How to pass string array from VBScript to COM+

Question

I have written a C++ COM which is running as COM+ application. I am trying to access COM functionality from VBScript (ASP application). I am able to call a function of COM from VBScript which takes a string. But when I try to call a COM function which takes an array of string, I could get length of array but I could not retrieve elements from that array at COM side.

VBScript (ASP application)

    dim myComObj
    Set myComObj = Server.CreateObject("ProgId_PerlCOMSimple.1")
    Dim myArray(3)
    myArray(0) = "Clean Underwear"
    myArray(1) = "Vacuum Cleaner"
    myArray(2) = "New Computer"
    myArray(3) = "Talking Bass"
    strDfStatus = myComObj.TestArray1 (myArray)

C++ COM which runs as COM+ application (through dllHost.exe)

    STDMETHODIMP CPerlCOMSimple::TestArray1(VARIANT* testArray, LONG* lResult)
    {
        // TODO: Add your implementation code here
        *lResult = testArray->parray->rgsabound->cElements;
        BSTR** StrPtr = 0;
        //LONG* pVals;
        long LowerBound = 0;
        long UpperBound = 0;
        int i;

        SafeArrayGetLBound(testArray->parray, 1, &LowerBound);
        SafeArrayGetUBound(testArray->parray, 1, &UpperBound);

        SafeArrayAccessData(testArray->parray, (void**)&pVals);

        for (i = LowerBound; i <= UpperBound; ++i)
        {
            BSTR* lVal = StrPtr[i];
            lVal++;
        }
        SafeArrayUnaccessData(testArray->parray);
        return S_OK;
    }

You are looking to pass a variant. Have you looked here? stackoverflow.com/questions/295067/passing-an-array-using-com — Jacob Bruinsma
– Jacob Bruinsma, Commented Oct 20, 2017 at 11:50

Ben · Accepted Answer · 2017-10-20 13:05:16Z

VBScript will not generate a SAFEARRAY with vartype VT_BSTR, which is what you are expecting. It will have VARTYPE VT_VARIANT.

// check all your parameters
if(testarray == null) return E_INVALIDARG;
if(testarray->vartype != VT_ARRAY|VT_BSTR
  && testarray->vartype != VT_ARRAY|VT_VARIANT)
    return E_INVALIDARG;
if(testarray->parray == null) return E_INVALIDARG;


// Now we have established we have an array, and that it
// is either a string array or a variant array.

VARTYPE vt = VT_EMPTY;
SafeArrayGetVarType(testarray->pArray, &vt);
// Now we need to take different actions based on the vartype.
if(vt == VT_BSTR){
    // we have an array of strings
    // Proceed as above.
}else if(vt == VT_VARIANT){
    // we have an array of variants, probably supplied by VBScript
    // Read them one by one and use VariantChangeType to get a string

}else{
    // We have some other array type we don't support
    return E_INVALIDARG;
}

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