[Pyrex] Sharing a C pointer between Pyrex objects

[Anand Patil]

It really works! Thanks!

On Thu, Jan 8, 2009 at 5:01 PM, John Arbash Meinel
<john at arbash-meinel.com>wrote:

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> Anand Patil wrote:
> > Hi all,
> >
> > I'd like to make an int* pointer stored in one Pyrex object available to
> > another:
> >
> > cdef class NumberHolder:
> >     cdef int number
> >     def __init__(self):
> >         self.number = 0
> >
> > cdef class PointerHolder:
> >     cdef int* my_pointer
> >     def __init__(self, number_holder):
> >         my_pointer = number_holder.number
> >
> > If I try it this way, of course, I get errors like 'NumberHolder' object
> > has no attribute 'number'. I'm currently creating a NumPy array in
> > NumberHolder and using PyArray_DATA from PointerHolder, but it seems
> > excessive and possibly dangerous, since PointerHolder may change
> > *my_pointer later. What's the best way to do this?
> >
> > Thanks,
> > Anand
> >
>
> I believe you can do:
>
>
> cdef class PointerHolder:
>    cdef int* my_pointer
>    def __init__(self, number_holder):
>         cdef NumberHolder real_holder
>        real_holder = number_holder
>        self.my_pointer = &real_holder.number
>
> You need to indicate to pyrex that number_holder is really a
> NumberHolder object, and not just a generic python object. Further, I'm
> pretty sure the & is necessary, since you want to point to the int, and
> not point at whatever the int points at.
>
> John
> =:->
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