[Numpy-discussion] Record Arrays and ctypes Interfacing

Robert Kern robert.kern@gmail....
Tue Mar 18 13:18:27 CDT 2008


On Tue, Mar 18, 2008 at 9:48 AM,  <vel.accel@gmail.com> wrote:
> Hi all,
>
>  How do I handle numpy record arrays (heterogenous dtype) with ctypes?
>  The python side is reasonably obvious to me, but I'm confused about
>  how to declare my C function's signature; whether I need to include
>  the numpy array interface header file or not... etc...
>
>  It's not obvious to me how a heterogeneous dtype is handled on the C
>  side. Could someone give me a quick and dirty example.

Record arrays (loosely) correspond to arrays of C structs. The
correspondence is only loose because the C standard does not specify
how the struct members should be aligned. Different systems may place
padding in places where numpy didn't. There are often #pragmas one can
use to force a particular kind of padding. Here is a reasonably good
article on the subject:

  http://en.wikipedia.org/wiki/Data_structure_alignment

You shouldn't need any numpy headers.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
 -- Umberto Eco


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