How to skip getchar in C?

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10-01-2010

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How to skip getchar in C?

Hi,
I would like to read an input from keyboard using getchar. However, if no input (No Carriage return/new line none whatsoever) is given after say, 5 seconds, I would like to skip the getchar and move on. How do I do this in C. I'm using GNU compiler set.

Thanks,

cprogdude

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10-01-2010

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You can't do this with getchar(), you'll have to use read() instead. More details in a bit.

---------- Post updated at 03:31 PM ---------- Previous update was at 03:19 PM ----------

This should timeout at 5 seconds. The timeout happens in the terminal itself.

Code:

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

int main(void)
{
        int c;
        // Save sane TTY settings
        system("stty -g > ~/.stty-save");
        // Set TTY timeout of 50 tenths of a second, minimum read size 0
        system("stty -icanon min 0 time 50");

        while(read(STDIN_FILENO, &c, 1) == 1)
        {
                fprintf(stderr, "read 1 bytes\n");
        }

        // Restore sane tty settings
        system("stty $(cat ~/.stty-save)");
        return(0);
}

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10-02-2010

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Be sure to check your man page for termios. termios has tcgetattr and tcsetattr to perform terminal settings from within C.

Last edited by jim mcnamara; 10-02-2010 at 11:12 AM..

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10-04-2010

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Quote:

Originally Posted by Corona688

You can't do this with getchar(), you'll have to use read() instead. More details in a bit.

---------- Post updated at 03:31 PM ---------- Previous update was at 03:19 PM ----------

This should timeout at 5 seconds. The timeout happens in the terminal itself.

Code:

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

int main(void)
{
        int c;
        // Save sane TTY settings
        system("stty -g > ~/.stty-save");
        // Set TTY timeout of 50 tenths of a second, minimum read size 0
        system("stty -icanon min 0 time 50");

        while(read(STDIN_FILENO, &c, 1) == 1)
        {
                fprintf(stderr, "read 1 bytes\n");
        }

        // Restore sane tty settings
        system("stty $(cat ~/.stty-save)");
        return(0);
}

Thanks man. I use "select" it works but the problem is I'm unable to flush my input stream. How do I do that?

cprogdude

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10-04-2010

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Quote:

Originally Posted by cprogdude

I'm unable to flush my input stream. How do I do that?

I'm not quite sure of your meaning. Discard existing input? Won't read() do that?

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10-04-2010

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I have never used it, but does setting the non-blocking flag on stdin work?

Code:

int ctrlflags;
ctrlflags = fcntl(stdin, F_GETFL);
ctrlflags |= O_NONBLOCK;
fcntl(stdin, F_SETFL, ctrlflags);

If so, then you can loop on that until you get something.

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