Re: How to pass two dimensional arrays to C

["Jeffrey R. Carter" <spam.not.jrcarter@acm.not.spam.org>]

Bj�rn Persson wrote:
> 
> I think something like this should work:
> 
> procedure PLmesh
>   (x   : PL_Float_Array;
>    y   : PL_Float_Array;
>    z   : PL_Float_Array_2D;
>    opt : PLINT)
> is
>    Pointer_Array : PLFLT_Ptr_Array(z'Range(1));
> begin
>    for Index in z'Range(1) loop
>       Pointer_Array(Index) := z(Index, 1)'Access;
>    end loop;
>    c_plmesh(x, y, Pointer_Array, z'Length(1), z'Length(2), opt);
> end PLmesh;

No, you need to create a collection of C-compatible
1D arrays, put the rows of Z into them, and store C-compatible
pointers to them in the C-compatible 1D array of pointers. More like

    type Z_Length is new PL_Float_Array (Z_Range (2) );
    pragma Convention (C, Z_Length);

    type Ptr is access Z_Length;
    pragma Convention (C, Ptr);

    type Ptr_List is array (Z'range (1) ) of Ptr;
    pragma Convention (C, Ptr_List);

    A : Ptr_List;
begin
    All_Rows : for Row in Z'range (1) loop
       A (Row) := new Z_Length;

       All_Columns : for Column in Z'range (2) loop
          A (Row) (Column) := Z (Row, Column);
       end loop All_Columns;
    end loop All_Rows;

    C_Plmesh (...);

    -- Reclaim storage? Should be reclaimed automatically since
    -- Ptr goes out of scope
end;

-- 
Jeff Carter
"Don't knock masturbation. It's sex with someone I love."
Annie Hall
45