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For the typical VB program, the programmer can set break points
and step slowly through the execution while checking the values
of variables. You can do that with VBWeb as well but it takes a
trick. The problem is if you try running a script right from
within the VB editor, it won't get any entries to process. It
needs to get a request such as a query string or entries in an
HTML form. That usually means that the script must be an
executable. To get around this, VBWeb writes a backup of the
request out to a file when it is run as an executable and
restores the request when it is run from within the VB editor.
Since writing the file can add to the response time of the
script, the backup is only made if the IsCgiDebugOn
variable is set to True. This instruction should
come before the call to LoadRequest. For example:
Public Sub Main()
On Error GoTo Trap
IsCgiDebugOn = True
Call LoadRequest
Call ProcessRequest
Exit Sub
Trap:
Call ErrorHandler("")
Exit Sub
End Sub
Once this line is added, the script must be compiled and then
run from the web site. After that, return to the VB editor and
step through the code as you see fit.
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Workstation User Tip:
If you edit the project
from a different directory than the executable in the web server,
then you will need to retrieve the backup file and move it to the
current directory. This is usually the directory containing the
VB project file.
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If you do not have a VB error that needs fixing, we can find
one in a demo application.
- If you have not yet done so, download and install the vbshop
demo project. There are instructions in the NEWMAN VBWeb
web site.
- Next, we find an error. You can cause an error by
clicking Check Out when the shopping cart is empty. Once
you see the error, don't do anything else with the site.
At this point, the request has been backed up. If you
cause another request, it will get backed up and written
over the one we want. Your browser should show the
following error:
A Message from the Server
The server had trouble processing your request. Back up
and try again.
Nothing has been ordered yet. (10000).
- Open the vbshop project in the VB editor and and run it.
This is when VBWeb gets a chance to restore the backup so
that vbshop runs just as it did for the browser. And
that's when the following error message pops up. Click Debug
to see just where the error occurred.
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How to only back up your own requests.
The IsCgiDebugOn line as coded above, causes every
request to get backed up. If another visitor sneaks in shortly
after you find an error, a new backup gets written over the one
you want. To prevent this, you can restrict backups to only the
requests that come from you and your browser. To do this, find
your IP address and use it in the following way:
If Environ$(CGI_REMOTE_ADDR) = "256.256.256.256" Then
IsCgiDebugOn = True
End If
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OUT ON THE INTERNET
