Howto do unbuffered keyboard input.

[Michel van Bergen]

Hi,

I'm new to Linux. For a C console application I need unbuffered keyboard input
(non blocked). I have tried to use select() and poll() but they both buffer
until a '\n'. setvbuf() to set the stream unbuffered don't seem to work.

In some operating systems it's posible to set a signal/event on data available.

Is there a way to do a timed read() that isn't buffered. How to set the the
input stream to unbuffered.

Thanks in advancd for any help.

Michel.

[Nils O. Selåsdal]

Post by Michel van Bergen
Hi,
I'm new to Linux. For a C console application I need unbuffered keyboard input
(non blocked). I have tried to use select() and poll() but they both buffer
until a '\n'. setvbuf() to set the stream unbuffered don't seem to work.

select/poll/read/write works on descriptors, setvbuf on FILE*s, you
shouldn't mix them.

Post by Michel van Bergen
In some operating systems it's posible to set a signal/event on data available.
Is there a way to do a timed read() that isn't buffered. How to set the the
input stream to unbuffered.

an input stream(well, not a FILE* stream) connected to a terminal/tty is
usually
line buffered, you can turn off that
http://www.iso-9899.info/wiki/Snippet_POSIX_STDIN_mode

[Kasper Dupont]

Post by Michel van Bergen
Hi,
I'm new to Linux. For a C console application I need unbuffered keyboard input
(non blocked). I have tried to use select() and poll() but they both buffer
until a '\n'. setvbuf() to set the stream unbuffered don't seem to work.

http://www.daimi.au.dk/~kasperd/comp.os.linux.development.faq.html#termios

[Lew Pitcher]

Post by Michel van Bergen
Hi,
I'm new to Linux. For a C console application I need unbuffered keyboard input
(non blocked). I have tried to use select() and poll() but they both buffer
until a '\n'. setvbuf() to set the stream unbuffered don't seem to work.

That's because you are going down the wrong path, and haven't really
changed the buffering.

What you want to do is read the termios(3) manpage ("man 3 termios") and
tty_ioctl(4) manpage ("man 4 tty_ioctl"), and turn off ICANON parsing on
your terminal.

You have your choice of the termios(3) interface, or the ioctl(2)
interface; ioctl(2) is a low-level interface, while termios(3) is higher
level. I'd suggest sticking with the termios(3) interface.

Your code will look something like...

#include <termios.h>

set_to_raw(int tty_fd)
{
struct termios tty_attr;

tcgetattr(tty_fd,&tty_attr);
tty_attr.c_lflag &= ~ICANON;
tcsetattr(tty_fd,&tty_attr);
}

Of course, you will, at some point, need to set the fd back to ICANON
processing. Just OR back in the ICANON flag at that point.





- --

Lew Pitcher, IT Specialist, Corporate Technology Solutions,
Enterprise Technology Solutions, TD Bank Financial Group

(Opinions expressed here are my own, not my employer's)

[Jan Panteltje]

On a sunny day (Fri, 03 Mar 2006 14:38:37 +0100) it happened Michel van Bergen

Post by Michel van Bergen
Hi,
I'm new to Linux. For a C console application I need unbuffered keyboard input
(non blocked). I have tried to use select() and poll() but they both buffer
until a '\n'. setvbuf() to set the stream unbuffered don't seem to work.
In some operating systems it's posible to set a signal/event on data available.
Is there a way to do a timed read() that isn't buffered. How to set the the
input stream to unbuffered.
Thanks in advancd for any help.
Michel.

You had many nice suggestions, I used this a lot:


#include <stdio.h>

int main(int argc, char **argv)
{
int c;

while(1)
{
/* read a user key */
system("stty raw");

c = getc(stdin);
if(c == 27) break; /* ESCAPE exits */

system("stty sane"); // you can do this later

printf(": c = %d\n", c);
}

exit(0);
}

[Michel van Bergen]

On Fri, 03 Mar 2006 14:38:37 +0100, Michel van Bergen <***@unknown.nl> wrote:

Thanks all.

You put me on the right path

Michel.