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Q221743: FIX: NVL() Releases Object Ref and Causes Fatal Error C0000005

Article: Q221743
Product(s): Microsoft FoxPro
Version(s): WINDOWS:5.0,5.0a,6.0
Operating System(s): 
Keyword(s): kberrmsg kbservicepack kbOOP kbvfp500aBUG kbvfp600 kbvfp600bug kbVS600sp2 kbVS600SP1 kb
Last Modified: 27-JUL-1999

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, versions 5.0, 5.0a, 6.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

Calling the NVL() function multiple times in Visual FoxPro 5.0 causes the
following error message:

  Property <property name> is not method or event.

If you click the Ignore button in the error dialog box and run the program again,
you normally see the following error:

  An application error has occurred and an application log is being generated.
  VFP.exe
  Exception: access violation (0x0000005), Address: <memory address>

In some instances, the first error message is skipped and the second error is
displayed.

The following error can also occur:

  The instruction at "0x00401e44" referenced memory at "0x010bb018". The memory
  could not be "read".

In Visual FoxPro 6.0, the following error often appears after calling the NVAL()
function the third time:

  Fatal error: Exception code: C0000005

CAUSE
=====

The NVL() function saved the handle, but it released the object reference.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article.

This bug was corrected in Visual Studio 6.0 Service Pack 3.

For more information about Visual Studio service packs, please see the following
articles in the Microsoft Knowledge Base:

  Q194022 INFO: Visual Studio 6.0 Service Packs, What, Where, Why

  Q194295 HOWTO: Tell That Visual Studio 6.0 Service Packs Are Installed

MORE INFORMATION
================

Steps to Reproduce Behavior
---------------------------

1. Create a program that contains the following code:

  ox = CreateObject("Lbltest")
  ox.Test()
  ox.Test()
  ox.Test()

  Define Class Lbltest as Label
   Procedure Test
   oObj = NVL(.NULL.,This)
   ?oObj.name
   EndProc
   
  Enddefine

2. Run the program.

After accessing the Test procedure the third time, one of the errors listed in
the SYMPTOMS section above appears.

Additional query words:

======================================================================
Keywords          : kberrmsg kbservicepack kbOOP kbvfp500aBUG kbvfp600 kbvfp600bug kbVS600sp2 kbVS600SP1 kbVS600sp3fix kbGrpDSFox 
Technology        : kbVFPsearch kbAudDeveloper kbVFP500 kbVFP600 kbVFP500a
Version           : WINDOWS:5.0,5.0a,6.0
Issue type        : kbbug
Solution Type     : kbfix

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