From: 7stud -- <bbxx789_05ss@...>
Date: 2007-11-06T08:27:34+09:00
Subject: Re: File Save Question

Tj Superfly wrote:
> Hello!
> 
> I've created a program that will run and update the array storing the
> information within that program. When the program is over, I would like
> the file to save, so th next time I run it, the same information is in
> the array and it will be able to start back where it left off; if that
> makes sense.
> 

You can't.  You have to save the data to a file and then read the data 
back from the file.  One approach would be to write each item in the 
array to a file.   Then, the next time your program runs, you could read 
each item back in from the file and insert it in an array.  However, 
each item you read back will be a string, so if the original item was a 
number, you have to convert to the string back to a number.  That's kind 
of a hassle to do all that.

The ruby standard library yaml will do that all for you.  It allows you 
to write the whole array to the file and then read the whole array back 
in one shot.

One problem you are going to encounter is what to do when you run the 
program the first time.  You can either create the file beforehand and 
leave it blank, e.g.

$touch my_array.yaml  #creates a blank file

and then do this:

arr = YAML.load_file("my_array.yaml")

if !arr
  arr = []
end


Or, you can have your program create the file if it doesn't exist, 
something like this:

require 'yaml'

begin
  arr = YAML.load_file("my_array.yaml")

rescue Errno::ENOENT  #error type is from the error message
                                    #when you open a file that doesn't 
exit

  #The first time the program is run you will
  #get an error saying the file doesn't exist
  #which will make execution jump into here.
  #By putting this rescue block here,
  #the error won't cause your program to
  #terminate.

end

if !arr  #then the file didn't exist
  arr = []
end

p arr

#Your program then adds items to arr, e.g.:
arr << 10 << 12.5 << "hello"

#At end of program, write array to file:
File.open("my_array.yaml", "w") do |file|
  YAML.dump(arr, file)
end


If you run that a few times, you will see that the data keeps getting 
added to the array.
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