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From: std-unix@ut-sally.UUCP (Moderator, John Quarterman)
Newsgroups: mod.std.unix
Subject: negative time_t values
Message-ID: <5729@ut-sally.UUCP>
Date: Mon, 15-Sep-86 12:17:41 EDT
Article-I.D.: ut-sally.5729
Posted: Mon Sep 15 12:17:41 1986
Date-Received: Mon, 15-Sep-86 20:54:50 EDT
References: <5663@ut-sally.UUCP> <5673@ut-sally.UUCP>
Organization: IEEE 1003 Portable Operating System for Computer Environments Committee
Lines: 60
Keywords: RFC.001, time zones
Approved: jsq@sally.UUCP

From: mnetor!utzoo!dciem!msb@seismo.UUCP  (Mark Brader)
Date: Thu, 11 Sep 86 18:37:22 edt

> Another example where time values outside the currently supported
> (or proposed) range would be useful:  some of us like to play with
> genealogical software;  I have known ancestors back to the thirteenth
> century and frequently work with data to the sixteenth century.
> But time_t probably isn't the appropriate format to keep such dates,
> considering Julian vs. Gregorian calendars, old and new style new years,

I would say that time_t WOULD be the appropriate format, for PRECISELY
those reason, if the range was available.  To say otherwise is to say
that time_t is inappropriate for the way it's normally used because of
time zones and daylight and standard time.

[ Not precisely, since the form a date is recorded in may vary according
to not only present location but national origin of the recorder or of the
person whose date it is, since there are relatively odd formats (1617/18
is a common format, being used with a date between Jan 1 and Mar 15),
since many dates are incomplete (e.g., only year is known), and since
accuracy to the hour is very rare, not to even mention minutes or seconds.

Incidentally, the Mormon Church is coordinating the development of
something called GEDCOM (GEnealogical Data COMmunications), which is
a genealogical data interchange format.  (It looks rather like a network
presentation layer to me, even resembling XDR a bit.)  They must have
produced some standard for genealogical dates.  I believe I will write
off for a copy for myself.  The address (if anyone else is interested)
is probably

	Genealogical Department
	Ancestral File Operations Unit
	50 E. North Temple St.
	Salt Lake City, UT 84150

However, I suspect that general discussions on genealogy belong in
another newsgroup, so submissions to mod.std.unix related to genealogy
should probably be kept related to date formats or other implementation
issues.  -mod ]

While I'm writing I must correct the common assertion that time_t represents
a time in the UT (GMT) system.  It doesn't.  It represents a time in seconds
from a certain epoch.  The time in time_t form at the moment, for instance, is
526,841,748.  The corresponding time in UT is 4:55:48 pm.  Granted that
the latter is derived from the former by slightly simpler arithmetic than
is my local zone time, that doesn't mean that a time_t represents a time
in UT in particular.

I don't think this is of sufficient interest to post to mod.std.unix,
but you may post any or all if you wish.

Mark Brader, utzoo!dciem!msb
	If ... it seems easier to subvert UNIX systems than most other systems,
	the impression is a false one.  The subversion techniques are the same.
	It is just that it is often easier to write, install, and use programs
	on UNIX systems than on most other systems, and that is why the UNIX
	system was designed in the first place.
				-- Frederick T. Grampp & Robert H. Morris

Volume-Number: Volume 6, Number 48