A copybook contains everything you need to use a module, f. e. prototypes, constants, template variables.
If a service program consists of multiple modules then I create a main copybook which just includes all the copybooks from the modules which are included in the service program.
I use the /if, /define, /eof and /endif compiler directives to make sure that a copybook only gets included once.
/if defined(STREAM_EMITTER)
/eof
/endif
/define STREAM_EMITTER
//
// here starts the code for the copybook
//
...
If a program consists of multiple modules the other modules need to know how to call the procedures provided by each module. I then create an extra copybook for internal use in the program only, internal.rpginc. It contains the necessary prototypes, templates and constants needed by the other modules to use the exported procedures.
Example: A web service offers multiple resources/subdomains. I would split up the web service setup from the end points. Each resource would be in a separate module. So there would be
- application module
- resource module A
- resource module B
The procedures from the resource modules would be exported and the prototypes listed in the copybook internal.rpginc.
Example: A service program consists of multiple modules and some procedures are only exporte inside the service program to be called internally by the other modules.
- module A with public procedures
- module B with public procedures
- module C with internal procedures
The copybook internal.rpginc would contain the prototypes, templates and constants need for using the internal procedure.