Passing unsigned integers from C++ COM object to VB6

I am trying to access (from a VB6 application) an unsigned 32 bit integer data type returned by the method of a C++ COM object. The part of an interface is declared like:

...
interface ICOMCanvasPixelBuffer : IUnknown
{
    HRESULT GetWidth([retval][out] DWORD *pWidth);
    HRESULT GetHeight([retval][out] unsigned __int32 *pHeight);
    ...

When I am browsing this interface using the Object Browser in VB6, it shows Function开发者_运维百科 GetWidth() As <Unsupported variant type> hint for both of these methods.

Is there way to pass the unsigned integer data type to VB6?

VB6 does not have unsigned datatypes. Is the COM object yours? Just change the interface to a regular, signed int. Do you really have images with width and height over 2 billion?

If the COM object is not yours, sorry, its interface is not Automation-compliant. You can put together a proxy C++ object that would convert all the unsigned's to int's.

Here is an excerpt from Wnidows SDK which is really helpful in understanding which types to use:

enum VARENUM {
    VT_EMPTY = 0,
    VT_NULL = 1,
    VT_I2 = 2,
    VT_I4 = 3,
    VT_R4 = 4,
    VT_R8 = 5,
    VT_CY = 6,
    VT_DATE = 7,
    VT_BSTR = 8,
    VT_DISPATCH = 9,
    VT_ERROR = 10,
    VT_BOOL = 11,
    VT_VARIANT = 12,
    VT_UNKNOWN = 13,
    VT_DECIMAL = 14,
    VT_I1 = 16,
    VT_UI1 = 17,
    VT_UI2 = 18,
    VT_UI4 = 19,
    // on and on

You will be absolutely safe staying above 16 (with possibly VT_ARRAY | VT_UI1 for byte arrays, which is also common) and this set is flexible enough to cover a lot of scenarios.

In your particluar case you will want VT_I4 which is type LONG.