Dates - back to basics.

Hello ..

Occasionaly I realise that I take certain functionality for granted and
don't understand it as well as perhaps I should.
This is one of those times.

Regarding the behaviour of integer timestamps -
Can anyone tell me why the full dates returned [below] from two timestamps
have different timezone offsets?

<?php
// the epoch.
echo date('Y-m-d H:i:s O', 0);
// prints "1970-01-01 01:00:00 +0100"
// offset +1 hour

// exactly two years later
echo date('Y-m-d H:i:s O', 63072000);
// prints "1972-01-01 00:00:00 +0000"
// offset 0
?>


This seems pretty fundamental - any help is much appreciated.

I don't know what you've done to your computer, but I get:

1970-01-01 00:00:00 +0000

and

1972-01-01 00:00:00 +0000

dave.

"Fabian Hore" <fabianhore@email.com> wrote in message
news:QR4wd.771$qv4.299@newsfe1-win.ntli.net...
> Hello ..
>
> Occasionaly I realise that I take certain functionality for granted and
> don't understand it as well as perhaps I should.
> This is one of those times.
>
> Regarding the behaviour of integer timestamps -
> Can anyone tell me why the full dates returned [below] from two timestamps
> have different timezone offsets?
>
> <?php
> // the epoch.
> echo date('Y-m-d H:i:s O', 0);
> // prints "1970-01-01 01:00:00 +0100"
> // offset +1 hour
>
> // exactly two years later
> echo date('Y-m-d H:i:s O', 63072000);
> // prints "1972-01-01 00:00:00 +0000"
> // offset 0
> ?>
>
>
> This seems pretty fundamental - any help is much appreciated.
>
>
>
>

On Thu, 16 Dec 2004 00:42:24 GMT, "Fabian Hore" <fabianhore@email.com> wrote:

>Occasionaly I realise that I take certain functionality for granted and
>don't understand it as well as perhaps I should.
>This is one of those times.
>
>Regarding the behaviour of integer timestamps -
>Can anyone tell me why the full dates returned [below] from two timestamps
>have different timezone offsets?
>
><?php
>// the epoch.
>echo date('Y-m-d H:i:s O', 0);
>// prints "1970-01-01 01:00:00 +0100"
>// offset +1 hour
>
>// exactly two years later
>echo date('Y-m-d H:i:s O', 63072000);
>// prints "1972-01-01 00:00:00 +0000"
>// offset 0
>?>
>
>
>This seems pretty fundamental - any help is much appreciated.

Searching on Google finds that the above result is in fact correct. From 1968
to 1972, the UK didn't change the clocks in winter.

http://wwp.greenwichmeantime.com/inf...ightsaving.htm

If you want to stick to GMT/UTC, you probably want to use gmdate().

--
Andy Hassall / <andy@andyh.co.uk> / <http://www.andyh.co.uk>
<http://www.andyhsoftware.co.uk/space> Space: disk usage analysis tool

>> Searching on Google finds that the above result is in fact correct. From
1968
>> to 1972, the UK didn't change the clocks in winter.

Perfect. as long as I know why, I can sleep at night.
thanks

But what about the fact that it doesn't do it all the time? On my machine,
both of your examples yielded the expected result - both +0000...

"Fabian Hore" <fabianhore@email.com> wrote in message
news:xtmwd.1385$Fz4.1155@newsfe4-gui.ntli.net...
>>> Searching on Google finds that the above result is in fact correct. From
> 1968
>>> to 1972, the UK didn't change the clocks in winter.
>
> Perfect. as long as I know why, I can sleep at night.
> thanks
>
>
>
>
>
>

> But what about the fact that it doesn't do it all the time? On my machine, both of your examples yielded the expected result -
> both +0000...

It depends on timezone settings on your system, which is used by "date"
function (and other time manipulation functions).

Hilarion

On Fri, 17 Dec 2004 11:32:09 GMT, "d" <d@example.com> wrote:

>But what about the fact that it doesn't do it all the time? On my machine,
>both of your examples yielded the expected result - both +0000...

Timezone settings.

andyh@server:~/tmp$ echo $TZ
Europe/London

andyh@server:~/tmp$ php -q tz.php
1970-01-01 01:00:00 +0100
1972-01-01 00:00:00 +0000

andyh@server:~/tmp$ TZ=UTC php -q tz.php
1970-01-01 00:00:00 +0000
1972-01-01 00:00:00 +0000

--
Andy Hassall / <andy@andyh.co.uk> / <http://www.andyh.co.uk>
<http://www.andyhsoftware.co.uk/space> Space: disk usage analysis tool

"d" <d@example.com> wrote in message
news:Zszwd.416$Qo4.13@fe1.news.blueyonder.co.uk...
> But what about the fact that it doesn't do it all the time? On my
machine,
> both of your examples yielded the expected result - both +0000...
>

Adding the `T' token into your date format string shows whats going on.
<?php
echo "\n", date('Y-m-d H:i:s TO', 0); // "1970-01-01 01:00:00
BST+0100"
echo "\n", date('Y-m-d H:i:s TO', 63072000); // "1972-01-01 00:00:00
GMT+0000"
?>

This makes sense of Andy's first reply regarding the UK's clock changing
nuance.

On my system, the date() function is automatically selecting between British
Summer Time and Greenwich Mean Time.
I'd rather it didn't, so I guess there's a lesson here, Don't be flippant
with timestamps. they're handy and portable but not without their caveats.


A appropriate warning appears in the PHP docs in reference to the mktime()
func.
<<
This can be more reliable than simply adding or subtracting the number of
seconds in a day or month to a timestamp because of daylight savings time.
>>