How to check is timezone identifier valid from code?

Question

I\'ll try to explain what\'s the problem here.

According to list of supported timezones from PHP manual, I can see all valid TZ identifiers in PHP.

My first

Answer 1

Why not use @ operator? This code works pretty well, and you don't change default timezone:

function isValidTimezoneId($timezoneId) {
    @$tz=timezone_open($timezoneId);
    return $tz!==FALSE;
}

If you don't want @, you can do:

function isValidTimezoneId($timezoneId) {
    try{
        new DateTimeZone($timezoneId);
    }catch(Exception $e){
        return FALSE;
    }
    return TRUE;
} 

Answer 2

When I tried this on a Linux system running 5.3.6, your Example #2 gave me 411 zones and Example #3 gave 496. The following slight modification to Example #2 gives me 591:

$zoneList = timezone_identifiers_list(DateTimeZone::ALL_WITH_BC);

There are no zones returned by Example #3 that are not returned with that modified Example #2.

On an OS X system running 5.3.3, Example #2 gives 407, Example #3 gives 564, and the modified Example #2 gives 565. Again, there are no zones returned by Example #3 that are not returned with that modified Example #2.

On a Linux system running 5.2.6 with the timezonedb PECL extension installed, Example #2 gives me 571 zones and Example #3 gives me only 488. There are no zones returned by Example #3 that are not by Example #2 on this system. The constant DateTimeZone::ALL_WITH_BC does not seem to exist in 5.2.6; it was probably added in 5.3.0.

So it seems the simplest way to get a list of all time zones in 5.3.x is timezone_identifiers_list(DateTimeZone::ALL_WITH_BC), and in 5.2.x is timezone_identifiers_list(). The simplest (if not fastest) way to check if a particular string is a valid time zone is still probably @timezone_open($timezoneId) !== false.