Ways to include C #define'd constants in Cython .PXD file

[Vogon]

Hi,

I'm wondering what different ways there are to directly include C
compile-time constants in a PXD file. So far I've found that the
following works:

// foo.h
#define C_BAR 1

# foo.pxd
cdef extern from 'foo.h':
int C_BAR

However, I'm worried that the PXD version of the constant is allocated
on the "stack" instead of the "heap" and having an enormous amount of
such definitions would cause a performance hit. Is this what happens
in reality? If so, are there any more efficient/convenient ways to do
the same thing?

[Robert Bradshaw]

The extern block only tells Cython what it can count on finding in the
referenced header file. In this case the literal "C_BAR" will get
written write out to the .c file wherever it is used, and the C
compiler will do the right thing (in this case, probably inserting a
compile time constant).

- Robert

[Vogon]

Good to know. Thanks!

On Dec 17, 3:03 pm, Robert Bradshaw <rober...@math.washington.edu>
wrote:

[Lisandro Dalcín]

On Thu, Dec 17, 2009 at 9:16 AM, Vogon <jus...@gmail.com> wrote:
> Hi,
>
> I'm wondering what different ways there are to directly include C
> compile-time constants in a PXD file. So far I've found that the
> following works:
>
> // foo.h
> #define C_BAR 1
>
> # foo.pxd
> cdef extern from 'foo.h':
>    int C_BAR
>

For integrals, I think it is better to do it like this:

cdef extern from 'foo.h':
   enum: C_BAR

That way, Cython is going to treat C_BAR as a constant, you can do for example:

cdef double my_array[C_BAR]

--
Lisandro Dalcín
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