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From: Emile8 <pocchiola.yves@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: ACCESS TO SYSTEM VARIABLES
Date: Mon, 7 Mar 2011 12:14:47 -0800 (PST)
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Date: 2011-03-07T12:14:47-08:00
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On 7 mar, 12:47, Georg Bauhaus <rm.dash-bauh...@futureapps.de> wrote:
> On 07.03.11 10:34, Emile8 wrote:
>
>
>
> > with Ada.Environment_Variables; use Ada.Environment_Variables;
> > with Ada.Text_Io; use Ada.Text_Io;
>
> > procedure Print_Env is
> > begin
> > Put_Line("Columns : " & Value("COLUMNS"));
> > Put_Line("Lines : " & Value("LINES"));
> > Put_Line("Path : " & Value("PATH"));
> > end Print_Env;
>
> > I would like to understand the reasons of this behavior. Are there
> > different kinds of system variables in Linux ? Those as HOME, PATH
> > whose values depend only on the user session and those as LINES,
> > COLUMNS defined for each used terminal. Is there a way in Ada to
> > overcome this limitation ?
>
> Variables LINES and COLUMNS might not have been marked for export.
> Try export -p.
>
> With the above program, I see constraint errors for LINES and
> COLUMNS when these don't exist in the environment (which is
> expected behavior).
>
> $ LINES=$LINES COLUMNS=$COLUMNS ./print_env
> Columns : 255
> Lines : 42
> Path : /usr/local/bin:/usr/bin:/bin:/usr/games

I tried your suggestion which in fact solves only part of the problem.
With this approach the Ada program manages well to get the right
initial values for the Lines and Columns of the terminal, but  when I
use it in a loop to monitor a manual resizing of the terminal, it does
not see the changes in LINES and COLUMNS and reports always the same
initial values. This behavior persists even if each  LINES and COLUMNS
variables acquisitions are preceded by an export-p command.

I finally found a solution making in the Ada program the bash command
"stty size > TermSize.txt" which reports in the dedicated file
TermSize.txt the two numbers for LINES and COLUMNS. A reading of this
file brings back in the  Ada program the two numbers. This approach
works well when the terminal is resized. The next best thing would be
now to be able to manage the terminal as a protected object in Ada and
to have always an exact knowledge of its dimensions when I want tu use
it. But it is certainly only a dream...

It is not a very elegant solution and I should look also at how the
Ada version of ncurses manages to get the same informations.