Hey I think I got it! Instead of: data = POINTER(c_ubyte)()
I did: data = (c_ubyte*2048)() Now it's working perfectly! On Mon, Aug 17, 2009 at 12:13 AM, px<p...@qualm.net> wrote: > Hi, Sorry to bring this back up but I'm still stumped, and I feel very > close!! Thomas I took your suggestion and changed the 'out' to 'in'. > > From: > COMMETHOD([], HRESULT, 'Read', > ( ['out'], POINTER(c_ubyte), 'data' ), > ( ['in'], c_int, 'len' ), > ( ['out'], POINTER(c_int), 'actual' )), > ...] > > To: > COMMETHOD([], HRESULT, 'Read', > ( ['in'], POINTER(c_ubyte), 'data' ), > ( ['in'], c_int, 'len' ), > ( ['out'], POINTER(c_int), 'actual' )), > ...] > > However defining it this way, it now seems to expect a single c_ubyte > instead of a pointer to a c_ubyte. > > When I try: > data = POINTER(c_ubyte)() > res = y.Read(byref(data), len) > > I get this exception, which seems odd since we defined it as > POINTER(c_ubyte) in the type library: > ctypes.ArgumentError: argument 1: <type 'exceptions.TypeError'>: > expected LP_c_ubyte instance instead of pointer to LP_c_ubyte > > However, when I try: > data = c_ubyte() > res = y.Read(byref(data), len) > > then it executes successfully, but of course data only has 1 value and > Python crashes after the next Read attempt. > > I think maybe I need to redefine to something else? > > Thanks again for your help so far. > > On Thu, Jun 18, 2009 at 11:57 AM, px<p...@qualm.net> wrote: >> 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 >>> >>> >>> >>> ------------------------------------------------------------------------------ >>> Crystal Reports - New Free Runtime and 30 Day Trial >>> Check out the new simplified licensing option that enables unlimited >>> royalty-free distribution of the report engine for externally facing >>> server and web deployment. >>> http://p.sf.net/sfu/businessobjects >>> _______________________________________________ >>> comtypes-users mailing list >>> comtypes-users@lists.sourceforge.net >>> https://lists.sourceforge.net/lists/listinfo/comtypes-users >> >> > ------------------------------------------------------------------------------ Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day trial. Simplify your report design, integration and deployment - and focus on what you do best, core application coding. Discover what's new with Crystal Reports now. http://p.sf.net/sfu/bobj-july _______________________________________________ comtypes-users mailing list comtypes-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/comtypes-users
