Bug 341157

FWIW, I tried qterminal (https://github.com/qterminal), whose code was originally based on konsole. As in konsole, the qt4 version works OK but the qt5 version does not send CTRL+Space so either qterminal and konsole both do the same thing wrong or this is broken at a deeper level in qt5. Notice that you can't send CTRL+@ either, so this looks like something deeper than keyboard bindings, i.e., it looks like konsole/qterminal cannot send ASCII char 0.

Arch Linux x86_64

Name           : konsole
Version        : 14.12.1-1

Name           : plasma-workspace
Version        : 5.1.2-5

Name           : qt5-base
Version        : 5.4.0-3

Prior to "Transition of KDE software to the KDE Framework and Qt 5" update in Arch Linux, Ctrl-Space & Ctrl-@ were working in Konsole (Emacs).  They continue to work in rxvt and in the Emacs GUI app.  

This bug can be reproduced using `showkey -a' in Konsole.

This bug is a major annoyance for all Emacs developers using  "Konsole" since Ctrl-Space is one of the most heavily used and fundamental keybindings.

I found the same behaviour when trying to use the vimwiki vim plugin, which uses ctrl+space to tick items as done in todo lists. I'm using konsole 14.12 / qt5-base 5.4.0 / kde worskpace 4.11.15 on Arch Linux.

If it is of any help, I found that Yakuake running Qt4 still get the null-byte, while Konsole running Qt5 does not. Both are in from the same plasma5 session

$ yakuake --version
Qt : 4.8.6
Plate-forme de développement de KDE : 4.14.4
Yakuake : 2.9.9

$ konsole --version
Qt: 5.4.0
KDE Development Platform: TODO
Konsole: 3.0.1


Archlinux again

If you edit terminal layout and find "Ctrl + Space" and set it to \x0 then press ok and open again edit window the binding has been erased. This does not happen when \x1 is set as binding

In midnight commander is used Ctrl + space to show size of directory.
Work around is to use F9 -> Command -> Shou directory sizes. It is not user friendly.
So bug is not only for emacs users...

I can still reproduce this with Konsole 3.0.1 from Applications 14.12.2.

cool-retro-term also has this exact issue: https://github.com/Swordfish90/cool-retro-term/issues/203

It appears to be related to Qt 5.4.

*** Bug 343097 has been marked as a duplicate of this bug. ***

Have submitted a review request: https://git.reviewboard.kde.org/r/122711/

Thanks - I'll look at this to get into the next release

Git commit 9d062f1f522a50aa5ec2ae2a95ce6124b4427b5b by Kurt Hindenburg.
Committed on 07/03/2015 at 14:42.
Pushed by hindenburg into branch 'master'.

Make Ctrl+Space work again

Qt5.4 appears to have caused this issue. Test using showkey, mc, emacs

Thanks to Chirag Anand anand chirag gmail com for fix
REVIEW: 122711

M  +1    -1    src/KeyboardTranslator.cpp
M  +1    -1    src/Vt102Emulation.cpp

http://commits.kde.org/konsole/9d062f1f522a50aa5ec2ae2a95ce6124b4427b5b

Git commit c16fc7d4671edf14c47132be0c621b08bce7dc82 by Kurt Hindenburg.
Committed on 07/03/2015 at 14:42.
Pushed by hindenburg into branch 'Applications/15.04'.

Make Ctrl+Space work again

Qt5.4 appears to have caused this issue. Test using showkey, mc, emacs

Thanks to Chirag Anand anand chirag gmail com for fix
REVIEW: 122711
(cherry picked from commit 9d062f1f522a50aa5ec2ae2a95ce6124b4427b5b)

M  +1    -1    src/KeyboardTranslator.cpp
M  +1    -1    src/Vt102Emulation.cpp

http://commits.kde.org/konsole/c16fc7d4671edf14c47132be0c621b08bce7dc82

Since I am using chinese input method, so ctrl-space is used by the ime. To use emacs, I have to use the ^@ in order to set mark.

However this bug seems still present in the following version:

fortitude@fortitude:~$ konsole --version
QCoreApplication::arguments: Please instantiate the QApplication object first
Qt: 5.5.1
KDE Frameworks: 5.19.0
Konsole: 15.12.2

While in urxvt everything is ok.

(In reply to fortitude.zhang@gmail.com from comment #14)
> Since I am using chinese input method, so ctrl-space is used by the ime. To
> use emacs, I have to use the ^@ in order to set mark.
> 
> However this bug seems still present in the following version:
> 
> fortitude@fortitude:~$ konsole --version
> QCoreApplication::arguments: Please instantiate the QApplication object first
> Qt: 5.5.1
> KDE Frameworks: 5.19.0
> Konsole: 15.12.2
> 
> While in urxvt everything is ok.

If I added a 2+Ctrl keybinding for konsole profile manually, Ctrl+2 will work for emacs. However, add @+Ctrl or 2+Shift+Ctrl does not work yet.

This issue is not resolved for me:

Linux 4.4.0-31-generic #50-Ubuntu SMP Wed Jul 13 00:06:14 UTC 2016 i686 i686 i686 GNU/Linux

Qt: 5.5.1
KDE Frameworks: 5.18.0
Konsole: 15.12.3

(In reply to fortitude.zhang@gmail.com from comment #15)
> If I added a 2+Ctrl keybinding for konsole profile manually, Ctrl+2 will
> work for emacs. However, add @+Ctrl or 2+Shift+Ctrl does not work yet.

(In reply to sabrewolfy from comment #16)

Can you please post the output of $ showkey -a?

Chirag Anand: That command waits for me to press keys. Pressing Ctrl-Space doesn't do/output anything. It's not clear what you're asking for ... ?

(In reply to sabrewolfy from comment #18)
> Chirag Anand: That command waits for me to press keys. Pressing Ctrl-Space
> doesn't do/output anything. It's not clear what you're asking for ... ?

If you can try running that command in another application, say xterm, then we would make sure this is a Konsole issue and not some system/keymap or some other issue.

Ctrl-Space works in xterm on the same system.