Continue running program until user type Ctrl + a

Question

Hi, I'm practicing C programming for Linux for an exam. I don't know how to exit the program when user press Ctrl + a ( not Ctrl+c ) For example, looping something until user press Ctrl+a Could anyone tell me how to check Ctrl+a input?

Notes: I'm using 'gcc' and run output with './a.out'

Thanks in advance for everyone!

Answer 1

There is special support for Ctrl-C, which is translated into a signal by the system. If you want your program to stop as soon as another specific key combination is used, it will be much harder.

• you will need to check the standard input of your program, and you will need to set the standard input so the inputs are not buffered (otherwise you won't see any input until it is validated by the user pressing "return"). The latter part would be done with a ioctl() call and would not be portable;

• you will need either threads or polling, none of which is very palatable in C.

There are more interesting things to practice in C than these.

Answer 2

Turbo C and other implementations of C for Windows had a function call getch() which would read single characters from the keyboard; those would have done what you want.

In POSIX environments, such as are implemented by gcc-compiled programs under Unix/Linux, that functionality isn't directly there.

There's a library called curses which allows C programs to do full-screen output processing, and there is also getch() functionality in curses. This may end up being the simplest answer to your problem. You'll need to read the documentation on curses and link the header files and library into your program.

Answer 3

catching ctrl-c event

This post answers your question

Answer 4

Someone posted first with following code which works for me but I don't know why he deleted his answer.

Original Link : http://www.c.happycodings.com/Gnu-Linux/code18.html

#include <stdio.h>
#include <unistd.h>  /* sleep(1) */
#include <signal.h>

void ex_program(int sig);

int main(void) {
 (void) signal(SIGINT, ex_program);

 while(1)
  printf("sleeping .. ZZZzzzz ....\n"), sleep(1);

 return 0;
}

void ex_program(int sig) {
 printf("Wake up call ... !!! - Catched signal: %d ... !!\n", sig);
 (void) signal(SIGINT, SIG_DFL);
}

Answer 5

This will do what you want:

stty intr ^a
./a.out

For extra credit, do the equivalent of "stty intr ^a" using the appropriate library function, e.g. "man termios".

Answer 6

did you looking for something like this ??? this program won't be stopped since you hit ctrl+A and Enter.

#include <stdio.h>

int main() {
    char a;
    while( a!=1 ) //Ascii code for ctrl + A == 1
    {
        a=getchar();
        printf("still looping ...\n");
    }
    printf( "HA! You pressed CTRL+A\n" );
    return 0;
}

But if you wanna terminate your program just after pressing ctrl+A (without hitting enter after that), here you are:

#include <stdio.h>
#include <ncurses.h>

int main() {
    char a;
    initscr();
    raw();

    while( a!=1 )
        a=getch();

    endwin();
    return 0;
}

for compiling second code using GCC, try this command:

gcc -o program.o -lncurses program.cpp

Answer 7

This is how to set CTRL-A as interrupt to break the process. Notice too that CTRL-C doesn't break it after tcsetattr is called.

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

int main(int argc, char* argv[]) {
    struct termios termios;

    if ( tcgetattr(0, &termios) != -1 ) {
        termios.c_cc[VINTR] = '\x01'; /* CTRL-A */
        if ( tcsetattr(0, 0, &termios) != -1 ) {
            printf("Ready. Press CTRL-A to break this program\n");
            while ( 1 ) {
                printf("*\n");
                sleep(1);
            }
        }
    }
}