DOCUMENT:Q214674  11-JAN-2001  [vbwin]
TITLE   :PRB: Cannot Simultaneously Write to Disk File and Have It Opened
PRODUCT :Microsoft Visual Basic for Windows
PROD/VER:WINDOWS:5.0,6.0
OPER/SYS:
KEYWORDS:kbActiveX kbDLL kbVBp kbVBp500 kbVBp600 kbGrpDSVB

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

 - Microsoft Visual Basic Learning Edition for Windows, versions 5.0, 6.0 
 - Microsoft Visual Basic Professional Edition for Windows, versions 5.0, 6.0 
 - Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

When you attempt to write to the file number of a file that was opened in an
ActiveX DLL or vice versa, the following run-time error is generated:

   Error '52' Bad File name or number

CAUSE
=====

The file number created when a file is opened cannot be shared between separate
projects or executable modules.

RESOLUTION
==========

If a file must be accessed by both an EXE and an associated DLL, wrap all of the
file access activities in a class module in the ActiveX DLL.

STATUS
======

This behavior is by design.

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

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

1. Create an ActiveX DLL project. Class1 is added by default.

2. From the Project menu, click Project Properties. Change the Project Name to
   DllFileNumber and click OK.

3. Add the following code to the General Declarations section of Class1:

   Option Explicit

   Private m_Fn As Integer

   Public Sub WriteFile(Fn As Variant)
      Write #Fn, "This is a text from the DLL."
   End Sub

   Public Sub OpenFile()
      m_Fn = FreeFile
      Open "C:\DllTEST.txt" For Append As #m_Fn
   End Sub

   Private Sub Class_Initialize()
      m_Fn = 0
   End Sub

   Public Property Get DLLFileNum() As Variant
      DLLFileNum = m_Fn
   End Property

   Public Sub CloseFile()
      If m_Fn <> 0 Then
         Close #m_Fn
         m_Fn = 0
      End If
   End Sub

4. Save the ActiveX Dll project.

5. From the File menu, click Add Project and add a Standard EXE project. Form1
   is added by default.

6. In the project window, set the Standard EXE project as the Start Up project
   by right-clicking on the project name and clicking "Set as Start Up" in the
   pop-up menu.

7. From the Project menu, click References and check the DllFileNumber entry.

8. Add two CommandButtons to Form1: Command1 and Command2 will be added by
   default. If a size larger than the default is used, the captions will be more
   readable.

9. Add the following code to the General Declarations section of Form1:

   Option Explicit

   Private Sub Command1_Click()
      Dim objvar As New DllFileNumber.Class1
      Dim sVar As String

      sVar = "This is text from the main program."
      objvar.OpenFile
      objvar.WriteFile objvar.DLLFileNum
      Write #objvar.DLLFileNum, sVar 'Error 52 occurs here.
      objvar.CloseFile
   End Sub

   Private Sub Command2_Click()

      Dim FileNumber As Variant
      Dim objvar As New DllFileNumber.Class1

      FileNumber = FreeFile

      Open "C:\TEST.txt" For Append As #FileNumber
      Write #FileNumber, "This is text from the main program."

      objvar.WriteFile FileNumber  'Error 52 occurs here.

      Close #FileNumber
   End Sub

   Private Sub Form_Load()
      Command1.Caption = "Write to a file opened in the DLL"
      Command2.Caption = "Write to a file opened in the main program"
   End Sub

10. Run the program and click on the button labeled "Write to a file opened in
   the DLL." A Run-Time error 52 will occur on the line of Write statement. End
   the program.

11. Run the program again and click on the button labeled "Write to a file
   opened in the main program." A Run-Time error 52 will occur on the line
   containing the WriteFile method.

Resolution
----------

1. Comment out the code lines containing the following comment:

   ' Error 52 occurs here.

2. Run the program again and click each CommandButton. No error will occur.

Additional query words: kbGrpVB

======================================================================
Keywords          : kbActiveX kbDLL kbVBp kbVBp500 kbVBp600 kbGrpDSVB 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVBA500 kbVBA600 kbVB500 kbVB600
Version           : WINDOWS:5.0,6.0
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 2001.