How to read user input without pressing ENTER?

Question

I'm writing code where I need to get input without the user pressing ENTER. The code is basically that I need to get 4 numbers from 1-6 without the user pressing ENTER all in one line.

I tried doing so with getchar(), but it doesn't work.

How do I do that?

Here's that part of the code:

int p1 = 0;
int p2 = 0;
int p3 = 0;
int p4 = 0;
p1 = getchar() - 48;
p2 = getchar() - 48;
p3 = getchar() - 48;
p4 = getchar() - 48;

There is no standard function for this. You will have to use something OS-specific. Note that the original designers of C used a separate terminal that didn't send anything to the computer until you pressed Enter. — BoP
– BoP, Commented Jan 1, 2022 at 10:05
Enter them all on one line, without spaces, and press <Enter> once. For example 1234<Enter>. Aside: please replace the "magic number" 48 with '0'. — Weather Vane
– Weather Vane, Commented Jan 1, 2022 at 10:11
How about getting input as a string line, split and convert it to integer ? — Gresta
– Gresta, Commented Jan 1, 2022 at 11:54

Jens · Accepted Answer · 2022-01-01 11:32:12Z

This is a C FAQ: 12.5 How can I read one character at a time, without waiting for the RETURN key?

To quote:

Depending on which operating system you're using and what libraries you have available, you may be able to use one (or more!) of the following techniques:

If you can use the curses library, you can call cbreak [footnote] (and perhaps noecho), after which calls to getch will return characters immediately.
If all you're trying to do is read a short password without echo, you may be able to use a function called getpass, if it's available. (Another possibility for hiding typed passwords is to select black characters on a black background.)
Under classic versions of Unix, use ioctl and the TIOCGETP and TIOCSETP (or TIOCSETN) requests on file descriptor 0 to manipulate the sgttyb structure, defined in <sgtty.h> and documented in tty(4). In the sg_flags field, set the CBREAK (or RAW) bit, and perhaps clear the ECHO bit.
Under System V Unix, use ioctl and the TCGETAW and TCSETAW requests on file descriptor 0 to manipulate the termio structure, defined in <termio.h>. In the c_lflag field, clear the ICANON (and perhaps ECHO) bits. Also, set c_cc[VMIN] to 1 and c_cc[VTIME] to 0.
Under any operating system (Unix or otherwise) offering POSIX compatibility, use the tcgetattr and tcsetattr calls on file descriptor 0 to manipulate the termios structure, defined in <termios.h>. In the c_lflag field, clear the ICANON (and perhaps ECHO) bits. Also, set c_cc[VMIN] to 1 and c_cc[VTIME] to 0.
In a pinch, under Unix, use system (see question 19.27) to invoke the stty command to set terminal driver modes (as in the preceding three items).
Under MS-DOS, use getch or getche, or the corresponding BIOS interrupts.
Under VMS, try the Screen Management (SMG$) routines, or curses, or issue low-level $QIO's with the IO$_READVBLK function code (and perhaps IO$M_NOECHO, and others) to ask for one character at a time. (It's also possible to set character-at-a-time or ``pass through'' modes in the VMS terminal driver.)
Under other operating systems, you're on your own.

Rillian Grant · Accepted Answer · 2022-01-01 11:19:03Z

0

There is no standard function for this.

There are some custom solutions e.g. https://www.cs.uleth.ca/~holzmann/C/system/ttyraw.c But your mileage may vary.

However if this kind of dynamic use of the terminal is core to your program I would recommend using ncurses or something similar.

answered Jan 1, 2022 at 11:19

Rillian Grant

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