Hi,
I need to access ctype array's b_ptr. The array is defined in
Python-2.6.2/Modules/_ctypes/ctypes.h as:
struct tagCDataObject {
PyObject_HEAD
char *b_ptr; /* pointer to memory block */
int b_needsfree; /* need _we_ free the memory? */
CDataObject *b_base; /* pointer to base object or NULL */
Py_ssize_t b_size; /* size of memory block in bytes */
Py_ssize_t b_length; /* number of references we need */
Py_ssize_t b_index; /* index of this object into base's
b_object list */
PyObject *b_objects; /* dictionary of references we need to
keep, or Py_None */
union value b_value;
};
So I wrote this cython code:
cdef extern from "Python.h":
ctypedef void PyTypeObject
cdef struct CDataObject:
Py_ssize_t ob_refcnt
PyTypeObject *ob_type
char *b_ptr
and then I use it like this:
cdef object b = ptr
cdef CDataObject *a = <CDataObject *>b
cdef char *x = a.b_ptr
c_glNormalPointer(type, stride, <GLvoid *> x)
where "ptr" is a normal python variable, which contains the ctype
array, I then extract the b_ptr and use it. It works.
However, this assumes some particular form of PyObject_HEAD. Once it
changes, my code will segfault. So I guess the right way to do this is
to write my own C header file with the above struct (e.g. using the
PyObject_HEAD macro) and then just reference it using:
cdef extern from "Python.h":
ctypedef void PyTypeObject
cdef extern from "my_header.h":
ctypedef struct CDataObject:
char *b_ptr
which should always work.
What do you think?
Ondrej
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