Re: strptime doesn't fill in tm_wday and tm_yday.

[Corinna Vinschen <corinna-cygwin at cygwin dot com>]

On May 12 11:01, Peter Rosin wrote:
> Den 2011-05-11 19:34 skrev Corinna Vinschen:
> > On May 11 16:52, Peter Rosin wrote:
> >> Hello!
> >>
> >> The following STC hints at a problem in strptime:
> ...
> >> Opengroup has this to say about only filling in some fields:
> >>
> >> 	"It is unspecified whether multiple calls to strptime()
> >> 	using the same tm structure will update the current
> >> 	contents of the structure or overwrite all contents of
> >> 	the structure. Conforming applications should make a
> >> 	single call to strptime() with a format and all data
> >> 	needed to completely specify the date and time being
> >> 	converted."
> >>
> >> but I don't think it applies since indeed I do completely specify
> >> the date in my strptime call.
> > 
> > The Cygwin implementation of strptime is taken from NetBSD and enhanced
> > only in terms of support for the E and O modifiers.  The NetBSD and
> > OpenBSD versions also support a non-POSIX format specifier %u (day of
> > week, monday = 1).  Other than that, the Cygwin strptime behaves exactly
> > as the BSD implementation.  tm_wday is only set if you specify %a, %A or
> > %w.  tm_yday is only set if you specify %j.
> > 
> > Despite the example in the strptime man page of POSIX.1-2008, POSIX does
> > not specify that strptime has to fill out tm fields which are not also
> > specified in the format string.  You should better memset the tm
> > structure to 0 before calling strptime.
> 
> Since you pulled out your "POSIX does not require it" card, I'm grasping
> for my "Cygwin should behave like Linux" card. :-)

I'm not so much pulling the POSIX card, but rather the BSD/upstream
card.  Consider this:  The Cygwin version behaves pretty exactly like
the BSD version since it *is* the BSD version.  Should you ever have
to port your application to Open/Free/NetBSD, you will see the exact
same problem.  Whatever we do with the Cygwin strptime eventually,
you still have to consider that your application is *not* portable.

> Seriously, of course I need to handle quirks in strptime if I want the
> users of my application to be happy, but that does not mean that strptime
> can't be a little bit more helpful on Cygwin.  Maybe someone with a
> copyright assignment can find some inspiration in the patch [1] I sent
> for the newlib strptime?

I'll take a look.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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