How to pass a Safe Array to an Automation server?

I added an Automation object to the application I am working on.  This allows our clients using Visual Basic to access our application's functionality easily.  Everything works fine except when I want to pass arrays of data between a Visual Basic application and my MFC application.  The type of the Variant is VT_ARRAY as expected but the dimension and the element size are random values.

I added a method to my CCmdTarget-derived class using Class Wizard.  This gives...

BOOL CApplication::GetDoubleArray(const VARIANT FAR& varArray)
// Make sure the input value in an array
VARTYPE vType=V_VT(&varArray);
if (vType & VT_ARRAY)
   // Things do not work as expected starting from here...

   // lDim and lElemSize are never OK (They seem to be random.)
   long lDim=SafeArrayGetDim(V_ARRAY(&varArray));
   long lElemSize=SafeArrayGetElemsize(V_ARRAY(&varArray));

   // Show that lDim and lElemSize are random values
   CString strMsg;
   strMsg.Format("lDim=%d  lElemSize=%d", lDim, lElemSize);

return TRUE;


[id(3)] boolean GetDoubleArray(VARIANT varArray);

in the ODL file.

On Visual Basic side, the code is...

Dim MyObj As Object
Set MyObj = CreateObject("MyObj.Application")
Dim dArray() As Long
ReDim dArray(0 To 10)
MyObj.GetDoubleArray dArray

I have the same problem with in-process and out-of-process Automation servers.
If I add the same method in an ActiveX Control, everything works fine!

Any help will be appreciated.

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Tommy HuiEngineerCommented:
My guess is that you should check the type of the array to see if it has VT_BYREF. I'm betting the type is different in the two cases.

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blarivieAuthor Commented:
You are right, I have VT_BYREF in the Automation server and not in the ActiveX Control.
Now, what should I do to make it work in my Automation server?
blarivieAuthor Commented:
Finally, your answer led me to a solution: use "VARIANT FAR*" instead of "const VARIANT FAR&"...  (The other solution is to use the pparray field of the input const VARIANT FAR&. - not discussed here)

BOOL CApplication::GetDoubleArrayPointer(VARIANT FAR* pvarArray)
   if (pvarArray!=NULL)
      VARTYPE vType=V_VT(pvarArray);

      ASSERT((vType&VT_ARRAY) && (vType&VT_R8));
      if ((vType&VT_ARRAY) && (vType&VT_R8))
         SAFEARRAY FAR* psa=V_ARRAY(pvarArray);

         long lDim=SafeArrayGetDim(psa);
         long lElemSize=SafeArrayGetElemsize(psa);

         ASSERT((lDim==1) && (lElemSize==sizeof(double)));
         if ((lDim==1) && (lElemSize==sizeof(double)))
            long lUpper, lLower;
            SafeArrayGetLBound(psa, 1, &lLower);
            SafeArrayGetUBound(psa, 1, &lUpper);
            long lNumItems=lUpper - lLower + 1;

            HRESULT hres;
            if (hres=SafeArrayLock(psa))
               throw hres;

            for (long lIndex=0; lIndex<lNumItems; lIndex++)
               // Testing: return square of index

            if (hres=SafeArrayUnlock(psa))
               throw hres;

   return TRUE;

In Dispatch Map:
DISP_FUNCTION(CApplication, "GetDoubleArrayPointer", GetDoubleArrayPointer, VT_BOOL, VTS_PVARIANT)

In ODL file:
[id(3)] boolean GetDoubleArrayPointer(VARIANT* pvarArray);

In Visual Basic:
Dim MyObj As Object
Set MyObj=CreateObject("MyApp.Application")
Dim v As Variant
ReDim v(0 To 10) As Double
For i=0 To 10
   MsgBox Str(v(i)), vbOkOnly, "GetDoubleArrayPointer()"
Next i

I found this solution in a Microsoft Knowledge Base Article: "HOWTO: Pass a SafeArray of Strings in a VARIANT*" (Q167668)

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