Getting CTRL characters with NCurses

Question

How are control keys obtained from the NCurses library? I need to know if a result from getch () is a character pressed with ctrl, and what character was pressed with it. I googled "ctrl keys ncurses" and "control keys ncurses" without much results.

I know from a quick test that (at least in my case) all the CTRL characters are related to the characters by a difference of 96.

ie

akey is 97
^Akey is 1
bkey is 98
^Bkey is 2
ckey is 99
^Ckey is 3

But this doesn't seem like reliable information to write a program with. Does anyone know a way of doing this?

Community · Accepted Answer · 2020-06-20 09:12:55Z

2

Beyond the straight ASCII-tests, with ncurses you can use the unctrl or keyname functions to return a string which has the relevant information parsed:

if the length of the returned string is one, it is a simple character
if the length is two, and the first character is ^, then it is a control character and the corresponding canonical pressed-with character is the second character of the string.

Keep in mind that there may be several possibilities for pressed-with, since Shift is ignored, and there are a few special cases such as ControlSpace versus Control@ which can produce the same result.

That's with ncurses: other implementations of unctrl may return a null pointer for character codes 128-255. X/Open Curses is vague on what should be done in that case.

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Nov 1, 2017 at 8:24

Thomas Dickey

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Comments

Mwiza · Accepted Answer · 2017-10-31 21:21:11Z

1

That actually is reliable (but with 64, not 96). Ctrl+A all the way through Ctrl-_ are handled properly (use of Ctrl-@ is discouraged due to other meanings of NUL).

edited Oct 31, 2017 at 21:21

Mwiza

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answered Jul 14, 2013 at 0:16

Ignacio Vazquez-Abrams

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1 Comment

tay10r Over a year ago

I see, the difference between lower and upper case is 32, which is why I saw 96 instead of 64. Thanks!

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