Passing Variables to ON ERROR and ON Event Handlers (21863)

MORE INFORMATION

Variables can be passed through the COMMON SHARED or DIM SHARED statement to ON ERROR and ON "event" handler routines compiled separately from the main program. Variables that do not follow a COMMON SHARED or DIM SHARED statement are not accessible to the handler routines (unless the handler is in the same source file as the main program).

The following is an example of a separately compiled subprogram that shares a flag variable with its error handler routine:

   ' TEST.BAS
   COMMON SHARED FLAG  'Used if FLAG is to be global between modules
   'DIM SHARED FLAG    'Will also work, if FLAG is to be global only
                       'to this module
   errortrap:
      ' The error is handled here:
      PRINT "Error Number Trapped="ERR
      FLAG=5
      RESUME NEXT  ' Resumes to line after where error occurred.
   SUB test STATIC
   ON ERROR GOTO errortrap
   FLAG=0
   ERROR 5  ' Forces a test error number 5 to occur.
   PRINT "FLAG=",FLAG  ' Execution resumes here after the error.
   END SUB
				

This program is called by the following separate main program module:

   ' MAIN.BAS
   CALL TEST
				

First, compile as follows:

   BC MAIN/X;
   BC TEST/X;
				

You then can LINK MAIN+TEST; run the resulting program as an example.

You cannot use the linenumber or linelabel option of RETURN or RESUME in conjunction with subprograms.

In QuickBasic versions 1.0, 1.01, 1.02, 2.0, 2.01, 3.0, and 4.0, error and event handling routines are local to each separately compiled module. A given error or event handling routine serves all subprograms compiled in the same module. The ON ERROR GOTO or ON event GOSUB statement should appear in each subprogram that is compiled separately from the main program.

QuickBasic versions 4.0b and 4.5, Microsoft Basic Compiler versions 6.0 and 6.0b, and Microsoft Basic PDS versions 7.0 and 7.1 offer global error handling, which is described in a separate article. For more information, query on the following words: