|
TRY .. CATCH .. FINALLY .. END_TRY |
Exception/Error Trapping |
TRY [WITH ERROR_HANDLER]
... logic to run with the option to enable error handler
CATCH
... logic to execute should an error occur
FINALLY
... optional logic to execute after the TRY or CATCH logic completes
END_TRY
Using the TRY .. CATCH .. FINALLY allows you to execute a block of code and trap any/all errors that might occur within it.
The basic construct of a TRY .. CATCH block of code is as follows:
try
! Logic to execute
! Any errors that occur in this code or code that it
! calls via GOSUB, PERFORM, CALL or Object Method
! will invoke the CATCH logic.
catch
! Execution will transfer to this block of code should an exception occur in the TRY block.
! If no exception occurs in the TRY block, the CATCH block will be skipped.
finally
! This optional block of code will always get executed regardless
! whether an exception occurs or not. Generally this logic will attempt
! clean up from either the TRY block or CATCH block, such as closing
! files, resetting the display, etc.
end_try
The TRY, CATCH, FINALLY and END_TRY directives must appear in the above sequence. There must be only one CATCH and FINALLY block within the structure, with the CATCH block being mandatory, and the FINALLY block being optional. Any error in the structure of the logic will be reported as an Error #67: Invalid Try/Catch/Finally structure or transfer.
Execution of a CATCH, FINALLY or END_TRY outside the scope of a TRY directive will result in an error. In addition, transferring out of TRY structure without completing it will result in an internal stack error being generated: Error #27 - Unexpected or incorrect WEND, RETURN, WITH or NEXT.
A TRY/CATCH logic block will trap errors that are not handled by ERR= clauses or other error handling logic and that normally would have been trapped by ERROR_HANDLER or SETERR or returned to the user. While a TRY/CATCH is in effect, the system will ignore any ERROR_HANDLER or SETERR you may have set unless you add the WITH ERROR_HANDLER clause to the TRY directive. If a SETERR is set within a TRY, the SETERR is ignored unless you add the WITH ERROR_HANDLER clause. Inclusion of the ERROR_HANDLER clause will result in an error being forwarded to your error handler for processing, and only if it initiates the error will the TRY/CATCH logic take effect. If a SETERR is set outside either a TRY or TRY WITH ERROR_HANDLER, it is always ignored.
(The TRY .. CATCH ..FINALLY .. END_TRY directives were added in PxPlus v10.10.)
(Support for the TRY WITH ERROR_HANDLER directive was added in PxPlus 2016.)
ERROR_HANDLER Define Generic Handler
SETERR Set Error Transfer