Re: Variable file name in rpg /or cl -- RPG400-L

This is a good question, and one I have contemplated myself.  Why do an 
override in CL instead of using USROPN in an RPG program?  There are a 
few reasons I can think of.

1. Easier to maintain.  Easier to find the CL program and see the OVRDBF and 
change it
   then to find the same thing in an RPG program (finding the USROPN, tracking 
the
   point in the program where the OPEN opcode is used, finding out where QCMDEXC
   is called and then finding out what parameters are passed, then finding out 
where
   the variable is set, and if the variable is being passed, finding out where 
it is
   being passed from, etc..  A lot faster in CL to find the OVRDBF and then 
finding
   the variable if used and where it's set or passed.

2. Segregation of logic.  Now I have a CL calling the RPG.  If I decide for test
   purposes, or a different company or subdivision, to use a different file 
set, I can
   change the CL program and still have it call the RPG program.  I am 
separating
   Input from Program logic.  If I do it in the RPG I will have to either copy 
the
   program, then have 2 programs to maintain much harder than maintaining 2 CLs,
   or change the program logic to reflect 2 possible sets of files.

Okay, there are also reasons I can think to use USROPN instead of CL.

1. Integration of system.  Use the USROPN and CALL QCMDEXC but move the QCMDEXC 
into
   a directory.  Have the directory look at the logic as to which set of files 
to open
   from however it wants to, it is now transparent to the RPG program (just as 
the CL
   then RPG was).  Again, easier to maintain as now I don't have to worry at 
all in the
   RPG program which set of files I am opening, I just have to work on the 
program logic.
   The library can be as complicated or simple as I need and desire.  In fact, 
it now
   becomes a simple matter ot give the RPG program to a junior programmer to 
maintain, and
   have the programmer/analyst maintain the library in all its complexity.

2. Less overhead and files to maintain.  Now I just have the RPG program to 
maintain, and
   now 2 or more separate files.  Using either method I should be using a 
binding directory
   anyway, so that doesn't really become an issue.

In conclusion, in a smaller shop, or maintaining an older system, or stand 
alone programs,
I would use the OVRDBF in CL.  In a new package or rewriting a system, use the 
USROPN and
move the which file logic to the binding directory (okay, what is the official 
term for a set
of programs put into a directory to be linked at run time?  On PCs this would 
be a Library.).

Just my $0.02.

Regards,

Jim Langston

A smart man learns from his own mistakes.  A wise man learns from the mistakes 
of others.

rob@dekko.com wrote:
> 
> Lots of good suggestions pouring in on this.  I go with the OVRDBF.  My
> only suggestion is why write two programs - an RPG and a CL?  Use the
> USROPN keyword on your F spec.  Use CALL QCMDEXC, (or the alternatives), to
> OVRDBF the file from within the RPG program.  Then use the OPEN opcode to
> open the file.  When you are done, use the CLOSE op code.  I've really cut
> back on CL.  In fact if you use the alternatives to QCMDEXC you get the
> error return code.  Which I think is easier to handle than a MONMSG.
> 
> For example, which is more thorough:
> MONMSG CPF000 GOTO(ERROR)
> GOTO NOERROR:
> ERROR:  /* Find out which error code we actually got and then process
> accordingly */
> 
> - or -
> eval    error=runthis(cmd)
> Select
> when error=*blanks
> when error='CPF....'
> ...
> when error='CPF,,,,'
> ...
> other
> ....
> endsl
> 
> 
>                     Quazy
>                     <quazy@SoftHome.n        To:     rpg400-l@midrange.com
>                     et>                      cc:
>                     Sent by:                 Subject:     Variable file name 
>in rpg /or cl
>                     owner-rpg400-l@mi
>                     drange.com
> 
> 
>                     10/13/00 09:18 AM
>                     Please respond to
>                     RPG400-L
> 
> 
> 
> I need to have a cl program pass a variable to either a rpg or cl program.
> 
> This variable is the file name that the program needs to read from.
> 
> Any suggestions on how to do this???
> 
> Thanks
> 
> Chris
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