how to implement 'press n within 5 secs to terminate..' type of code

aru_04 · 11-17-2005, 04:48 AM

greetings everybody!
I was trying to write a piece of code in C (similar to the messages found during bootup in Linux sometimes.)
The program should display a message like-
'Proceeding to phase2...(press 'n' within 5 secs to exit)'
if the user types in 'n' before 5 secs are up, the program should
exit,else after 5 secs, the program should go on to the next phase.
I am trying to use alarm(5) and loop type of mechanism to implement this
but the problem is:
To take an input from the user we have to use input-fns like getchar(),
which block for user-input and if the user doesn't input anything,the
loop continues forever and the program doesn't move forward.
Any ideas how to implement this ,mates?
(forgive me if this proves to be childishly simple though..sometimes,
during programming, your mind really gets blocked misses the little things.
regards,
aru

bigearsbilly · 11-17-2005, 05:27 AM

HAHA that old chestnut

you will need to play with termios.
tcsetattr tcgetattr.

look up man pages.
here's a shell script (messy) to give you a clue to values to set.
the stty bits are basically the same as what you need for tcsetattr

Code:

#!/bin/ksh


trap cleanup EXIT HUP TERM

save=`stty -g`
count=0

cleanup()
{
    stty $save
    echo '\033c'
}

get_key()
{
     2>/dev/null dd bs=10 count=1
}

ttyset()
{
# if min is zero it won't wait
# if min is 1 it waits for 1 char etc.
#
#
# if it's zero it doesn't wait if it's non-zero
# it returns the minimum amount
     
stty    cs8 -icanon igncr \
             min 1\
             time 0\
             -echo isig -xcase \
             -inpck -opost
}

ESC=


echo '\033c'
echo "\n\nPress a key (q = quit)"
ttyset
while true ;do
    x=`get_key`
    count=`expr $count + 1`
     [ "$x" = q ] && exit
    # [ "$x" = $ESC ] && break

    echo '\033[H' "$count\033[10H\033[1K got"
    print  -n "$x           "|od -c
done
print  -n "$x"|od -c

Wim Sturkenboom · 11-17-2005, 08:56 AM

My solution would be:
Use select and add stdin to the rdfds. Select will timeout if nothing has happened on the filedescriptor, else you can check the input with e.g. read.
To just handle a keypress instead of having to wait for <enter> as well, have a look at cfmakeraw.

vivekr · 11-17-2005, 11:02 AM

Hai buddy,
I think this piece of code will work.

Code:

#include<stdio.h>
#include<time.h>
#include<conio.h>

void main()
{
	char ch;
	time_t t;
	printf(" Press \'n\' within 5 secs:");
	t=time(NULL);
	while(!kbhit())
               {	
		if(time(NULL)-t>=5)
		{
			printf("\n Provided time expired");
                                               return;   
		}
	}    
	if((ch=getche())=='n')
	{
		printf("Hello"); // do whatever u want
	}
}

I did this using MS Visualstudio-
Good luck

Wim Sturkenboom · 11-17-2005, 01:54 PM

Quote:

Originally posted by vivekr
[B]Hai buddy,
I think this piece of code will work.
.....
.....
I did this using MS Visualstudio-

Although it's not stated that the code should run under Linux, I assume that that's more than likely the case on this forum.
I could not compile the code on my RH8 box.
1) I could not find conio.h in the include files on my RH8 box (and the compiler complains)
2) man kbhit does not give results on RH8 or Slack10 (and the linker complains as well)

keefaz · 11-17-2005, 07:02 PM

You could use select() like :

Code:

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/errno.h>

#define SECONDS_2_WAIT 5

int main (int argc, char * argv[]) {

	fd_set set;
	struct timeval timeout;
	int t = 1;
	
	/* Initialize the file descriptor set. */
	FD_ZERO (&set);
	FD_SET (STDIN_FILENO, &set);

	/* Initialize the timeout data structure. */
	timeout.tv_sec = SECONDS_2_WAIT;
	timeout.tv_usec = 0;

	printf("Proceeding to phase2...(press 'n' within 5 secs to exit)\n");

	while(1) {
		/* select returns 0 if timeout, 1 if input available, -1 if error. */
		t = select (FD_SETSIZE, &set, NULL, NULL, &timeout);
		if(t == 1) {
			
			if('n' == getchar()) {
				printf("Exiting, char 'n' was typed...\n");
				return 0;
			}
		
		} else if(t == 0) { /* timeout */
			break;

		} else { /* error */
			printf("select() error: %i\n", errno);
			return 1;
		}
		
	}
	printf("Ok timeout, continue...\n");
	return 0;
}

See more infos at :
http://www.gnu.org/software/libc/man...r-I_002fO.html

vivekr · 11-18-2005, 01:17 AM

To keefaz,
can u explain about select function please.

Thank you.

paulsm4 · 11-18-2005, 01:44 AM

vivekr -

1. The problem with "conio.h" and "kbhit()" is that it's specific to DOS (not even Windows, unless you're in a command prompt).

2. "select()" is an EXTREMELY powerful, EXTREMELY useful Unix call for waiting on the first of any number of possible inputs: for example, a mouse click OR a key press OR a socket read OR a timeout. You can find more here:

a) man 2 select

b) http://linuxgazette.net/issue76/marinov.html
<= THIS IS A *GREAT* LITTLE HOWTO;
AMONG OTHER THINGS, IT DISCUSSES HOW TO DO A "KBHIT()" USING "SELECT()"...