Q61340: Watchpoints Set at Module Level Won’t Break in a SUBprogram

Article: Q61340
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S900415-5 B_BasicCom | mspl13_basic
Last Modified: 2-MAY-1990

Watchpoints put on variables (which are set in QuickBASIC's Debug
menu) have a local scope. That is, you must reset the watchpoint on a
variable in each SUBprogram or FUNCTION, even if the variable is in a
SHARED or COMMON SHARED statement. This is by design.

If you add a watchpoint in the module-level code of a shared variable,
and a SUBprogram or FUNCTION changes the variable so the watchpoint
should break, the program will not break until the SUBprogram or
FUNCTION returns to the module-level code.

This information applies to the QB.EXE environment in QuickBASIC
versions 4.00, 4.00b, and 4.50, and to the QBX.EXE environment of
Microsoft BASIC Professional Development System (PDS) version 7.00.

The following program, when run in the QuickBASIC or QuickBASIC
Extended environment, demonstrates that watchpoints are local:

   DECLARE SUB test ()
   COMMON SHARED a
   a = 0
   CALL test
   PRINT "After call"
   END

   SUB test
      a = 3
      PRINT "in sub - does not break"
   END SUB

To demonstrate this, set a watchpoint on "a<>0" (to break when the
variable "a" changes from being zero). When the program is run, the
watchpoint will not activate until control is returned to the
module-level code. The program will break on the line "PRINT 'After
call'," even though the value of variable "a," was changed in the
SUBprogram.

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