DOCUMENT:Q259211  12-APR-2000  [foxpro]
TITLE   :PRB: COMRETURNERROR() Only Works Properly if Error Has Occurred
PRODUCT :Microsoft FoxPro
PROD/VER:WINDOWS:6.0
OPER/SYS:
KEYWORDS:kbCOMt kbvfp600 kbGrpDSFox kbDSupport kbCodeSnippet

======================================================================
-------------------------------------------------------------------------------
The information in this article applies to:

 - Microsoft Visual FoxPro for Windows, version 6.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

The COMRETURNERROR() function populates the COM exception structure with
information that Automation clients can use to determine the source of Visual
FoxPro Automation errors. However, if this function is called without an error
having occurred, it does not properly populate the structure. Visual FoxPro
clients display the information that was sent, but other clients may display
only a generic "Automation Error" message.

RESOLUTION
==========

One resolution to this problem is to always call the COMRETURNERROR function
from the Error method of your Automation server. The ERROR cErrorMessage command
throws Error 1098 (User-defined error) when used. You can test for this in the
Error method and call the COMRETURNERROR function with the cErrorMessage
command.

STATUS
======

This behavior is by design.

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

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

1. Create a new project and save it as "ThrowErr.pjx" (without the quotation
   marks).

2. On the the Code tab, click New.

3. Save the following code as "ThrowErr.prg" (without the quotation marks):

   DEFINE CLASS RetErr AS custom OLEPUBLIC

   	Name = "RetErr"
   	
   	PROCEDURE ThrowErrBad
   		COMRETURNERROR("ThrowErr", "109")
   	ENDproc
   	
   	PROCEDURE ThrowErrGood
   		ERROR "109"
   	ENDproc
   	
   	PROCEDURE Error
   		LPARAMETERS nError, cMethod, nLine

   		IF nError = 1098
   		   COMRETURNERROR("ThrowErr", MESSAGE())
   		ENDif
   	ENDproc
   ENDdefine

4. On the Build menu, select Multi-threaded COM server, and save it as
   "ThrowErr.dll" (without the quotation marks).

5. To test this in FoxPro, run the following code in the Command window. You
   should see the same error box pop up both times.

   loServer = CREATEOBJECT("ThrowErr.RetErr")
   loServer.ThrowErrBad()
   loServer.ThrowErrGood()

6. To test this in Microsoft Access, create a new database and a new form. Put
   two CommandButtons named Command1 and Command2 and three Labels named Label1,
   Label2, and Label3 on the form.

7. In Command1, put the following code:

   Private Sub Command1_Click()
   On Error Resume Next
   Set x = CreateObject("ThrowErr.RetErr")
   Call x.ThrowErrBad
   Label1.Caption = Str(Err.Number)
   Label2.Caption = Err.Source
   Label3.Caption = Err.Description
   End Sub

8. In Command2, put the following code:

   Private Sub Command2_Click()
   On Error Resume Next
   Set x = CreateObject("ThrowErr.RetErr")
   Call x.ThrowErrGood
   Label1.Caption = Str(Err.Number)
   Label2.Caption = Err.Source
   Label3.Caption = Err.Description
   End Sub

9. Run the form, click Command1, and then click Command2. Command1 displays 440
   for the Error Number, the name of the database for the Error Source, and
   Automation Error for the Error Description.

   Command2 displays 98 for the Error Number, ThrowErr for the Error Source, and
   109 for the Error Description.

   Further clicks on Command1 display the correct error information.

REFERENCES
==========

For more information about COMRETURNERROR(), the ERROR command, or building COM
servers, please see the Visual FoxPro documentation.

Additional query words:

======================================================================
Keywords          : kbCOMt kbvfp600 kbGrpDSFox kbDSupport kbCodeSnippet 
Technology        : kbVFPsearch kbAudDeveloper kbVFP600
Version           : WINDOWS:6.0
Issue type        : kbprb

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS
PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND.  MICROSOFT DISCLAIMS
ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  IN NO
EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR
ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.  SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 2000.