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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