Quit, if a specific key is hit

Excuse me, if this is already discussed… but from from here
http://www.rubyrailways.com/implementing-15-exercises-for-learning-a-new-programming-language/
the author concludes that the following problem cannot be solved… whats
the reason?
“Display series of numbers (1,2,3,4, 5…etc) in an infinite loop. The
program should quit if someone hits a specific key (Say ESCAPE key).”

On Jan 16, 2008, at 11:43 PM, Pavankumar Kulkarni wrote:

Excuse me, if this is already discussed… but from from here <http://www.rubyrailways.com/implementing-15-exercises-for-learning-a-new-programming-language/

… the author concludes that the following problem cannot be
solved… whats the reason?
“Display series of numbers (1,2,3,4, 5…etc) in an infinite loop.
The program should quit if someone hits a specific key (Say ESCAPE
key).”

It can definitely be solved. Here’s a solution that works on most
Unix-like operating systems, for example:

#!/usr/bin/env ruby -wKU

require “io/wait”

state = stty -g
begin
system “stty raw -echo cbreak isig”

 1.upto(1.0/0.0) do |n|
   puts n
   exit if $stdin.ready? and $stdin.getc == 27
 end

ensure
system “stty #{state}”
end

END

What the author actually said was that it can’t solve it without
writing some platform specific code or threads. I don’t know how to
do it without using one of those tricks either.

The reason is that all terminals are different and you are needing to
interact with it on two levels at once (reading while writing). This
is what introduces the need for the platform specific code.

James Edward G. II

On Jan 17, 2008, at 7:28 AM, James G. wrote:

It can definitely be solved. Here’s a solution that works on most
1.upto(1.0/0.0) do |n|
What the author actually said was that it can’t solve it without
writing some platform specific code or threads. I don’t know how
to do it without using one of those tricks either.

The reason is that all terminals are different and you are needing
to interact with it on two levels at once (reading while writing).
This is what introduces the need for the platform specific code.

James Edward G. II

In many of the game libraries, input for different platforms is
addressed.
This one of those cases where the game libraries, such as Gosu or
rubygame, or Ruby/SDL are going to be very useful for a non game.
most game libs have a very fundamental need for input control, and a
pretty important need for crossplatform code abstraction.
You don’t need to know much about them, just enough to get the keys
under your control!
But the plus is, you can also get a GUI up without much work.

Cool… that clears some air!.. Cheers guys!!..
Hail Ruby Community!! :slight_smile:


Pavan
Software Developer
Persistent Systems Ltd, Goa, India

I found a platform independent solution to this in one of the comments
of that link(below) here
http://www.rubyrailways.com/implementing-15-exercises-for-learning-a-new-programming-language/#comment-1145.

i=0
loop do
begin
break if STDIN.read_nonblock(1000)
rescue Errno::EAGAIN
end
puts i
i += 1
end

Cheers,
Pavankumar Kulkarni * Software Developer * Persistent Systems Ltd

On Jan 18, 2008 4:19 AM, Pavankumar Kulkarni wrote:

I found a platform independent solution to this in one of the comments
of that link(below) here
http://www.rubyrailways.com/implementing-15-exercises-for-learning-a-new-programming-language/#comment-1145.
rescue Errno::EAGAIN

I could be wrong, but I was under the impression that all Errnos
were platform-dependant.

Daniel Brumbaugh K.

On Jan 18, 2008 4:19 AM, Pavankumar Kulkarni
[email protected] wrote:

I found a platform independent solution to this in one of the comments
of that link(below) here
http://www.rubyrailways.com/implementing-15-exercises-for-learning-a-new-programming-language/#comment-1145.

That does not fulfill the stated requirements, does it?

i=0
loop do
begin
break if STDIN.read_nonblock(1000)

C defines stdin to be buffered, so characters will pile up in the
buffer until an EOL is seen or the buffer is full. It might be the
case that some platform does not do this, but in general the program
won’t stop until you press a lot of keys or (usually), press enter.

Marcelo

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