winsup/cygwin/libc/strptime.cc(__strptime) strptime %F issue

Corinna Vinschen corinna-cygwin@cygwin.com
Wed Aug 30 00:09:00 GMT 2017


On Aug 24 11:11, Brian Inglis wrote:
> On 2017-08-24 03:40, Corinna Vinschen wrote:
> > On Aug 24 11:32, Corinna Vinschen wrote:
> >> On Aug 23 13:25, Brian Inglis wrote:
> >>> Cygwin strptime(3) (also strptime(1)) fails with default width, without an
> >>> explicit width, because of the test in the following code:
> >>>
> >>> case 'F':	/* The date as "%Y-%m-%d". */
> >>> 	{
> >>> 	  LEGAL_ALT(0);
> >>> 	  ymd |= SET_YMD;
> >>> 	  char *tmp = __strptime ((const char *) bp, "%Y-%m-%d",
> >>> 				  tm, era_info, alt_digits,
> >>> 				  locale);
> >>> 	  if (tmp && (uint) (tmp - (char *) bp) > width)
> >>> 	    return NULL;
> >>> 	  bp = (const unsigned char *) tmp;
> >>> 	  continue;
> >>> 	}
> >>>
> >>> as default width is zero so test fails and returns NULL.
> >>>
> >>> Simple patch for this as with the other cases supporting width is to change the
> >>> test to:
> >>>
> >>> 	  if (tmp && width && (uint) (tmp - (char *) bp) > width)
> >>>
> >>> but this does not properly support [+0] flags or width in the format as
> >>> specified by glibc (latest POSIX punts on %F) for compatibility with strftime(),
> >>> affecting only the %Y format, supplying %[+0]<w-6>F, to support signed and zero
> >>> filled fixed and variable length year fields in %F format.
> >>
> >> Ok, I admit I didn't understand this fully.  What is '<w-6>'?
> >> Can you give a real world example?
> 
> Width prefix for %F minus six for "-mm-dd" to get the width for %Y.
> Look at POSIX strftime %F handling
> 	http://pubs.opengroup.org/onlinepubs/9699919799/functions/strftime.html
> or
> 	man 3p strftime | less +/\ F\
> for what strftime allows and strptime should handle for symmetry and consistency.
> 
> >>> So do you want compatible support or just the quick fix?
> >>
> >> Quick and then right?  Fixing this in two steps is just as well.
> > 
> > Btw., FreeBSD's _strptime only calls _strptime recursively, without any
> > checks for field width:
> > 
> >       case 'F':
> > 	      buf = _strptime(buf, "%Y-%m-%d", tm, GMTp, locale);
> > 	      if (buf == NULL)
> > 		      return (NULL);
> > 	      flags |= FLAG_MONTH | FLAG_MDAY | FLAG_YEAR;
> > 	      break;
> 
> As did Cygwin, which just did a goto recurse, before it was changed to support
> explicit width. Your call and option to go back and ignore it, patch bug, or
> forward and support flags and width based on strftime documentation.

Well, I guess it depends on how much time you're willing to invest here.
If you're inclined to fix this per POSIX, you're welcome, of course.


Thanks,
Corinna

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