Convert local date time to UTC date time - php

Question

When user enters Date and time using 'input type=date name="date"' && 'input type=time name="time"' tags according to his/her timezone,
for eg :- If a user from India, (Asia/Kolkata) timezone entered a date : 1/22/14 and time : 5:30pm , I need to Convert it into UTC time stamp for storing it to DB, To Achive that
I used below code:-
$year=substr($date,0,4);
$month=substr($date,5,2);
$day=substr($date,8);
$hour=substr($time,0,2);
$minute=substr($time,3);
$clientzone=mysql_result(mysql_query("select timezone from c_users_extra where c_id='{$_SESSION['clientid']}'"),0,0); //Fetches the timezone of user
date_default_timezone_set($clientzone);//Setting default timezone to client timezone
$datetime = new DateTime("$year-$month-$day $hour:$minute:00");
$la_time = new DateTimeZone('UTC');
$datetime->setTimezone($la_time);
$values=$datetime->format('Y-m-d H:i:s');
$year=substr($values,0,4);
$month=substr($values,5,2);
$hour=substr($values,11,2);
$minutes=substr($values,14,2);
$seconds=substr($values,17,2);
$timestamp=mktime($hour,$minutes,$seconds,$month,$day,$year);//creating new timestamp from coverted
print_r(getdate($timestamp));//Result : Array ( [seconds] => 0 [minutes] => 30 [hours] => 6 [mday] => 22 [wday] => 3 [mon] => 1 [year] => 2014 [yday] => 21 [weekday] => Wednesday [month] => January [0] => 1390372200 )
//Expected Result : Array ( [seconds] => 0 [minutes] => 0 [hours] => 12 [mday] => 22 [wday] => 3 [mon] => 1 [year] => 2014 [yday] => 21 [weekday] => Wednesday [month] => January [0] => 1390372200 )
Why I get this wrong time stamp ?

Answer 1

Here is an object oriented example:
<?php
$date = '2014-01-22 18:15:00'; // assumed date is formatted correctly
$clientzone = 'America/New_York'; // assumed timezone is a valid one from your SQL
$dateObj = new DateTime($date, new DateTimeZone($clientzone));
echo "Original: " . $dateObj->format('Y-m-d H:i:sP') . "\n";
$dateObj->setTimezone(new DateTimeZone('UTC')); // convert to UTC
echo "Converted: " . $dateObj->format('Y-m-d H:i:sP') . "\n";
echo "Epoch: ".$dateObj->format('U');
?>
You can format that just like the date function.
The $date and $clientzone are assumed to be valid.

Answer 2

Can't you do something simpler like:
$user_time = strtotime($date);
$dateTimeZone = new DateTimeZone($timezone);
// get the offset from server time (UTC)
$tzOffset = $dateTimeZone->getOffset(new DateTime());
$result_time = $user_time - $tzOffset;

Answer 3

Try following function to convert Local date time to UTC date time
function LocaltoUTC($date_to_convert)
{
$local_timestamp = strtotime($date_t);
$UTC_timestamp += ((-(5.5)) * 3600); // 5.5 is UTC timezone or local timezone
$gmt_datetime = gmdate('y-m-d H:i:s', $UTC_timestamp);
return $gmt_datetime;
}

Answer 4

Here is a similar question. Take a look at Adjusting time zone in PHP with DateTime / DateTimeZone
There is a solution and a more comfortable way to do your task.