Passing an array using COM?

Question

I am a COM object written in ATL that is used from a C++ application, and I want to pass an array of BYTEs between the two. My experience of COM/IDL so far is limited to passing simple types (BSTRs, LONGs, etc.).

Is there a relatively easy way to have the COM object pass an array to the caller? For example, I want to pass a raw image (TIFF) instead of messing with temporary files.

Answer 1

Try passing a safearray variant to the COM Object. Something like this to put a BYTE array inside a safearray variant....

bool ArrayToVariant(CArray<BYTE, BYTE>& array, VARIANT& vtResult)
{
SAFEARRAY FAR*  psarray;
SAFEARRAYBOUND sabounds[1]; 

sabounds[0].lLbound=0;
sabounds[0].cElements = (ULONG)array.GetSize();

long nLbound;

psarray = SafeArrayCreate(VT_UI1, 1, sabounds);
if(psarray == NULL)
    return false;

for(nLbound = 0; nLbound < (long)sabounds[0].cElements ; nLbound++){
    if(FAILED(SafeArrayPutElement(psarray, &nLbound, &array[nLbound]))){
        SafeArrayDestroy(psarray);
        return false;
    }
}

VariantFree(vtResult);
vtResult.vt = VT_ARRAY|VT_UI1;
vtResult.parray = psarray;
return true;
}