Which keyboard characters can be read with getchar() on Linux

Question

I have a C++ application running on Ubuntu that waits for a key press using getchar() function. The input is not used, I just end my program with any keypress.

I noticed I could type basically any printable character, but also some unprintable characters such as the escape and backspace keys. Keys that did not trigger the ending of my program were keys such as shift and ctrl.

So my question is, which key presses get read by getchar()? How can I classify those, since apparantly not only printable characters trigger getchar()?

I could not find the answer in the man page or the C++ reference.

This is basically all the code I wrote:

std::cout << "Ready for input ..." << std::endl;
std::getchar();
std::cout << "A key was pressed, landing ..." << std::endl;

Mind that I do manipulate termios to not wait for a newline character and to not echo.

Is it not all characters? in windows, it is working for almost keys. did u write any code? — MasOOd.KamYab, Apr 26 '18 at 08:31
Try to use curses library if you want an easy way to handle it — Ôrel, Apr 26 '18 at 08:32
I did not ask how I could handle it @Ôrel, just how getchar() works. — Marthe Veldhuis, Apr 26 '18 at 08:39
https://code.woboq.org/userspace/glibc/libio/getchar.c.html `getchar()` uses a _buffered_ input, you can read the raw input if you really need it — Ôrel, Apr 26 '18 at 09:10

score 1 · Accepted Answer · answered Apr 26 '18 at 14:10

1

So it turns out the keys that getchar() does not catch are Modifier keys. Maybe just because they are simply "modifiers" and always are used together with another key to create a specific charater. If anyone knows the particular reason, I would like to know.

answered Apr 26 '18 at 14:10

Marthe Veldhuis

316
2
16

That's a bit too simple. Is '\`' a modifier key? On my keyboard, the answer varies depending on the language I'm using. When I'm writing code or English, the answer is no. When I use languages that have the letter à, I use ` as a modifier. – MSalters Apr 26 '18 at 15:02
1

@MSalters In the references I saw, modifier keys are defined as not triggering an action by themselves, just entering a sort of [mode](https://en.wikipedia.org/wiki/Mode_(computer_interface)#Quasimodes). So I do not think '`' is a modifier key, you kinda proved it by typing it? Wikipedia calls those [dead keys](https://en.wikipedia.org/wiki/Dead_key) apparently, since you have to press and release them before they modify the next character typed. – Marthe Veldhuis Apr 27 '18 at 21:28
I type ` by typing a space afterwards. So yes, that's two keys for one character. – MSalters Apr 27 '18 at 22:58
1

So again that is a "dead key" then, and not a "modifier key" since you need to press and release them before they alter te next character instead of just the press. – Marthe Veldhuis Apr 28 '18 at 11:33

score -1 · Answer 2 · answered Apr 26 '18 at 09:24

-1

getchar reads from stdin, not directly from the keyboard. The bit that you're missing is hinted at by your assumption of "keyboard characters". That's missing the translation from key presses to characters. For instance, the key presses Shift+a produces A. How you enter à depends on the xact keyboard configuration.

answered Apr 26 '18 at 09:24

MSalters

173,980
10
155
350

I see the difference now, though this does not answer my question. See my answer below. – Marthe Veldhuis Apr 26 '18 at 14:12

Which keyboard characters can be read with getchar() on Linux

2 Answers2