Re: Date difference

[david.kahn@xxxxxxxxxxxxxxxxxx]

Rick Renkema <rick@createprint.com.au> wrote:

>May I please retract the e-mail I posted re the Date difference problem

Rick, you're not alone. Trying to do arithmetic with Julian dates is a very
common error. I hate Julian dates. Avoid them like the plague. Once you
cross the year boundary you run into all kinds of problems. In particular,
be very aware that the standard Julian date format only has 2 characters
for the year. The worst Julian date error I've seen in a live system was a
custom program using CVTDAT from within J.D. Edwards, assuming that the
Julian format was compatible with JDE's YYYDDD format and therefore
re-introducing Y2K bugs into a Y2K compatible release of JDE.

To do date arithmetic in RPG/III you need to obtain an absolute date based
on some arbitrary starting value. The following code will get you a usable
absolute date from a _long_ Julian date contained in numeric fields $YYYY
and $DDD. It copes with leap years and leap centuries but does not take
account of the Gregorian reform.

    C           $YYYY     SUB  1         ABS     70
    C           ABS       DIV  100       $WK50   50
    C           ABS       DIV  400       $WK50B  50
    C                     MULT 365.25    ABS
    C                     SUB  $WK50     ABS
    C                     ADD  $WK50B    ABS
    C                     ADD  $DDD      ABS

No guarantees, so use at your own risk. Maybe Rick can find an error. :-)

The sensible option, of course, is to use RPG/IV which has date data types
and arithmetic built in.

Dave Kahn, ABB Steward Ltd.


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