1.6 Transfer of Control
In the Procedure Division, unless there is an explicit control transfer or there is no next executable statement, program flow transfers control from statement to statement in the order in which the statements are written. (See Note below.) This normal program flow is an implicit transfer of control.
In addition to the implicit transfers of control between consecutive statements, implicit transfer of control also occurs when the normal flow is altered without the execution of a procedure branching statement. The following examples show implicit transfers of control, overriding statement-to-statement transfer of control:
- After execution of the last statement of a procedure being executed
under control of another COBOL statement, control implicitly
transfers. (COBOL statements that control procedure execution are,
for example: MERGE, PERFORM, SORT, and USE.) Further, if a paragraph
is being executed under the control of a PERFORM statement which
causes iterative execution, and that paragraph is the first paragraph
in the range of that PERFORM statement, an implicit transfer of
control occurs between the control mechanism associated with that
PERFORM statement and the first statement in that paragraph for each
iterative execution of the paragraph.
- During SORT or MERGE statement execution, control is implicitly
transferred to an input or output procedure.
- During execution of any COBOL statement that causes execution of a
declarative procedure, control is implicitly transferred to that
procedure.
- At the end of execution of any declarative procedure, control is
implicitly transferred back to the control mechanism associated with
the statement that caused its execution.
Note: The term "next executable statement" refers to the next COBOL statement to which control is transferred, according to the rules given above. There is no next executable statement under these circumstances:
- When the program contains no Procedure Division
- Following the last statement in a declarative section when the
paragraph in which it appears is not being executed under the control
of some other COBOL statement
- Following the last statement in a program or method when the paragraph
in which it appears is not being executed under the control of some
other COBOL statement in that program
- Following the last statement in a declarative section when the
statement is in the range of an active PERFORM statement executed in a
different section and this last statement of the declarative section
is not also the last statement of the procedure that is the exit of
the active PERFORM statement
- Following a STOP RUN statement or EXIT PROGRAM statement that
transfers control outside the COBOL program
- X Following a GOBACK statement that transfers control outside the COBOL
X program - X Following an EXIT METHOD statement that transfers control outside the
X COBOL method - X The end program or end method header
X Similarly, if control reaches the end of the Procedure Division of a
X method, and there is no next executable statement, an implicit EXIT METHOD
X statement is executed.
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