Note that it handles and reports on both packed and zoned numerics. There are a lot of comments so hopefully it will be understandable even without the accompanying article.
Code:
**Free
// This code is provided only as a teaching example of a concept
// It is not complete and should not be used in production code
ctl-opt Option(*NoDebugIO : *SrcStmt ) DftActgrp(*No);
ctl-opt CCSID(*GRAPH:*JOBRUN);
// FieldData is the oufile from:
// DSPFFD FILE(PRODUCT) OUTPUT(*OUTFILE) OUTFILE(FIELDDATA)
// Normally that command would be built in to this program via QCMDEXC
// or system() but we're "cheating" here to keep the example short.
dcl-f FieldData;
// These are the DS images of the before and after state of the records
// They could be pointer mapped to trigger buffer images, or mapped from
// journal records, or simply be before and after images from an
// operator's screen. Basically anything where you need to know what changed
// For this proof of concept example we will simply hard-code some values
// in the "after" DS to ensure a difference between "before" and "after"
dcl-ds before ExtName('PRODUCTEXT') Qualified Inz end-ds;
dcl-ds after ExtName('PRODUCTEXT') Qualified Inz end-ds;
// The following DS array contains the details of the fields in
// the DS. Their name, data type, position, etc.
// It provides the data needed for comparing before and after images
// In this case it was built from DSPFFD data but it could have
// been from (say) SYSCOLUMNS2 or the QUSLFLD API.
dcl-ds fieldDetail Dim(99) Qualified;
startPosn Like(WHIBO); // Offset within the record
length like(WHFLDB); // Length in bytes
name like(WHFLDI);
dataType like(WHFLDT);
decimals like(WHFLDP); // Number of decimal places
End-Ds;
dcl-s fieldBefore varchar(256); // This length assumes that no fields
dcl-s fieldAfter varchar(256); // will exceed 256 bytes in length
// Adjust size as needed
// This structure is used to enable the bytes that represent a
// numeric field's value to be processed as numeric in
// this program. It basically re-maps bytes as packed or zoned numeric
dcl-ds mapNumeric;
zonedValue zoned(15);
packedValue packed(29) Overlay(zonedValue);
end-Ds;
dcl-s decimalValue packed(29:5);
dcl-s i int(5);
dcl-s count int(5);
dcl-s start int(5);
// Data types for numeric fields - this code assumes that only
// character/packed/zoned fields are present in the DS
dcl-c PACKED 'P';
dcl-c ZONED 'S';
// This loop simply reads the file produced by DSPFFD and stores
// the required data in the fieldData array for later reference
// Normally this code would be in a Service Program and might use
// SQL or API calls as noted earlier.
read FieldData;
DoU %Eof(FieldData);
count += 1;
fieldDetail(count).name = WHFLDI;
fieldDetail(count).dataType = WHFLDT;
fieldDetail(count).startPosn = WHIBO;
fieldDetail(count).length = WHFLDB;
fieldDetail(count).dataType = WHFLDT;
fieldDetail(count).decimals = WHFLDP;
read FieldData;
EndDo;
// To show the logic works we'll change some values in DS after.
// The rest of the after DS & all of before DS has blanks/zeros
after.STOH = 99;
after.SELLPR = 123.45;
after.MAXDISC = 9.999;
// This loop will process each field in turn reporting on
// any that have changed.
For i = 1 to count;
// Copy relevant portions of before/after images to a
// temporary field to simplify subsequent logic
fieldAfter = %subst(after:fieldDetail(i).startPosn:fieldDetail(i).length);
fieldBefore = %subst(before:fieldDetail(i).startPosn:fieldDetail(i).length);
if fieldAfter <> fieldBefore;
// Field has changed so report it
// Replace with any logic needed to report before & after values
Dsply ('Field ' + fieldDetail(i).name + ' has changed');
// Determine where numeric field data starts in the
// mapNumeric DS.
start = %Len(mapNumeric) - fieldDetail(i).length + 1;
// To handle packed and numeric values we convert them
// and scale them so that we can display them. The logic
// here is intended to give you ideas - it is not a definitive
// solution for all data types and sizes.
If fieldDetail(i).dataType = PACKED;
packedValue = 0; // Initialize packed work field
%subst(mapNumeric: start ) = fieldAfter;
// Now scale the numeric value to account for decimals
If fieldDetail(i).decimals > 0;
decimalValue = packedValue / (10 ** fieldDetail(i).decimals);
Else;
decimalValue = packedValue;
EndIf;
Dsply ('New value ' + %Char(decimalValue) ) ;
ElseIf fieldDetail(i).dataType = ZONED;
zonedValue = 0; // Initialize all positions in zoned work field
%subst(mapNumeric: start ) = fieldAfter;
If fieldDetail(i).decimals > 0;
decimalValue = zonedValue / (10 ** fieldDetail(i).decimals);
Else;
decimalValue =zonedValue;
EndIf;
Dsply ('New value ' + %Char(decimalValue) ) ;
EndIf;
EndIf;
EndFor;
*InLr = *On;
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