Q129827: Use ByVal to Pass a Control as an Argument to a DLL or VBX

Article: Q129827
Product(s): Microsoft Visual Basic for Windows
Version(s): 
Operating System(s): 
Keyword(s): 
Last Modified: 11-JAN-2001

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The information in this article applies to:

- Microsoft Visual Basic Standard Edition, 32-bit, for Windows, version 4.0 
- Microsoft Visual Basic Professional Edition, 16-bit, for Windows, version 4.0 
- Microsoft Visual Basic Professional Edition, 32-bit, for Windows, version 4.0 
- Microsoft Visual Basic Enterprise Edition, 16-bit, for Windows, version 4.0 
- Microsoft Visual Basic Enterprise Edition, 32-bit, for Windows, version 4.0 
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In previous versions of Visual Basic, when you passed a control to a DLL or
VBX, your function declaration looked like this:

     Declare Function fDoNothing Lib "MyFun.vbx" (ctlX as Control) As Integer

Now, in Microsoft Visual Basic version 4.0, the keyword ByVal must
be used when passing the same control, so now your function declaration
must look like this:

     Declare Function fDoNothing Lib "MyFun.vbx" (ByVal ctlX as Control)_
        As Integer

The Visual Basic API was changed. Now, functions expecting a control as a
parameter require a handle to the control, an HCTL. Omitting ByVal within
the parameter list causes a pointer to the HCTL to be passed instead of the
HCTL itself. To ensure an HCTL is passed, use the ByVal keyword. This
behavior is by design.

Additional query words: 4.00 vb4win vb4all

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Keywords          :  
Technology        : kbVBSearch kbAudDeveloper kbVB400Search kbVB400 kbVB16bitSearch

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