Thank you all for the responses. Markus exactly explained the why. (In my application, I needed to get the local-broken-down-time format of the transition time point, but do NOT apply the STD/DST transition to it. The one mentioned in my previous email is the result that the DST transition has been applied to it, which was my fault. I figured out a way to fix it and get the right result.) Yuming -----Original Message----- From: Markus Kuhn [mailto:Markus.Kuhn@cl.cam.ac.uk] Sent: Thursday, February 03, 2005 11:04 AM To: Fei Yuming-CYF001 Cc: tz@elsie.nci.nih.gov Subject: Re: FW: glibc, Linux: about the time zone transition values in the lo calt ime file "Olson, Arthur David (NIH/NCI)" wrote on 2005-02-03 13:57 UTC: Fei Yuming <Yuming.Fei@motorola.com> wrote:
On Linux systems, it seems that the transitions stored in the localtime file are not the current time to start the transition, but the new local current time right after the transition.
The following might help to clarify what I suspect you might got confused about: The transition times are stored in the "Seconds Since The Epoch (time_t)" time scale, which itself (like UTC) has *no* DST transitions. The effect you observed occured only *after* the application of the time_t->local-broken-down-time conversion, which you applied to convert the time_t value back into a human-consumable local-time yyyy-mm-dd hh:mm:ss display. It is only natural, that the transition time point itself is displayed using the same convention as the time point immediately afterwards. [By the way: This is for the same reason for which most digital clocks show 00:00 and not 24:00 at the midnight transition. Note that 24:00 would be valid only for the infinitesimal point in time at exactly midnight (and therefore invisible to the human eye), whereas 00:00 is a valid truncation until 00:01 is reached. Therefore, we use the backwards-looking notation 24:00 only when we refer to the end of a time interval (as in tonight 22:00-24:00), but not when we refer to the current time (as in "It is now 00:00.").] Markus -- Markus Kuhn, Computer Lab, Univ of Cambridge, GB http://www.cl.cam.ac.uk/~mgk25/ | __oo_O..O_oo__