how to make datetime class to work with DST and without DST in php?

I have wrote the code where i am using DateTime class which also converts dst following countries time into GMT format. But i want the functionality where i need the DateTime class should work on checkbox selection. when a user checks dst then only that functionality should work. here my code goes........

function ConvertOneTimezoneToAnotherTimezone($time,$currentTimezone,$timezoneRequired)
{
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     $current_zone = new DateTimeZone($currentTimezone);
    // print_r($current_zone);
     //$gmt = new DateTimeZone('GMT');

     $date = new DateTime($time, $current_zone);
    //var_dump($date);
     //$date->setTimezone($gmt);
     $date->setTimezone(new DateTimeZone($timezoneRequired));

     return  $date->format('Y-m-d H:i:s');

    // Convert it back to Original timezone
     //$date->setTimezone($current_zone);
     //return  $date->format('Y-m-d H:i:s');
 }

 $time='2011-03-29 16:07:00.000';

 echo  "Current Date/Time is=".ConvertOneTimezoneToAnotherTimezone($time,'Asia/Kolkata','UTC');

................ please help me.....how to make this to work.......

Try this code and let me know does it work?

function ConvertOneTimezoneToAnotherTimezone($time,$currentTimezone,$timezoneRequired,$considerDST=true) {
  // save current timezone
  $backup_tz = date_default_timezone_get();
  date_default_timezone_set($currentTimezone);
  $t = strtotime($time);
  date_default_timezone_set($timezoneRequired);
  if (!$considerDST && (date('I', $t) == 1)) {
    if ($timezoneRequired == 'Australia/Lord_Howe') $dst='-30 minutes';
    else $dst = "-1 hour";
    $t = strtotime($dst, $t);
    }
  // restore old timezone
  $res = date('Y-m-d H:i:s', $t);
  date_default_timezone_set($backup_tz);
  return $res;
  }

$mytime = '2011-03-29 12:40:00.000';
$myzone = 'UTC';

echo ConvertOneTimezoneToAnotherTimezone($mytime, $myzone, 'Australia/Adelaide', true) . " (Adelaide DST=Yes)<br>";
echo ConvertOneTimezoneToAnotherTimezone($mytime, $myzone, 'Australia/Adelaide', false) . " (Adelaide  DST=No)";

Additional parameter $considerDST is boolean so pass true (or skip this parameter; its default) if you want DST or false if you don't.

Man if you want to convert times to UTC... you need to pass same time as input params of the function.

YOU CANT DO THIS!

$mytime = '2011-03-30 12:52:00.000';
$myzone = 'Europe/Belgrade';
...
$mytime = '2011-03-30 12:52:00.000';
$myzone = 'America/New_York';

and expect same UTC because it snot same time... When it is 12:52 in Belgrade, its 06:52 in NewYork, so...

2011-03-20 12:52:00.000 [Europe/Belgrade]
2011-03-30 06:52:00.000 [America/NewYork]
2011-03-30 16:22:00.000 [Asia/Calcutta] or [Asia/Kolkata]
2011-03-30 19:52:00.000 [Asia/Pyongyang]
etc...

has same UTC time 2011-03-20 10:52:00.000

FROM MY CODE...

$mytime = '2011-03-30 21:00:00.000';
$myzone = 'Australia/Melbourne';

echo ConvertOneTimezoneToAnotherTimezone($mytime, $myzone, 'UTC', true) . " (Melbourne->UTC DST=Yes)<br>";
echo ConvertOneTimezoneToAnotherTimezone($mytime, $myzone, 'UTC', false) . " (Melbourne->UTC DST=No)<br><br>";


$mytime = '2011-03-30 15:30:00.000';
$myzone = 'Asia/Kolkata';

echo ConvertOneTimezoneToAnotherTimezone($mytime, $myzone, 'UTC', true) . " (India->UTC DST=Yes)<br>";
echo ConvertOneTimezoneToAnotherTimezone($mytime, $myzone, 'UTC', false) . " (India->UTC DST=No)<br>";

THATS SAME UTC 10:00... I don't understand! Tell me what are you doing with your code again?

OUTPUT:

2011-03-30 10:00:00 (Melbourne->UTC DST=Yes)
2011-03-30 10:00:00 (Melbourne->UTC DST=No)

2011-03-30 10:00:00 (India->UTC DST=Yes)
2011-03-30 10:00:00 (India->UTC DST=No)