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Q39860: Cannot Nest ON ERROR GOTO Error-Trapping Routines in BASIC

Article: Q39860
Product(s): See article
Version(s): 2.00 2.01 3.00 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom SR# G881215-8171 | mspl13_basic
Last Modified: 14-DEC-1989

After control is passed to an error handler in a Microsoft QuickBASIC
program, additional errors cannot be trapped until a RESUME, RESUME
label, or RESUME NEXT occurs. This behavior is by design and applies
to Microsoft QuickBASIC Versions 2.00 2.01 3.00 4.00 4.00b and 4.50,
to Microsoft BASIC Compiler Versions 6.00 and 6.00b for MS-DOS and MS
OS/2.

This also applies to Microsoft BASIC PDS for MS-DOS and MS OS/2 when
using global or "module level" error trapping. However, error trapping
is possible inside a local error handler invoked with an ON LOCAL
ERROR statement available in Microsoft BASIC PDS Version 7.00 for
MS-DOS and MS OS/2.

Error-trapping routines perform best when they help notify you or the
program of an error condition, allow for the error to be corrected,
and then RESUME back into the program.

For example, the following error-trapping structure could be used when
attempting to open a user-supplied filename. If more coding was used
and an error occurred while in the TRAP routine, the error would not
be trapped by the program.

The following is a code example:

ON ERROR GOTO TRAP
10  INPUT "Enter a FileName: ";a$
20  OPEN a$ for input as #1
END
TRAP:
   IF ERL = 20 THEN
      RESUME 10
   ELSE
      Print "The error Number is: ";err
      RESUME NEXT
   END IF

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