Unique pointers in COM interfaces

re: Unique pointers in COM interfaces

Dru Nelson — Sun, 30 May 2004 22:07:00 GMT

Actually, I would like to hear some good references on the 'standard' or 'universal' marshaller in this context. It's too much pain to use the other marshallers.

re: Unique pointers in COM interfaces

runtime — Thu, 27 May 2004 15:47:00 GMT

BSTRs are length-prefixed, but they ALSO include a NUL-terminator!

Larry, I would love to hear more about the BSTR vs LPCWSTR debate. I really enjoy reading your behind-the-scenes stories.

re: Unique pointers in COM interfaces

Larry Osterman — Wed, 26 May 2004 22:03:00 GMT

Absolutely Mike Dimmick. I think it's facility win32 because it's a win32 error code?

Mike Dunn: If you passed a structure as a parameter to a routine and the structure contained a pointer, then that pointer value is controled by pointer_default().

re: Unique pointers in COM interfaces

Rob — Wed, 26 May 2004 21:53:00 GMT

Via structures or unions.

re: Unique pointers in COM interfaces

Mike Dunn — Wed, 26 May 2004 21:05:00 GMT

>The pointer_default attribute on the interface specifies the behavior of all pointers EXCEPT the pointers passed in as parameters to routines.

I'm unclear what you mean there. How else would a routine get a pointer other than via a parameter?

re: Unique pointers in COM interfaces

Mike Dimmick — Wed, 26 May 2004 19:00:00 GMT

Just a quick note: 0x800706f4 == MAKE_HRESULT( SEVERITY_ERROR, FACILITY_WIN32, RPC_X_NULL_REF_POINTER ). Basically, COM's telling us about the underlying RPC error.

Odd that it doesn't get a FACILITY_RPC code, but there you go...

re: Unique pointers in COM interfaces

Larry Osterman — Wed, 26 May 2004 17:25:00 GMT

Sort-of.

COM will quite happily use zero terminated strings. It also uses BSTRs.

AUTOMATION uses BSTR's, but automation isn't COM. Automation's all about interoperability with Visual Basic. But COM's a lot more than just making stuff that can be called from VB.

The interface above was taken from one of the COM objects I work with - nary a BSTR there.

The BSTR vs LPCWSTR is a fascinating internal debate that I may write about some day (if I can figure out what the pros and cons of each side are, to be honest it's too esoteric for me).

re: Unique pointers in COM interfaces

Jerry Pisk — Wed, 26 May 2004 17:22:00 GMT

AFAIK COM does not use zero terminated strings. It uses BSTR type, which is a Lstring and can contain embedded zero byte characters.