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Re: about cvs time

From: David Taylor
Subject: Re: about cvs time
Date: Wed, 19 Sep 2001 17:41:51 -0700

Eric Siegerman wrote:

> On Tue, Sep 18, 2001 at 11:03:03AM -0400, Larry Jones wrote:
> > The problem is that the offset between UTC and local (civil) time
> > changes from time to time (at least twice per year in the case of those
> > countries that have "daylight saving" or "summer" time).  So, knowing
> > what the offset is *right now* doesn't tell you anything about what the
> > offset was some time in the past.
> I thought localtime(3) took care of all that.  Or isn't it
> portable enough?

On Solaris 7, according to the man page, localtime(3) takes care of daylight
savings time for the US  only:

"These functions know about the peculiarities of this conversion  for
various  time periods for the U.S. (specifically, the years 1974, 1975, and
1987). They will  handle  the  new daylight  savings  time  starting  with
the first Sunday in April, 1987."

Since it also  uses the value of the TZ environment variable, it gives
correct answers for *current* time for other regions also.  But it does not
deal with changes in the rules for daylight savings time outside the US
(e.g., EU changed the rules in 1996). If  region has changed its daylight
savings time rules, the current TZ may be wrong for a date before the
change.  So using localtime(3) for a date before the change may give an
incorrect answer.

More details at Sun's "Symptoms and Resolutions"  at

Given the difficulties of knowing rules for calculating dates for all
regions for all times since 1970, I would be surprised if this limitation
only existed on Solaris 7.


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