How do I extract a hexBinary attribute value?

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I wrote a function that gets a attribute value that is in hex. Am I reinventing the wheel? The problem is that I can't get it to work. Here was my first attempt which failed because it didn't convert to hex (even though the the type is xsd:hexBinary):

HRESULT		hr;
CComVariant	value;

hr = pElement->getAttribute( CComBSTR( sName ), &value );
hr = value.ChangeType( VT\_UINT );

Here is my second attempt which works for values using digits '0'-'9' but fails for values using digits 'a'-'f' (and 'A'-'F') (VarParseNumFromStr returns DISP_E_TYPEMISMATCH):

HRESULT		hr;
CComVariant	value;
NUMPARSE		np	= { 10, NUMPRS\_HEX\_OCT|NUMPRS\_USE\_ALL, 0, 0, 4 };
unsigned char	digits\[10\];
CComVariant	vHex;

hr = pElement->getAttribute( CComBSTR( sName ), &value );

hr = VarParseNumFromStr( value.bstrVal, GetUserDefaultLCID(),
			 NUMPRS\_HEX\_OCT|NUMPRS\_USE\_ALL,
			 &np, digits );
np.nBaseShift = 4;
hr = VarNumFromParseNum( &np, digits, VTBIT\_UI4, &vHex );
hr = vHex.ChangeType( VT\_UINT );

Anyone know what is wrong or what the right way to do this is?