Re: another problem interfacing prolog and C

[Erick Alphonse]

Hello Daniel,

Daniel Diaz wrote:
> the problem comes from the fact you invoke Prolog from your call_c/2
>  foreign code. This one uses 2 arguments (a and _L) which are stored
> into an array (accessible via macros X(0) and X(1)). But since
> write/1 itself is partly written in Prolog it also uses X(...)
> variables. So, the clean way to fix it would be to inform the
> compiler a foreign code calls Prolog (and thus the compiler would
> emit code to save/restore the X(...) vars used).
>
> For the moment you can do it by hand (okay it is a bit dirty) as
> follows:

Thanks a lot for your help and the explanations!

I have another question. In the documentation, you explain another way 
to output results:

> When +term is specified the term passed to the function is the
> original Prolog term. It can be read and/or unified. It is also the
> case when term is specified without any mode symbol.

and use this in one of your examples.

Do we need to save/restore the X() vars in that case too, or only when 
we pass pointers to the C function (like -term or +string).

> So, the clean way to fix it would be to inform the
> compiler a foreign code calls Prolog (and thus the compiler would
> emit code to save/restore the X(...) vars used).

If you want to talk about this issue further, I would be very interested 
to do so with you.

Thanks again,
Best regards,
Erick.