PRB: Passing Parameters By Reference to a VC COM Object

• Active Server Pages
• Microsoft Visual C++, 32-bit Editions, versions 5.0, 6.0
• Microsoft Internet Information Server versions 4.0, 5.0

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

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."



3. 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();
        return S_OK;
      } 

   
   
   



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'

1. Change the IDL declaration in the ByRefProj.idl file, to add 'retval': [id(1), helpstring("method ByRefMethod")] HRESULT ByRefMethod([out, retval] BSTR* bstrVal);



2. Change the ASP page as follows:

   
   %
    Dim objTest
    Set objTest = Server.CreateObject("ByRefProj.ByRefObj")
    Response.Write objTest.ByRefMethod()         
   > 

Additional query words:

Keywords : kberrmsg kbASP kbCOMt kbVBScript kbGrpASP kbCodeSnippet kbiis400 kbiis500
Version : winnt:5.0,6.0
Platform : winnt
Issue type : kbprb