[Sbcl-devel] Re: sb-grovel vs. sb-alien

[Andreas F. <as...@bo...>]

Today, Julian Stecklina <der...@we...> wrote:
> if I define a structure in a grovel constants file,
> e.g. foo. I get a macro called with-foo that creates a foo structure
> to be used in the dynamic extent of its body. 

Right.

> Now I need to pass a pointer to this structure to a C function. How
> would I accomplish this? sb-alien:addr does not work. :-/

That's true, too. What you're trying to do depends on the version of
SBCL that you're using; if you're using an SBCL before 0.8.10, you
have to do something like:

(with-alien-structure alien-object
                      ()
  (c-function (sb-grovel:array-data-address alien-object)))

On SBCL 0.8.10 and later (recommended anyway), you'd just pass the
alien-object, as they're of type (alien (* the-structure)), like so:

(with-alien-structure alien-object
                      ()
  (c-function alien-object))

See also the readdir functions in your version of sb-posix for an
example.
  
If this doesn't work for you, I'd like to hear about it.

Happy hacking,
-- 
Andreas Fuchs, <as...@bo...>, as...@ja..., antifuchs