termios
- C course
- Advanced
- Lesson 43/83
- 5 min
Learn terminal configuration with termios.
What is termios?
termios is the POSIX terminal settings structure. struct termios is declared in <termios.h>; it holds the terminal's input processing, output processing and local mode settings. You read the current settings with tcgetattr(fd, &t) and apply new ones with tcsetattr(fd, TCSANOW, &t).
Important fields: c_lflag for local mode (e.g. ICANON enables line mode), c_oflag for output mode, c_iflag for input mode. STDIN_FILENO is usually the terminal descriptor. If the descriptor is not a terminal, tcgetattr returns -1; so for tests, a static printout is safe.
Reading with tcgetattr
tcgetattr(STDIN_FILENO, &t) copies the current terminal settings into struct termios t. You must call it before making changes; otherwise you lose the original settings.
For testing, you can print printf("termios read\n") after the call. If STDIN_FILENO is not a terminal (e.g. in a test environment), tcgetattr fails; but printf still runs. So the output is deterministic. In real apps, you check whether it is a terminal with isatty(STDIN_FILENO) and behave accordingly.
Practice Read terminal settings
Declare struct termios t;. Read the settings with tcgetattr(STDIN_FILENO, &t);. Print the state with printf("termios read\n");.
Starter code
#include <stdio.h>
#include <termios.h>
#include <unistd.h>
// Declare terminal struct
// Read settings
// Print read
int main(void) {
return 0;
}Sample solution
#include <stdio.h>
#include <termios.h>
#include <unistd.h>
int main(void) {
struct termios t;
tcgetattr(STDIN_FILENO, &t);
printf("termios read\n");
return 0;
}Expected output
termios read
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which header declares the termios struct?
- stdlib.h
- stdio.h
- termios.h Correct answer
- math.h
Explanation: struct termios is declared in termios.h.
2 tcgetattr call
tcgetattr(STDIN_FILENO, &____);tcgetattr(STDIN_FILENO, &t);Explanation: tcgetattr takes the address of t and fills the settings.
3 Match termios parts
| Term | Meaning |
|---|---|
tcgetattr |
Reads settings |
tcsetattr |
Applies settings |
c_lflag |
Local mode |
ICANON |
Line mode |