FW: Questions
Fan_Zhenqiang at emc.com
Fan_Zhenqiang at emc.com
Wed Apr 4 22:00:36 UTC 2007
Hi Michael,
Thank you for your reply.
Sorry that I used ambiguous example. What I really asked is:
Is there a function that takes a time zone, say America/Los_Angles, and
a date value such as "2007-11-04 01:30", and tells whether the given
date/time value is a DST in that time zone? If no, how easy is it to
write such a function?
Thanks again.
Zhenqiang Fan
-----Original Message-----
From: Michel Bourget [mailto:michel at sgi.com]
Sent: Wednesday, April 04, 2007 12:39 PM
To: tz at elsie.nci.nih.gov
Cc: Fan, Zhenqiang; tz at lecserver.nci.nih.gov
Subject: Re: FW: Questions
On Wed, 2007-04-04 at 10:41 -0700, Paul Eggert wrote:
> Fan_Zhenqiang at emc.com writes:
>
> > What if a time zone is specified together with the date/time value?
For
> > instance, is there any function that call whether "2007-11-04 01:30
PST"
> > is DST?
>
> Sorry, no; in general that's not possible, as in some locations the
> same abbreviation is used for both standard and daylight time. One
> could do a reasonable job in most cases, as in the other problems you
> mentioned; it shouldn't be that hard, but the functions aren't there
> now.
Bottom line, you need to know the *context*( the geographic location )
of the date, hence the Country/City TZ value information, and not the
abbreviation ( DST, PST, WAT, ... ). Then, as explained earlier, use
localtime() returned 'struct tm'->tm_isdst value. Unfortunately, the %Z
format still gives the abbreviation, not the time zone itself.
Briefly. To compute isdst, you need date and TZ( not its abbreviation ).
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