Microsoft KB Archive/129827

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

Article ID: 129827

Article Last Modified on 12/9/2003

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APPLIES TO


 * Microsoft Visual Basic 4.0 Standard Edition
 * Microsoft Visual Basic 4.0 Professional Edition
 * Microsoft Visual Basic 4.0 Professional Edition
 * Microsoft Visual Basic 4.0 16-bit Enterprise Edition
 * Microsoft Visual Basic 4.0 32-Bit Enterprise Edition

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This article was previously published under Q129827



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

Keywords: KB129827

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