PHP daylight saving time detection

Question

I need to send an email to users based wherever in the world at 9:00 am local time. The server is in the UK. What I can do is set up a time difference between each user and

Answer 1

As Jimmy points out you can use timezone transitions, but this is not available on PHP <5.3. as dateTimeZone() is PHP>=5.2.2 but getTransitions() with arguments is not! In that case here is a function that can give you timezone data, including whether in DST or not.

function timezonez($timezone = 'Europe/London'){
    $tz = new DateTimeZone($timezone);
    $transitions = $tz->getTransitions();
    if (is_array($transitions)){
        foreach ($transitions as $k => $t){
            // look for current year
            if (substr($t['time'],0,4) == date('Y')){
                $trans = $t;
                break;
            }
        }
    }
    return (isset($trans)) ? $trans : false;
}

Having said that, there is a simpler method using date() if you just need to know whether a timezone is in DST. For example if you want to know if UK is in DST you can do this:

date_default_timezone_set('Europe/London');
$bool = date('I'); // this will be 1 in DST or else 0

... or supply a timestamp as a second arg to date() if you want to specify a datetime other than your current server time.