Talk:Date manipulation

Task is Region specific

I live in the UK and tried the Tcl example: <lang tcl>loading history file ... 29 events added buffer line limit: 512 max line length: unlimited Main console display active (Tcl8.5.7 / Tk8.5.7) (HP DV8025EA) 30 % set date "March 7 2009 7:30pm EST" March 7 2009 7:30pm EST (HP DV8025EA) 31 % set epoch [clock scan $date -format "%B %d %Y %I:%M%p %z"] 1236472200 (HP DV8025EA) 32 % set later [clock add $epoch 12 hours] 1236515400 (HP DV8025EA) 33 % puts [clock format $later] Sun Mar 08 12:30:00 GMT 2009 (HP DV8025EA) 34 % </lang> As you can see, this is different from the answer given in the article.

How about making the task work for any region? --Paddy3118 03:15, 14 May 2009 (UTC)

Better yet, use Date or Time objects. --IanO

The task itself does not specify what the answer should be -- only the answers may/will be region specific. The result of the Tcl solution merely happens to show that I live in the Eastern time zone. --glennj 10:36, 14 May 2009 (UTC)

You can always use the -timezone option to print in another format.

<lang tcl>% set date "March 7 2009 7:30pm EST"

March 7 2009 7:30pm EST % set epoch [clock scan $date -format "%B %d %Y %I:%M%p %z"] 1236472200 % set later [clock add $epoch 12 hours] 1236515400 % clock format $later Sun Mar 08 12:30:00 GMT 2009 % clock format $later -timezone America/New_York Sun Mar 08 08:30:00 EDT 2009 % clock format $epoch Sun Mar 08 00:30:00 GMT 2009</lang>

The last one is just to check that it really is doing the time math right. Forgot that there was a DST change at that point in time... —Dkf 10:58, 14 May 2009 (UTC)

Indeed I've tried to implement something not region specific... but coping with timezones and DST is a mess if not "directly" supported by a library... (currently I believe POSIX is not too much interested in doing conversions to any timezones; the results are driven by a environment variable; maybe one can setenv it properly... anyway EST alone gives not the required information directly...) --ShinTakezou 11:07, 14 May 2009 (UTC)

Date and time parsing and formatting really are inherently region-specific. Don't kid yourself otherwise. And feel free to show off the library in conjunction with the language; that'd make for the most valuable kind of contribution to this site. —Dkf 12:11, 14 May 2009 (UTC)

Maybe the task should be changed so the example time given is in terms of a base string plus some indication of your local timezone, such as that given, for EST. If the fact that the calculation should include a change in daylight saving time, then that should be added to the task description too. --Paddy3118 12:42, 14 May 2009 (UTC)