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From: devine@vianet.UUCP (Bob Devine)
Newsgroups: comp.unix.wizards
Subject: Re: Daylight Savings Time: how to fix ctime.c
Message-ID: <161@vianet.UUCP>
Date: Wed, 18-Mar-87 21:35:52 EST
Article-I.D.: vianet.161
Posted: Wed Mar 18 21:35:52 1987
Date-Received: Fri, 20-Mar-87 04:39:05 EST
References: <4992@brl-adm.ARPA>
Organization: Western Digital, Boulder Tech Ctr
Lines: 26

In article <4992@brl-adm.ARPA>, Makey@LOGICON.arpa (Jeff Makey) writes:
> Those of you with UNIX source who plan to fix your ctime routine so it
> knows about the 1987+ daylight savings time rules should be interested
> in the following information about daylight time in the United States.

  A better way exists.  Hardcoding a change into the "ctime" library
is painful (tracking down and changing the affected programs is no fun)
and the changes never stop.  There have been proposals for changes in
the Daylight Saving Time rules for Presidential election years in the
US and individual states may change the rules locally.

  Check mod.sources archives for a file-based public-domain version
of how to deal with timezones and seasonal time changes for many
countries (original author is Arthur Olson; reachable at elsie!ado).

Bob Devine

>     before 1967     no daylight time at all
>     1967 -> 1973    last Sunday in April -> last Sunday in October
>     1974            first Sunday in January -> last Sunday in October
>     1975            last Sunday in February -> last Sunday in October
>     1976 -> 1986    last Sunday in April -> last Sunday in October
>     beginning 1987  first Sunday in April -> last Sunday in October

  The "before 1967" rule is plainly wrong.  Also, each of the above
rules has major exceptions!