Why no Description on error 80070002? - windows

Question

From some Visual Basic Script I accidentally tried to launch a program that did not exist:
Dim WshShell
Set WshShell = CreateObject("Wscript.Shell")
On Error Resume Next
WshShell.Run "incorrect"
WScript.Echo "Error:" & vbTab & Err.Description & vbCrLf & _
"Code:" & vbTab & Hex(Err.Number)
That gives:
Error:
Code: 80070002
So no description.
When I disable error checking (comment out the On Error Resume Next), I do get a description:
---------------------------
Windows Script Host
---------------------------
Script: D:\Folder\MyScript.vbs
Line: 3
Char: 1
Error: The system cannot find the file specified.
Code: 80070002
Source: (null)
---------------------------
OK
---------------------------
Is this difference in behavior a bug? Or am I missing something? I cannot find this documented anywhere.

Answer 1

I've done some testing myself and it appears to only happen with WshShell.Run().
For example try the following code which will work the same way but note the output.
Dim WshShell
Set WshShell = CreateObject("WScript.Shell")
On Error Resume Next
'This line will fail because there is no Type of 88.
WshShell.LogEvent 88, "incorrect"
WScript.Echo "Error:" & vbTab & Err.Description & vbCrLf & _
"Code:" & vbTab & Hex(Err.Number)
Output (with On Error Resume Next):
Error: Invalid procedure call or argument
Code: 5
Output (without On Error Resume Next):
Error: Invalid procedure call or argument
Code: 5
My guess is that WshShell.Run() is only reading from StdOut and not StdErr when On Error Resume Next is used, this is unique to WshShell.Run() because it is attempting to create a new process.
You could take this further by perhaps testing using WshShell.Exec() which gives access to both output streams.
Dim WshShell
Set WshShell = CreateObject("WScript.Shell")
On Error Resume Next
Set WshExec = WshShell.Exec("incorrect")
WScript.Echo "Error:" & vbTab & Err.Description & vbCrLf & _
"Code:" & vbTab & Hex(Err.Number)
Weirdly checked both WshExec.StdOut and WshExec.StdErr and neither contain the error output but the method behaves as expected when On Error Resume Next is used.
So not by any means conclusive.
But as the accompanying article states;
Just remember, scripting without mysteries would be insipid and boring
Useful Links
Doctor Scripto's Script Shop: To Err Is VBScript – Part 1