Troubles : New_Page & Get_Immediate

Troubles : New_Page & Get_Immediate

[Ray Tindall]

Help for a novice?

Using Ada95 and the GW-Gnat compiler.

When trying to use New_Page as in
   New_Page;
to simply refresh the screen in output of text to the screen all I'm
getting is a weird symbol, the control character that represents a page
terminator I guess.  Does anyone know why and or if there is a specific way
it must be used or if it's inappropriate to do what I'm trying.

The LRM states that Get_Immediate can be used to get a character from the
keyboard immediately ie. without the enter key.   But says should be used
with 'unbuffered' input.   Are there any references or suggestions as to
how to do low_level IO or 'unbuffered' input to do this.  End goal to have
something like the well known 'hit any key to continue'.

Re: Troubles : New_Page & Get_Immediate

[Jerry van Dijk]

In article <01bcdae4$3f70ffa0$0f02000a@default> bjyxxl@echidna.stu.cowan.edu.au writes:

>When trying to use New_Page as in
>   New_Page;
>to simply refresh the screen in output of text to the screen all I'm
>getting is a weird symbol

As New_Page suggests, this is a printer-like command. The funny character
you are seeing is called the 'form-feed' code, instructing the printer
to move to the next page.

On some consoles, sending a form-feed will actually clear the screen,
on others it will simply display the character. On Win95 (if that is
what you are using) the latter is the case.

A very simple solution is:

   Num_Rows : constant := 25; -- number of screen rows;

   procedure Clear_Screen is
   begin
      for I in 1 .. Num_Rows loop
         New_Line;
      end loop;
   end Clear_Screen;

--

-- Jerry van Dijk | Leiden, Holland
-- Consultant     | Team Ada
-- Ordina Finance | jdijk@acm.org

Re: Troubles : New_Page & Get_Immediate

[Jerry van Dijk]

In article <01bcdae4$3f70ffa0$0f02000a@default> bjyxxl@echidna.stu.cowan.edu.au writes:

>The LRM states that Get_Immediate can be used to get a character from the
>keyboard immediately ie. without the enter key.   But says should be used
>with 'unbuffered' input.   Are there any references or suggestions as to
>how to do low_level IO or 'unbuffered' input to do this.  End goal to have
>something like the well known 'hit any key to continue'.

As this was asked twice:

a) Get_Immediate comes in two flavors: blocking and non-blocking.

   The blocking form waits until a key is pressed befor returning

   The non-blocking form returns immediately, reporting if a keypress
   was detected.

   Here's a simple example of both:

      with Ada.Text_IO; use Ada.Text_IO;

      procedure Test is
         C         : Character;
         Available : Boolean := False;
      begin

         -- Waiting for a key pressed - blocking
         Put ("Press almost any key to continu: ");
         Get_Immediate(C);
         New_Line;
         Put_Line ("Ok, continuing...");

         -- Polling for a key pressed - non-blocking
         Put ("Again waiting for some keypress: ");
         While not Available loop
            -- Do useful things here
            Get_Immediate (C, Available);
         end loop;
         New_Line;
         Put_Line ("Ok, thanks for pressing a key.");
      end Test;

The buffered/unbufferd issue gives a compiler the option of
not implementing this, but wait for an Enter key to be
pressed first.

Fortunately for you, both OA Special and GNAT support the
(IMHO) proper behavior with their Win95/NT compilers.

--

-- Jerry van Dijk | Leiden, Holland
-- Consultant     | Team Ada
-- Ordina Finance | jdijk@acm.org

Re: Troubles : New_Page & Get_Immediate

[John English]

Jerry van Dijk (jerry@jvdsys.nextjk.stuyts.nl) wrote:
:    Num_Rows : constant := 25; -- number of screen rows;

:    procedure Clear_Screen is
:    begin
:       for I in 1 .. Num_Rows loop
:          New_Line;
:       end loop;
:    end Clear_Screen;

... or of course just "New_Line(Num_Rows)" instead of "Clear_Screen".

---------------------------------------------------------------
 John English              | mailto:je@brighton.ac.uk
 Senior Lecturer           | http://www.comp.it.bton.ac.uk/je
 Dept. of Computing        | fax: (+44) 1273 642405
 University of Brighton    |
---------------------------------------------------------------

Re: Troubles : New_Page & Get_Immediate

[Anonymous]

<01bcdae4$3f70ffa0$0f02000a@default>

On Sat, 18 Oct 97 07:22:54 GMT, jerry@jvdsys.nextjk.stuyts.nl (Jerry van
Dijk) wrote:
>...
> 
> A very simple solution is:
> 
>    Num_Rows : constant := 25; -- number of screen rows;
> 
>    procedure Clear_Screen is
>    begin
>       for I in 1 .. Num_Rows loop
>          New_Line;
>       end loop;
>    end Clear_Screen;
> 

Or simply

   New_Line (Spacing => Num_Rows);

Jeff Carter  PGP:1024/440FBE21
My real e-mail address: ( carter @ innocon . com )
"We call your door-opening request a silly thing."
Monty Python & the Holy Grail

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Re: Troubles : New_Page & Get_Immediate

[Jerry van Dijk]

In article <199710201340.PAA11416@basement.replay.com> nobody@REPLAY.COM writes:

>   New_Line (Spacing => Num_Rows);

And before another dozen simular postings arrive <g> let me point out that
I was not trying to advertise a solution, just pointing in a direction.

Jerry.

--

-- Jerry van Dijk | Leiden, Holland
-- Consultant     | Team Ada
-- Ordina Finance | jdijk@acm.org