Re: Using CL to call RPG pgms

[Scott Klement <rpg400-l@xxxxxxxxxxxxxxxx>]

> I have almost 1,5 year expirience in ILE RPG IV and now I realized that
> almost evry RPG pgm I've made needed additional CL pgm that shold prepare
> LIBL, clear output PFs and perform similar actions after pgm finises...

That's interesting.  Why would you want to prepare the library list?  I 
can understand why you'd want to clear an output PF, but how often does 
that come up?  And it's easy to do that in the RPG program.

> I'm wondering would it be to complicated to perform all this within RPG
> pgm (for example in separate module or subprocedure) with use of different
> APIs (QCMDEXC) and explicit file OPENing. (inexaple. if I define file in f
> spec with USROPN keyword would I get err. message if file is not in LIBL
> on pgm start).

You'll get an error message when you use the OPEN op-code to open the 
file.  If your code is structured so that this OPEN is at the start of 
your program, then yes, you'll get an error at that time.


> I suppose there exist some actions (as file override options for RPG pgm
> that will be run) that must be defined in CL??

That's not true, overrides can be done anywhere, as long as it's before 
the files are opened.

However, I almost never need to do overrides. What do you use them for? 
The only time I use them is when I want to specify something like 
DFRWRT(*NO) on a display file, or a DTAQ on a display file...  I use an 
override so I don't have to remember to specify these things when the 
display file is created.

But, again, this is unusual.  If you're just pointing the file to a 
different name, library or member, use the EXTFILE and EXTMBR keywords. 
You can use a variable (if necessary) to specify the file or member, and 
you can even make that variable a parameter if you need an outside program 
to control which file you use.


> What is better practice? It's probably metter of programers style but it
> would be nice to know how other programers do that.

Yeah, what's "better" is always a subjective question.  Personally, I've 
always though it was an RPG program's responsibility to control how it's 
files are opened, so I've always felt it made more sense to control it via 
parameters than it did external overrides.

Not everyone feels that way, however.


> Is there any situation when this start actions should be performed in CL?

Sometimes there are things that are much easier or more intuitive when 
performed in CL. For example, some of the RTV commands in CL provide 
functions that are otherwise only available via APIs -- so they're much 
easier to code in CL.

I have to admit, I don't often need to use these things, but when I do, I 
general do them in CL.