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Message-ID: <20150814150823.GG27440@port70.net>
Date: Fri, 14 Aug 2015 17:08:23 +0200
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com, Jan V??el?k <jan.vcelak@....cz>
Subject: Re: strptime() lacks support for %z
* Szabolcs Nagy <nsz@...t70.net> [2015-08-14 17:00:39 +0200]:
> * Rich Felker <dalias@...c.org> [2015-08-14 10:15:40 -0400]:
> > On Fri, Aug 14, 2015 at 11:34:32AM +0200, Szabolcs Nagy wrote:
> > > * Jan V??el?k <jan.vcelak@....cz> [2015-08-14 10:00:23 +0200]:
> > > > On Thursday, August 13, 2015 10:06:50 PM Szabolcs Nagy wrote:
> > > > > the problem with parsing timezones is that it's not posix
> > > > > so the desired semantics is not clear (struct tm has no
> > > > > tz field in posix and it is not obvious how that should
> > > > > be treated in other apis that use struct tm.. glibc does
> > > > > something but it should be verified to give consistent
> > > > > behaviour if we add this to musl and there might be parsing
> > > > > corner cases when %z is not surrounded by spaces..).
> > > >
> > > > I know it's not specified in POSIX strptime, however it is specified in
> > > > strftime. I'm not sure how strictly do you want to stick to POSIX, but it
> > > > seems reasonable to me to have the equivalent format support in both
> > > > functions, so you can write the time stamp and parse it back.
> > > >
> > > > Anyway, the format in strftime is simple and on fixed width, +hhmm or -hhmm.
> > > >
> > >
> > > strftime uses tzset (timezone from TZ) but strptime cannot
> > > set TZ so it must put the timezone somewhere else.
> > >
> > > so strptime can't be consistent with strftime.
> > > with tz in struct tm, mktime/localtime no longer roundtrip.
> >
> > I don't follow. strftime uses the extended fields from struct tm. I
> > don't see anywhere it depends on tzset, nor reasons why strptime would
> > need tzset to be called. Am I missing something?
> >
>
> it seems %z does not use it in musl, %Z does
>
> __tm_to_tzname calls do_tzset()
>
> posix says
> "Local timezone information is used as though strftime() called tzset()"
ah ok, the tz name and offset are independent
i expected both of those would be used from TZ in
strftime, but musl already uses the tm struct offset.
then implementing %z in strptime is less intrusive
than i thought.
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