Re: Pointer

[Ludovic Brenta <ludovic@ludovic-brenta.org>]

Sébastien wrote:
> char* get_nth(char** data, unsigned int n) {
>    return data[i];
> }
>
> Ada binding:
> function get_nth(data: System.Address; n: Int) return Char_Ptr;
> pragma Import(C, get_nth, "get_nth");
>
> Then:
> for i in Natural range 0 .. N loop
>     MyString := Interfaces.C.Strings.Value(get_nth(CharPtrPtr, i));
> end loop;
>
> I know it's working, but I have to code a C function in order to do
> that, is there a way to replace get_nth by an ada code function?
>
> Hope it's a better explanation ;-)

OK, then how about:

type Array_Of_C_Strings is array (Positive range <>) of
Interfaces.C.Strings.chars_ptr;
pragma Convention (C, Array_Of_C_Strings);

type Array_Of_Strings is array (Positive range <>) of access String;

function Get return Array_Of_C_Strings is
   function How_Many_Strings return Natural;
   pragma Import (C, How_Many_Strings,
"MYCFunctionTellingMeHowManyStrings");
   Length : constant Natural := How_Many_Strings;

   function Get_Array return Array_Of_C_Strings;
   pragma Import (C, Get_Array, "MyCFunctionReturninCharStarStar");

   Raw_Result : Array_Of_C_Strings (1 .. Length) := Get_Array;
   Result : Array_Of_Strings (1 .. Length);
begin
   for K in Result'Length loop
      Result (K) := new String'(Interfaces.C.Strings.Value (Raw_Result
(K)));
   end loop;
   return Result;
end Get;

This duplicates the strings and creates an array of access values;
each access value remembers the length of the string it points to.
There is probably another solution that avoids this duplication.

--
Ludovic Brenta.