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Q187908: HOWTO: Use COMRETURNERROR() Function in a OLE Server

Article: Q187908
Product(s): Microsoft FoxPro
Version(s): WINDOWS:6.0
Operating System(s): 
Keyword(s): 
Last Modified: 20-MAY-2000

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The information in this article applies to:

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

The ComReturnError function allows Visual FoxPro 6.0 to make reporting errors
from the Visual FoxPro OLE Servers easier. This function gives programmers the
ability to create more meaningful messages to return to the client, instead of
having the client receive a cryptic message that does not make sense.

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

ComReturnError has two parameters, Source and Description. The Source parameter
is at which place the error occurs in code. You may use the Program function or
the cMethod parameter in the Error event to populate the Source parameter.

The Description parameter can be anything needed to describe the error. The
information that you may want to return to the client is the actual error
message and error number from Visual FoxPro and on which line number that error
message occurs. The following class is an example of how to use the
ComReturnError function:

1. Create a program named Test.prg and add the following code:

  

  DEFINE CLASS sampleclass AS CUSTOM OLEPUBLIC
     NAME = "sampleclass"

     *!* GenError accepts one numeric parameter, which is the error number
     *!* of the Visual FoxPro (VFP) error to generate.
     PROCEDURE GenError
        LPARAMETERS nError
        
        *!* This raises the error.
        ERROR nError
     ENDPROC

     *!* When the error is generated, it triggers the Error event, which
     *!* creates a return statement to pass back to the client.
     PROCEDURE Error
        LPARAMETERS nError, cMethod, nLine
        LOCAL lcRetVal
        
        lcRetVal = ALLTRIM(STR(nError)) + ": " + MESSAGE() + ;
           " on Line " + ALLTRIM(STR(nLine)) + ;
           " in the sample DLL that was created for this article"
           
        COMRETURNERROR(cMethod, lcRetVal)
     ENDPROC
  ENDDEFINE

2. Create a project and name it MySample. Add the Test.prg file to the project
  and make sure it is marked as the main file. Save the project and build a COM
  DLL.

3. Create an object reference to the class, and call the GenError method by
  issuing the following code in the Command window:

  

        oX = CreateObject('Mysample.sampleclass')
        oX.generror(1)

An error message dialog box appears with the following message:

  OLE IDispatch error code 120 from generror: 1: File does not exist. On line
  3..

Once you issue the ComReturnError function, program execution stops there. The
client is still able to call methods from the object, but any code that occurs
after the ComReturnError function does not execute.

REFERENCES
==========

Visual FoxPro 6.0 Help; search on: "ComReturnError"

(c) Microsoft Corporation 1998, All Rights Reserved. Contributions by David
Botzenhart, Microsoft Corporation


Additional query words: kbvfp600

======================================================================
Keywords          :  
Technology        : kbVFPsearch kbAudDeveloper kbVFP600
Version           : WINDOWS:6.0
Issue type        : kbhowto

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