[Pyrex] How to deal with a void *

[Stefan Behnel]

Hi Travis,

Travis Caldwell wrote:
>  I am trying to wrap a C API which uses void * as the type of an opaque
> token that gets passed around.
> 
>  Basically you have things like:
> 
>  void *initResource(....)
> 
>  int doSomething( void *resourceID,...) 
> 
>  where you get a void * at resource creation and then do nothing with
> it excpet to pass it back into other API functions to identify the
> resource you wish the function to operate on.
> when I try to return the void * directly I get and
> error that it can't be turned into a PyObject. 

Obviously, it's not a Python object.


>  I can get the error message to go away by defining a C long varriable
> and casting the void * to that. ex:
> 
>   cdef void *foo
>   cdef unsigned long bar
> 
>   foo = initResource()
>   bar = <unsigned long> foo

Don't ever do these things.

A possible approach is to write an extension class that contains the pointer
as data field and pass that through the API calls.

cdef class MyContext:
  void* _something

def initWrapper():
  cdef void* c_resource
  # ... create resource as 'c_resource'
  context = MyContext()
  context._something = c_resource
  return context

def pyDoSomething(MyContext context, myarg):
  doSomething(context._something, myarg)


Does that help?

Stefan