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Re: timestamp
From: |
tomas |
Subject: |
Re: timestamp |
Date: |
Sat, 12 Feb 2022 13:32:58 +0100 |
On Sat, Feb 12, 2022 at 12:49:10PM +0100, Ricardo Wurmus wrote:
>
> Hi adriano,
>
> I’ve got no good answers as to “why” things are the way they are, but
> the manual explains the range of these values:
>
> > It seesm to be
> >
> > (tm:mon %3)
> >
> > This returns
> >
> > 11
> >
> > I expected 12 but ok, I recognize this kind of weirdness
>
> -- Scheme Procedure: tm:mon tm
> -- Scheme Procedure: set-tm:mon tm val
> Month (0-11).
>
> > I'm unhappy with
> >
> > (tm:year $3)
> >
> > This returns
> >
> > 120
> >
> > it's 2020
> >
> > Why would 120 represent 2020 ?
>
> -- Scheme Procedure: tm:year tm
> -- Scheme Procedure: set-tm:year tm val
> Year (70-), the year minus 1900.
>
> I don’t know why this would be useful, but that’s what it is ¯\_(ツ)_/¯
Oh. That is old POSIXy tradition :-)
Guile actually only passes along what libc provides, and I think it is a
good idea, in general. See the man page of localtime(3) on your next Linux-ish
box for all the details. If you prefer an online version, perhaps [1], [2]
convey an idea.
The year... those interfaces were developed well before the year 2000. It was
usual, Back Then (TM) to write down the year as a two-digit number (the 19
prefix was implied). Nobody could predict that the year 2000 was about to
arrive, honestly ;-)
As to the month... zero based numberings ease computations and setting up
name arrays (as in: 0: January, 1: February and so on).
Don't ask me why, though, the day of the month (1..31) is one-based. It is
the only exception :-)
But it makes for an easy calculation where you can add up the year (times
year length, taking leap years into account), the days-in-month so far for
full months and the current month day and things to arrive at the current
Epoch day. Guess one has to be one-based, otherwise you'll have to add 1 at
the end.
(This is all somewhat tongue-in-cheek ;-P
But it illustrates some other point: for folks coming from C and POSIX, (I
do), all that stuff feels "pretty natural", although it isn't, of course.
Cheers
[1] https://en.cppreference.com/w/c/chrono/localtime
[2] https://en.cppreference.com/w/c/chrono/tm
--
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- timestamp, adriano, 2022/02/12
- Re: timestamp, Vivien, 2022/02/12
- Re: timestamp, adriano, 2022/02/12
- Re: timestamp, Ricardo Wurmus, 2022/02/12
- Re: timestamp,
tomas <=
- Re: timestamp, Eli Zaretskii, 2022/02/12
- Re: timestamp, adriano, 2022/02/12
- Re: timestamp, adriano, 2022/02/12
- Re: timestamp, Ricardo Wurmus, 2022/02/12
- Re: timestamp, adriano, 2022/02/12
- Guile cookbook ?, adriano, 2022/02/12
- Re: Guile cookbook ?, Ricardo Wurmus, 2022/02/12
- Re: Guile cookbook ?, adriano, 2022/02/12
- Re: Guile cookbook ?, Olivier Dion, 2022/02/12
- Re: Guile cookbook ?, Zelphir Kaltstahl, 2022/02/12