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From: olof@ikaros.fysik4.kth.se (Olof Franksson)
Subject: Re: a unix terminal question
In-Reply-To: dps@delhi.esd.sgi.com's message of 11 Jan 93 22:48:02 GMT
Message-ID: <OLOF.93Jan12134356@ikaros.fysik4.kth.se>
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Organization: Physics IV, Royal Institute of Technology, S-100 44 Stockholm,
Sweden
References: <1iql6kINNisk@ub.d.umn.edu>
<1993Jan11.215312.2080@fcom.cc.utah.edu> <uonuhjc@zola.esd.sgi.com>
Date: Tue, 12 Jan 1993 12:43:56 GMT
Lines: 42
> In article <1iql6kINNisk@ub.d.umn.edu> cbusch@ub.d.umn.edu (Chris) writes:
> >
> > How does one read in a character from standard input without having
> >the program wait for the key. Basically, I want to do something like:
> > if(kbhit()) c=getch();
> >Except that is not standard, and I want it to work on all platforms.
>
> This is a bad thing to do, unless you have processing to do when characters
> aren't present, and you do your checks relatively infrequently compared to
> the procesing itself; otherwise, you will be in a buzz-loop and suck your
> CPU through the floor. This is common practice under DOS where there is
> nothing else running, but is a generally bad thing to do.
>
> The CORRECT way to do this: use the select() or poll() system call to
> wait for an interval or a character to be present. Resoloution is
IF one would like to read from a tty in the manner described in
the question from cbusch@ub.d.umn.edu, the fcntl()-call might be
used. The following short example print *-characters with 0-1s
intervalls on standard output until a character appears on standard
input, or 20 *-characters have been printed.
#include <fcntl.h>
main()
{
int ret, fflag, nfflag, i;
fflag = fcntl(0, F_GETFL, 0); /* No wait for char input */
nfflag = fflag | O_NDELAY;
nfflag = fcntl(0, F_SETFL, nfflag);
putchar('*');
for (i = 0; i < 20 && (ret = getchar()) == -1; i++) {
putchar('*');
sleep(1);
}
fcntl(0, F_SETFL, fflag);
putchar('\n');
}