Module

A module is a non-runnable object (type *MODULE) which is the output of an ILE compiler. It is the basic building block for creating runnable ILE Objects. This Module object acts as a significant difference between ILE and OPM programs where the output of an OPM compiler is a runnable program.

Below Diagram shows about Modules which are non-executable object that holds procedures and then the same can be bind to *PGM and or *SRVPGM.

Common concepts in ILE RPG, ILE COBOL, ILE C & ILE C++

• Exports

An export is the method of a procedure or data item, coded in a module object, that is available for use by other ILE objects. The export is identified by its name and its associated type, either procedure or data. An export can also be called a definition.

• Imports

An import is the use of, or reference to the name of a procedure or data item not defined in the current module object. The import is identified by its name and its associated type, either procedure or data. An import can also be called a reference.

Since, module object is the basic building block of an ILE runnable object. Hence, when a module object is created, the following may also be generated.

• Debug Data

This is the data necessary for debugging a runnable ILE object.

• Program Entry Procedure (PEP)

This is the compiler-generated code that is the entry point for an ILE program on a dynamic program call. It is similar to the code provided for the entry point in an OPM program.

• User Entry Procedure (UEP)

A user entry procedure, written by a programmer, is the target of the dynamic program call. It is the procedure that gets control from the PEP. The main() function of a C program becomes the UEP of that program in ILE.

Conceptual View of a Module

The below example shows Module object M1 exports 2 procedures (Get_Employee and Upd_Employee) and a data item (rtn_code). The same Module object M1 imports a procedure called Del_Employee. It contains PEP, a corresponding UEP and debug data as well.

Creating a Program with the CRTRPGMOD and CRTPGM Commands

The two-step process of program creation consists of compiling source into modules using CRTRPGMOD and then binding one or more module objects into a program using CRTPGM. This process helps to create permanent modules.

Key Features

• I. Allows to modularize an application without recompiling the whole application.
• II. To reuse the same module in different applications.

Creating a Module Object

An ILE RPG module consists of one or more procedures, data item specifications, and static storage used by all the procedures in the module. It is possible to directly access the procedures or data items in one module from another ILE object.

Following are the procedures that can make up an ILE RPG module,

1. Cycle-Main Procedure:

An optional procedure which consists of the set of H, F, D, I, C, and O specifications that begin the source. The cycle-main procedure has its own LR semantics and logic cycle, neither of which is affected by those of other ILE RPG modules in the program.

• Sub-Procedure:

Zero or more procedures, which are coded on P, D, and C specifications which do not use the RPG cycle. A sub procedure may have local storage that is available for use only by the sub procedure itself. One of the sub procedures may be designated as a linear-main procedure, if a cycle-main procedure is not coded.

The main procedure (if coded) can always be called by other modules in the program. Sub-procedures may be local to the module or exported. If they are local, they can only be called by other procedures in the module; if they are exported from the module, they can be called by any procedure in the program.

Module creation consists of compiling a source member, and, if that is successful, creating a *MODULE object. The *MODULE object includes a list of imports and exports referenced within the module.

Note:

• I. A module cannot be run by itself. We must bind one or more modules together to create a program object (type *PGM) or a service program object (type *SRVPGM)
• II. Then the procedures can be accessed within the bound modules through static procedure calls.

Advantages of combining modules into a PGM or a Service PGM:

• I. Allows to reuse the pieces of code which generally results in smaller programs. Smaller programs provide better performance and easier debugging capabilities.
• II. Allows to maintain shared code with less chance of introducing errors to other parts of the overall program.
• III. Manage large programs more effectively. It allows to divide the old program into parts that can be handled separately. If the program needs to be enhanced, only recompiling of the changed modules is sufficient.

Module Creation using CRTRPGMOD Command

Using a standard ILE RPG Compiler Command – CRTRPGMOD, we can create the *MODULE Object. This command can be used interactively, as part of a batch input stream, or from a Command Language (CL) Program.

Example of CRTRPGMOD

CRTRPGMOD MODULE (Module Lib / Module Name) SRCFILE (Source Lib / SRCPF)