strptime doesn't fill in tm_wday and tm_yday.

strptime doesn't fill in tm_wday and tm_yday.

[Peter Rosin]

Hello!

The following STC hints at a problem in strptime:

-----------------------8<----------------------------
#include <stdio.h>
#include <time.h>

int
main(void)
{
	/* seed tm with some garbage */
	struct tm tm = {
		0, 0, 0, /* s m h */
		0, 0, 0, /* d m y */
		290774, 2280577, 81
	};
	const char date[] = "2011-05-11 14:06:11";

	if (!strptime(date, "%Y - %m - %d %T", &tm)) {
		fprintf(stderr, "strptime error\n");
		return 1;
	}

	printf("%s", asctime(&tm));
	printf("tm_yday %d\n", tm.tm_yday);
	printf("tm_wday %d\n", tm.tm_wday);
	printf("tm_isdst %d\n", tm.tm_isdst);
	return 0;
}
-----------------------8<----------------------------

I get this output with Cygwin 1.7.9-1:
 May 11 14:06:11 2011
tm_yday 2280577
tm_wday 290774
tm_isdst 81

I expect:
Wed May 11 14:06:11 2011
tm_yday 130
tm_wday 3
tm_isdst whatever

I get the expected output on the Linux host I tried (with tm_isdst=81),
but not on Solaris 10.

On Solaris 10 I get (for completeness):
Sun May 11 14:06:11 2011
tm_yday 0
tm_wday 0
tm_isdst 0

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.

In my "real" program, the call to asctime with the crippled tm
causes a seg-fault instead of "just" missing weekday output, I guess
it depends...

Cheers,
Peter

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

[Corinna Vinschen]

On May 11 16:52, Peter Rosin wrote:
> Hello!
> 
> The following STC hints at a problem in strptime:
> 
> -----------------------8<----------------------------
> #include <stdio.h>
> #include <time.h>
> 
> int
> main(void)
> {
> 	/* seed tm with some garbage */
> 	struct tm tm = {
> 		0, 0, 0, /* s m h */
> 		0, 0, 0, /* d m y */
> 		290774, 2280577, 81
> 	};
> 	const char date[] = "2011-05-11 14:06:11";
> 
> 	if (!strptime(date, "%Y - %m - %d %T", &tm)) {
> 		fprintf(stderr, "strptime error\n");
> 		return 1;
> 	}
> 
> 	printf("%s", asctime(&tm));
> 	printf("tm_yday %d\n", tm.tm_yday);
> 	printf("tm_wday %d\n", tm.tm_wday);
> 	printf("tm_isdst %d\n", tm.tm_isdst);
> 	return 0;
> }
> -----------------------8<----------------------------
> 
> I get this output with Cygwin 1.7.9-1:
>  May 11 14:06:11 2011
> tm_yday 2280577
> tm_wday 290774
> tm_isdst 81
> 
> I expect:
> Wed May 11 14:06:11 2011
> tm_yday 130
> tm_wday 3
> tm_isdst whatever
> 
> I get the expected output on the Linux host I tried (with tm_isdst=81),
> but not on Solaris 10.
> 
> On Solaris 10 I get (for completeness):
> Sun May 11 14:06:11 2011
> tm_yday 0
> tm_wday 0
> tm_isdst 0
> 
> 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.


Corinna

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

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

[Peter Rosin]

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. :-)

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?

Cheers,
Peter

[1] http://sourceware.org/ml/newlib/2011/msg00177.html

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

[Corinna Vinschen]

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

[Corinna Vinschen]

On May 12 13:11, Corinna Vinschen wrote:
> On May 12 11:01, Peter Rosin wrote:
> >   Maybe someone with a copyright assignment [...]

Btw., that could be you!  It's not that hard to send one.  See the
"Before you get started" section on http://cygwin.com/contrib.html,.


Corinna

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

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