Data Areas in CLLE

Learning Objective

By the end of this lesson, you will understand what a data area is, and be able to use RTVDTAARA and CHGDTAARA to read and update one from a CLLE program.

Simple Explanation

In the Common IBM i Object Types lesson, you learned about object types such as *LIB, *FILE, and *PGM. A data area, object type *DTAARA, is another kind of IBM i object: a small, simple piece of storage that holds a single value, persisting on the system independently of any one job or program run.

Unlike a CL variable, declared with DCL and existing only while a specific program runs, a data area continues to exist and hold its value between separate runs of a program, and can even be shared across different jobs. A CLLE program reads a data area's current value using RTVDTAARA (Retrieve Data Area), and updates it using CHGDTAARA (Change Data Area):

DCL VAR(&LASTORDERNBR) TYPE(*DEC) LEN(9 0)

RTVDTAARA DTAARA(MYAPPLIB/LASTORDNBR) RTNVAR(&LASTORDERNBR)

CHGVAR VAR(&LASTORDERNBR) VALUE(&LASTORDERNBR + 1)

CHGDTAARA DTAARA(MYAPPLIB/LASTORDNBR) VALUE(&LASTORDERNBR)

Here, RTVDTAARA reads the current value stored in the LASTORDNBR data area into the CL variable &LASTORDERNBR. After incrementing that value, CHGDTAARA writes the new value back into the same data area, so the next time any program reads it, whether later today or after the system has been restarted, it sees the updated value.

Why It Matters

Data areas give a CLLE program a simple way to remember a value across separate runs, something a regular CL variable cannot do on its own, since variables only exist while their program is actually running. This makes data areas a common, lightweight choice for things like the next available order number in the example above, a simple status flag, or a small setting a process needs to remember between runs.

Practical Example

Imagine a nightly batch job that needs to know the last order number it assigned, so the next run continues numbering from where the previous run left off. Storing that number in a data area, rather than only in a CL variable, means the value survives between separate runs of the job, correctly continuing the sequence each time, rather than starting over or losing track after each run finishes.

This is a simplified, illustrative example rather than a specific real numbering scheme, but it reflects a genuinely common, practical reason CLLE developers use data areas.

Common Confusions

"Is a data area the same thing as a physical file?" No. A physical file, covered in earlier Db2 for i lessons, stores many structured records made up of fields. A data area is much simpler: a single object holding one value, without the record-and-field structure a physical file has.

"Does a CL variable declared with DCL persist the same way a data area does?" No. A DCL-declared variable exists only while its specific program run is active, and is gone once that run ends. A data area is a separate object that continues to exist and hold its value independently of any one program run.

"Do I need to create a data area from within the CLLE program that uses it?" Not necessarily. A data area is commonly created once, ahead of time, using a command such as CRTDTAARA, and then read and updated by CLLE programs afterward using RTVDTAARA and CHGDTAARA, rather than being created fresh every time a program runs.

Quick Recap

• A data area (*DTAARA) is a simple IBM i object holding a single value that persists independently of any one job or program run.
• RTVDTAARA reads a data area's current value into a CL variable; CHGDTAARA writes a new value back into the data area.
• Unlike a DCL-declared CL variable, a data area's value survives between separate runs of a program.
• Data areas are a common, lightweight choice for small values a process needs to remember over time, such as a next-number counter or a status flag.

Try Asking the AI Tutor

Use the AI Tutor to ask follow-up questions about this lesson. For example, try asking:

• "What command is used to create a new data area?"
• "What happens if two jobs try to update the same data area at almost the same time?"