suggested improvements for C9x `New formats for strftime()' (N733)

[Antoine Leca]

Paul Eggert wrote:
> 
> You propose new conversion specifiers for strftime in C9x, the new C standard,
> in your document ISO/IEC JTC1/SC22/WG14 N733
> <http://www.gold.net/users/cdwf/c/wg14n733.txt> (1997-07-01).

I noticed another doc, N735, about wider changes in the library.
<URL:http://www.gold.net/users/cdwf/c/wg14n735.txt> (1997-07-04).
Item 20-25 (at the end) are relevant to the date and time functions.


In particular, Item 22 is relevant to the same problem Paul quoted.

In N733, Paul read
>       %V   is replaced by the ISO 8601 week number of the year

Clive's document add that the admissible range is [00-53].


It should be put in relief that N735 adds:
	%#W - ISO 8601 week number            ) If %W would be zero, the date is
	%#y - ISO 8601 week number year % 100 ) treated as belonging to week 53
	%#Y - ISO 8601 week number year       ) of the previous year

(Note: it could be week *52* of the previous year).


I read this the following way (this is nothing official):

For Tuesday 1996-12-31, we should have:
	%y	96
	%U	52
	%W	52
	%V	53
	%#W	01	the correct ISO 8601 week
	%#y	97	the correct ISO 8601 year associated with the week number	

For Friday 1999-01-01, we should have:
	%y	99
	%U	00
	%W	00
	%V	00
	%#W	53	the correct ISO 8601 week
	%#y	98	the correct ISO 8601 year associated with the week number	

For Sunday 1999-01-03, we should have:
	%y	99
	%U	01
	%W	00
	%V	00
	%#W	53	still in the previous year
	%#y	98

For the fun, I add Saturday 2000-01-01:
	%y	00	but still in the 20th century !
	%U	00
	%W	00	
	%V	00
	%#W	53
	%#y	99



> To work around this shortcoming, I propose that C9x add Robbins's
> %G and %g formats, as follows:
> 
>    %G is replaced by the year containing the ISO 8601 week
>    %g is replaced by %G modulo 100

So %G is the same as %#Y, and %g the same as %#y.

But as I showed before, there is a difference between %V, showing
the week number _in_the_year_ based on Monday, the first Thrusday
being in week 01 (and thus able to be 00), and the real ISO 8601
week number, %#W (restricted in range to 01-53).

So we probably need two specifiers, instead of one in current art.
I remember a discussion some time ago in the tz list about this:
in particular, some point as strange to have a week number like
53 at the beginning of the year, or a low number at the end...


Antoine