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cobol

What is the use of the EXIT keyword?

I've seen many COBOL programs contain sections with at the end

XX-99.
    EXIT.

Many times that paragraph is used to exit the section, for instance with GO TO XX-99. I have read that EXIT is a no-operation, as it doesn't do anything. But the same goes for CONTINUE. One could easily replace EXIT with CONTINUE. Alternatively, one could replace GO TO XX-99 with EXIT SECTION.

Is there any compelling reason to use EXIT rather than CONTINUE? Why was EXIT introduced anyway? Was EXIT introduced before CONTINUE was?

Note: I'm not talking about EXIT in combination with another reserved word, like EXIT PROGRAM or EXIT PERFORM.

Solution

  • Is there any compelling reason to use EXIT rather than CONTINUE?
    Why was EXIT introduced anyway?
    Was EXIT introduced before CONTINUE was?

    There is no "compelling" reason to choose one over the other. There is no practical difference. The reason to choose EXIT over CONTINUE is conformance to existing coding standards.

    EXIT was part of the original COBOL 60 Report where it was a "Compiler Directing Verb." Its purpose was to mark the end of a performed procedure, directing the compiler to transfer control to the statement following the invoking PERFORM statement or to the PERFORM statement for the next iteration of a loop.

    In the ANSI COBOL 68 standard, it became a statement to mark the end of a performed procedure. It was no longer required, since the end of the perform range was the end of the last (or only) performed paragraph or section. It remained as a convenient target for a GO TO statement.

    [With the introduction of the SORT statement, an EXIT statement may also be used to mark the end of an input or output procedure.]

    CONTINUE was introduced in the 1985 standard as part of the changes for structured programming. It purpose was to replace the NEXT SENTENCE statement used within the IF and SEARCH statements or wherever an imperative statement is required by a statement format, but nothing need be done. It is in this last use that a CONTINUE statement may be used to replace an EXIT statement.

    EXIT SECTION was introduced in the 2002 standard.