Hey Lars > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:numpy- > [EMAIL PROTECTED] On Behalf Of Lars Friedrich > Sent: 25 July 2006 12:50 > To: numpy-discussion@lists.sourceforge.net > Subject: [Numpy-discussion] ctypes, numpy-array > > Hello, > > I would like to work with some data using python/numpy. The data is > generated with C. To bring the data from C to python, I would like to > use ctype. I am using python 2.4.3 on a windows-System. > > To accomplish the described task, I have the following plan. Please tell > me, if this is possible, respectively if there is a better way. > > 1) In C, I write a .dll, that has a function > int foo(PyObject *arg) > > 2) In python, I generate a numpy-array with the appropriate size. e.g. > a = zeros((3,3), dtype=int) > > 3) From python, I call my .dll-function with a as an argument: > windll.mydll.foo(a)
What's might be happening here is that a.ctypes.data is in fact being passed to your function via ctypes's from_param magic (check the ctypes tutorial for details). In [10]: x = N.array([]) In [11]: x.ctypes.data Out[11]: c_void_p(15502816) In [12]: x._as_parameter_ Out[12]: 15502816 > 4) In the foo-function in the C-.dll I cast the pointer and access the > data-field. > PyArrayObject *myPtr = (PyArrayObject*) arg; > myPtr->data[0] = 1; > return 0; > > However, when I do this, I get an "AccessViolationError writing > 0x000000000" So what's probably happening here is that you already have a pointer to the array's data which you then cast to a PyArrayObject pointer. Dereferencing myPtr->data is looking for a pointer inside the array's data, which contains zeros. Here's a few things to try: - look at ctypes's PyDLL option if you want to pass around Python objects - Write your function as: int foo(int* x); Then do something like this: x = N.array([...], dtype=N.intc) mydll.foo.restype = None mydll.foo.argtypes = [POINTER(c_int)] mydll.foo(x.ctypes.data) This might also work: x = N.array([...], dtype=N.intc) mydll.foo.restype = None mydll.foo(x) Cheers, Albert ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys -- and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Numpy-discussion mailing list Numpy-discussion@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/numpy-discussion
