[in] Pointer to the IUnknown object implementing IStream.
[in] Pointer to the interface identifier (IID) for the stream object. Any of the following values can be passed in the lpInterface parameter: NULL, IID_IStream, or IID_ILockBytes. Passing NULL in lpInterface is the same as passing IID_IStream.
[in] Bitmask of flags that controls how the storage object is to be created relative to the stream. The default setting is STGSTRM_RESET, which gives the storage object read-only access and starts it at position zero of the stream. The following flags can be set in any combination, except as noted:
Creates a new storage object for the stream object. This flag cannot be set if the STGSTRM_RESET flag is set.
Starts storage at the current position of the stream. This flag cannot be set if the STGSTRM_RESET flag is set.
Allows the calling service provider to write to the returned storage. This flag cannot be set if the STGSTRM_RESET flag is set.
Starts storage at position zero. This flag cannot be set if any other flag is set.
[out] Pointer to a pointer to the returned IStorage object.
Message store providers support the HrIStorageFromStream function using the IStorage interface for attachments. Store providers must implement the IStream interface. HrIStorageFromStream provides the IStorage interface for the IStream object. It is possible to pass either an ILockBytes or an IStream interface in lpUnkIn.