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From: johnherro@aol.com (John Herro)
Subject: Re: Getting a single key stroke
Date: 1996/05/05
Message-ID: <4mj956$687@newsbf02.news.aol.com>#1/1
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sender: root@newsbf02.news.aol.com
references: <4metj6$ll5@netra.oscs.montana.edu>
organization: America Online, Inc. (1-800-827-6364)
newsgroups: comp.lang.ada
Date: 1996-05-05T00:00:00+00:00
List-Id: <comp.lang.ada>


gje9947@msu.oscs.montana.edu (James Eder) writes:
> How do you, in Ada, get a single keystroke
> such as an arrow key from the user?  Oh,
> and it must be a somewhat portable method.
> I'm writing the program for an open VMS
> system with an Ada 83 compiler.
     I don't think it's possible to get a single keystroke in a "somewhat
portable" manner in Ada 83.  Even in Ada 95, which has a "portable"
routine to do that, there are no guarantees that the routine will work on
all systems!
     Here's how I did it in VAX Ada [83] for VMS in my Ada Tutor program. 
Unfortunately, this isn't portable.  Sorry, it's as close as I can come to
what you want:

package Custom_IO is
   ...
   procedure Get(Char : out Character);
   ...
end Custom_IO;

with Starlet, System; use Starlet, System;
package body Custom_IO is
   Chan : Starlet.Channel_Type;
   IOSB : System.Unsigned_Quadword;
   Stat : System.Unsigned_Longword;
   procedure QIOW(
        Stat   :    out Unsigned_Longword;
        EFN    : in     Integer;
        Chan   : in     Channel_Type;
        Func   : in     Short_Integer;
        IOSB   :    out Unsigned_Quadword;
        ASTadr : in     Integer;
        ASTPRM : in     Integer;
        P1     : in out String;
        P2, P3 : in     Integer;
        P4     : in     Unsigned_Quadword;
        P5, P6 : in     Integer);
   pragma Interface(System_Library, QIOW);
   pragma Import_Valued_Procedure(
        Internal        => QIOW,
        External        => "SYS$QIOW",
        Parameter_Types => (
             Unsigned_Longword,
             Integer,
             Channel_Type,
             Short_Integer,
             Unsigned_Quadword,
             Integer,
             Integer,
             String,
             Integer,
             Integer,
             Unsigned_Quadword,
             Integer,
             Integer),
        Mechanism       => (
             Value,
             Value,
             Value,
             Value,
             Reference,
             Value,
             Reference,
             Reference,
             Value,
             Reference,
             Reference,
             Reference,
             Reference));

   procedure Get(Char : out Character) is
      S : String(1 .. 1);
   begin
      QIOW(Stat, 0, Chan, 16#7A#, IOSB,
           0, 0, S, 1, 0, (0,0), 0, 0);
      Char := S(1);
   end Get;
   ...
end Custom_IO;

     It appears that, for the portion of the package that I posted, the
"use Starlet, System;" clause may be unnecessary.  However, I no longer
have access to VMS to test this.
     I hope that this helps, or at least that it's better than nothing.
- John Herro
Software Innovations Technology
http://members.aol.com/AdaTutor
ftp://members.aol.com/AdaTutor