On 11 February 2004 20:26, Richard Day wrote:
> Hello:
>
>
> Environment:
> Linux server
> PHP 4.3.4
>
> This code:
>
> echo '<br>'.strftime('%T %Z',mktime()).', Timestamp='.mktime();
> echo '<br>'.strftime('%T GMT',gmmktime()).',
> Timestamp='.gmmktime();
>
> yields this result:
>
> 23:52:08 EST, Timestamp=1076475128
> 18:52:08 GMT, Timestamp=1076457128
>
> Why? GMT should be 5 hours ahead of EST, not 5 behind. Right?
> What am I
> missing here??
Well, that looks very suspicious, and probably not for the reasons you're
thinking.
I can explain why you get that result, but it means that either (a) there's
a bug in gmmktime(), or (b) the documentation for gmmktime() is wrong (or,
at least, misleading). So, let's take it step-by-step:
1. gmmktime(), according to the manual, should use the "current
corresponding GMT value" for it's omitted arguments.
2. In my book, at 23:52:08 EST that means it should be using 04:52:08 GMT on
the following day (we'll discuss this later, since, whilst giving a
different result, it still wouldn't produce what you're expecting!).
3. However, let's guess that gmmktime() is actually using the *local* time
value of 23:52:08, but treating it as if it were GMT.
4. In which case, you'll get a timestamp for 23:52:08 GMT.
5. Because timestamps are absolute (not adjusted for timezone), this is also
the timestamp for 18:52:08 EST.
6. 18:52:08 is what you're getting printed.
7. QED.
This behaviour is *not* what the manual says should happen, and in my
opinion is counter-intuitive. However, if gmmktime() were to behave as the
manual, at least how I read it, suggests, this is what would happen:
1. gmmktime() would calculate a timestamp for 04:52:08 GMT (next day).
2. Because timestamps are absolute, this is also the timestamp for 23:52:08
EST.
3. So strftime() still outputs 23:52:08.
Ergo, this is not the way to produce an adjusted time. One way to do what
you're looking for is to feed the same timestamp to date('%H:%i:%s') and
gmdate('%H:%i:%s). If you want something you can feed to strftime() for the
GMT date, you need to acquire your timezone's offset from GMT in seconds
(e.g. with date('Z');) and subtract that from the timestamp.
HTH
Cheers!
Mike
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Mike Ford, Electronic Information Services Adviser,
Learning Support Services, Learning & Information Services,
JG125, James Graham Building, Leeds Metropolitan University,
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