Calling nested COBOL programs
By calling nested programs, you can create applications
that use structured programming techniques. You can also call nested
programs instead of PERFORM
procedures to prevent
unintentional modification of data items.
About this task
Use either CALL
literal or CALL
identifier statements
to make calls to nested programs.
You
can call a nested program
only from its directly containing program unless you identify the nested program as COMMON
in
its PROGRAM-ID
paragraph. In that case, you can call
the common program from any program that is nested (directly or indirectly)
in the same program as the common program. Only nested programs can be identified
as COMMON
. Recursive calls are not allowed.
Follow these guidelines when using nested program structures:
- Code
an
IDENTIFICATION DIVISION
in each program. All other divisions are optional. - Optionally make the name of each nested program unique. Although the names of nested programs are not required to be unique (as described in the related reference about scope of names), making the names unique could help make your application more maintainable. You can use any valid user-defined word or an alphanumeric literal as the name of a nested program.
- In the
outermost program, code any
CONFIGURATION SECTION
entries that might be required. Nested programs cannot have aCONFIGURATION SECTION
. - Include
each nested program
in the containing program immediately before the
END PROGRAM
marker of the containing program. - Use an
END PROGRAM
marker to terminate nested and containing programs.