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Q39587: QB Advisor 4.50 "Help: ON ERROR Statement Details" Correction

Article: Q39587
Product(s): See article
Version(s): 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | docerr SR# S881206-71 | mspl13_basic
Last Modified: 19-JAN-1989

The paragraph in the QuickBASIC Version 4.50 QB Advisor (on-line help
facility) that describes how to perform error trapping in a SUB or
FUNCTION procedure or DEF FN function is incorrect, and an incorrect
example is shown.

The paragraph incorrectly states that a SUB, FUNCTION, or DEF FN block
can contain an error-handling routine. The error handler-label and
RESUME must be at the main-program level or module level.

The "Help: ON ERROR Statement Details" should instead say the
following:

   To have an error-handling routine trap errors occurring within a
   SUB, FUNCTION, or DEF FN block, you need to place the error-
   handling routine at the module-level code (before the SUB or
   FUNCTION procedure definition). A label (such as Labelx) marks the
   start of the error-handler routine. The ON ERROR GOTO Labelx
   statement must be an executable statement within the same module as
   Labelx, but Labelx is put OUTSIDE the SUB...END SUB or
   FUNCTION...END FUNCTION procedure block, and the
   ON ERROR GOTO Labelx statement can be put INSIDE the
   procedure block or main program.

Note: QuickBASIC Version 4.50 uses global-error handling. For more
information about global-error handling, please search for "GLOBAL",
"ERROR", "HANDLING", and "4.50" in this KnowledgeBase.

The following program correctly demonstrates the flow of control when
an error occurs in a SUB procedure:

DECLARE SUB dork ()
  CALL dork
  PRINT "This is the last statement in main module"
END

handler:
  PRINT "error 50 has occurred"
  RESUME NEXT

SUB dork()
  ON ERROR GOTO handler
  ERROR 50              'This forces an error to occur
  PRINT "In the subroutine"
END SUB

You can find the incorrect paragraph in the QB Advisor "Help: ON ERROR
Statement Details," as follows:

1. Run QB.EXE Version 4.50.

2. Press SHIFT+F1 to invoke the QB Advisor Help menu.

3. Select Index.

4. Press PAGE DOWN key, or press "O" to jump directly to the Keywords
   beginning with the letter "O", then cursor to the ON ERROR statement
   and select it.

5. Select Details. The following window title appears:

      "Help: ON ERROR Statement Details"

6. Scroll down to the seventh paragraph. This paragraph and the
   example program below contain errors.

The following is the INCORRECT paragraph and example that can be found
in the HELP facility:

   " [ The following information is in error: ]
   SUB and FUNCTION procedures and DEF FN functions can contain their
   own error handlers. The error handler must be located after the
   last executable statement but before the END SUB, END FUNCTION, or
   END DEF statement. To keep the error handler from executing when
   there is no error, the procedure or function must terminate with an
   EXIT SUB, EXIT FUNCTION, or EXIT DEF statement immediately ahead of
   the error handler, as in the following example:

SUB InitializeMatrix (var1, var2, var3, var4)
      .
      .
   ON ERR GOTO ErrorHandler    ' [ Should be ON ERROR, not ON ERR! ]
      .
      .
   EXIT SUB         ' [ EXIT SUB is optional (not required). ]

   ErrorHandler:    ' [ Must move this after END SUB !]
      .
      .
   RETURN           ' [ Use RESUME, not RETURN!  Must move
                    '   ErrorHandler...RESUME to after END SUB ]

END SUB
[ end of incorrect HELP example. ] "

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