key.c

/*
 * Example of getting keystrokes non-blocking
 * 2014 - Rafael Zurita 
 * Based on : http://cc.byexamples.com/2007/04/08/non-blocking-user-input-in-loop-without-ncurses/
 */

#include<stdio.h>
#include<termios.h>
#include<unistd.h>
#include<sys/select.h>
#include<sys/time.h>


//kbhit, Non-blocking keypress detector, when go keypress, return 1 else always return 0
int kbhit()
{
    struct timeval tv;
    fd_set fds;
    tv.tv_sec = 0;
    tv.tv_usec = 0;
    FD_ZERO(&fds);
    FD_SET(STDIN_FILENO, &fds); //STDOUT_FILENO is 0
    select(STDIN_FILENO+1, &fds, NULL, NULL, &tv);
    return FD_ISSET(STDIN_FILENO, &fds);
}

#define NB_DISABLE 1
#define NB_ENABLE 0

void nonblock(int state)
{
    struct termios ttystate;

    //get the terminal state
    tcgetattr(STDIN_FILENO, &ttystate);

    if (state==NB_ENABLE)
    {
        //turn off canonical mode
        ttystate.c_lflag &= ~ICANON;
        //minimum of number input read.
        ttystate.c_cc[VMIN] = 1; 
    }
    else if (state==NB_DISABLE)
    {
        //turn on canonical mode
        ttystate.c_lflag |= ICANON;
    }
    //set the terminal attributes.
    tcsetattr(STDIN_FILENO, TCSANOW, &ttystate);

}

int main()
{
    char c;
    int i=0;
    
    nonblock(NB_ENABLE);
    while(!i)
    {
        usleep(1);
        i=kbhit();
        if (i!=0)
        {
            c=fgetc(stdin);
            if (c=='q')
                i=1;
            else
                i=0;
        }

//        fprintf(stderr,"%d ",i);
    }
    printf("\n you hit %c. \n",c);
    nonblock(NB_DISABLE);

    return 0;
}