Cython - Wrapping pointer to structure from C to python - cython

Question

I have a C function which take pointer to struct and i want to use it in python by C-Extensions by Cython way but when i want to pass pointer to struct from python give me an error: "Cannot convert Python object to 'Foo *'"
In the below example i make object to call the C function but what passed to C function is NULL pointer.
My Trial:
hello.h
#include <stdio.h>
typedef struct
{
int x;
} Foo;
int hello(Foo* what);
hello.c
#include "hello.h"
int hello(Foo* what)
{
printf("Hello Wrapper\n");
printf("what: %p\n", what);
what->x = 5;
return what->x;
}
phello.pxd
cdef extern from "hello.h":
ctypedef struct Foo:
int x
cdef int hello(Foo* what)
phello.pyx
cimport phello
cdef class Foo_c:
cdef phello.Foo* s
def hello_fn(self):
return phello.hello(self.s)
setup.py
from distutils.core import setup, Extension
from Cython.Distutils import build_ext
setup(
cmdclass = {'build_ext': build_ext},
ext_modules=[ Extension("hellomodule",
sources=["phello.pyx", "hello.c"],
) ]
test.py
import hellomodule
print "Hello test.py"
tobject = hellomodule.Foo_c()
print "Object:", tobject
tobject.hello_fn()
So i want create "Foo" struct in "test.py" and pass it to "hello_fn()" function to call the C function "hello()" after passing this struct, so i can read or write on this structure from both sides python & C.
Can Anyone help me in this, please?

Answer 1

Your code does not allocate memory for phello.Foo. Allocation can be done in __cinit__ with calloc (or malloc) and deallocation in __dealloc__ with free.
cimport phello
from libc.stdlib cimport calloc, free
cdef class Foo_c:
cdef phello.Foo* s
def __cinit__(self, int n):
self.s = <phello.Foo *>calloc(1, sizeof(phello.Foo))
def __dealloc__(self):
free(<void *>self.s)
def __init__(self, int n):
self.s.x = n