COMMAREA

COMMAREA (communication area) is how a pseudo-conversational program remembers things between screens. Working storage is wiped clean on every restart — the COMMAREA is not.

What is a COMMAREA

• A COMMAREA is a data area passed from one execution of a program to the next.
• It is the standard way to keep context (customer number, action chosen, screen state) between tasks.
• The program declares it in the LINKAGE SECTION as DFHCOMMAREA.
• EIBCALEN tells the program how long the incoming COMMAREA is — zero means this is the first run.
• The maximum length is 32767 bytes, but keep it small — a few hundred bytes is typical.

How it is passed

• RETURN ... COMMAREA(data-name): CICS saves the area and passes it to the next execution of the same transaction.
• XCTL ... COMMAREA(data-name): passes the area to the next program in the transfer.
• LINK ... COMMAREA(data-name): passes the area to the called program and gets changes back.
• Typical contents: key fields, the last action, message text, and counters — never passwords or huge tables.

The standard coding pattern

• On the first run (EIBCALEN = 0) initialize your working area; otherwise move DFHCOMMAREA into it.
• Do all the screen logic, then RETURN with TRANSID and COMMAREA to continue — or plain RETURN to finish.
• Example of the full pattern:-
  
  WORKING-STORAGE SECTION. 01 CA-AREA PIC X(124). LINKAGE SECTION. 01 DFHCOMMAREA PIC X(124). PROCEDURE DIVISION. IF EIBCALEN = ZERO MOVE SPACES TO CA-AREA ELSE MOVE DFHCOMMAREA TO CA-AREA END-IF. *--- ... screen and file logic goes here ... --- EXEC CICS RETURN TRANSID('PRGA') COMMAREA(CA-AREA) END-EXEC.