Q21805: < RESUME Linenumber > Is Not Allowed for Subprograms

Article: Q21805
Product(s): See article
Version(s): 1.00 1.01 1.02 2.00 2.01 3.00
Operating System(s): MS-DOS
Keyword(s): ENDUSER | docerr | mspl13_basic
Last Modified: 16-NOV-1988

Question:

How can I use ON ERROR GOTO to trap errors that occur inside of
subprograms separately compiled from the main program in QuickBASIC
Versions 1.00, 1.01, 1.02, 2.00, 2.01, 3.00, and 4.00 for MS-DOS?

Response:

The following information should be added to the "Microsoft QuickBASIC
Compiler" documentation for Versions 1.x, 2.x, and 3.00:

Error handling in separately compiled subprograms should be coded in
the following fashion:

   SUB test STATIC
   ON ERROR GOTO errortrap
      ' body of subprogram
   END SUB
   errortrap:
      ' The error is handled here:
      PRINT "Error Number Trapped="ERR
      RESUME NEXT

In QuickBASIC Versions 1.00, 1.01, 1.02, 2.00, 2.01, 3.00, and 4.00,
the ON ERROR GOTO Label statement must be established for each module;
otherwise, an error occurring in that module will not be trapped, and
the program will stop. In QuickBASIC Versions 4.00 and earlier, error
handling routines are local to each separately compiled module. A
given error handling routine serves all subprograms that are compiled
in the same module. To trap errors, the ON ERROR GOTO statement should
appear in each subprogram that is compiled separately from the main
module.

In contrast to earlier versions, QuickBASIC Versions 4.00b and 4.50,
and the Microsoft BASIC Compiler Versions 6.00 and 6.00b for MS-DOS
and MS OS/2 offer global handling of ON ERROR (as explained in the
UPDATE.DOC disk file). With global error-handling, an ON ERROR handler
in the main program handles errors occurring in separate modules when
those modules do not have their own ON ERROR handlers.

All versions of QuickBASIC do not allow you to use < RESUME
linenumber > or < RESUME linelabel > to handle errors that occur in
subprograms. QuickBASIC only allows the use of RESUME or RESUME NEXT
with subprograms. This fact needs to be added to Pages 128 and 129 of
the "Microsoft QuickBASIC Compiler" documentation for Versions 2.x and
3.00.

In Version 1.02, if a < RESUME linenumber > or < RESUME linelabel >
statement is used in a separately compiled subprogram, an "SB"
(subprogram) error displays, but an OBJ file still will be created.
You should not LINK the OBJ file if it receives an "SB" error, or if
it uses < RESUME linenumber > or < RESUME linelabel > with
subprograms. If you did use the file, you could receive unpredictable
errors at run time due to eventual stack overflow.

QuickBASIC Versions 2.00 and later will properly give you a
"Subprogram Error" message and will not produce an OBJ file if you use
< RESUME linenumber > or < RESUME linelabel >.

Note also that < RETURN linenumber > or < RETURN linelabel > is not
allowed with "ON event GOSUB" trapping used with subprograms; only
RETURN is allowed. This fact applies to ON TIMER GOSUB, ON KEY GOSUB,
ON PLAY GOSUB, ON STRIG GOSUB, and ON PEN GOSUB. Event trapping should
be structured similar to error trapping in the sample program above.

For a related article, you may query on "subprogram module error
resume QuickBASIC" in this database.

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