Re: Procedure parameters -- RPG400-L

Hello,

    D ValFldNum       PI             1N
    D FldNme                          14A   CONST
    D FldVal                            20A   Options(*Varsize)

[SNIP]

    D FldIsNum        PR             1N
    D  String                            20A   Options(*Varsize)

[SNIP]

I expected that the field used by the FldIsNum procedure would contain
just the 5 bytes, but when I debug it, I actually get the 20 bytes
starting from the start of the HDR_KSAID field.

Yes, that's what options(*VARSIZE) does. IT disables the compiler's normalvalidity checking. Normally the compiler wouldn't let you pass a 5A fieldin place of a 20A field because when a parameter is passed by reference,all you really get is the address of the field. And the address tells theposition of the computer's RAM where the field starts -- it doesn't tellthe data type or length or anything else like that. So, if you have thefield defined as 20A and it's in the same spot of memory as a 5Afield, what happens? The first 5 bytes are valid. Everything else iswhat just happens to be in memory after those 5 bytes.

That's why the compiler stops you from passing it, because you'd otherwisebe able to corrupt memory. Options(*VARSIZE) does nothing but disablethat check.

In this case, I don't see why you'd need to be able to change the value ofthis field. It should be input only, since you're checking it forvalidity, you're not changing it. So, the parameter should be CONST.

If you want it to vary, I'd make it VARYING CONST. Granted, VARYING is adifferent data type, but since you specify CONST, the compiler will helpyou by converting it to the VARYING data type as needed. One of the nicethings about converting fixed-length to VARYING in this manner is that thecompiler will set the length of the VARYING field to be the same as thefixed-length field that you passed in.

Granted, it's slightly less efficient than using a fixed length field withoptions(*VARSIZE), but think about it.... it's 20 bytes. The speed ittakes to copy 20 bytes is insignificant. In the lifetime of the program,I doubt that the total time you spend copying it will add up to the amountof time it took me to write this paragraph!


So, I guess this is what I'm suggesting you use for your prototypes:

     D ValFldNum       PI             1N
     D FldNme                        14A   CONST
     D FldVal                        20A   VARYING CONST

     D FldIsNum        PR             1N
     D  String                       20A   VARYING CONST

Then, you can get the length by doing %len(String) or %len(FldVal).

Tip: When a field doesn't need to be changed in a subprocedure, you shouldALWAYS make it either CONST or VALUE. That helps make the subprocedureself-documenting, it makes it more flexible since the compiler will dofield conversions for you, and allows expressions. It makes it easier tomaintain because you know that the field won't be affected...