Bryan's RPG IV Journal

Q. I've heard you say that I can pass a data structure as a parameter, or accept it as a return value. How do I do this?

A. There are a couple of additional coding requirements when you are prototyping a data structure as a parameter or a return value.

First, you need to define the layout in a separate data structure. There's no special requirement for this data structure; it can be program-described or externally-described.

Next, to use the data structure as a parameter or a return value, you code the LIKEDS keyword, referring to the data structure as the reference:

D Myproc          PR             1N
D  Parm1                              Likeds(Mail)

D Mail            DS
D  Identifier                    5U 0
D  Name                         35
D  Address1                     35
D  Address2                     35
D  City                         21
D  State        
                2
D  Zipcode                      10

Note that I named the parameter (Parm1) in the prototype. While it is not usually necessary to name parameters in a prototype, in this case, the notation in columns 7-21 serves to separate the parameter from the return value. If I had not included the Parm1 notation, the compiler would have treated the LIKEDS line as a continuation of the return value, not as a separate parameter. (This is also necessary when you code a parameter with LIKE or LIKEREC.)

Of course, in the called procedure, you'll need to include the LIKEDS keyword in the procedure interface as well. If the called procedure is a NOMAIN procedure (i.e., it's in a separate module), you'll need to also code the reference procedure in that module.

Although this example doesn't show it, I also recommend that the data structure be a qualified data structure. Then you would refer to subfields by their qualified name -- Mail.Identifier, Mail.Name, Mail.Address1, etc.

At V5R2, you can also use the LIKEREC keyword on a prototype and a procedure interface, to define a parameter or return value like a record format. For example, the following prototype would pass a record format to a procedure:

FMaillist  UF   E           K Disk

D Myproc          PR             1N
D  Parm1                              Likerec(Mailfmt:*All)