Brian Hulley wrote:
I assume that this means that on 32 bit Windows, the format of a BSTR is: Word16 -- low word of length Word16 -- high word of length Word16 -- first char of string ...
The above is not quite correct. It appears from http://www.oreilly.com/catalog/win32api/chapter/ch06.html that the length must preceed the actual BSTR, thus you must give VBA a pointer to the first *char* in the string not the actual start of the array of Word16's in memory. Furthermore, it appears that a terminating NULL is still needed even though the string itself can contain NULL characters. No only that, but the length must be given as the number of *bytes* (excluding the terminating NULL) not the number of characters. Therefore here is a revised attempt at creating a Win32 BSTR: import Data.Word import Data.Bits import Foreign.Marshal.Array import Foreign.Ptr type BSTR = Ptr Word16 createBSTR :: [Char] -> IO BSTR createBSTR s = do let len :: Word32 = fromIntegral (length s * 2) low :: Word16 = fromIntegral (len .&. 0xFFFF) high :: Word16 = fromIntegral (shiftR len 16 .&. 0xFFFF) arr <- newArray ([low, high] ++ map (fromIntegral . fromEnum) s ++ [0]) return $! plusPtr arr 4 foreign export stdcall hello :: IO BSTR hello :: IO BSTR hello = createBSTR "Hello world!" Regards, Brian.