12
Interprogram Communication
COBOL programs can communicate with each other, as well as with non-COBOL
programs. Program-to-program communication is conducted by using one (or
combinations) of the following:
The CALL statement
External data
cobcall
routine
cobcancel
routine
cobfunc
routine

12.1 Multiple COBOL Program Run Units

A multiple COBOL program run unit consists of either of the following:
One main (driver) program and one or more separately compiled programs;
each program may or may not have contained programs
One main program with one or more contained (nested) programs
Separately compiled programs can be concatenated in one source file, or can be
written as separate source files.

12.1.1 Examples of COBOL Run Units

Example 12–1 shows a run unit with three separately compiled programs, none of
which have contained programs. MAIN-PROGRAM (1) calls separate program
SUB1 (2), that calls separate program SUB2 (3).
Interprogram Communication 12–1