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When writing scripts in any language, it is critical to be able to catch and handle errors within your

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script.

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In Visual Basic script, there is a global error object that contains information about the last error

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encountered.

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Taking a look at the Wink Help file, looking under the Visual Basic scripting section.

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Under Basic Principles of VB script, there is a keyword list and we can find the error object.

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The error object is an intrinsic object with a global scope, so there's no need to create an instance.

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It's important to note that in wink, all Visual Basic scripts in a system are compiled together in

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one big script when you go to runtime.

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Therefore, an error that is not handled in one script could affect another script without you realizing

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it, and this can be very difficult to troubleshoot.

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So the error object gives you a number which indicates the type of error that happens.

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And it also allows you to get the source and description of the error.

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And you can raise your own errors as well as clear the current error.

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So let's take a quick look at an example of using the error object.

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Here I have a button called Division test and it merely does division and prints out the results.

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There's a hard coded number called my number.

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It's hard coded to six.

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There is a variable called test division and then a variable called divisor, which gets this value

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from an internal tag that we are going to enter on the screen.

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It then performs the division dividing my number by divisor and storing the results in test division.

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And then it uses my runtime trace to just print out the results.

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The test for errors button just checks the global Error objects number to see if it's anything other

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than zero, indicating an error has occurred, and if it does, it prints out information about the

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error.

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If not, it just prints out there are no errors.

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Again, this is a completely different subroutine than the one on this button.

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So let's go to runtime and see what we've got.

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First, I'll just test for errors and there are no current errors.

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And then I'm going to put something valid in divisor and press our division test.

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And it just prints out six divided by two is equal to three.

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No errors there.

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But if I introduce an error a divide by zero error then I'll hit the button.

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Notice that when CC prints out information about the error and this is helpful, it tells you what page

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the error occurred on, what object and event that the error occurred on, and what the error was.

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But notice that my print statement did not execute.

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But what's interesting is if I hit test for errors, the error object has not been cleared in this case.

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So if we have another script that is checking for errors, then it mistakenly may have an error that

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was caused by a completely different script.

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So what we want to do is handle our own errors using the error object.

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So when we're handling our own errors, there are three things that we need to do in this script.

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The first thing is we need to disable the when CC error reporting so that we can handle it.

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The second thing we need to do is check for errors at different areas of the script where they may occur.

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And the third thing is to handle the error and then clear the error object.

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So in order to do the first thing before we get into any real code, we are going to declare on error

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resume next.

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This prevents when CC from handling the errors.

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Now if I just leave it like this.

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Let's watch what happens so that you can understand it better.

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I'll just click okay.

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I'll hit save and run.

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First.

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We will give it a valid result that looks good and then an error result.

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All right.

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It still prints out.

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But notice we don't get anything.

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So we haven't caught the error.

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All we've done is turned off Winky's ability to handle it.

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So now let's go handle that error.

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Go back into the script.

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And right after we do, the division is a good place to test for errors, and what we can do is make

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use of the error number property.

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So I'll just paste in the code here.

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It just tests error number to be anything other than zero.

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Now you may see some code online where they do this, but that's not going to catch all errors.

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So I always look for the not equal.

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And then the other thing that we can do I've got error number and error description.

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But there is also an error source that we can use.

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So I'm just going to paste that in here.

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And this isn't specifically spelled out in the help file.

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But I found out that it does support it.

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And so now if there is an error then we're simply just going to print out that it exists.

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We're not going to do anything to go rerun the script.

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And then importantly, we're going to clear the error so it doesn't affect any other scripts.

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And then finally, if there was an error, we are just going to exit sub, which gets us out of the

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script because this is going to be meaningless.

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So now I'll just click okay.

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We'll hit save and go to runtime.

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And first we will do the good test.

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Everything's okay.

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And then we will introduce an error.

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And it prints out it was error number 11.

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The source is Microsoft VBScript runtime error and the actual error was division by zero.

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If we print out test for errors, you can see that there are no current errors because we did clear

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the error object.

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And if we run this again then we have a good result.

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Now let's go back to our Edo script and see how we can implement checking for errors and handling them

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using the error object.

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So before we get into any real code we put in on error resume.

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Next.

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And this disables the automatic error reporting so we can handle it.

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Once you do this you do need to make sure you have code in to handle the scripts because since when

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CC isn't handling it, it's not going to print out any information.

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So our first point where we might have an error is when we try to open our connection.

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So we just test if error number is zero.

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And if it is we'll continue on with the script.

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And the second place we may encounter an error is when we execute our SQL command with our record set.

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So we open our record set and then again check if we have no errors.

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Then we will continue on and print out the results.

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After that loop, we test and see if there is anything other than zero in there and just print out the

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information.

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And so these two lines are where the end if statements are for our test for the connection object and

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the record set object.

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So if there is a connection error it just skips to this line.

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If there's a record set error then it just skips to this line.

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And then we check for errors, print out the information and clear.

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And then the only code is going to be our housekeeping code, where we clean up our record setting connection,

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which we want to do anyway.

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So now let's go introduce some errors and see how it does.

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So the first error I'm going to put in a non-existent table name and see what kind of error we get.

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I'll click okay.

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Save and run.

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And when we run the script, notice that the error is not greater than zero.

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It's a really big less than zero number.

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So that's why you always check for does not equal zero rather than greater than zero.

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And then it tells you that the Ole DB provider is throwing the error and it's an invalid object name.

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Next let's go back and test if our connection string is wrong.

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So I will fix this error and then I will just put Z-z-z here.

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So now we have an invalid provider and we'll click okay.

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Save and go to runtime.

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Test our script.

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Now it tells us that the problem is that Adodb connection and it says the provider cannot be found.

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And so we'll go back to the script and of course we can fix this.

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Now, of course, if there is an error down here.

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So let's just say that we're putting something incorrect here.

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I'll just put some nonsense in there.

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Click okay.

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Save it and run it.

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Okay, so now it will print out the headers.

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It can't print out the loops because it doesn't have the correct code.

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And then it tells you there's a VBScript runtime error.

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It just says object doesn't support this property or method.

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So that is kind of a generic error.

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But you should be able to go back and find that.

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So once we fix this now let's see if it runs without errors we'll save.

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And run.

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And there's our code.

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So now we have an adult script that can detect and handle errors.

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In the next assignment, you're going to get a chance to add error handling to our Ado script.

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So I'll see you there.