DFHCOMMAREA

DFHCOMMAREA is the communication area: a block of storage that CICS passes from one program to another, or from one invocation of a program to the next. It is how CICS programs share data.

What DFHCOMMAREA is

• It is a data area whose layout you define yourself, as a 01-level item in the Linkage Section.
• CICS passes its address to the receiving program at entry, like a parameter.
• Maximum size is 32,767 bytes. Keep it as small as the data you really need to pass.
• The translator inserts the DFHCOMMAREA definition into the Linkage Section if you do not code it.

How data flows through it

• Program A calls program B with EXEC CICS LINK PROGRAM('PROGB') COMMAREA(WS-AREA) LENGTH(50).
• Program B sees the same 50 bytes as its DFHCOMMAREA, updates them, and returns.
• When B returns, A sees the updated values in WS-AREA.
• With EXEC CICS XCTL the control passes permanently and the commarea goes along with it.
• With EXEC CICS RETURN TRANSID COMMAREA, the commarea is saved and passed to the next invocation of the transaction (pseudo-conversational programming).

The EIBCALEN = 0 rule

• On the first call, when no commarea was passed, CICS sets EIBCALEN to zero.
• Always test EIBCALEN before touching DFHCOMMAREA. Referencing DFHCOMMAREA when EIBCALEN is zero causes an abend.
• If EIBCALEN is zero, initialize your working fields instead of reading the commarea.
• Also check that EIBCALEN matches the length you expect before moving the commarea to your working area.

Example: passing a commarea with LINK