Thanks Thomas. I tried your suggestion and changed out to in but it seems
to not expect a pointer
COMMETHOD([], HRESULT, 'Read',
( ['in'], POINTER(c_ubyte), 'data' ),
( ['in'], c_int, 'len' ),
( ['out'], POINTER(c_int), 'actual' )),
...]
--
data = POINTER(c_ubyte)()
len = 2
res = y.Read(byref(data), len)
ArgumentError: argument 1: <type 'exceptions.TypeError'>: expected
LP_c_ubyte instance instead of pointer to LP_c_ubyte
On Wed, Jun 17, 2009 at 2:06 AM, Thomas Heller <thel...@ctypes.org> wrote:
> px schrieb:
> > Thanks Thomas! This was very helpful indeed. Working great now :)
> >
> > Came across another problem trying to read back an unsigned byte buffer..
> > I'm pretty stumped
> >
> > # COMMETHOD([], HRESULT, 'Read',
> > # ( ['out'], POINTER(c_ubyte), 'data' ),
> > # ( ['in'], c_int, 'len' ),
> > # ( ['out'], POINTER(c_int), 'actual' )),
> >
> > When I call Read(2048), I always just get 13 back for the data field
> (first
> > element in returned tuple) but I actually expect more bytes.
> >
> > I took a shot at doing a ctypes style call, but when I try to make the
> call
> > x.Read(byref(data), len, byref(actual))
> > I get
> > TypeError: call takes exactly 2 arguments (4 given)
> >
> > It seems that comtypes only wants the in 'len' parameter.
> >
> >>From the IDL:
> > HRESULT Read(
> > [out, size_is(length), length_is(*actual)] BYTE* data,
> > [in] long length,
> > [out] long* actual);
>
> comtypes isn't able to handle the 'length_is(...)' attribute. Besides,
> the info from this attribute isn't present in the TLB at all. So,
> you should override the generated 'Read' method in this way,
> which passes the pointer as 'in' argument, and later unpacks it:
>
>
> COMMETHOD([], HRESULT, 'Read',
> ( ['in'], POINTER(c_ubyte), 'data' ),
> ( ['in'], c_int, 'len' ),
> ( ['out'], POINTER(c_int), 'actual' )),
> ...]
>
> def Read(self, len):
> data = POINTER(c_ubyte)()
> actual = self._Read(byref(data), len)
> result = data[:actual]
> # I guess you need to free the memory here?
> # windll.ole32.CoTaskMemFree(data)
> return result
>
> Thomas
>
>
>
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