Thank you for your reply.

I discovered the OlsonNames() function to get the time-zone names in my
system. Rui get a warning message when using a not recognized tz. On my
system this doesn't succed.

I solved as follow:

dt1 = as.POSIXct("2014-04-18 09.00", format="%Y-%m-%d %H.%M", tz =
"Europe/Rome")

dt2 = as.POSIXct("2014-04-18 09.00", format="%Y-%m-%d %H.%M", tz =
"America/Los_Angeles")

dt1[1] "2014-04-18 09:00:00 CEST"dt2[1] "2014-04-18 09:00:00
PDT"dt1-dt2Time difference of -9 hours


Thank you,
Nicola



2014-04-18 21:59 GMT+02:00 Prof Brian Ripley <ripley@stats.ox.ac.uk>:

> On 18/04/2014 19:46, Rui Barradas wrote:
>
>> Hello,
>>
>> The reason why is that you've misspelled CET (not CEST)
>>
>
> Neither CET nor CEST are portable time-zone names.  We have not been given
> the 'at a minimum' information required by the posting guide, so please
> read ?Sys.timezone on your system.
>
>
>
>
>>  > dt1 = as.POSIXct("2014-04-18 09.00", format="%Y-%m-%d %H.%M", tz =
>> "CEST")
>> Warning messages:
>> 1: In strptime(x, format, tz = tz) : unknown timezone 'CEST'
>> 2: In as.POSIXct.POSIXlt(as.POSIXlt(x, tz, ...), tz, ...) :
>>    unknown timezone 'CEST'
>>  > dt2 = as.POSIXct("2014-04-18 09.00", format="%Y-%m-%d %H.%M", tz =
>> "GMT")
>>  > dt1 = as.POSIXct("2014-04-18 09.00", format="%Y-%m-%d %H.%M", tz =
>> "CET")
>>  > dt1-dt2
>> Time difference of -2 hours
>>
>>
>> Hope this helps,
>>
>> Rui Barradas
>>
>> Em 18-04-2014 17:13, Nicola Sturaro Sommacal escreveu:
>>
>>> Hi.
>>>
>>> I am new to POSIX and I'd like to understand the reason of this
>>> difference.
>>>
>>> dt1 = as.POSIXct("2014-03-29 09.00", format="%Y-%m-%d %H.%M")
>>> dt2 = as.POSIXct("2014-03-30 09.00", format="%Y-%m-%d %H.%M")
>>> dt2-dt1
>>>
>>>  dt1[1] "2014-03-29 09:00:00 CET"> dt2[1] "2014-03-30 09:00:00 CEST">
>>>> dt2-dt1
>>>>
>>>
>>> Time difference of 23 hours
>>>
>>> This is right, because on Mar 31 at 2 PM we jump directly to 3PM, DST.
>>>
>>> On the contrary, I don't understand the following:
>>>
>>> dt1 = as.POSIXct("2014-04-18 09.00", format="%Y-%m-%d %H.%M", tz =
>>> "CEST")
>>> dt2 = as.POSIXct("2014-04-18 09.00", format="%Y-%m-%d %H.%M", tz =
>>> "GMT")
>>>
>>>  dt1[1] "2014-04-18 09:00:00 CEST"> dt2[1] "2014-04-18 09:00:00 GMT">
>>>> dt1-dt2Time difference of 0 secs
>>>>
>>>
>>>
>>> I should expected a time difference of 2 hours, as CEST is GMT+2.
>>>
>>> Anyone can help me?
>>>
>>> Thank you,
>>> Nicola
>>>
>>>     [[alternative HTML version deleted]]
>>>
>>> ______________________________________________
>>> R-help@r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide
>>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>>
>> ______________________________________________
>> R-help@r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
>
> --
> Brian D. Ripley,                  ripley@stats.ox.ac.uk
> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> University of Oxford,             Tel:  +44 1865 272861 (self)
> 1 South Parks Road,                     +44 1865 272866 (PA)
> Oxford OX1 3TG, UK                Fax:  +44 1865 272595
>

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