Screen Editing

[someone]

I was just wondering if there is any way of editing anything already
printed on the screen with out using the system("cls") command.

[J. J. Farrell]

Tak-Shing Chan wrote:

On Thu, 17 Aug 2006, Keith Thompson wrote:

Andrew Smallshaw <an*****@sdf.lo nestar.orgwrite s:
[...]

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.

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).

[Tak-Shing Chan]

On Fri, 18 Aug 2006, Thomas Dickey wrote:

Tak-Shing Chan <t.****@gold.ac .ukwrote:

>On Fri, 18 Aug 2006, Thomas Dickey wrote:

>>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.

Which are the ones running a widely-used non-vt100-compatible terminal?

Widely-used? I don't know. But there exists systems where
you can access the console thru the serial port---I've seen a
few of those.

Tak-Shing

[Thomas Dickey]

Tak-Shing Chan <t.****@gold.ac .ukwrote:

On Fri, 18 Aug 2006, Thomas Dickey wrote:

>Tak-Shing Chan <t.****@gold.ac .ukwrote:

>>On Fri, 18 Aug 2006, Thomas Dickey wrote:

>>>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.

Which are the ones running a widely-used non-vt100-compatible terminal?

Widely-used? I don't know. But there exists systems where
you can access the console thru the serial port---I've seen a
few of those.

A serial port is a data connection (a wire)
It doesn't present data (a terminal).

Again, unless it's widely used, it doesn't add to the "most" category.

--
Thomas E. Dickey
http://invisible-island.net
ftp://invisible-island.net

[Tak-Shing Chan]

On Fri, 17 Aug 2006, J. J. Farrell wrote:

>
Tak-Shing Chan wrote:

>On Thu, 17 Aug 2006, Keith Thompson wrote:

>>Andrew Smallshaw <an*****@sdf.lo nestar.orgwrite s:
[...]
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.

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).

OK. Let me trim it down to just one item: the Sun console.
It is certainly still in use today, and it does clear the screen
with '\f'. But you are absolutely right, this has little
relevance to ``most terminals''. Perhaps I should s/most/some/g.

Tak-Shing

[Tak-Shing Chan]

On Fri, 18 Aug 2006, Thomas Dickey wrote:

Tak-Shing Chan <t.****@gold.ac .ukwrote:

>On Fri, 18 Aug 2006, Thomas Dickey wrote:

>>Which are the ones running a widely-used non-vt100-compatible terminal?

> Widely-used? I don't know. But there exists systems where
you can access the console thru the serial port---I've seen a
few of those.

A serial port is a data connection (a wire)
It doesn't present data (a terminal).

The serial driver doesn't, but the console driver does.

Again, unless it's widely used, it doesn't add to the "most" category.

Fair enough.

Tak-Shing

[Thomas Dickey]

Tak-Shing Chan <t.****@gold.ac .ukwrote:

On Fri, 17 Aug 2006, J. J. Farrell wrote:

>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).

OK. Let me trim it down to just one item: the Sun console.
It is certainly still in use today, and it does clear the screen
with '\f'. But you are absolutely right, this has little
relevance to ``most terminals''. Perhaps I should s/most/some/g.

yes - "some". As a colleague pointed out to me (quite a while ago),
as I was modifying a terminal driver to do form-feeds, _printers_
do form-feeds, terminals are not expected to do this.

--
Thomas E. Dickey
http://invisible-island.net
ftp://invisible-island.net

[Ian Collins]

Tak-Shing Chan wrote:

On Fri, 18 Aug 2006, Thomas Dickey wrote:

>Tak-Shing Chan <t.****@gold.ac .ukwrote:

>>On Fri, 18 Aug 2006, Thomas Dickey wrote:

>>>Which are the ones running a widely-used non-vt100-compatible terminal?

>> Widely-used? I don't know. But there exists systems where
you can access the console thru the serial port---I've seen a
few of those.

A serial port is a data connection (a wire)
It doesn't present data (a terminal).

The serial driver doesn't, but the console driver does.

>Again, unless it's widely used, it doesn't add to the "most" category.

Fair enough.

Getting rather off topic....

--
Ian Collins.

[Tak-Shing Chan]

On Fri, 18 Aug 2006, Ian Collins wrote:

Tak-Shing Chan wrote:

>On Fri, 18 Aug 2006, Thomas Dickey wrote:

>>Tak-Shing Chan <t.****@gold.ac .ukwrote:

On Fri, 18 Aug 2006, Thomas Dickey wrote:
Which are the ones running a widely-used non-vt100-compatible terminal?
Widely-used? I don't know. But there exists systems where
you can access the console thru the serial port---I've seen a
few of those.
A serial port is a data connection (a wire)
It doesn't present data (a terminal).

The serial driver doesn't, but the console driver does.

>>Again, unless it's widely used, it doesn't add to the "most" category.

Fair enough.

Getting rather off topic....

Sorry. I should volunterily ban myself from comp.lang.c
for a month...

Tak-Shing

[Keith Thompson]

Tak-Shing Chan <t.****@gold.ac .ukwrites:

On Thu, 17 Aug 2006, Ancient_Hacker wrote:

>someone wrote:

>>I was just wondering if there is any way of editing anything already
printed on the screen with out using the system("cls") command.

There is no "C" way to do this, as C precedes most CRT terminals,

What about ISO 9899:1990, 5.2.2, where escape sequences for
display devices (such as '\f', '\b' and '\r') are defined? The
only problem with these are quality of implementation issues.

It says that \f (form feed) "moves the active position to the initial
position at the start of the next logical page."

I don't see anything there about clearing the screen.

I think we all know by now that *some* terminals and terminal
emulators will clear the screen in response to a formfeed characters,
and some will not. (It happens that most of the ones I use or have
access to don't. I suspect my experience in this case is typical; I
certainly don't claim that it's universal.)

In my opinion, the statement in question 19.4 of the FAQ that clearing
the display by printing a formfeed character is "halfway portable" is
incorrect, or at least over-stated.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Tak-Shing Chan]

On Fri, 18 Aug 2006, Keith Thompson wrote:

Tak-Shing Chan <t.****@gold.ac .ukwrites:

>On Thu, 17 Aug 2006, Ancient_Hacker wrote:

>>someone wrote:
I was just wondering if there is any way of editing anything already
printed on the screen with out using the system("cls") command.

There is no "C" way to do this, as C precedes most CRT terminals,

What about ISO 9899:1990, 5.2.2, where escape sequences for
display devices (such as '\f', '\b' and '\r') are defined? The
only problem with these are quality of implementation issues.

It says that \f (form feed) "moves the active position to the initial
position at the start of the next logical page."

I don't see anything there about clearing the screen.

I think we all know by now that *some* terminals and terminal
emulators will clear the screen in response to a formfeed characters,
and some will not. (It happens that most of the ones I use or have
access to don't. I suspect my experience in this case is typical; I
certainly don't claim that it's universal.)

In my opinion, the statement in question 19.4 of the FAQ that clearing
the display by printing a formfeed character is "halfway portable" is
incorrect, or at least over-stated.

I agree with you vis-a-vis '\f', but my reply above was an
attempt to paint a larger picture---that it is indeed possible to
``edit'' something that is already written on the screen, if not
by '\f', then by '\r' or '\b' on the current line.

Tak-Shing