Minimizing Code Size by Handling Errors in a Central Location

As you add error handlers to your applications, you'll soon discover that you're handling the same errors over and over again. You can reduce code size and save yourself time and effort by writing a few procedures that your error handlers can call to handle common error situations.

The following code is a function called FileErrors that can be called by an error handler. This function displays a message corresponding to the error that has occurred and, where possible, allows the user to choose a button to specify which action the function should take next. It then returns a code number to the procedure that called it (the calling procedure isn't shown in the example). The code number indicates which action — out of a set of actions — the program should take.

Public Const RESUME_STATEMENT = 0        'Resume
Public Const RESUME_NEXT = 1                'Resume Next
Public Const UNRECOVERABLE = 2            'Unrecoverable error
Public Const UNRECOGNIZED = 3            'Unrecognized error
Public Const Err_DeviceUnavailable = 68
Public Const Err_BadFilenameOrNumber = 52, Err_PathDoesNotExist = 76
Public Const ERR_BADFILEMODE = 54

Function FileErrors (errVal As Integer) As Integer
Dim MsgType As Integer, Msg As String, Response As Integer
    MsgType = vbExclamation
    Select Case errVal
        Case Err_DeviceUnavailable                      ' Error #68
            Msg = "That device appears unavailable."
            MsgType = MsgType + vbAbortRetryIgnore
        Case Err_BadFilenameOrNumber  ' Errors #52
            Msg = "That filename is not valid."
            MsgType = MsgType + vbOKCancel
        Case Err_PathDoesNotExist                      ' Error #76
            Msg = "That path doesn't exist."
            MsgType = MsgType + vbOKCancel
        Case Err_BadFileMode                              ' Error #54
            Msg = "Can't open your file for that type of access."
            MsgType = MsgType + vbOKCancel
        Case Else
            FileErrors = UNRECOGNIZED
            Exit Function
    End Select
    Response = MsgBox(Msg, MsgType, "Disk Error")
    Select Case response
        Case vbOK, vbRetry
            FileErrors = RESUME_STATEMENT
        Case vbIgnore
            FileErrors = RESUME_NEXT
        Case vbCancel, vbAbort
            FileErrors = UNRECOVERABLE
        Case Else
            FileErrors = UNRECOGNIZED
    End Select

End Function

What Happens to Errors That Your Error Handler Doesn't Handle?

The function in the preceding example handles a select group of file-related and disk-related errors. If an error you encounter doesn't belong to this set of errors, the function returns the value 3. The procedure that calls this function should then either handle the error itself, call another procedure to handle it, or just let the original run-time error occur again, as shown in the following example.

Function FileOperationsDemo(FileName As String)
'Demo of how you would call the FileErrors Function
On Error GoTo ConfirmFileError
.
.
.
'Code that attempts some file operation
.
.
.
ConfirmFileError:
Action = FileErrors(Err)            'Call the FileErrors function
    Select Case Action
        Case RESUME_STATEMENT    'User chose OK or Retry when FileErrors 
                                'displayed its message, so try again.
            Resume
        Case RESUME_NEXT            'User chose Ignore when FileErrors
                                'displayed its message, so ignore error
                                'and continue.
            Resume Next
        Case UNRECOVERABLE         'User chose Cancel or Abort when
                                'FileErrors displayed its message,
                                'so abort procedure.
            Exit Function
        Case Else                'Cannot handle original run-time
                                'error, so repeat it and display
                                'the normal System error.
            Error Err
    End Select
End Function