Exceptions: Difference between revisions

=={{header|Visual Basic for Applications}}==

For historical reasons, Exceptions are called 'Errors' in VBA and VB Classic.

VBA inherited several distinct exception handling models, which may be freely mixed and matched.

The major limitations are that nested Try/Catch blocks must be constructed by the user, and that the User Defined Labels required for the Catch/Finally blocks may not be reused within a subroutine. For these reasons, it is conventional to only have only 1 Try/Catch block per subroutine.

===Throw exceptions===

<lang vba>Sub foo1()

err.raise(vbObjectError + 1050)

End Sub

Sub foo2()

Error vbObjectError + 1051

End Sub

</lang>

===Catching exceptions===

<lang vba>Sub bar1()

'by convention, a simple handler

On Error Goto Catch

fooX

Exit Sub

Catch:

'handle all exceptions

Exit Sub

Sub bar2()

'a more complex handler, illustrating some of the flexibility of VBA exception handling

on error goto catch

100 fooX

200 fooY

'finally block may be placed anywhere: this is complexity for it's own sake:

goto finally

catch:

if erl= 100 then

' handle exception at first line: in this case, by ignoring it:

resume next

else

select case err.nummber

case vbObjectError + 1050

' handle exceptions of type 1050

case vbObjectError + 1051

' handle exceptions of type 1051

case else

' handle any type of exception not handled by above catches or line numbers

resume finally

finally:

'code here occurs whether or not there was an exception

'block may be placed anywhere

'by convention, often just a drop through to an Exit Sub, rather tnan a code block

Goto end_try:

end_try:

'by convention, often just a drop through from the catch block

exit sub