[Pyrex] How to deal with a void *

[Tomasz Primke]

>  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.
>  Just like him, when I try to return the void * directly I get and
> error that it can't be turned into a PyObject.

Just as Stefan Behnel has written, void* is not a PyObject.

I don't know, what exactly you're doing in your code, but if you deal with C 
pointers, you can return them only from C functions in Pyrex, that means 
you have do declare such a functions using cdef statement:

  cdef some_C_type* func_name ( ... ):

Such a functions will be accessible only in your Pyrex code, not in Python.

>  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
>
>  However I'not really sure if this is safe or if there is a chance of
> the value getting mangled in the casting to long and back.

According to my knowledge of C, I doubt it.

Have you tried:

   cdef void *foo
   cdef unsigned long int *bar

   foo = initResource()
   bar = <unsigned long int*> foo

and then refer to bar[0] when you need unsigned long int value?

I'm doing such a "tricks" in my code and they work.


Best regards,

	Tomek