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From: candycanearter07 <candycanearter07@candycanearter07.nomail.afraid>
Newsgroups: comp.lang.c
Subject: Re: "A diagram of C23 basic types"
Date: Wed, 16 Apr 2025 14:00:03 -0000 (UTC)
Organization: the-candyden-of-code
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Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote at 23:42 this Tuesday (GMT):
>>BGB <cr88192@gmail.com> writes:
>> On 4/15/2025 9:10 AM, Scott Lurndal wrote:
>>> BGB <cr88192@gmail.com> writes:
>>>> On 4/14/2025 5:33 PM, Lawrence D'Oliveiro wrote:
>>>>> On Mon, 14 Apr 2025 13:36:07 -0500, BGB wrote:
>>>>>
>>>>>> On 4/14/2025 12:40 PM, candycanearter07 wrote:
[snip]
>>>>> Relative to what epoch?
>>>>>
>>>>
>>>> Probably still Jan 1 1970...
>>> Technically, it depends on the timezone:
>
> Technically, it does not.
>
> POSIX defines the epoch as follows:
>
>     Historically, the origin of UNIX system time was referred to as
>     "00:00:00 GMT, January 1, 1970". Greenwich Mean Time is actually not
>     a term acknowledged by the international standards community;
>     therefore, this term, "Epoch", is used to abbreviate the reference
>     to the actual standard, Coordinated Universal Time.
>
> The epoch is a specified moment in time.  That moment can be
> expressed as midnight UTC Jan 1 1970, as 4PM PST Dec 31 1969,
> or (time_t)0.  GMT/UTC is just a convenient way to specify it.

You could also be GoLang and use MST January 2 2006 at 3:04:05 PM.
(1/2 03:04:05 PM 2006 GMT-7)

>>> $ date --date="@0"
>>> Wed Dec 31 16:00:00 PST 1969
>
> Yes, the date command by default uses the local time zone by default.
>
>> Well, and however much error there is from decades worth of leap
>> seconds, etc...
>
> Yes, leap seconds are an issue (and would be for any of the proposed
> alternatives).
>
>> But, yeah, better if one had a notion of time that merely measured
>> absolute seconds since the epoch without any particular ties to the
>> Earth's rotation or orbit around the sun. Whether or not its "date"
>> matches exactly with the official Calendar date being secondary.
>
> That's called TAI; it ignores leap seconds.  See clock_gettime()
> (defined by POSIX, not by ISO C).  (Not all systems accurately record
> the number of leap seconds, currently 37.)
>
> Most systems don't use TAI for the system clock, because matching civil
> time is generally considered more important than counting leap seconds.
>
> [...]


Datetime is a nightmare, this is why we use a simple seconds-since-X
system.
-- 
user <candycane> is generated from /dev/urandom