GNU bug report logs - #10182
Century bug in date utility?

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Krzysztof Kowalski <krzysztof7kowalski <at> gmail.com>
To: bug-coreutils <at> gnu.org
Subject: Century bug in date utility?
Date: Thu, 01 Dec 2011 16:34:09 +0100

Hello,

We have 2011,

HOWEVER:

korn% date +%C
20
korn% date
Thu Dec  1 16:26:30 CET 2011


apc%
apc% date +%C
20
apc%
apc% date
Thu Dec  1 16:26:51     2011

And many other call returns that we live in 20 century :)

For a test I changed system time to 1997 and date utility returned 20
century as well :)

-- 
best regards
  -- Kowalski Krzysztof

Message #12 received at 10182-done <at> debbugs.gnu.org (full text, mbox):

From: Eric Blake <eblake <at> redhat.com>
To: Krzysztof Kowalski <krzysztof7kowalski <at> gmail.com>
Cc: 10182-done <at> debbugs.gnu.org
Subject: Re: bug#10182: Century bug in date utility?
Date: Thu, 01 Dec 2011 10:35:31 -0700

[Message part 1 (text/plain, inline)]

tag 10182 notabug
thanks

On 12/01/2011 08:34 AM, Krzysztof Kowalski wrote:
> Hello,
> 
> We have 2011,
> 
> HOWEVER:
> 
> korn% date +%C
> 20
> korn% date
> Thu Dec  1 16:26:30 CET 2011

Yep.  And this behavior is mandated by POSIX for strftime(), so it is
not a bug.

http://pubs.opengroup.org/onlinepubs/9699919799/functions/strftime.html

C
    Replaced by the year divided by 100 and truncated to an integer, as
a decimal number. [ tm_year]

That is, it is NOT the "century" in the vernacular (where years in the
range [2001,2100] are collectively called the 21st century), but the
first two digits of the year.  The idea is that you combine %C%y to form %Y.

> 
> For a test I changed system time to 1997 and date utility returned 20
> century as well :)

No, %C in 1997 returned 19.

-- 
Eric Blake   eblake <at> redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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Message #13 received at 10182-done <at> debbugs.gnu.org (full text, mbox):

From: Krzysztof Kowalski <krzysztof7kowalski <at> gmail.com>
To: Eric Blake <eblake <at> redhat.com>
Cc: 10182-done <at> debbugs.gnu.org
Subject: Re: bug#10182: Century bug in date utility?
Date: Thu, 01 Dec 2011 19:45:48 +0100

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W dniu 2011-12-01 18:35, Eric Blake pisze:
> tag 10182 notabug
> thanks
>
> On 12/01/2011 08:34 AM, Krzysztof Kowalski wrote:
>>
>
> Yep. And this behavior is mandated by POSIX for strftime(), so it is
> not a bug.
>
> http://pubs.opengroup.org/onlinepubs/9699919799/functions/strftime.html
>
> C
> Replaced by the year divided by 100 and truncated to an integer, as
> a decimal number. [ tm_year]
>
> That is, it is NOT the "century" in the vernacular (where years in the
> range [2001,2100] are collectively called the 21st century), but the
> first two digits of the year. The idea is that you combine %C%y to form %Y.
>

OK, thank you for answer, but it still isn't logical,
century is century by common sense,
if there's 21st century right now 21 should be returned.

- -- 
best regards
  -- Kowalski Krzysztof
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Message #14 received at 10182-done <at> debbugs.gnu.org (full text, mbox):

From: Eric Blake <eblake <at> redhat.com>
To: Krzysztof Kowalski <krzysztof7kowalski <at> gmail.com>
Cc: 10182-done <at> debbugs.gnu.org
Subject: Re: bug#10182: Century bug in date utility?
Date: Thu, 01 Dec 2011 11:53:11 -0700

[Message part 1 (text/plain, inline)]

On 12/01/2011 11:45 AM, Krzysztof Kowalski wrote:
> 
> OK, thank you for answer, but it still isn't logical,

What's not logical, that %C follows POSIX?

> century is century by common sense,
> if there's 21st century right now 21 should be returned.

Maybe the confusion is coming from the fact that 'date --help' mentions
the word "century" as a mnemonic for %C, even though the POSIX wording
for %C specifically avoids "century" because %C is _not_ a century in
the vernacular usage.  Would a patch to the 'date --help' wording
alleviate your concerns?  If so, could you propose better wording for
what 'date --help' should say for %C that is still concise and accurate,
but does not mention a misleading mnemonic?

-- 
Eric Blake   eblake <at> redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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Message #15 received at 10182-done <at> debbugs.gnu.org (full text, mbox):

From: Krzysztof Kowalski <krzysztof7kowalski <at> gmail.com>
To: Eric Blake <eblake <at> redhat.com>
Cc: 10182-done <at> debbugs.gnu.org
Subject: Re: bug#10182: Century bug in date utility?
Date: Thu, 01 Dec 2011 19:54:33 +0100

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Hash: SHA1
 
W dniu 2011-12-01 19:53, Eric Blake pisze:
> On 12/01/2011 11:45 AM, Krzysztof Kowalski wrote:
>>
>> OK, thank you for answer, but it still isn't logical,
>
> What's not logical, that %C follows POSIX?
>
>> century is century by common sense,
>> if there's 21st century right now 21 should be returned.
>
> Maybe the confusion is coming from the fact that 'date --help' mentions
> the word "century" as a mnemonic for %C, even though the POSIX wording
> for %C specifically avoids "century" because %C is _not_ a century in
> the vernacular usage. Would a patch to the 'date --help' wording
> alleviate your concerns? If so, could you propose better wording for
> what 'date --help' should say for %C that is still concise and accurate,
> but does not mention a misleading mnemonic?
>
That would make sense ;),
I can patch it.


- -- 
best regards
  -- Kowalski Krzysztof
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Message #18 received at 10182 <at> debbugs.gnu.org (full text, mbox):

From: Bob Proulx <bob <at> proulx.com>
To: Krzysztof Kowalski <krzysztof7kowalski <at> gmail.com>
Cc: 10182 <at> debbugs.gnu.org
Subject: Re: bug#10182: Century bug in date utility?
Date: Thu, 1 Dec 2011 14:42:34 -0700

Krzysztof Kowalski wrote:
> For a test I changed system time to 1997 and date utility returned 20
> century as well :)

Of course you know you don't need to change the system time to test
this.  You can do it easily with date.

  $ date -d '1997-01-01 12:00 UTC' +%C
  19

Bob

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