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Q306079: PRB: SET PROCEDURE TO Causes Unknown Error with FoxPro DLL

Article: Q306079
Product(s): Microsoft FoxPro
Version(s): 5.0,5.0a,6.0,7.0
Operating System(s): 
Keyword(s): kbCOMt kbvfp kbvfp500a kbvfp600 kbGrpDSFox kbDSupport kbCodeSnippet kbvfp500xSearch kbv
Last Modified: 30-AUG-2001

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, versions 5.0, 5.0a, 6.0, 7.0 
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SYMPTOMS
========

If a COM dynamic-link library (DLL) which uses SET PROCEDURE TO is instantiated
more than once, the Init method of the second instance may fail with one of the
following messages:

  OLE error code 0x80004005: Unspecified error.

  OLE error code 0x80020009: Exception occurred.

CAUSE
=====

To instantiate an OLEPUBLIC class, Visual FoxPro must be able to find all the
code for the class. There is an internal SET PROCEDURE/SET CLASSLIB to detect
all the related code; if you try to change this setting, an error occurs.

RESOLUTION
==========

Use SET PROCEDURE TO with the ADDITIVE keyword.

STATUS
======

This is by design.

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

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

To see this behavior, run the following code. Uncomment the ADDITIVE clause for
the code to work.

  CLOSE ALL
  SET SAFETY OFF
  ERASE testLib.*
  ERASE comTest.*

  SET TEXTMERGE TO testLib.prg NOSHOW
  TEXT 
     *!* Dummy function library
  ENDTEXT

  SET TEXTMERGE TO comTest.prg NOSHOW
  TEXT 
     DEFINE CLASS comTest AS Custom OLEPUBLIC
        FUNCTION SetProc
           SET PROCEDURE TO testlib &&ADDITIVE
        ENDFUNC
     ENDDEFINE
  ENDTEXT

  BUILD PROJECT comtest FROM comtest.prg
  BUILD DLL comtest FROM comtest

  loComTest1 = CREATEOBJECT("ComTest.ComTest")
  loComTest1.SetProc()
  loComTest2 = CREATEOBJECT("ComTest.ComTest")  && This line will give error.

Additional query words:

======================================================================
Keywords          : kbCOMt kbvfp kbvfp500a kbvfp600 kbGrpDSFox kbDSupport kbCodeSnippet kbvfp500xSearch kbvfp700 _IK283 
Technology        : kbVFPsearch kbAudDeveloper kbVFP500 kbVFP600 kbVFP700 kbVFP500a
Version           : :5.0,5.0a,6.0,7.0
Issue type        : kbprb
Solution Type     : kbpending

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