[pypy-dev] For embedding pypy, how to deal with None value

[Armin Rigo]

Hi Ryan,

On 19 May 2015 at 20:09, Ryan Gonzalez <rymg19 at gmail.com> wrote:
> Why not return a pointer to a double? Like (UNTESTED!):
>
> d = ffi.new('double*')
> d[0] = 9.0
> return d

This doesn't work!  You can't return a ffi.new() pointer, because the
'd' variable is not kept alive.

>>> The document Embedding PyPy shows good examples, but did not tell how to
>>> deal with None value.

I'm still unsure I understand the question.  You need to know at least
a bit of C in order to use cffi.  In C you can't write a function that
returns either a double or NULL.  First start by thinking about a
valid C interface, and then use cffi to implement it.  Maybe you want
something like

    int foo(int argument, double *result);

which returns a status code as an integer (e.g. 0=ok, -1=error), and
in the ok case, fills in "*result".


A bientôt,

Armin.