Knowledge Base

PRB: Passing Parameters By Reference to a VB COM Object

Article ID: 197956

Article Last Modified on 3/14/2005

Microsoft Active Server Pages 4.0
Microsoft Visual Basic 5.0 Learning Edition
Microsoft Visual Basic 6.0 Learning Edition
Microsoft Visual Basic 5.0 Professional Edition
Microsoft Visual Basic 6.0 Professional Edition
Microsoft Visual Basic 5.0 Enterprise Edition
Microsoft Visual Basic 6.0 Enterprise Edition
Microsoft Internet Information Server 4.0
Microsoft Internet Information Services 5.0

This article was previously published under Q197956

SYMPTOMS

When passing a parameter to a COM Component's method in Active Server Pages (ASP), the following error occurs:

Microsoft VBScript runtime error '800a000d' Type mismatch

Or the value stored in the variable passed to the method is not changed.

CAUSE

VBScript will pass parameters to a method by value if the argument's data type is NOT declared as a variant and the parameter is passed by reference if the argument's data type is declared as variant by the method.

RESOLUTION

Parameters to be passed by reference to a method should always be declared as a variant data type by the method, while parameters to be passed by value can be declared as any type by the method.

STATUS

This behavior is by design.

MORE INFORMATION

Steps to Reproduce Behavior

Create a Visual Basic ActiveX DLL Project called "ByRefProj."
Add class module called "ByRefObj."

Implement the following method:

Public Sub ByRefMethod( ByRef strVal as String )
  strVal = "This variable is passed by Reference"
End Sub

Create an ASP Page that calls this Method:

<%
  Dim objTest, strByRefVal
  Set objTest = Server.CreateObject("ByRefProj.ByRefObj")
  objTest.ByRefMethod strByRefVal
%>

Run ASP. The following error occurs:

Microsoft VBScript runtime error '800a000d'
Type mismatch: 'ByRefMethod'

To correct this behavior:

Change the implementation of the method ByRefMethod as follows:

Public Sub ByRefMethod( ByRef strVal as Variant )
  strVal = "This variable is passed by Reference"
End Sub

Keywords: kberrmsg kbcodesnippet kbprb KB197956