Function PyArray_AsCArray

numpy/core/src/multiarray/multiarraymodule.c:261–317

NUMPY_API * Simulate a C-array * steals a reference to typedescr -- can be NULL */

 * steals a reference to typedescr -- can be NULL
 */
NPY_NO_EXPORT int
PyArray_AsCArray(PyObject **op, void *ptr, npy_intp *dims, int nd,
                 PyArray_Descr* typedescr)
{
    PyArrayObject *ap;
    npy_intp n, m, i, j;
    char **ptr2;
    char ***ptr3;

    if ((nd < 1) || (nd > 3)) {
        PyErr_SetString(PyExc_ValueError,
                        "C arrays of only 1-3 dimensions available");
        Py_XDECREF(typedescr);
        return -1;
    }
    if ((ap = (PyArrayObject*)PyArray_FromAny(*op, typedescr, nd, nd,
                                      NPY_ARRAY_CARRAY, NULL)) == NULL) {
        return -1;
    }
    switch(nd) {
    case 1:
        *((char **)ptr) = PyArray_DATA(ap);
        break;
    case 2:
        n = PyArray_DIMS(ap)[0];
        ptr2 = (char **)PyArray_malloc(n * sizeof(char *));
        if (!ptr2) {
            PyErr_NoMemory();
            return -1;
        }
        for (i = 0; i < n; i++) {
            ptr2[i] = PyArray_BYTES(ap) + i*PyArray_STRIDES(ap)[0];
        }
        *((char ***)ptr) = ptr2;
        break;
    case 3:
        n = PyArray_DIMS(ap)[0];
        m = PyArray_DIMS(ap)[1];
        ptr3 = (char ***)PyArray_malloc(n*(m+1) * sizeof(char *));
        if (!ptr3) {
            PyErr_NoMemory();
            return -1;
        }
        for (i = 0; i < n; i++) {
            ptr3[i] = (char **) &ptr3[n + m * i];
            for (j = 0; j < m; j++) {
                ptr3[i][j] = PyArray_BYTES(ap) + i*PyArray_STRIDES(ap)[0] + j*PyArray_STRIDES(ap)[1];
            }
        }
        *((char ****)ptr) = ptr3;
    }
    if (nd) {
        memcpy(dims, PyArray_DIMS(ap), nd*sizeof(npy_intp));
    }
    *op = (PyObject *)ap;
    return 0;
}