How to get time of all timezones in PHP

To get an array of all time zones with their time offset from Greenwich, use the following function:

function get_time_timezones()
{
	$zones_array = array();
	$timestamp = time();
	
	$default_timezone = date_default_timezone_get();
	$timezone_list = timezone_identifiers_list();
	
	foreach ($timezone_list as $zone)
	{
		date_default_timezone_set($zone);
		$zones_array[$zone] = date('P', $timestamp);
	}
	
	date_default_timezone_set($default_timezone);
	
	return $zones_array;
}

What do we have here:
$zones_array — our resulting array of time zones with their time offsets
$timestamp — current time in timestamp format
$default_timezone — the current time zone
$timezone_list — list of all time zones

Then, we loop through the list of time zones and set each as the current one for our site:

foreach ($timezone_list as $zone)
{
	date_default_timezone_set($zone);
	$zones_array[$zone] = date('P', $timestamp);
}

Using the function `date()` with the parameter `'P'`, we determine the time offset from Greenwich.
And finally, we restore the original time zone:

date_default_timezone_set($default_timezone);