termios

/****************************************************************************
 * Terminal I/O                                                             *
 * Normally, on Unix, ctrl-C refers to "cancel" and ctrl-D refers to EOF.   *
 * What if we want to change that? This program will change the default     *
 * keys to something else using <termios.h> defined in POSIX.1 standard.    *
 * ** Note: this program can't run on ideone.com as we have to enter input  *
 * interactively. I presume that ideone.com only take input in HTML form    *
 * prior to running the program. So I use pastebin.com, instead.            *
 * You can still copy the code and paste it on Unix terminal to test it.    *
 ****************************************************************************/

#include <unistd.h>     /* isatty(3), fpathconf(2) */
#include <termios.h>    /* tcgetattr(3), tcsetattr(3) */
#include <stdio.h>
#include <stdlib.h>     /* exit(3) */

int main(void)
{
    struct termios newterm, oldterm; /* Declare new and old terminal. */
    long vdisable;

    /* Check if stdin is a terminal (tty) using isatty(3).                  *
     * isatty stands for "Is A TTY?".                                       *
     * Note: stdin is a (FILE *) and  STDIN_FILENO is a file descriptor.    *
     * But both refer to the same thing.                                    */
    if (isatty(STDIN_FILENO) == 0) {
        fprintf(stderr, "standard input is not a terminal device");
        exit(EXIT_FAILURE);
    }

    /* pathconf or fpathconf family is used to get configurable pathname    *
     * variables. It returns the current variable value.                    *
     * - pathconf(2) takes (FILE *) as the first argument.                  *
     * - fpathconf(2) takes a file descriptor as the first argument.        *
     * The following lines of code, we are trying to get terminal character *
     * disabling value (_PC_VDISABLE). We can also get the others value,    *
     * see fpathconf(2). The following lines, we call fpathconf(2) and set  *
     * char disabling value to vdisable.                                    */
    if ((vdisable = fpathconf(STDIN_FILENO, _PC_VDISABLE)) == -1) {
        fprintf(stderr, "fpathconf error or _POSIX_VDISABLE not in effect");
        exit(EXIT_FAILURE);
    }

    /* tcgetattr stands for Terminal Control Get Attribute. We get the      *
     * current attribute of STDIN_FILENO (stdin) and store it in 'oldterm'. */
    if (tcgetattr(STDIN_FILENO, &oldterm) == -1) {
        fprintf(stderr, "tcgetattr");
        exit(EXIT_FAILURE);
    }
    newterm = oldterm;              /* Copy "oldterm" to "newterm".         */
    newterm.c_cc[VINTR] = vdisable; /* Disable INTR character in "newterm". */
    newterm.c_cc[VEOF] = 2;         /* EOF is now ctrl-B in "newterm".      */
    /* We can find c_cc index in /usr/include/termios.h . */

    /* We now set the attribute of our modified "newterm" to STDIN_FILENO.  *
     * For details for the 2nd arg, consult man pages tcsetattr(3).         *
     * This example, we want it to take into effect immediately. So we use  *
     * TCSANOW.                                                             */
    if (tcsetattr(STDIN_FILENO, TCSANOW, &newterm) == -1) {
        fprintf(stderr, "tcsetattr");
        exit(EXIT_FAILURE);
    }
    printf("try repeating ^C, ^D then close with ^B or <enter>:");
    getchar();

    /* We now restore "oldterm", which we previously saved, back to normal  *
     * attribute, prior to end of program.                                  */
    if (tcsetattr(STDIN_FILENO, TCSANOW, &oldterm) == -1) {
        fprintf(stderr, "tcsetattr");
        exit(EXIT_FAILURE);
    }
    fputs("\n", stdout);

    return 0;
}