ISO8901: Week numbers and year

[Keesver 23]

According to this document ISO 8601 - Wikipedia
 

Monday 29 December 2008 is written as "2009-W01-1" when a week number is used.

 

As you can see, instead of 2008, the value 2009 is shown. What date formatting function supports this in Delphi?

 

Thanks

[Roger Cigol 103]

I can't help here. But I can offer a warning to inexperienced "week number" users (which you may NOT be, I realise) and that is to beware of the week number 53 that does occur from time to time. I spent a long time debugging someone elses code once that stored week data in an array size [52] and overflowed causing corruption when week 53 came along.

[timfrost 78]

The functions in system.dateutils claim to be ISO8601 compliant.  Are you saying that they return the wrong results?  WeekOfTheYear has an overload which sets the year as well as returning the week

[Keesver 23]

WeekOfTheYear is working. I was looking for something like DateTimeToString which supports displaying dates like above using week numbers (aka "2009-W01")

Edited January 21, 2022 by Keesver

[Attila Kovacs 629]

28 minutes ago, Keesver said:

I was looking for something like DateTimeToString

There is no such thing in Delphi. You have to roll your own. Should not be that hard.

Edited January 21, 2022 by Attila Kovacs

[dummzeuch 1505]

I was about to point to my iso8601 unit in dzlib, but when I checked, I found the ToWeekDate method to be possibly faulty in exactly these cases. Should be easy to fix though.

 

https://osdn.net/projects/dzlib-tools/svn/view/dzlib/trunk/src/u_dzIso8601.pas?view=markup&root=dzlib-tools

 

It's ISO 8601 btw. not 8901.

 

 

[dummzeuch 1505]

7 hours ago, dummzeuch said:

I was about to point to my iso8601 unit in dzlib, but when I checked, I found the ToWeekDate method to be possibly faulty in exactly these cases. Should be easy to fix though.

 

https://osdn.net/projects/dzlib-tools/svn/view/dzlib/trunk/src/u_dzIso8601.pas?view=markup&root=dzlib-tools

Fixed it. Also added unit tests for this (I could have sworn I already had some. Another faulty thing: My memory.)