使用可变时区从PHP转换为UTC

Question

I store timestamps on my server using a simple timestamp in SQL. When I pull down that timestamp, I run it through the following function in order to format the time.

How do I add to the following function in order to convert $timestamp into whatever timezone the user is querying from?

// Returns the formatted time
function displayDate($timestamp)
{
    $secAgo = time() - $timestamp;
    // 1 day
    if ($secAgo < 86400)
        return date('h:i:A', $timestamp);
    // 1 week
    if ($secAgo < (86400 * 7))
       return date('l', $timestamp);
    // older than 1 week
    return date('m/t/y', $timestamp);
}

Answer 1

If you have timezone name to change, you can use something like:

$date = new DateTime(date('Y-m-d H:i:s', $timestamp), new DateTimeZone('UTC'));
$date->setTimezone(new DateTimeZone('Asia/Vladivostok'));
return $date->format('m/t/y');

Where Asia/Vladivostok is the user's custom timezone.