Word Document Properties

Chapter 6: Trapping Errors and Squashing Bugs
11_046500 ch06.qxp 12/5/06 5:35 PM Page 145

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The 
If...Then
statement performs a special task. This is one method for
performing a range check — something that you should do for every instance
of input that you receive from a user. The check ensures that the input is
within a specific range. If the input isn’t within the specified range, the code
uses the 
Err.Raise
function to generate an error. User-defined errors fall
within a specific range, so you should always add your custom error number
to 
vbObjectError
to ensure that the number is within the proper range. All
error numbers must be less than 65,535.
Whenever you define a 
custom error
(one that you define), you should tell
yourself exactly where the error occurred. I always include the filename, the
module name, and the 
Function
or 
Sub
name. Notice that the description
information for this error is complete and descriptive. Just because Microsoft
provides ambiguous information doesn’t mean that you have to follow its bad
example. Always include descriptive error messages so that you have a good
idea of what went wrong.
The error handler begins at the 
MyHandler
label. The handler shows the var-
ious 
Err
object properties that you can access to determine the source and
cause of an error. The example could easily include a retry feature, but I
chose to keep things simple. See the earlier “Recovering from an error” sec-
tion for details on a retry feature.
The last statement might not look like much, but it’s very important. Always
clear errors after you handle them, by using the 
Err.Clear
method. If you
don’t, VBA might think that the error is still a problem and fail again.
Reporting errors
It’s essential to report program errors. You can’t overcome problems with
your program when you don’t know about them. In addition, knowing about
errors makes it possible to create a recovery plan. Here are some techniques
that you can use to report errors: