Raw mode

Learn to put the terminal in raw mode.

What is raw mode?

Raw mode turns off the terminal's line mode and other processing; each keystroke reaches the program immediately. The cfmakeraw(&t) helper function brings the struct termios struct into raw mode; it clears ICANON, ECHO and many other flags.

It can also be done manually: t.c_lflag &= ~(ICANON | ECHO);. Before switching to raw mode, save the old settings with tcgetattr and restore them on exit with tcsetattr. For testing, printf("raw: 1\n") after cfmakeraw gives a deterministic output.

The cfmakeraw pattern

The typical flow: struct termios t;, read with tcgetattr(STDIN_FILENO, &t);, switch to raw with cfmakeraw(&t);, apply with tcsetattr(STDIN_FILENO, TCSANOW, &t);. On exit, restore the old settings.

For testing, the goal is to show the cfmakeraw call. tcsetattr may fail without a real terminal; but printf("raw: 1\n") still runs and is deterministic. In real apps, a function that restores the old settings is registered with atexit; so the terminal returns to normal mode when the program exits.

Exercise Switch to raw mode

Declare struct termios t;. Read with tcgetattr(STDIN_FILENO, &t);. Switch to raw mode with cfmakeraw(&t);. Print the state with printf("raw: 1\n");.

Show example solution

#include <stdio.h>
#include <termios.h>
#include <unistd.h>

int main(void) {
    struct termios t;
    tcgetattr(STDIN_FILENO, &t);
    cfmakeraw(&t);
    printf("raw: 1\n");
    return 0;
}

Test yourself

Match raw mode parts

cfmakeraw

Sets raw mode
ICANON

Line mode
ECHO

Echo back
c_lflag

Local mode
Which flag is cleared in raw mode?
- O_NONBLOCK
- F_SETLK
- STDIN_FILENO
- ICANON
Show answer

ICANON — ICANON, the line mode flag, is cleared; each key arrives instantly.
cfmakeraw call
```
cfmakeraw(&____);
```
Show answer
```
cfmakeraw(&t);
```

Next lesson: Non-blocking input

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies