[Pyrex] Callback help

[Dale Cieslak]

Hi all,

I apologize if this has already been answered or if it's a dumb question...I tried looking through the archives and haven't found 
anything similar so far.  I'm trying to wrap a C API that makes use of 
callbacks, and I looked at the cheesefinder callback demo code in the 
Pyrex distribution.  If I write my code to match the cheesefinder 
example, it works fine.  However, it appears that the cheesefinder 
example passes the Python function pointer as the user_data itself, but 
what if I want to ALSO pass user data to my Python callback?   I should 
point out that it's been several years since I did any serious C coding 
(which is why I'm trying to wrap the thing in Python), so I'm hoping 
it's just a simple n00b-level  solution.   I tried various permutations 
of using PyCObject_AsVoidPtr instead of just casts, but to no avail.  
Essentially it compiles fine, but Bus Errors/Seg Faults when it goes to call the python callback.  Here's the gist of what I tried.

Thanks in 
advance,
Dale

cdef extern from "cheesefinder.h":
    
ctypedef void (*cheesefunc)(char *name, void *user_data)
    void 
find_cheeses(cheesefunc user_func, void *user_data)

ctypedef 
struct my_cheese_data:
       void *py_callback
       void 
*py_data

def find(f, data):
    cdef my_cheese_data user_data
    my_cheese_data.py_callback = <void *>f
    
my_cheese_data.py_data = <void *>data

    
find_cheeses(super_callback, <void*>&user_data)
    
cdef void callback(char *name, void *f):
    (<object>f)(name)

cdef void super_callback(char *name, void *cheese_data):
    cdef void *f
    cdef void *user_data

    f = <void 
*>cheese_data.py_callback
    user_data = <void 
*>cheese_data.py_data
       (<object>f)(name, user_data)