Program Cycle

The ILE RPG compiler supplies part of the logic for an RPG program. For a cycle-main procedure, the logic the compiler supplies is called the program cycle or logic cycle. The program cycle is a series of ordered steps that the main procedure goes through for each record read.

The information that you code on RPG IV specifications in your source program need not explicitly specify when records should be read or written. The ILE RPG compiler can supply the logical order for these operations when your source program is compiled. Depending on the specifications you code, your program may or may not use each step in the cycle.

Primary (identified by a P in position 18 of the file description specifications) and secondary (identified by an S in position 18 of the file description specifications) files indicate input is controlled by the program cycle. A full procedural file (identified by an F in position 18 of the file description specifications) indicates that input is controlled by program-specified calculation operations (for example, READ and CHAIN).

To control the cycle, you can have:

• One primary file and, optionally, one or more secondary files
• Only full procedural files
• A combination of one primary file, optional secondary files, and one or more full procedural files in which some of the input is controlled by the cycle, and other input is controlled by the program.
• No files (for example, input can come from a parameter list or a data area data structure).