Re: [ctypes-users] system crash problem

[<jU...@ar...>]

Luca Politti schrieb:
> Good morning group!!!!
>
> I have a problem that drives me crazy!!!!
>
> I'm working with TAPI, and I have to use the function "lineGetAddressCaps"
> that have this definition:
>
> LONG WINAPI lineGetAddressCaps(
>     HLINEAPP hLineApp,
>     DWORD dwDeviceID,
>     DWORD dwAddressID,
>     DWORD dwAPIVersion,
>     DWORD dwExtVersion,
>     LPLINEADDRESSCAPS lpAddressCaps
>     );
>
> This function fills the structure poited by lpAddressCaps.
> The structure has a dwTotalSize attribute that indicates the total size 
> (in bytes)
> of the structure, and it has to be set before calling lineGetAddressCaps.
> So, I know that the structure needs 3392 bytes to work. Correctly, if I 
> set dwTotalSize
> to 3391 or less, TAPI raise a LINEERR_STRUCTURETOOSMALL error...and I 
> understand it...
> So I say: "let's allocate more bytes to the structure" and I set 
> dwTotalSize to 4096...
> but the system crashes and appears the window: "send an error report..." 
> with the
> Python icon...
> It has the same behaviour if I set dwTotalSize exactly to 3392...
> What could it be?
>
> I post you some of my code:
>
> lineAddressCaps = LINEADDRESSCAPS() # the structure
> lineAddressCaps.dwTotalSize = 3392 # setting the max size
> dwDeviceID = DWORD(209) # the phone device ID
> dwAddressID = DWORD(0)
> dwExtVersion = DWORD(0)
>    
> lReturn = l.lineGetAddressCaps(hLineApp, dwDeviceID, dwAddressID,
>     dwTapiVersion, dwExtVersion, addressof(lineAddressCaps))
>
>
> I also found some C code that do the same thing and it work like this:
>
> lpAddressCaps = LocalAlloc(LPTR, 4096) // LPTR = 0x0040
> lpAddressCaps -> dwTotalSize = 4096
>
> I've tried to do like it usig LocalAlloc from kernel32.dll, but when I do
> lpAddressCaps.dwTotalSize = 4096 Python raises an error like "int object 
> have no
> attribute dwTotalSize"...
>
> I hope have been clear enough...please help me...
>
> Thanks in advance
>
> Luca
>
>
>   

Still struggeling ;-)
I didn't look closely at the api, but my best guess is
that you make a first call to it, find out about the
required size, allocate as much as needed and pass
the memory in a second call. Never hard code any sizes.

So, maybe you should try first with "dwTotalSize"
set to 0 or maybe sizeof(LINEADDRESSCAPS) and check
"dwNeededSize" as the function returns.

Next you could set up a a byte array of the required size,
pass it over and read the data from the buffer.
--------------------------------------

lineAddressCaps = LINEADDRESSCAPS()
lineAddressCaps.dwTotalSize = sizeof(lineAddressCaps)
(...)

result = lineGetAddressCaps(......, byref(lineAddressCaps))
buf = (c_ubyte*lineAddressCaps.dwTRequiredSize)()
result = lineGetAddressCaps(......, byref(buf))

lineAddressCaps = LINEADDRESSCAPS.from_address(addressof(buf))
# interpret data at the offsets as specified in the struct


See also: [http://msdn2.microsoft.com/en-us/library/ms735674.aspx]


Jürgen