Sandy Walsh wrote:
Hi,
I have a C++ COM Server with an IDL entry of:
[
object,
uuid(D989CB9A-0013-4E1A-BFB6-98A7946BD255),
dual,
helpstring("IFoo Interface"),
pointer_default(unique)
]
interface IFoo : IDispatch
{
[ id(1), helpstring("method Connect")]
HRESULT Connect([in] BSTR x, [in] short y, [in] BSTR z, [out,
retval] long* error);
};
A call from Python to the C++ object works fine unless I return
something other than S_OK for "error".
What does the C++ code look like?
self.assertEqual(0, self.control.Connect("10.0.0.0", "9999",
""))
That looks strange - your IDL says y is an integer, but you are passing
a string.
The call failed with code 80020009: Exception occurred.
The source of the error is None
The error message is None
More info can be found in None (id=0)
Win32 exception occurred releasing IUnknown at 0x00e84c58
(where HR of 0x80020009 is DISP_E_EXCEPTION)
So something is returning DISP_E_EXCEPTION as the HRESULT for the method
(which is quite different than having a dispatch "return value" (which
is passed as a param to the C++ implementation) named error.
I've traced the python side of the code and how it appears to me is the
"error" out variable is not being created in the argument list.
No - it is a return value: it comes back in the VARIANT holding the
result. Note we are going via IDispatch, so something, presumably ATL,
is converting the IDispatch::Invoke call into a native vtable based call
into your implementation.
I'm not sending extended error messages on the C++ side, just setting
this error code out variable.
How are you setting it exactly? And what do you mean by "sending
extended error messages" - how would they be sent?
> I can only assume that the exception is
being generated in the MS Com libraries when it tries to marshal the
error variable into a non-existent spot?
I don't think the COM libraries would throw that kind of exception.
Is it possible that your C++ implementation is returning the error code
instead of setting it? Your C++ method should always return S_OK, but
set "error" via a pointer passed to your function.
Cheers,
Mark
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