Screen Editing

Thomas Dickey · Aug 17, 2006

Tak-Shing Chan said:
I don't need to know the answer, since Steve Summit's C-FAQ
rofl...

19.4 covered this (``for clearing the screen, a halfway portable
solution is to print a form-feed character ('\f'), which will
cause some displays to clear''). Presumably, those displays that
would clear are still in use.

The faq does contain some archaisms (and outright errors).

p.s: appeals to authority are generally regarded as inferior to direct
observation - something to consider if you choose to pursue a
technical career ;-)

Tak-Shing Chan · Aug 17, 2006

The faq does contain some archaisms (and outright errors).

p.s: appeals to authority are generally regarded as inferior to direct
observation - something to consider if you choose to pursue a
technical career ;-)

Direct observations aren't always statistically significant.

Tak-Shing

Thomas Dickey · Aug 17, 2006

Direct observations aren't always statistically significant.

You forgot to cite an authority for that claim.

Mark McIntyre · Aug 17, 2006

On Thu, 17 Aug 2006 22:40:44 +0100, in comp.lang.c , Tak-Shing Chan

(stuff to some guy called Dickey).

Chan, given that my kill filters automatically picked this guy up, I
suspect "Dickey" is a sock puppet for an existing troll. I suggest you
killfile him.
--
Mark McIntyre

"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it."
--Brian Kernighan

Thomas Dickey · Aug 17, 2006

(stuff to some guy called Dickey).

hmm - this seems to be your usual level, so I won't follow your lead.

Chan, given that my kill filters automatically picked this guy up, I
suspect "Dickey" is a sock puppet for an existing troll. I suggest you
killfile him.

not at all.
Unlike present company, I happen to know what I'm talking about.

Keith Thompson · Aug 17, 2006

Ancient_Hacker said:
and it's not clear terminal control falls under the baliwick of the C
language or th standard C libraries..

In fact, it's perfectly clear that terminal control does *not* fall
under the bailiwick of the standard C language and library.

The most portable way is dorky, but works most every place I can think
of:

for( i=1; i <= 66 + 24 /* for those TALL full page displays,plus
lagniappe */; i++ )
puts( "\n" );

There's no reason to assume that the terminal window is no taller than
66 rows. I'm typing this in a 65-row window, and I could easily
expand it.

Also, depending on what kind of terminal or emulator you're using, the
"erased" lines can just be scrolled off the top of the screen/window,
where they can be recovered. If I clear the screen, it's often
because I want to erase some sensitive information, and scrolling it
out of sight isn't good enough.

And, of course, it leaves the cursor at the bottom of the window.

Clearing the screen, or, more generally, controlling cursor position,
is one of those things that can *almost* be done in standard C with
some really ugly tricks, but there's almost always a much cleaner
system-specific solution. Don't waste your time trying to do it
portably.

Keith Thompson · Aug 17, 2006

Andrew Smallshaw said:
Most terminals, particularly modern ones, will clear the screen if
you simply send them a formfeed. It's not guaranteed, but it's a
similar kind of assumption to backspace will move the cursor left
which seems pretty much standard these days.

I haven't found that to be the case for any of the terminal emulators
I use. I've just tried xterm, dtterm, gnome-terminal, a Windows
command window, the GNU "screen" program, and rxvt; none of them clear
the screen in response to a formfeed character.

Tak-Shing Chan · Aug 17, 2006

hmm - this seems to be your usual level, so I won't follow your lead.

not at all.
Unlike present company, I happen to know what I'm talking about.

Tak-Shing Chan · Aug 17, 2006

I haven't found that to be the case for any of the terminal emulators
I use. I've just tried xterm, dtterm, gnome-terminal, a Windows
command window, the GNU "screen" program, and rxvt; none of them clear
the screen in response to a formfeed character.

I have just posted a long list elsethread.

Tak-Shing

Steve Summit · Aug 17, 2006

Keith said:
I haven't found that to be the case for any of the terminal emulators
I use. I've just tried xterm, dtterm, gnome-terminal, a Windows
command window, the GNU "screen" program, and rxvt; none of them clear
the screen in response to a formfeed character.

I had no idea that \f had fallen into disuse.
I'm updating FAQ 19.4 accordingly.

Thomas Dickey · Aug 17, 2006

Tak-Shing Chan said:
hmm - this seems to be your usual level, so I won't follow your lead.

not at all.
Unlike present company, I happen to know what I'm talking about.

[/QUOTE]

Really? Do you know anything about these 120 terminals?

Sure. And I know how to use google too. Since you don't, I'll help:

xterm supports ANSI color, VT220 emulation and UTF-8
There's an faq at
http://invisible-island.net/xterm/xterm.faq.html
ftp://invisible-island.net/xterm/

The current version of ncurses is 5.5 (20051010)
There's an faq at
http://invisible-island.net/ncurses/ncurses.faq.html

According to my termcap (yes, appealing to authority again), they
all respond to form feeds by clearing the screen:

Let's stick to "most" and "modern". Do you understand the terms?
I'm assuming you don't, given the list you presented -
even ignoring the duplicates.
(and no, I won't waste time here by giving a chronology ;-)

most+modern would imply something like "in widespread use during the past
ten years". There - add that to your glossary.

Ben Pfaff · Aug 17, 2006

Keith Thompson said:
There's no reason to assume that the terminal window is no taller than
66 rows. I'm typing this in a 65-row window, and I could easily
expand it.

(The above actually works with displays up to 180 rows high.)

For some reason, no one liked this suggestion of mine when I
brought it during the last discussion of this issue:

for (;

putchar('\n');

It should be effective just about everywhere, even on very tall
terminals or those with a circular scrollback buffer. It will
even get the attention of those using printing terminals.

Tak-Shing Chan · Aug 18, 2006

Sure. And I know how to use google too. Since you don't, I'll help:

xterm supports ANSI color, VT220 emulation and UTF-8
There's an faq at
http://invisible-island.net/xterm/xterm.faq.html
ftp://invisible-island.net/xterm/

The current version of ncurses is 5.5 (20051010)
There's an faq at
http://invisible-island.net/ncurses/ncurses.faq.html

Irrelevant.

Let's stick to "most" and "modern". Do you understand the terms?
I'm assuming you don't, given the list you presented -
even ignoring the duplicates.
(and no, I won't waste time here by giving a chronology ;-)

most+modern would imply something like "in widespread use during the past
ten years". There - add that to your glossary.

Are you saying that Sun SPARC machines are not ``in
widespread use during the past ten years''? That is news to me.

By the way, I believe that ``modern'' on comp.lang.c means
post-1989 (when ANSI C is born).

Tak-Shing

Thomas Dickey · Aug 18, 2006

Tak-Shing Chan said:
Are you saying that Sun SPARC machines are not ``in
widespread use during the past ten years''? That is news to me.

You cited several duplicates. "Widespread" is debatable in this case,
since (aside from the rarely-used console, Sun hasn't supported a terminal
emulator for this for more than ten years - it's been that long that the
openwin programs have been regarded as unsupported/legacy/doomed).

For the others - spend a few moments to see how long it's been since the
actual terminals were sold as new.

By the way, I believe that ``modern'' on comp.lang.c means
post-1989 (when ANSI C is born).

no - the topic changed from ANSI C to terminal emulators, and the modern
era for that was the related curses work in X/Open. 1996.

Tak-Shing Chan · Aug 18, 2006

You cited several duplicates. "Widespread" is debatable in this case,
since (aside from the rarely-used console, Sun hasn't supported a terminal
emulator for this for more than ten years - it's been that long that the
openwin programs have been regarded as unsupported/legacy/doomed).

For the others - spend a few moments to see how long it's been since the
actual terminals were sold as new.

no - the topic changed from ANSI C to terminal emulators, and the modern
era for that was the related curses work in X/Open. 1996.

That is only true if you are using UNIX. Many modern systems
do not use curses.

Tak-Shing

Thomas Dickey · Aug 18, 2006

That is only true if you are using UNIX. Many modern systems
do not use curses.

Those that don't, either use vt100-compatible terminals (OpenVMS), or do
not make use of terminals (barring the miniscule fraction running Plan 9 ;-)

hmm - a few readers of this group could tell if 9term clears the screen
on a form-feed (it doesn't appear so to me, from reading its code).

Tak-Shing Chan · Aug 18, 2006

xterm supports ANSI color, VT220 emulation and UTF-8
There's an faq at
http://invisible-island.net/xterm/xterm.faq.html
ftp://invisible-island.net/xterm/

The current version of ncurses is 5.5 (20051010)
There's an faq at
http://invisible-island.net/ncurses/ncurses.faq.html

No wonder you are so keen on xterm and ncurses---I just
noticed that you are the current maintainer of both!

Tak-Shing

Tak-Shing Chan · Aug 18, 2006

Those that don't, either use vt100-compatible terminals (OpenVMS), or do
not make use of terminals (barring the miniscule fraction running Plan 9 ;-)

There are embedded Linux systems without curses.

Tak-Shing

J. J. Farrell · Aug 18, 2006

Tak-Shing Chan said:
I have just posted a long list elsethread.

You posted a long list which has no obvious relevance to the point in
question. The list is a long way from "most terminals" and few of the
ones listed count as modern (one was recently sold as a rare antique
computer, many are archaic museum pieces).

Thomas Dickey · Aug 18, 2006

Tak-Shing Chan said:
No wonder you are so keen on xterm and ncurses---I just
noticed that you are the current maintainer of both!

That's been the case for more than ten years.

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Screen Editing

Thomas Dickey

Tak-Shing Chan

Thomas Dickey

Mark McIntyre

Thomas Dickey

Keith Thompson

Keith Thompson

Tak-Shing Chan

Tak-Shing Chan

Steve Summit

Thomas Dickey

Ben Pfaff

Tak-Shing Chan

Thomas Dickey

Tak-Shing Chan

Thomas Dickey

Tak-Shing Chan

Tak-Shing Chan

J. J. Farrell

Thomas Dickey

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