Question

How would I effectively cancel a call for user input if there is no input within a certain time? (I’m programming a game for a terminal/cmd window with Mac OS X).

I have tried turning off canonical buffering and using a timer thread that joins after the call for user input. I also tried implementing the call to pthread_join() within the parameters of the while loop. Still nothing. The problem is that even though canonical buffering is off, the call for user input is still held up when there is no input. It works fine if there is input though.

It would be great if I could do this without fiddling around with downloading and installing ncurses, but I’ll do it if I have to.

Edit: Source code:

//Most headers only pertain to my main program. 
#include <iostream>
#include <termios.h>
#include <pthread.h>
#include <time.h>
#include <cstring>
#include <stdio.h>
#include <string.h>

using namespace std;

//Timer function.
void *Timer(void*) {

    time_t time1, time2;

    time1 = time(NULL);

    while (time2 - time1 < 1) {
        time2 = time(NULL);
    }

    pthread_exit(NULL);
}

int main() {

    //Remove canonical buffering.
    struct termios t_old, t_new;
    tcgetattr(STDIN_FILENO, &t_old);
    t_new = t_old;
    t_new.c_lflag &= ~ICANON;
    tcsetattr(STDIN_FILENO, TCSANOW, &t_new);

    cout << "Press any key to continue." << endl;

    string szInput;

    int control = 0;

    do {

        pthread_t inputTimer;

        pthread_create(&inputTimer, NULL, Timer, NULL);

        szInput = "";

        while (szInput == "") {

            szInput = cin.get();


            //Handle keypresses instantly.
            if (szInput == "a") {
                cout << endl << "Instant keypress." << endl;
            }
        }    

        pthread_join(inputTimer, NULL); 

        cout << endl << "One second interval." << endl;

        control ++;

    } while (control < 25);

    cout << "Game Over." << endl;

    return 0;

}

Answer 1

One way of checking if there is input is to poll the file descriptor STDIN_FILENO using e.g. the select system call. If STDIN_FILENO is readable, then you can read at at least one character. You can also pass a timeout to the select call.