From ripley@stats.ox.ac.uk  Thu Apr 18 14:07:44 2002
From: ripley@stats.ox.ac.uk (ripley@stats.ox.ac.uk)
Date: Thu, 18 Apr 2002 14:07:44 +0100 (BST)
Subject: [Rd] strptime mysteriously adds a day - 0S-specific: Linux and
 Windows (so far) (PR#1466)
In-Reply-To: <15550.48917.887461.113981@gargle.gargle.HOWL>
Message-ID: <Pine.LNX.4.31.0204181353250.32748-100000@gannet.stats>

On Thu, 18 Apr 2002, Martin Maechler wrote:

> >>>>> "Jason" == Jason Turner <jasont@indigoindustrial.co.nz> writes:
>
>     Jason> strptime() mysteriously adds a day to a date, unless the year
>     Jason> is specified.  Tested on:
>     Jason> Linux (RedHat 6.0) - R version 1.4.1 and R-devel.
>     Jason> Windows - R version 1.4.1
>
>     Jason> Bug isn't found on OpenBSD, R version 1.4.1.
>
> I confirm the bug (R-devel, Redhat 7.1)
> To reproduce, it's sufficient to work with
> "%d %B" or "%d %b" .
>
> What happens is that January and February work okay, and all
> months from March produce the problem,
>
> e.g.
>
> > strptime("28 Feb",format="%d %b")# ok
> [1] "2002-02-28"
> > strptime("19 March",format="%d %B")# wrong
> [1] "2002-03-20"

The issue is that an unspecified year is assumed *by the IS* to be 1900, a
leap year. I'm not sure why glibc does this when the tm_year field is not
being set, but it confidently says this is day 101 of the year, and that's
the result you get.

The only portable workaround is to give the year: there is (at least in
R-devel) a warning in the help file about this.

-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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[Rd] strptime mysteriously adds a day - 0S-specific: Linux and Windows (so far) (PR#1466)
ripley@stats.ox.ac.uk