Rolling String Buffer needed

Ruby
1

I have constant ascii data streaming in, each message terminated with
\n, currently I look for something specific and throw away the other
stuff and then look for something specific and throw away the other
stuff…etc

What I need now is a way to keep everything received exactly as is, in a
rolling string buffer. So say the last 100 messages (a message to me is
a whole string terminated with \n) which could be available at any time
in a string variable, maybe called: last_100_messages

And when I append another variable length message/line to this string
buffer that ends with a \n, I want the oldest message to go
away(specifically go into a text file), so ALL messages are available in
a text file for later.

Problem is the append << method, puts the new lines on the end of the
string, I want the end of the string to always be the oldest message
that is about to be placed into a txt file that has all messages at some
point.

So in short, a rolling buffer that holds a specific amount of \n
terminated messages(100 strings terminated with \n’s), not a specific
amount of data/bytes. Where the front of the string holds the most
recent addition to the rolling buffer, and where the end of the string
holds the message that is about to be added to a file.

Also if easier, an array where each element is one message would work as
well, where array[0] is the most recent message.

I have been looking at strio, but not sure how to use it in this manner.

Thanks a lot for your input,
Matt

2

On Oct 2, 2009, at 9:55 AM, Matt B. wrote:

time

holds the message that is about to be added to a file.

Also if easier, an array where each element is one message would
work as
well, where array[0] is the most recent message.

I have been looking at strio, but not sure how to use it in this
manner.

I think you could just write a class that wraps up a list. Something
like this:

class MyBuff
def initialize max_size, filename
@max_size = max_size
@list = []
@file = File.open(filename, ‘wb’)
end

def push string
@list.push string
while @list.length > @max_size
@file.write @list.pop
end
end

def [] i
@list[i]
end
end

Aaron P.
http://tenderlovemaking.com

3

Aaron P. wrote:

class MyBuff
def initialize max_size, filename
@max_size = max_size
@list = []
@file = File.open(filename, ‘wb’)
end

def push string
@list.push string
while @list.length > @max_size
@file.write @list.pop
end
end

def [] i
@list[i]
end
end

Aaron P.
http://tenderlovemaking.com

That looks great! So when I do pop on an array it does the highest
index element? And when you push onto an array it puts it in index 0 ?

Thanks!
Matt

4

Justin C. wrote:

If you want it to act like a queue with the last element being the head,
then use pop/unshift.

irb(main):001:0> a = [1,2,3,4]
=> [1, 2, 3, 4]
irb(main):002:0> a.pop
=> 4
irb(main):003:0> a.unshift 5
=> [5, 1, 2, 3]
irb(main):004:0> a.pop
=> 3
irb(main):005:0> a
=> [5, 1, 2]

-Justin

Awesome, I think I need the last approach. So incorporating it into the
class, I have…

class MyBuff
def initialize max_size, filename
@max_size = max_size
@list = []
@file = File.open(filename, ‘wb’)
end

def add_to_front string
  @list.unshift string              #changed to unshift
  while @list.length > @max_size
    @file.write @list.pop
  end
end

def [] i
  @list[i]
end

end

Thanks to all, I think this will work great!
-Matt

5

Matt B. wrote:

 @list.push string

Actually, push/pop works like it’s a stack, with the top being the last
element. So pop removes and returns the last element, while push appends
to the end.

irb(main):001:0> a = [1,2,3,4]
=> [1, 2, 3, 4]
irb(main):002:0> a.pop
=> 4
irb(main):003:0> a.push 5
=> [1, 2, 3, 5]
irb(main):004:0> a.pop
=> 5
irb(main):005:0> a
=> [1, 2, 3]

If you want it to act like a queue with the first element being the
head, then use shift/push.

rb(main):001:0> a = [1,2,3,4]
=> [1, 2, 3, 4]
irb(main):002:0> a.shift
=> 1
irb(main):003:0> a.push 5
=> [2, 3, 4, 5]
irb(main):004:0> a.shift
=> 2
irb(main):005:0> a
=> [3, 4, 5]

If you want it to act like a queue with the last element being the head,
then use pop/unshift.

irb(main):001:0> a = [1,2,3,4]
=> [1, 2, 3, 4]
irb(main):002:0> a.pop
=> 4
irb(main):003:0> a.unshift 5
=> [5, 1, 2, 3]
irb(main):004:0> a.pop
=> 3
irb(main):005:0> a
=> [5, 1, 2]

-Justin

6

VTD-XML 2.7 is released and can be downloaded at

Below is a summary of what are the new features and enhancements.

Expanded VTD-XML’s Core API

  • VTDNav: toStringUpperCase, toStringLowerCase, contains(), endsWith(),
    startsWith()
  • Extended VTD added in-memory buffer support

Improved Xpath

  • added the following XPath 2.0 functions: abs(), ends-with(),
    upper-case(),
    lower-case()
  • added support for variable reference
  • significantly enhanced XPath syntax, checking error reporting (Special
    thanks to Mark Swanson)
  • Internal performance tuning

Bug fixes and Code Enhancement

  • C version significantly removed warning message, fix memory leak
    during
    Xpath expression parsing,
  • Various bug fies (Special thanks to Jon Roberts, John Zhu, Matej
    Spiller,
    Steve Polson, and Romain La Tellier)