XL5: Incorrect Use of "Is" Function Causes GP Fault

ID: Q112629

The information in this article applies to:

Microsoft Excel for Windows, version 5.0

SYMPTOMS

In Microsoft Excel version 5.0 for Windows, if you use the Visual Basic for Applications "Is" function incorrectly, you may receive a general protection (GP) fault.

MORE INFORMATION

The "Is" function is used to compare two object reference variables. The result of an Is operation is either TRUE (if the variables both refer to the same object) or FALSE (if they do not).

For example, if you have the following code:


   Set Alpha = ActiveWorkbook.Sheets(1)
   Set Bravo = ActiveWorkbook.Sheets(1)

   Set Charlie = Alpha
   Set Delta = Alpha

All of these commands will return the value TRUE:

Alpha Is Charlie
Alpha Is Delta
Charlie Is Delta

Note that Bravo Is <object>, where <object> is Alpha, Charlie, or Delta, will return FALSE, because the value of Bravo is not the same as the value of Alpha, Charlie, or Delta, even though they both refer to the same object.

If you use the "Is" function to compare a valid object reference (for example, Alpha) to an invalid object reference (for example, a numeric value, a string, or any other item that is not an object), you may receive a GP fault.

To prevent this error from occurring, make sure both items being compared are valid objects.

Visual Basic Code Example

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The following code example illustrates the proper use of the "Is" function.

To run this example, position the cursor in the line that reads "Sub GoodIsSubroutine()" and either press the F5 key or choose Start from the Run menu.


'----------------------------------------------------------------------
Option Explicit

Sub GoodIsSubroutine()

   'Dimension variables.
   Dim Alpha As Variant, Bravo As Variant, Charlie As Variant
   Dim Delta As Variant

   'Create object names.
   Set Alpha = ActiveWorkbook.Sheets(1)
   Set Bravo = ActiveWorkbook.Sheets(1)
   Set Charlie = Alpha
   Set Delta = Alpha

   'These are tests to see if one object Is another object. A message
   'box is displayed if the objects are the same. In this case, only the
   'first three messages will be shown.
   If Alpha Is Charlie Then
      MsgBox "Alpha is Charlie!"
   End If

   If Alpha Is Delta Then
      MsgBox "Alpha is Delta!"
   End If

   If Charlie Is Delta Then
      MsgBox "Charlie is Delta!"
   End If

   If Bravo Is Charlie Then
      MsgBox "Bravo is Charlie!"
   End If

   If Bravo Is Delta Then
      MsgBox "Bravo is Delta!"
   End If

End Sub
'----------------------------------------------------------------------

When you run GoodIsSubroutine, you will be shown three message boxes, one for each of the "Is" functions that succeeds.

Additional query words: hang stop responding gpf

Keywords : kbprg
Version : WINDOWS:5.0
Platform : WINDOWS
Issue type :