Numpy C++: How to iterate over PyArrayObject without a segfault - c++

Question

For me, the following all result in a segfault:
my_array->descr->subarray->shape;
my_array->dimensions;
PyArray_SHAPE(my_array);
PyArray_DIMS(my_array);
PyArray_ITEMSIZE(my_array);
PyArray_NBYTES(my_array);
My function looks like this:
static PyObject* exterior(PyObject* self, PyArrayObject* old_simplices_array)
{//code here
The rest of my cpp file looks like this:
#include "Python.h"
#include "numpy/arrayobject.h"
/* function */
static PyMethodDef compiled_methods[] =
{
{"_exterior",(PyCFunction)exterior , METH_VARARGS},
{NULL, NULL} /* Sentinel */
};
PyMODINIT_FUNC init_alto(void)
{
(void) Py_InitModule("_alto", compiled_methods);
import_array();
}
The python code that passes the array to "exterior" just passes an NxM uint array. That part works. I can access the array's strides and data. I just cannot determine the bounds of iteration. I am working from within sage if that makes any difference.
How am I supposed to iterate over an array without segfaulting? If the answer is obvious, please idiotproof your answer.
For a better idea of what the function looks like, see here.

Answer 1

In the past I have done the following to iterate over a PyArrayObject:
static PyObject *func1(PyObject *self, PyObject *args) {
PyArrayObject *X;
int ndX;
npy_intp *shapeX;
PyArray_Descr *dtype;
NpyIter *iter;
NpyIter_IterNextFunc *iternext;
PyArg_ParseTuple(args, "O!", &PyArray_Type, &X);
ndX = PyArray_NDIM(X);
shapeX = PyArray_SHAPE(X);
dtype = PyArray_DescrFromType(NPY_DOUBLE);
iter = NpyIter_New(X, NPY_ITER_READONLY, NPY_KEEPORDER, NPY_NO_CASTING, dtype);
if (iter==NULL) {
return NULL;
}
iternext = NpyIter_GetIterNext(iter, NULL);
dataptr = (double **) NpyIter_GetDataPtrArray(iter);
do {
cout << **dataptr << endl;
} while (iternext(iter));
NpyIter_Deallocate(iter);
return Py_BuildValue(something);
}
To find out more information check out this link: http://docs.scipy.org/doc/numpy/reference/c-api.iterator.html