PRB: Passing Parameters By Reference to a VC COM Object

ID: Q197957

The information in this article applies to:

SYMPTOMS

When passing a parameter to a COM Component's method in Active Server Pages (ASP) using VBScript, either 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 as [out] parameters (that is, by reference) to a method should always be declared as a pointer to a variant data type by the method, while [in] parameters (that is, passed by value) can be declared as any type.


STATUS

This behavior is by design.


MORE INFORMATION

Steps to Reproduce Behavior

  1. Create an ATL DLL Project called "ByRefProj."


  2. Insert an ATL Object named "ByRefObj."


    1. Add a Method with the following information:
      
      Method Name: ByRefMethod
      Parameters : [out]BSTR* bstrVal


    2. Implement the Method as follows:
      
      STDMETHODIMP CByRefObj::ByRefMethod( BSTR* bstrVal )
      {
        CComBSTR bstrRtnVal = L"This variable is passed by Reference";
        *bstrVal = bstrRtnVal.Detach();
      }




  4. Create an ASP Page that calls this Method:
    
      <%
        Dim objTest, strByRefVal
        Set objTest = Server.CreateObject("ByRefProj.ByRefObj")
        objTest.ByRefMethod strByRefVal
      %>


  5. Run ASP and the following error occurs:
    Microsoft VBScript runtime error '800a000d'
    Type mismatch: 'ByRefMethod' 



Keywords          : kberrmsg kbASP kbCOMt kbVBScript kbGrpASP 
Version           : WINNT:5.0,6.0
Platform          : winnt 
Issue type        : kbprb

Last Reviewed: May 25, 1999