Re: C interface confusion about char codes, lists and atoms...

Le 03/07/2013 16:44, emacstheviking a
écrit :

Hi,

I have been experimenting with the foreign interface and
managed to confuse myself.

Given this foreign declaration:

%% :- foreign( foo( +string ), [fct_name( foo )]). %%
+string => atom at call site

%% :- foreign( foo( +codes ), [fct_name( foo )]).

:- foreign( foo( +codes ), [fct_name( foo )]).

and this implementation:

// +string :: atom ==> char*, works

// +codes :: character-code list ==> char*, works as
foo("Hello").

// +chars :: character list ==> char*, fails on
call foo("HI"), foo([64,65]). Why?

PlBool

foo(char* s)

{

printf("FOO: ==> %s\n", s);

return PL_TRUE;

}

My problem is that when I use "+chars" I can't then say:

foo("Hello")

as I get a type_error so please can anybody explain to me
what "character list" is and how it looks in a command line
session? The flag that controls the interpretation of
double-quoted strings is at its default value as I have not
altered it but I am aware of its existence and the fact that ""
is syntactic sugaring of lists of codes.

Hi,

+atom means you pass an atom (e.g. abc) and you get the internal
reference of the atom in C (which is an integer)

+chars means you pass a list of characters (e.g. [a,b,c]) and you
get a NULL terminated string in C, ie. a char * (e.g. "abc")

+code means you pass a list of char codes (e.g. [97,98,99] which is
the same a "abc" in Prolog) an dyou get the same char * as above.

See http://gprolog.univ-paris1.fr/manual/html_node/gprolog068.html

Daniel

Thanks.

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