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Number   :  4441
Date     :  2003-04-25
Author   :  Garry Deane
Subject  :  Re: Date Macro
Size(KB) :  2


--- In xxcopy@yahoogroups.com, Kan Yabumoto  wrote:
 
> That's interesting. I could do that. I would use /$KK$
> rather than /$WW$ (see below for why). Also, for the
> convenience of adding the prefix, W to easily conform to the
> ISO 8601 standard, we can define /$WKK$ specifically for that.
> So, /$KK$ will expand to a value like 17 and /$WKK$ expands
> to W17.
> 
> Therefore, Garry's "clumsy" notation will be cleaned up;
> 
> /$yyyy-wkk-k$ (See below for the single /$K$)

I may not have thought this through enough because I forgot that when 
you are calculating ISO week, it is not complete without also giving 
the year because the year may not be the same as the calendar year 
e.g. 2002-12-31=2003-W01-2, 2000-01-01=1999-W52-6. It could get very 
messy if someone specifed say /$yyyy-wkk-k$ for the source and /$yyyy-
mm-dd$ for the destination. Xxcopy has to determine the year 
according to the context.

> I was not aware that the ISO standard assigns the radix
> value of 7 for Sunday. That seems contrary to my sense
> of tradition that most people consider Sunday as the
> beginning of the week. Look at Window's Date and Time
> display. The calendar clearly shows Sunday to the left
> which is the most common calendar I've seen.
> Apparently, ISO treats a week as starting on Monday and
> ending on Sunday.
> 
> The ISO web page does not tell it explicitly.
> 
> http://www.iso.ch/iso/en/prods-services/popstds/datesandtime.html
> 
> But, from its context, it is reasonable to interpret that
> ISO defines that a week starts on Monday.

Yes, that is correct e.g. the following from 
http://wwwcdf.pd.infn.it/MLO/Calendars/Notes.html#isoweek.

"ISO-8601 defines the week as starting with Monday and ending with 
Sunday; and the first week of a year as the first week which is 
mostly within the Gregorian year. That last definition is equivalent 
to the following two variants: the week which contains the first 
Thursday of the Gregorian year; and the week containing January 4th."



> Well, figuring the week-of-the-year value will be
> a bit of a pain to program. But, it should not be
> too bad (XXCOPY already knows how to convert a date
> to the day-of-the-week and also knows the leap-year
> rules).

Actually the algorithm is relatively straightforward and can be 
deduced from the above definition. I've seen code and pseudo code on 
several web sites and have even written NT batch code to do this in 
about a dozen lines (excluding wrapper code and comments).

Garry



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