RE: Pointer / Based issue -- RPG400-L


What about MODS?  Would all occurrences be available?

IBM hasn't created a prototype keyword to pass a MODS properly. I thinkthis has to do with the bizarre nature of a MODS -- you can'tunambiguously reference a particular element when you use the variablename! You have to select the element name with the OCCUR opcode or the%OCCUR BIF, and this makes it very difficult for the compiler to know thedifference between the current occurrence and the whole structure.

Data structure arrays are a better choice, and I suggest that you use theminstead of a MODS. Always.

But, since I know that not everyone will do that, here's how you pass aMODS:

A MODS is always stored in contiguous memory. The second occurrence isalways immediately after the first occurrence, the third is alwaysimmediately after the 2nd, etc. Therefore, if you can get a pointer tothe first occurrence, and base an identical MODS on that pointer, you'llbe good to go.


For example:

     D TestMods        ds                  occurs(50)
     D    field1                     10A
     D    field2                      9P 0

     D IsModsOk        PR             1N
     D    mods                             like(TestMods)

      /free

           %occur(TestMods) = 1;

           if IsModsOk(TestMods);
               // there was much rejoicing
           endif;
         .
         .
         .
     P IsModsOk        B
     D IsModsOk        PI             1N
     D    mods                             like(TestMods)
     D MyMods          ds                  occurs(50)
     D                                     based(p_Mods)
     D    field1                     10A
     D    field2                      9P 0
      /free
          p_Mods = %addr(mods);
          // MyMods is now the MODS from the caller, starting
          //   with the occurence that the caller had set when
          //   he called this procedure.
      /end-free
     P                 E

This is better than declaring a pointer on the prototype because:

a) The caller doesn't have to do any pointer logic to call you. Youshould always make it as easy for the caller as possible when writingre-usable routines!

b) The use of LIKE on the prototype makes it more self-documenting thatthis is what you want passed for this parameter.



However, it obviously doesn't work as nicely because:

a) You have to set the occurrence before calling.

b) You have to do pointer logic in the called procedure

c) You have to make a 2nd copy of the DS layout.

d) You can't use CONST to improve and clarify the interface.

So, again, I recommend using a data structure array instead. They workalmost exactly like MODS, so I don't understand why you'd use a MODS.


     D TestArray       ds                  dim(50)
     D                                     qualified
     D    field1                     10A
     D    field2                      9P 0

     D IsArrayOk       PR             1N
     D    ary                              likeds(TestArray)
     D                                     dim(50)

      /free

           if IsArrayOk(TestArray);
               // there was much rejoicing
           endif;

     P IsArrayOk       B
     D IsArrayOk       PI             1N
     D    ary                              likeds(TestArray)
     D                                     dim(50)
      /free
          for x = 1 to %elem(ary);
              if ( ary(x).field1 = 'foo' );
                  return *OFF;
              endif;
          endif;
      /end-free
     P                 E