Re: Passing Multi Occurance DS as parm btw modules -- RPG400-L


Hi Jeff,

On Tue, 14 Mar 2006, Jeff Young wrote:


 Occurs is not allowed on a prototype parm.  How do I define it then?


Here's a really simple example of how you might code this:

--------- /COPY member for MODULE B's prototype ------------

     D ModuleB         PR
     D   DS_A_p                            like(DS_A)
     D   Count                       10I 0

--------- Source for Module A ------------------------------

      /copy prototypes,moduleb

     D DS_A            DS                  occurs(15)
     D   Field1                       1A
     D   Field2                       3P 0

     D Count           s             10I 0
     D x               s             10I 0

      /free
            %occur(DS_A) = 1;
            ModuleB(DS_A: Count);

            for x = 1 to count;
               %occur(DS_A) = x;
               dsply (Field1 + ' ' + %char(Field2));
            endfor;

            *inlr = *on;
      /end-free

--------- Source for Module B ------------------------------

      /copy prototypes,moduleb

     D ModuleB         PI
     D   DS_A_p                            like(DS_A)
     D   Count                       10I 0

     D DS_A            DS                  occurs(15)
     D                                     based(p_DS_A)
     D   Field1                       1A
     D   Field2                       3P 0

     D Alphabet        s             15A   inz('ABCDEFGHIJKLMNO')
     D x               s             10I 0
      /free
          p_DS_A = %addr(DS_A_p);
          count = %elem(DS_A);

          for x = 1 to count;
              %occur(DS_A) = x;
              Field1 = %subst(Alphabet:x:1);
              Field2 = x;
          endfor;
          return;
      /end-free

--------- End Of Trivial Example ------------------------

It's important that you set the %occur() for DS_A to 1 prior to passing itto ModuleB. Remember that parameters work by sharing memory. Even thoughyou may think of passing DS_A as "passing the data structure" what itreally does is tell MODULEB where DS_A is located in the computer'smemory.

Since each occurrence of DS_A is located in a different spot in memory,you want to make sure you've set it to the first one. That way, you'llshare everything from occurrence 1 to the end of the MODS.

A pointer is a variable that stores memory addresses. Since MODULEB willbe getting a parameter that's in the same spot in memory as DS_A, you canget it's address and assign it to a pointer. Any variable that's based onthe pointer will occupy the same exact spot in the computer's memory asthe parameter passed in.

So even though only the first occurrence is passed in the DS_A_pparameter, the fact that a 15 occurrence DS is based in the same area ofmemory will allow MODULEB to access all 15 occurrences.

If this type of pointer logic confuses you, all I can suggest is that younot use MODS as parameters. Since prototypes don't support MODS, you caneliminate the ugly pointer logic by using an array of data structures.

I realize that you can't fetch multiple records into a DS array usingembedded SQL. However, you CAN fetch one record at a time from a cursorinto a DS defined with LIKEDS, and then copy that DS into one element of aDS array. Granted, this takes a little bit of extra processing time, butunless performance is absolutely critical, you won't notice it. That way,you can use arrays of qualified DSes with embedded SQL, and not worryabout the ugliness of trying to get MODS through a prototype.


Let me know if you want an example of that.

---
Scott Klement  http://www.scottklement.com