Re: Data Structure Constant

[Rory Hewitt <roryhewitt@xxxxxxxxx>]

Kurt,

A couple of options:

1. I have a routine which uses the 3-character MSGID prefix to determine the
name of the undelrying message file from which it comes. My DS definition
looks like the following:

D MsgPfxArrStr    S            483A   Inz('CB QCBLMSG   *LIBL     +
D                                          CEEQCEEMSG   *LIBL     +
D                                          CP QCPFMSG   *LIBL     +
D                                          DNSQTOBMSGF  QDNS      +
D                                          ED QEDTMSG   QPDA      +
D                                          GL QGLDMSG   QDIRSRV   +
D                                          HTPQHTTPMSG  QHTTPSVR  +
D                                          ID QIDUMSG   QIDU      +
D                                          IW QIWSMSG   QIWS      +
D                                          JVAQJVAMSGF  QJAVA     +
D                                          LN QLNCMSG   QCBLLE    +
D                                          MCHQCPFMSG   *LIBL     +
D                                          PL QPLIMSG   QPLI      +
D                                          QRGQRPGMSG   QRPG      +
D                                          QSHQZSHMSGF  QSHELL    +
D                                          RN QRPGLEMSG QRPGLE    +
D                                          RX KTIMSGF   *LIBL     +
D                                          SQLQSQLMSG   QSYS      +
D                                          TCPQTCPMSGF  QTCP      +
D                                          TX QIDUMSG   QIDU      +
D                                          USRQUSRMSG   *LIBL     ')
 *
D MsgPfxArrStr@   S               *   Inz(%addr(MsgPfxArrStr))
D MsgPfxArr       DS                  Based(MsgPfxArrStr@) Qualified
D MsgPfxElm                           Dim(20)
D   MsgIdPfx1                    1A   Overlay(MsgPfxElm)
D   MsgIdPfx2                    2A   Overlay(MsgPfxElm)
D   MsgIdPfx3                    3A   Overlay(MsgPfxElm)
D   qMsgf                       20A   Overlay(MsgPfxElm:*Next)

2. What's wrong with defining DS arrays over a CTDATA:

D JobTypeDS       DS
D   JobTypeNbr                  10I 0
D  JobTypeArr                         Dim(14) CTDATA
D   JobTypeInt                   2A   Overlay(JobTypeArr)
D   JobTypeExt                   8A   Overlay(JobTypeArr:*Next)
...
** CTDATA
A AUTO
B BATCH
BECMNEVK
BFM36
BDBCI
BJPJ
BPPDJ
BTMRT
I INTER
M SBSMON
R RDR
S SYS
W WTR
X SCPF

I don't know if my examples have helped at all (I've probably missed the
point totally), but what I'd say is that short of specifying separate
constants, there's not a lot you can do to *stop* programmers from changing
a DS. Except the threat of what will happen if they do...

Rory

On Thu, Apr 9, 2009 at 7:40 AM, Kurt Anderson
<kurt.anderson@xxxxxxxxxxxxxx>wrote:

> I have a data structure and I'd like for its contents to never be changed,
> enforced by the compiler.  How do I do this?
>
> One situation I've run into is where I want to initialize an output data
> structure parameter.  I can't reset it.  I can't cheat and base another DS
> on it and reset that DS.  I can clear the fields individually, but that
> sucks, right?  This will also be called a ton of times, so I want to pass
> the data by reference (so not using a return value).  What I ended up doing
> is creating a static DS to house all the default values so I can initialize
> the output parameter with it.  However it does leave the initialization DS
> open to being modified.
>
> Another situation is I tend to create data structure arrays, which long ago
> would have been compile time tables.  Each subfield is an element in an
> array (so each element has a given name if I ever need to reference one
> specific value).  However, these values could be changed, and I have to rely
> programmers not changing it (vs the compiler not letting them).
>
> Thoughts on creating a data structure constant?
>
> I'm on v5r4.