On Fri, Dec 18, 2015 at 2:41 AM, <jf...@ms4.hinet.net> wrote:
> ValueError: Procedure probably called with too many arguments (4 bytes in
> excess
The function's calling convention is x86 cdecl (CDLL, caller stack
cleanup), but you're using the x86 stdcall convention (WinDLL, callee
stack cleanup). For a 64-bit process they're actually the same, but
you're using 32-bit Python, so you have to pay attention to the
convention.
> _lib = windll.LoadLibrary("C:\\Windows\\System32\\libusb0.dll")
It should simply be
_lib = CDLL('libusb0')
windll/WinDLL is the wrong calling convention. Everything else is just
a waste of keystrokes. windll.LoadLibrary is an inferior way to call
WinDLL, since it can't pass constructor arguments such as use_errno or
use_last_error. The System32 directory is on the DLL search path, and
Windows will add the .dll extension for you.
The calling convention is declared in the header file lusb0_usb.h [1].
For example:
struct usb_bus *usb_get_busses(void);
Notice there's no mention of __stdcall there, so it's using the
default cdecl convention.
> _usb_dev_handle = c_void_p
You'll be better off using
class _usb_dev_handle(Structure):
pass
_usb_dev_handle_p = POINTER(_usb_dev_handle)
This provides stronger type safety. c_void_p is too permissive. It's
easier to debug a ctypes ArgumentError than a memory access violation
or data corruption.
[1]:
http://sourceforge.net/p/libusb-win32/code/413/tree/trunk/libusb/src/lusb0_usb.h
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