Working with Timezones and DST

Hello everyone.

I am creating a JavaScript project which will allow users to see what
time it is in other countries. I am wondering if there's any way to
have the server work this out, without having to update a database
constantly with the times and dates that certain countries set their
clocks back or forward.

Can this be done, or do I need to connect to a time server? Ideally, I
need a time server that will return a JavaScript object containing the
information I need, but I don't think one exists.

Please could someone suggest the steps I need to take to quickly
obtain the correct time for any given country, which will take DST
into account? Sadly, to my knowledge, the UK is the only country that
has hard-coded rules for when the clocks are changed, where as it
seems to be a political thing for all other countries.

If I have to run a database with this information, then so be it, but
it seems like a lot of manual work, and I'm not sure how often I'd
need to update it.

Many thanks in advance.

Daz.

On 27 May 2007 06:24:49 -0700, Daz <cutenfuzzy@gmail.com> wrote:

>I am creating a JavaScript project which will allow users to see what
>time it is in other countries. I am wondering if there's any way to
>have the server work this out, without having to update a database
>constantly with the times and dates that certain countries set their
>clocks back or forward.
>
>Can this be done, or do I need to connect to a time server? Ideally, I
>need a time server that will return a JavaScript object containing the
>information I need, but I don't think one exists.
>
>Please could someone suggest the steps I need to take to quickly
>obtain the correct time for any given country, which will take DST
>into account? Sadly, to my knowledge, the UK is the only country that
>has hard-coded rules for when the clocks are changed, where as it
>seems to be a political thing for all other countries.
>
>If I have to run a database with this information, then so be it, but
>it seems like a lot of manual work, and I'm not sure how often I'd
>need to update it.

Most operating systems have comprehensive timezone data available, which gets
taken into account via the TZ environment variable when formatting UNIX
timestamps (which are always based on UTC).

PHP 5.1 introduced improved timezone handling into the core of PHP itself,
see: http://uk2.php.net/manual/en/functio...mezone-set.php (which
is preferred over setting environment variables, if available).

<?php
foreach (array('US/Eastern', 'US/Central', 'UTC', 'Europe/London',
'Europe/Paris') as $tz)
{
putenv("TZ=$tz"); // or use date_default_timezone_set
print date("r") . " (TZ=$tz)\n";
}
?>

$ php test.php
Sun, 27 May 2007 09:56:21 -0400 (TZ=US/Eastern)
Sun, 27 May 2007 08:56:21 -0500 (TZ=US/Central)
Sun, 27 May 2007 14:56:21 +0100 (TZ=Europe/London)
Sun, 27 May 2007 15:56:21 +0200 (TZ=Europe/Paris)
Sun, 27 May 2007 13:56:21 +0000 (TZ=UTC)

--
Andy Hassall :: andy@andyh.co.uk :: http://www.andyh.co.uk
http://www.andyhsoftware.co.uk/space :: disk and FTP usage analysis tool

On May 27, 2:58 pm, Andy Hassall <a...@andyh.co.uk> wrote:
> On 27 May 2007 06:24:49 -0700, Daz <cutenfu...@gmail.com> wrote:
>
>
>
> >I am creating a JavaScript project which will allow users to see what
> >time it is in other countries. I am wondering if there's any way to
> >have the server work this out, without having to update a database
> >constantly with the times and dates that certain countries set their
> >clocks back or forward.
>
> >Can this be done, or do I need to connect to a time server? Ideally, I
> >need a time server that will return a JavaScript object containing the
> >information I need, but I don't think one exists.
>
> >Please could someone suggest the steps I need to take to quickly
> >obtain the correct time for any given country, which will take DST
> >into account? Sadly, to my knowledge, the UK is the only country that
> >has hard-coded rules for when the clocks are changed, where as it
> >seems to be a political thing for all other countries.
>
> >If I have to run a database with this information, then so be it, but
> >it seems like a lot of manual work, and I'm not sure how often I'd
> >need to update it.
>
> Most operating systems have comprehensive timezone data available, which gets
> taken into account via the TZ environment variable when formatting UNIX
> timestamps (which are always based on UTC).
>
> PHP 5.1 introduced improved timezone handling into the core of PHP itself,
> see:http://uk2.php.net/manual/en/functio...-set.php(which
> is preferred over setting environment variables, if available).
>
> <?php
> foreach (array('US/Eastern', 'US/Central', 'UTC', 'Europe/London',
> 'Europe/Paris') as $tz)
> {
> putenv("TZ=$tz"); // or use date_default_timezone_set
> print date("r") . " (TZ=$tz)\n";}
>
> ?>
>
> $ php test.php
> Sun, 27 May 2007 09:56:21 -0400 (TZ=US/Eastern)
> Sun, 27 May 2007 08:56:21 -0500 (TZ=US/Central)
> Sun, 27 May 2007 14:56:21 +0100 (TZ=Europe/London)
> Sun, 27 May 2007 15:56:21 +0200 (TZ=Europe/Paris)
> Sun, 27 May 2007 13:56:21 +0000 (TZ=UTC)
>
> --
> Andy Hassall :: a...@andyh.co.uk ::http://www.andyh.co.ukhttp://www.and....co.uk/space:: disk and FTP usage analysis tool

Hi Andy. That's wonderful. Thank you very much for such a great
example. Sadly, the server I am doing this project for, is running PHP
4...

Am I correct in saying that DST has been accounted for in your
example? It looks like it has, but I need to be certain.

Thanks again.

Daz.

On 27 May 2007 07:15:14 -0700, Daz <cutenfuzzy@gmail.com> wrote:

>Hi Andy. That's wonderful. Thank you very much for such a great
>example. Sadly, the server I am doing this project for, is running PHP
>4...

Not so bad, since the TZ environment variable will still work. From another
server:

$ php -v
PHP 4.3.10 (cli) (built: Jan 12 2005 13:10:04)
Copyright (c) 1997-2004 The PHP Group
Zend Engine v1.3.0, Copyright (c) 1998-2004 Zend Technologies

$ php test.php
Sun, 27 May 2007 14:34:24 +0000 (TZ=US/Eastern)
Sun, 27 May 2007 14:34:24 +0000 (TZ=US/Central)
Sun, 27 May 2007 14:34:24 +0000 (TZ=UTC)
Sun, 27 May 2007 15:34:24 +0100 (TZ=Europe/London)
Sun, 27 May 2007 16:34:24 +0200 (TZ=Europe/Paris)

OK, that server won't take US/Eastern or Central - they're wrongly coming out
as +0000. It apparently takes the city-based US timezones, though:

Sun, 27 May 2007 10:39:44 -0400 (TZ=America/New_York)
Sun, 27 May 2007 09:39:44 -0500 (TZ=America/Chicago)
Sun, 27 May 2007 14:39:44 +0000 (TZ=UTC)
Sun, 27 May 2007 15:39:44 +0100 (TZ=Europe/London)
Sun, 27 May 2007 16:39:44 +0200 (TZ=Europe/Paris)

The supported timezone names in PHP 4 rely entirely on the operating system -
in this case it seems FreeBSD's timezones list differs slightly from Linux.

PHP 5's improved support is useful as it has its own timezone database, so
it's more portable.

>Am I correct in saying that DST has been accounted for in your
>example? It looks like it has, but I need to be certain.

Yes, it has. See "Europe/London" being +1 as we're in British Summer Time at
the moment.
--
Andy Hassall :: andy@andyh.co.uk :: http://www.andyh.co.uk
http://www.andyhsoftware.co.uk/space :: disk and FTP usage analysis tool