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From: kst@sd.aonix.com (Keith Thompson)
Subject: Re: Clear Screen
Date: 1997/02/28
Message-ID: <E6AFB1.Ap2@thomsoft.com>#1/1
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References: <330FE569.29FA@bix.com> <5erk3a$a29@news.cict.fr>
 <dewar.856916794@merv>
Organization: Aonix, San Diego, CA, USA
Newsgroups: comp.lang.ada
Originator: kst@pulsar
Date: 1997-02-28T00:00:00+00:00
List-Id: <comp.lang.ada>


In <dewar.856916794@merv> dewar@merv.cs.nyu.edu (Robert Dewar) writes:
[...]
>     Clear_Screen : constant String := Ascii.ESC & "[2J";

On a more or less VT100-compatible terminal or emulator, the sequence
ESC [ 2 J will clear the screen without moving the cursor.  No problem
if that's what you want, but you usually want to move the cursor to the
upper left corner of the screen (window, whatever).

>      Put_Line (Clear_Screen);

And, of course, this will move the cursor down one line after clearing
the screen.

This might be closer to what you want:

    Clear_Screen : constant String := Ascii.ESC & "[H" & Ascii.ESC & "[2J";
    ...
    Put(Clear_Screen);

If the lack of a newline causes buffering problems, you might consider
writing to Standard_Error and/or calling Ada.Text_IO.Flush.

If you're on a Unix system and you may be using a non-VT100-compatible
terminal (unlikely these days), you might want to do something like this:

   with Interfaces.C;
   with Ada.Text_IO;
   procedure Clear_Screen is
      function System(S: String) return Interfaces.C.Int;
      pragma Import(C, System, "system");
      Command : constant String := "clear" & Ascii.Nul;
      Result : Interfaces.C.Int;
      use type Interfaces.C.Int;
   begin
      Result := System(Command);
      if Result /= 0 then
	 Ada.Text_IO.Put_Line
	    ( Ada.Text_IO.Standard_Error,
	      "clear failed, result = " & Interfaces.C.Int'Image(Result));
      end if;
   end Clear_Screen;

though it's likely to be inefficient.

If you're using an Etch-A-Sketch (R) compatible display, you need to
print a message asking the operator to turn it upside-down.

-- 
Keith Thompson (The_Other_Keith) kst@sd.aonix.com <http://www.aonix.com> <*>
TeleSo^H^H^H^H^H^H Alsy^H^H^H^H Thomson Softw^H^H^H^H^H^H^H^H^H^H^H^H^H Aonix
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