives a 'UTC' result for a detected '8.0/no DST'. Not much help.

So for those of us who for very good reasons really cannot set time zones in scripts of in .ini files, here is a function 
for use in a Windows environment that sets the default time zone to the OS time zone and returns the detected and set texts.

<?php
function date_system_timezone_set(){
  $shell = new COM("WScript.Shell") or die("Requires Windows Scripting Host");
  $time_bias = -($shell->RegRead(
"HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Control
\\TimeZoneInformation\\Bias"))/60;
  $ab = -($shell->RegRead(
"HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Control
\\TimeZoneInformation\\ActiveTimeBias"))/60;
  $sc = $shell->RegRead(
"HKEY_USERS\\.DEFAULT\\Control Panel\\International\\sCountry");
  foreach(timezone_abbreviations_list() as $tza) foreach($tza as $entry){
    $country = strtok($entry['timezone_id'],'/');
    $locale = strtok('|');
    if($country==$sc && $ab==($entry['offset']/60/60) && ($ds = $time_bias!=$ab)==$entry['dst']){
      date_default_timezone_set($timezone_identifier = $country."/".$locale);
      return sprintf('%.1f',$ab)."/".($ds?'':'no ').'DST'." ".$timezone_identifier;
     }
   }
  return false; 
 }
?>

Tom S (2010-09-11 06:22:54)

This is a good script if you know or control your system so that you know that the local TZ in your OS is correct. Unfortunately, this script still creates an warning message under BSD UNIX.
To fix this, just add an "@" in front of "localtime" as:
$arr = @localtime($iTime);

Dane Iracleous (2010-07-21 13:48:57)

Here is some useful code to set the default timezone to the user's local timezone. 

<?php
function getLocalTimezone()
{
    $iTime = time();
    $arr = localtime($iTime);
    $arr[5] += 1900; 
    $arr[4]++;
    $iTztime = gmmktime($arr[2], $arr[1], $arr[0], $arr[4], $arr[3], $arr[5], $arr[8]);
    $offset = doubleval(($iTztime-$iTime)/(60*60));
    $zonelist = 
    array
    (
        'Kwajalein' => -12.00,
        'Pacific/Midway' => -11.00,
        'Pacific/Honolulu' => -10.00,
        'America/Anchorage' => -9.00,
        'America/Los_Angeles' => -8.00,
        'America/Denver' => -7.00,
        'America/Tegucigalpa' => -6.00,
        'America/New_York' => -5.00,
        'America/Caracas' => -4.30,
        'America/Halifax' => -4.00,
        'America/St_Johns' => -3.30,
        'America/Argentina/Buenos_Aires' => -3.00,
        'America/Sao_Paulo' => -3.00,
        'Atlantic/South_Georgia' => -2.00,
        'Atlantic/Azores' => -1.00,
        'Europe/Dublin' => 0,
        'Europe/Belgrade' => 1.00,
        'Europe/Minsk' => 2.00,
        'Asia/Kuwait' => 3.00,
        'Asia/Tehran' => 3.30,
        'Asia/Muscat' => 4.00,
        'Asia/Yekaterinburg' => 5.00,
        'Asia/Kolkata' => 5.30,
        'Asia/Katmandu' => 5.45,
        'Asia/Dhaka' => 6.00,
        'Asia/Rangoon' => 6.30,
        'Asia/Krasnoyarsk' => 7.00,
        'Asia/Brunei' => 8.00,
        'Asia/Seoul' => 9.00,
        'Australia/Darwin' => 9.30,
        'Australia/Canberra' => 10.00,
        'Asia/Magadan' => 11.00,
        'Pacific/Fiji' => 12.00,
        'Pacific/Tongatapu' => 13.00
    );
    $index = array_keys($zonelist, $offset);
    if(sizeof($index)!=1)
        return false;
    return $index[0];
} 

date_default_timezone_set(getLocalTimezone());
?>

Frederick Hathaway (2010-03-04 08:54:40)

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 (2010-01-09 07:52:21)

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 (2008-12-02 23:13:13)

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 (2008-11-11 20:29:01)

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 (2008-09-27 22:34:15)

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 (2008-07-15 01:46:56)

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 (2007-02-12 04:21:36)

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 (2006-12-21 17:27:03)

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.