OpenEdge 4GL Unknown Value and the LITERAL-QUESTION Attribute

December 21, 2007 · Filed Under Development 

Sometimes a cigar is just a cigar, and sometimes a question mark is just a question mark.

You frequently need to assign character values to a buffer-field. Sometimes that value may be a question mark.

        bh:BUFFER-FIELD(’c1′):BUFFER-VALUE = ‘?’.

When you query the buffer-value, Progress reports that the value is unknown.

        MESSAGE
            bh:BUFFER-FIELD(’c1′):BUFFER-VALUE = ‘?’
            bh:BUFFER-FIELD(’c1′):BUFFER-VALUE = ?
            VIEW-AS ALERT-BOX.

If this behavior is not what you intended or you need to keep the Unknown Value distinct for a “?” character, then you have a bug in your program.

How do you get Progress to treat the “?” appropriately? The trick is the LITERAL-QUESTION attribute.

When LITERAL-QUESTION = FALSE, “?” and ? will both evaluate to the unknown value.
When LITERAL-QUESTION = TRUE, “?” is a question mark, and ? is the unknown value.

        bh:BUFFER-FIELD(’c1′):LITERAL-QUESTION = TRUE.
        bh:BUFFER-FIELD(’c1′):BUFFER-VALUE = ‘?’.
        MESSAGE bh:BUFFER-FIELD(’c1′):BUFFER-VALUE = ‘?’ VIEW-AS ALERT-BOX.

Sadly, there is no single-step way to make it always be true for all fields in a temp-table, but something like this may work for you:

        FUNCTION SetLiteralQuestion RETURNS LOGICAL
          ( INPUT bh AS HANDLE ):
          DEFINE VARIABLE i AS INTEGER NO-UNDO.
          IF NOT VALID-HANDLE(bh) THEN RETURN FALSE.
          IF bh:TYPE EQ ‘TEMP-TABLE’:U THEN bh = bh:DEFAULT-BUFFER-
        HANDLE.
          IF bh:TYPE NE ‘BUFFER’:U THEN RETURN FALSE.
          DO i = bh:NUM-FIELDS TO 1 BY -1:
            bh:BUFFER-FIELD(i):LITERAL-QUESTION = TRUE.
          END.
          RETURN TRUE.
        END FUNCTION.  /** SetLiteralQuestion() **/

You can then invoke the SetLiteralQuestion function using either a table-handle or a buffer-handle.

        SetLiteralQuestion(TEMP-TABLE ttFoo:HANDLE).
        SetLiteralQuestion(bh).
        SetLiteralQuestion(INPUT BUFFER customer:HANDLE).

Since this does some looping and other processing, you’ll want to make sure you’re not calling SetLiteralQuestion() in a loop.

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