March 2003
Intermediate to advanced
512 pages
14h 30m
English
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Chapter 4. Error Handling and Debugging
Errors, bugs, and therefore, debugging, are a part of life for a programmer. As the saying goes, if you haven’t found any mistakes, then you aren’t trying hard enough.
Dealing with errors actually involves two very different processes: error handling and debugging. Error handling is a combination of coding and methodology that allows your program to anticipate user and other errors. It allows you to create a robust program. Error handling does not involve weeding out bugs and glitches in your source code, although some of the error-handling techniques covered in this chapter can be used to great advantage at the debugging stage. In general, error handling should be part of your overall program plan, so that when you have an error-free script, nothing is going to bring it to a screeching halt. With some sturdy error handling in place, your program should be able to keep running despite all the misuse that your users can — and certainly will — throw at it.
The following ASP page illustrates some simple error handling:
<HTML>
<HEAD><TITLE>Error Checking</TITLE>
<BODY>
<SCRIPT LANGUAGE="VBSCRIPT" RUNAT="SERVER">
Dim n, x
n = 10
x = Request.Form.Item("txtNumber")
If x = 0 Or Not IsNumeric(x) Then
Response.Write "x is an invalid entry"
Else
y = n / x
Response.Write y
End If
</SCRIPT>
</BODY>
</HTML>The error handling in this example is the best kind — it stops an
error before it can occur. Suppose you hadn’t used the conditional
If...Else statement ...
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