You cannot explicitly transfer program execution to a CATCH or FINALLY code block.
Visual FoxPro determines scope for variables on a procedural, not block, basis. That is, variables declared in a TRY block are visible from a FINALLY block within the same TRY...CATCH...FINALLY structure. However, in a nested structure, variables that are declared in a TRY, CATCH, or FINALLY block have local scope.
You should not initialize variables or set up critical code inside the TRY block because the code is not guaranteed to run. If an error occurs at a particular line of code in the TRY block, all subsequent lines in the TRY block do not run.
Any errors that occur in an object's Error event must be handled by the object and are not escalated to an ON ERROR routine or TRY...CATCH...FINALLY handler. However, you can use a TRY...CATCH...FINALLY structure in the Error event to catch errors from an Error event. For more information, see Error Event (Visual FoxPro).
Using the COMRETURNERROR( ) function in a CATCH block ends all further processing and returns control of the program directly to the Component Object Model (COM) client. Therefore, if you have a FINALLY block, it does not run. For more information, see COMRETURNERROR( ) Function.
Avoid using the SET TEXTMERGE TO MEMVAR command within a TRY...CATCH...FINALLY structure because the memory variable will be lost if an error occurs in the statement.
To determine a course of action and the error handler in effect, use the SYS(2410) - Error Handler function in your TRY...CATCH...FINALLY code, for example, with a DO CASE structure, depending on the type of handler that handles the exception. For more information, see SYS(2410) - Error Handler.
You can use TRY...CATCH...FINALLY to handle errors that occur in menu and timer events and with commands such as ON KEY LABEL if the structure is properly wrapped. The following example illustrates how the READ EVENTS command retains control of the program within the TRY...CATCH...FINALLY structure so that you trap menu events. Error trapping is controlled by the position of TRY...CATCH...FINALLY on the call stack.
TRY
DO myMenu.mpr
DO FORM myForm
myForm.AddObject("tm1","mytimer")
READ EVENTS
CATCH TO oException
IF oException.ErrorNo = 1
STRTOFILE("Error occurred at: " + TRANSFORM(DATETIME());
+ CHR(13),"C:\Errors.log",.T.)
ENDIF
FINALLY
CLEAR EVENTS
ENDTRYFor more information, see READ EVENTS Command and ON KEY LABEL Command.
Visual FoxPro supports Set Next Statement debugging functionality only within a single code block. For example, when executing code in a TRY block, you can use Set Next Statement only to another line within the TRY block. You cannot jump to another line of code in a CATCH or FINALLY block. For more information, see Debugger Keyboard Shortcuts and Menus.
Visual FoxPro generates the appropriate system messages under the following conditions:
-
A mismatch or error occurs with the TRY...CATCH...FINALLY structure.
-
An unhandled exception occurs.
-
A command that is not permitted for a specific block appears in a TRY, CATCH, or FINALLY block. For more information, see Structured Error Handling.
-
A user-thrown error occurs.
Similar to other error handling in Visual FoxPro, exceptions that occur in TRY...CATCH...FINALLY exception handlers set the SET CONSOLE command to ON. For more information, see SET CONSOLE Command.