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From: "Jerry" <lanceboyle@qwest.net>
Newsgroups: comp.lang.ada
Subject: Re: How to pass two dimensional arrays to C
Date: 4 Aug 2006 18:03:21 -0700
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Date: 2006-08-04T18:03:21-07:00
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I want to close off this thread for the record.

Many thanks to everyone who helped me.

I have a working solution, pasted in sketch form below.

My only complaint with this solution is that I wanted to keep the thin
bindings, PlplotThin.ads, available and as a complete binding to anyone
who prefers it, if for no other reason than it is notationally closer
to the documentation (and _was_ essentially complete while the thick
binding will be finished only as my spare time permits). With this
solution, any PLplot subprogram which takes a two-dimensional array is
no longer accessible from the thin binding.

Maybe someday I'll learn enough Ada to find a way around this, but for
now, this works:


=============== my_common.ads
package My_Common is
    type Long_Float_Array_1D is array (Integer range <>) of aliased
Long_Float;
    type Long_Float_Array_2D is array (Integer range <>, integer range
<>) of aliased Long_Float;
end My_Common;



=============== plplotthin.ads
with
    My_Common;

package PLplotThin is
    subtype PLINT  is Integer;
    subtype PLFLT  is Long_Float;
    subtype PL_Float_Array    is My_Common.Long_Float_Array_1D;
    subtype PL_Float_Array_2D is My_Common.Long_Float_Array_2D;

    -- procedure plmesh is not defined in this package, but
	-- but in the thick binding PLplot wrapped in Mesh_3D.
	-- The same applies for the various other 3D plotters such
	-- as plmeshc, plot3d, plot3dc, and others which take a
	-- two-dimensional array as a parameter.
	-- These routines are unavailable from this thin binding.
end PLplotThin;


=============== plplot.adb
with
    PLplotThin,
    My_Common,
    Interfaces.C.Pointers,
    Interfaces.C;
use
    PLplotThin,
    My_Common,
    Interfaces.C;

package body PLplot is

    procedure Mesh_3D
       (x, y    : Long_Float_Array_1D; -- surface definition points
        z       : in out Long_Float_Array_2D; -- height of surface at
definition points
        Options : Integer) is

        package PL_Float_Pointers_Local is new Interfaces.C.Pointers
           (Index              => Integer,
            Element            => Long_Float,
            Element_Array      => Long_Float_Array_1D,
            Default_Terminator => 0.0);
        use type PL_Float_Pointers_Local.Pointer; -- as in RM B.3.2
        type PL_Float_Pointer_Array_Local is array (Integer range <>)
of PL_Float_Pointers_Local.Pointer; -- array of pointers to Long_Floats
which represent the first element of each row of z in C-land

        Index_Of_First_Column : Integer := z'First(2);
        z_As_Pointers : PL_Float_Pointer_Array_Local (z'range(1));

        procedure
        plmesh_local(x : PL_Float_Array; y : PL_Float_Array; z :
PL_Float_Pointer_Array_Local; nx : Integer; ny : Integer; opt :
Integer);
        pragma Import(C, plmesh_local, "c_plmesh");

    begin
        for Index in z'range(1) loop
            z_As_Pointers(Index) := z(Index,
Index_Of_First_Column)'access;
        end loop;
        plmesh_local(x, y, z_As_Pointers, x'Length, y'Length, Options);
-- pass z_As_Pointers here rather than z
    end Mesh_3D;

end PLplot;


=============== Testing_Thick_Binding.adb
with
    PlplotThin,
    PLplot,
    My_Common;
use
    PlplotThin,
    PLplot,
    My_Common;

package body Testing_Thick_Binding is
    procedure Main_Testing_Thick_Binding is
        z : aliased Long_Float_Array_2D (1..xpts, 1..ypts);
        pragma Convention(C, z); -- for compatibility with non-GNAT
        x : Long_Float_Array_1D (1..xpts);
        pragma Convention(C, x); -- for compatibility with non-GNAT
        y : Long_Float_Array_1D (1..ypts);
        pragma Convention(C, y); -- for compatibility with non-GNAT
    begin -- Main_Testing_Thick_Binding
		-- ...
		-- Calculate x, y, z.
		-- etc.
		-- ...
       	Mesh_3D(x, y, z, Options); -- call plmesh wrapper
		-- Clean up.
	end Main_Testing_Thick_Binding;
end Testing_Thick_Binding;