Yeah. There's a bit of overhead in getting a SMOB set up, but, it has
the advantage that you aren't keeping duplicate copies (a C copy and a
Scheme copy) of your information in memory.
--- Neil Jerram <[EMAIL PROTECTED]> wrote:
> Leonardo,
>
> Based on your replies to other people on the list, it sounds as
> though
> you probably want a SMOB. A SMOB is a way of passing a C pointer
> (such as to an arbitrary struct) around opaquely in Scheme, and the
> way to use them in quite well documented in a couple of places in the
> Guile manual (1.7/CVS version): nodes "Defining New Types (Smobs)"
> and
> "Dia Smobs".
>
> In case something simpler would do, however, I've also added a few
> comments below.
>
> Leonardo Lopes Pereira <[EMAIL PROTECTED]> writes:
>
> > Let me give a example. I can pass some simple data...
> >
> > --- scheme.scm ---
> > (define number 1)
> >
> > --- C program ---
> > #include <stdio.c>
> > #include <libguile.h>
> > #include <guile/gh.h>
> >
> > int main ()
> > {
> > int number
> > SCM s_symbol, s_value;
> > scm_init_guile ();
> >
> > scm_c_primitive_load ("scheme.scm");
> >
> > s_symbol = scm_c_lookup("number");
> > s_value = scm_variable_ref(s_symbol);
> > number = gh_scm2int(s_value, 0, "main");
> > }
> >
> > ---
> >
> > This convert the Scheme data in C data, but I do not know how to
> pass
> > a group of data together. ex.: How to convert a (cons x y) into a
> > struct?
>
> Well, for example:
>
> (define number (cons 3 4))
>
> instead of (define number 1), and then
>
> struct point number
> SCM s_symbol, s_value;
> scm_init_guile ();
>
> scm_c_primitive_load ("scheme.scm");
>
> s_symbol = scm_c_lookup("number");
> s_value = scm_variable_ref(s_symbol);
> number.x = gh_scm2int(SCM_CAR(s_value), 0, "main");
> number.y = gh_scm2int(SCM_CDR(s_value), 0, "main");
>
> instead of the C code above. Does that make sense?
>
> A scheme list can be as long as you like, so can hold more than 2
> values, and each value can be a different type. So you can equally
> well have 2 numbers and a string, for example.
>
> >
> > I want to create a wrap to a function that has a sruct as arg, so,
> I
> > need to create that struct in scheme and convert it to C, how to do
> > that?
>
> It depends what the C code expects as regards the lifetime of the
> struct. If the struct only needs to be value for the duration of the
> call to your C func, you can allocate it on the stack, initialize it
> from a Scheme pair/list as shown above, and then call the C func. If
> the struct needs to be longer lived than that, the SMOB approach is
> probably best.
>
> Regards,
> Neil
>
>
>
> _______________________________________________
> Guile-user mailing list
> Guile-user@gnu.org
> http://lists.gnu.org/mailman/listinfo/guile-user
>
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