dealing with timestamped data collected in one zone and reportedin another
 

I'm surprised I can't find what I'm trying to do in existing modules or
maybe I'm just not looking in the right places. 8-)

I'm creating some time based logs (recording the UTC as reported by
gettimeofday()) in one timezone and I want to play them back in another,
showing the times on the system where they were initially recorded. In
other words, if I record a file in stockholm which is GMT +2 and play it
back in Boston which is GMT -4, data recorded at midnight in stockholm
shows up 6 hours earlier because of the time difference.

The simple solution, and this is too simple as I'll get to in a minute,
is to just record the timezone where the data was recorded. That way
when I go to play it back I can tell there is a 6 hour difference and
simply adjust the times accordingly before calling localtime() to
convert them. This works like a champ, but...

Although many countries around the world support daylight savings time,
they do not do it on the same date! In other words, if I use my simple
algorithm above it will break when one country has adjusted its clocks
and the other hasn't. The one simple solution I can think of that will
make this all work is that if I were do know my offset from GMT not for
the current date, but for the date of the data I wish to process. But I
can't seem to find any such function.

Can someone help? Does someone have a better way to solve this problem?

-mark

Re: dealing with timestamped data collected in one zone and reportedin another
 

Mark Seger wrote:
[...]
> Although many countries around the world support daylight savings time,
> they do not do it on the same date! In other words, if I use my simple
> algorithm above it will break when one country has adjusted its clocks
> and the other hasn't. The one simple solution I can think of that will
> make this all work is that if I were do know my offset from GMT not for
> the current date, but for the date of the data I wish to process. But I
> can't seem to find any such function.
>
> Can someone help? Does someone have a better way to solve this problem?
>
> -mark

For dealing with timezones, try the modules available under DateTime.
See CPAN or http://datetime.perl.org/ for more information.

Re: dealing with timestamped data collected in one zone and reportedin another
 

Mark Seger wrote:
>
> Although many countries around the world support daylight savings time,
> they do not do it on the same date! In other words, if I use my simple
> algorithm above it will break when one country has adjusted its clocks
> and the other hasn't.

This is OS dependent. Most Unix systems (using Olson's time code)
would handle this correctly.

> Can someone help? Does someone have a better way to solve this problem?

Which OS are you using? Which OS is the final user going to be using?


--
Just because I've written it doesn't mean that
either you or I have to believe it.