How to make an MFC Class to be used in VB6 ??

[CornedBee]

And before you ask me about arrays...

// This function decodes a string to a byte array, wrapped up in a variant.
STDMETHODIMP CBase64Coder::DecodeStringToByteArray(BSTR strIn, VARIANT* arByteOut)
{
	// Many functions have a HRESULT as return value.
	HRESULT hr;
	// A pointer to move over the input buffer
	const wchar_t *p;
	// Random loop index
	UINT i=0;

	// Check for error conditions.
	// The output pointer could point to nothing.
	if(arByteOut == NULL)
	{
		return E_POINTER;
	}
	// If strIn is NULL this may have two causes: an error may have occured or
	// (more likely) the passed string is empty. For some reason VB passes NULL in that
	// case. So let's just return an empty variant.
	if(strIn == NULL)
	{
		// This most probably means that "" was passed.
		VariantInit(arByteOut);
		return S_OK;
	}

	// Find the length of the encoded data.
	UINT uiSourceLength = SysStringLen(strIn);

	// It's easier to work with CAtlString than with BSTR
	CAtlStringW strUse;

	// first go through string and kick out everything invalid
	for(p=(const wchar_t *)strIn, i=0; i<uiSourceLength &&
		(i==0 || (*(p-1) != L'=' || (*(p-1) == L'=' && *p == L'='))); ++p, ++i)
	{
		if(isbase64(*p))
			strUse += *p;
		else if(!isbase64allowed(*p))
		{
			// this character should not be there
			// possible reactions:
			// 1) warn
			// 2) ignore <- I have chosen this.
			// 3) fail
		}
	}

	// There should be padding characters so that the character count is an exact
	// multiple of 4. If not then something is wrong.
	UINT pad = (UINT)strUse.GetLength() % 4;
	if(pad != 0)
	{
		// again two options:
		// 1) add padding so that it works and maybe warn
		// 2) fail <-
		return E_INVALIDARG;
	}

	// Initialize the output value and set its type to byte array.
	VariantInit(arByteOut);
	arByteOut->vt = VT_ARRAY | VT_UI1;

	// Create a 1-dimensional array (1 to whatever is needed).
	SAFEARRAYBOUND bound;
	bound.cElements = strUse.GetLength()/4*3;
	bound.lLbound = 1;
	V_ARRAY(arByteOut) = SafeArrayCreateEx(VT_UI1, 1, &bound, NULL);
	// The only real reason this call could fail is because there is no memory
	// to allocate the array.
	if(V_ARRAY(arByteOut) == NULL)
		return E_OUTOFMEMORY;

	// Now access the data
	PBYTE pOut;
	hr = SafeArrayAccessData(V_ARRAY(arByteOut), (void **)&pOut);
	if(FAILED(hr))
		return hr;

	// Decode the string
	for(p=strUse; *p; p+=4, pOut+=3)
	{
		GrabByteTriple(pOut, p);
	}

	// Clean up
	hr = SafeArrayUnaccessData(V_ARRAY(arByteOut));
	if(FAILED(hr))
		return hr;

	return S_OK;
}

isbase64, isbase64allowed and GrabByteTriple are functions defined by me, all others are API or ATL.