Simple Ada-95 Question (regarding X11Ada bindings)

Simple Ada-95 Question (regarding X11Ada bindings)

[Ralf Lundberg]

I did some Ada programming som ten years ago, but I have been off
for quite some time. I have not used Ada95 until now.
However I now have to port an application from Telesoft Ada with
Telewindows X-bindings to gnat (GNU) with X11Ada Ada95 X-bindings.


In the library I will use the ada procedures matches the original
C-versions very closely.
Some arrays are passed as a pointer to the element type, plus a
number telling the length of the array, in the traditional C way.

---------
QUESTION:
How do I make something of type access A actually point to the
first element in an array of A's?
---------

I have found out that if I take 'Address on a variable of type
A that is declared as aliased I get something of the right type.
I would like to do that  with the first element in the array,
bu I can't make that aliased..

Anwer by mail preferred, but I will poll this newsgroup as well..

----------------------------------------------
This is one procedure I would like to call...

  procedure XFillPolygon(
            display: access XDisplay;
            d      : X.Drawable;
            gc     : access XGC;
            points : access XPoint;  -- ..and this is the evil one..
            npoints: X.signed_int;
            shape  : X.signed_int;
            mode   : X.signed_int);                     -- Xlib.h:2595

  type XPoint is                                        -- Xlib.h:398
    record
        XX: X.signed_short;                             -- Xlib.h:397
        y : X.signed_short;                             -- Xlib.h:397
    end record;

 
-- 
___________________________________________________________________
Ralf Lundberg           http://www.cd.chalmers.se/~ralf/index.html
<ralf@carmenta.se>      (email home: <ralf@cs.chalmers.se>)

Re: Simple Ada-95 Question (regarding X11Ada bindings)

[Keith Allan Shillington]

Ralf Lundberg <rl@carmenta.se> wrote in article
<32E34E8E.FDD@carmenta.se>...
> QUESTION:
> How do I make something of type access A actually point to the
> first element in an array of A's?

type A is ....
type A_Array is array(1..10) of aliased A;
type Access_A is access all A;

My_Array : A_Array;

First_One : Access_A := My_Array(1)'Access;

Re: Simple Ada-95 Question (regarding X11Ada bindings)

[G. Vincent Castellano]

% QUESTION:
% How do I make something of type access A actually point to the
% first element in an array of A's?
% ---------
% 
% I have found out that if I take 'Address on a variable of type
                                  ^^^^^^^^
Do you mean 'Access here?

% A that is declared as aliased I get something of the right type.
% I would like to do that  with the first element in the array,
% bu I can't make that aliased..
% 

You need to declare an 'array of aliased' objects, as illustrated
by the following declarations and call to a procedure with a
simlar interface:
   
       type Vector_Of_Point_Type is array (X11.Signed_Int range <>) 
          of aliased X.Xlib.XPoint;
   
       Points:  Vector_Of_Point_Type := ((C.X1, C.Y1),
                                         (C.X2, C.Y1),               
                                         (C.X2, C.Y2),
                                         (C.X1, C.Y2),
                                         (C.X1, C.Y1));
   begin
       X11.XLib.XDrawLines(
           Display,
           X11.Drawable(C.Gw.Window),
           C.Gw.Gc_Always,
           Points(Points'First)'Access,
           Points'Length,
           X11.Coordmodeorigin);
   
 == G. Vincent Castellano :: X/Ada WWW => http://www.ocsystems.com/xada ==
 ==  "If virtual memory did not exist, it would have                    ==
 ==     become necessary for us to invent it."                          ==