RE: Starting out with sub-procedures

Hope you don't mind me throwing my two cents in...
 
You can prototype a function and then call it with CallP or Eval
anywhere in your mainline, regardless of who wrote it, and what they
language they wrote it in.  Good examples are the C functions.  Scott
Klement has an excellent tutorial that deals with sockets, which calls
APIs written in C.  I don't know how the socket API allocates resources
and determines socket descriptors, but I don't need to, I just call the
function.
 
A lot has been said about the system API in recent threads and, in my
mind, it is just a slightly more useful QCMDEXC.  Its advantage is that
it returns an integer to tell you whether or not the call was
successful.  If you had prototyped the API, you could code something
like....
 
/COPY QRPGLESRC,SYSTEM_P
If (system('OVRDBF ) > 0)
....
EndIf                  
 
This allows you to do something different if your command failed.  I
think another good procedure example is the incrementing of an alpha
field.  It could be coded:
 
Eval  Alpha = atoi(Alpha) + 1
 
atoi is a function provided by IBM that returns the numeric value of a
string.  I don't know wrote the function, and aside from being grateful
it wasn't myself, I don't care. IMO starting with these procedures,
being the ones written by someone else, is the best place to start.
Looking inside the code is never a concern (also usually not an option).
 
> The question remains: do I need more than a /COPY statement and the
callp
> line in the main program(s)?

Getting back to your specific question:  No.  The prototype and the call
are all that you need to code, to use whatever function you choose.
Code origin is not an issue.  The only piece that you may still need is
to tell the linker where to find the procedure when you create your
program.  This can be entered on the CRTPGM (or CRTBNDx) commands, or
put into a binding directory.  I would strongly recommend doing a
tutorial (Scott's comes to mind) that is written in ILE and all the
confusion seems to melt away.  ILE seems complex at first, but it is
well worth the effort.
 
HTH,
Andy