Hello Robert, I dare to bother you again with some questions. this time I have a numpy array with fields ar = array([(1.0, 2.0, 3, 4), (2.0, 3.0, 4, 5)], dtype={'names': ['q','wl','cssid','br'], 'formats':['f4', 'f4', 'i4', 'i4'], 'offsets': [0, 4, 8, 12]}, order='F') on C API I want to match this struct typedef struct val1{ float q; float wl; int cssid; int br; }hm1dval1; to an element of this array I get the array object, i can see the fields. The type of the array elements is Pyarray_VOID however following code gives me a segfault hm1dval1 **s = PyArray_DATA(ao); fprintf(stdout, "q is %d\n", (**s).cssid); I also tried to use PyArray_BYTES but it failed too I was thinking to add 4 bytes to PyArray_DATA(ao) for each member of the struct and for each elem of the array and cast those pointers to the float, float respectively int, int values but that failed too. Can you see what am I doing wrong? Quoting Robert Kern <robert.kern@gmail.com>:

On Mon, Oct 4, 2010 at 00:41, Ioan Ferencik <ioan.ferencik@tkk.fi> wrote:

...

Hello list,

I am trying to pass elements of a custom defined with C API. I have successfully wrapped a type around a C struct. I intent to create a list with these objects and process it using numpy C API. So i  create an array:

array = (PyArrayObject *)PyArray_ContiguousFromObject(input, PyArray_OBJECT, 0, 0);

to my understanding each el. in this array is a pointer to my type so a cast to this type should work.

this is my custom type

typedef struct val{         PyObject_HEAD         float q;         float wl;         int cssid;         int br; }hm1dval;

I am passing only one element for testing purposes.

in python a = [hm1d1.hm1dval() for i in range(0,1)] for c in a:         c.set_values(q=3.0, wl=2.5, cssid=6, br=7)

So following code should be valid in C:

hm1dval s* = PyArray_DATA(array);

but the members are 0 after casting in spite they were set previously.

The elements of a dtype=object array are PyObject* pointers. In C, an array of pointers would look like this:

hm1dval **s = PyArray_DATA(array);

-- Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth."   -- Umberto Eco _______________________________________________ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion

Ioan Ferencik PhD student Aalto University School of Science and Technology Faculty Of Civil and Env. Engineering Lahti Center Tel: +358505122707