How do you change the timezone in PHP for an existing timestamp?

The code for the date and time function:

开发者_运维知识库function date_and_time($format,$timestamp) {

$date_and_time = date($format,$timestamp);
return $date_and_time;

}

And then the code to display it:

    <?php

        echo date_and_time("dS F Y", strtotime($profile[last_activity_date_and_time]));

    ?>

The value of $profile[last_activity_date_and_time] is 2010-01-18 14:34:04

When displayed it shows up as 18th January 2010 - 02:34pm

But, is there any way to change the timezone it is displayed in?

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Not sure if this what you're looking for, but try DateTime

date_default_timezone_set('Europe/London');

$datetime = new DateTime();
$datetime->setTimestamp($yourTimestamp);
echo $datetime->getTimezone()->getName();
echo $datetime->format(DATE_ATOM);

$la_time = new DateTimeZone('America/Los_Angeles');
$datetime->setTimezone($la_time);
echo $datetime->getTimezone()->getName();
echo $datetime->format(DATE_ATOM);

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You can use the this function to set default time zone:

date_default_timezone_set('Europe/London');