Recently, I was working on a script that was designed to take a set of data
as input, apply some formatting to each record, and output the results.
While the concept is simple enough, the problem was that the data being
provided to the script was not quite uniform. Not only was the data
being pulled from a text file which used spaces as delimiters and
included data which contained spaces, but we also occasionally
ran into records that were simply incomplete.
So as I saw it, I had two options. I could add tons of error handling
in an attempt to handle every possible failure or I could simply
omit the error handling, run the script, and see what happened.
Well we all know what happened... I got an error. In this case it was
Microsoft VBScript runtime error '800a0005' - Invalid procedure call or argument: 'Left'.
Anyone who's done any string wrangling in VB has probably seen this error, but
it's not very helpful in trying to find out what data caused the error.
What would be helpful in that regard would be being able to see the output of the
records that got processed before the error happened. And how do we do that?
Why we disable buffering of course.
If you're not familiar with buffering, you may want to take a moment and read
our tip which recommends enabling buffering to increase performance:
Set Response.Buffer = True.
By setting Response.Buffer = False, we tell the server to return the output of the script
as it is generated. That means we'll actually see all the data that the script has
processed right up until the error happens. This allows us to easily find the problem data
by simply taking the last record processed before the error and finding the corresponding entry
in the input. Then we simply look at the next record and we've almost certainly found
the one causing the problem.
While I don't recommend this type of approach on public sites or if others are
going to be using the script, it can be an invaluable debugging tool and a huge
time saver if you're trying to find and eliminate problems.
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webmaster@asp101.com.
