Re: last day of month (was MIDRANGE-L Digest V2 #1546)

Hi Jim,

We're guaranteed that data structures are NOT initialized unless specified
by code (INZ keyword, I in position 8, or EVAL as in your example).
Variables defined as a result field are initialized, and although I haven't
seen a *guarantee* in writing, I do believe that's what the manuals state,
and it has always been my experience.

Note that numeric and character fields are NOT initialized to their
respective *LOVAL values, they are initialized to zeros and blanks
respectively. *LOVAL for a 2.0 numeric field would be -99; for a 2-character
alpha field, it would be x'0000'.

Peter Dow
Dow Software Services, Inc.
909 425-0194 voice/fax


----- Original Message -----
From: Jim Langston <jlangston@conexfreight.com>
To: <MIDRANGE-L@midrange.com>
Sent: Monday, October 18, 1999 8:09 AM
Subject: Re: last day of month (was MIDRANGE-L Digest V2 #1546)


> Coming from various languages, I have learned never to trust the
> initialized value of any variable.  I understand that this shouldn't be a
> problem on the AS/400, but are we guaranteed that all variables will
> be initialized to 0 (or their respective *lowval's?)
>
> I find depending on an initialized value makes code very difficult to
> understand an maintain.  I would just as well take the 2 nanosecond "hit"
> and do an Eval   Isodd = 01     just to make my code crystal clear.
>
> Regards,
>
> Jim Langston
>
> bmorris@ca.ibm.com wrote:
>
> > >Date: Thu, 14 Oct 1999 09:16:48 -0700
> > >From: Jon Erickson <jerickson@800.com>
> > >
> > >Correct me if I'm wrong,
> > > ...
> > >
> > >d                 DS
> > >d Isodate                         d   Inz
> > >d  Isoyyyy                       4  0 Overlay(Isodate)
> > >d  Isomm                         2  0 Overlay(Isodate:6)
> > >
> > >c                   Eval      Isoyyyy = Pyear
> > >c                   Eval      Isomm = Pmonth
> > >Add 1 month via ADDDUR
> > >c                   AddDur    1:*Months     Isodate
> > >
> > >Subtract 1 day via SUBDUR
> > >c                   SubDur    1:*Days       Isodate
> >
> > Sure, that will work.  I was discussing Jon's code to solve the general
case of
> > getting the last day of the month containing a given date.
> >
> > Jon's code can be made to run a bit more quickly using overlays (you can
get rid
> > of the extract by just setting the days part to "01").  Maybe that's a
good
> > idea,
> > maybe not - it seems to me that using overlays makes the code a bit more
> > complex.
> >
> > If you start with numeric year and month as in your example, your way is
as good
> > as any.
> >
> > Hmm, I just thought of a way to use numeric year and month input
avoiding
> > overlays, with a single adddur:
> >
> > D date            s               d       datfmt(*iso)
inz(D'0001-01-31')
> >  * Find the number of months after 0001-01 for the given year and month
> >  * E.g. for 0002-03, there are 12 + 1 months
> > C                   eval      Pmonth = ((Pyear - 1) * 12) + (Pmonth - 1)
> >  * Add them to Jan 31, 0001.  Month-end adjustment will fix up any
results
> >  * where the number of days in the month is less than 31.
> > C                   adddur    Pmonth:*m     date
> >
> > With date operations, the contest should be regarding the number of date
> > opcodes,
> > not the number of statements.  (Date opcodes are very expensive.)
> >
> > Barbara Morris
> >
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