OpenOffice.org BASIC Guide - OpenOffice.org wiki

Error Handling
The following code is an example of an error handling procedure:
Sub Example
' Define error handler at the start of the function
On Error Goto ErrorHandler
' ... Here is the actual program code
On Error Goto 0 ' Deactivate error handling
' End of regular program implementation
Exit Sub
' Start point of error handling
ErrorHandler:
' Check whether error was expected
If Err = ExpectedErrorNo Then
' ... Process error
Else
' ... Warning of unexpected error
End If
On Error Goto 0 ' Deactivate error handling
End Sub
This procedure begins with the definition of an error handler, followed by the actual program code. At the end of
the program code, the error handling is deactivated by the On Error Goto 0 call and the procedure
implementation is ended by the Exit Sub command (not to be confused with End Sub).
The example first checks if the error number corresponds to the expected number (as stored in the imaginary
ExpectedErrorNo constant) and then handles the error accordingly. If another error occurs, the system outputs
a warning. It is important to check the error number so that unanticipated errors can be detected.
The On Error Goto 0 call at the end of the code resets the status information of the error (the error code in the
Err system variables) so that an error occurring at a later date can be clearly recognized.
Other Instructions
Type...End Type
A struct is a collection of data fields, that can be manipulated as a single item. In older terms, you may think of a
struct as a record, or part of a record.
The API often uses pre-defined structs, but these are UNO structs, a highly-specialized kind of struct.
Definition
With the Type...End Type statements, you can define your own (non-UNO) structs:
Type aMenuItem 'assign the name of the type
'Define the data fields within the struct. Each
' definition looks like a Dim statement, without the "Dim".
aCommand as String
aText as String
End Type 'close the definition
Instance
The Type definition is only a pattern or template, not a set of actual variables. To make an instance of the type,
actual variables that can be read and stored, use the Dim as New statement:
Dim maItem as New aMenuItem
32 OpenOffice.org 3.2 BASIC Guide · March 2010