Loading variables from a file [Noob Question]

Ruby
1

Hey everyone,
I’ve been working on some sort of a test-based game to learn ruby (and
programming in general :slight_smile: and I got stuck with my saving/loading system.
To show you what I mean, this is what I used to save the game. (I want
the code to be as modular as I can, I have some sort of an addon system
planned…)

def savegame(name, varstosave)
savegame = File.new(name + “.tsl”, “w”)
savegame.puts varstosave.to_s
while varstosave.length != 0
savegame.puts varstosave[0]
savegame.puts eval(varstosave[0]).to_s
varstosave.delete_at(0)
end
savegame.close
end

So, now I am trying to to load the variables from the file. I came up
with the start of a function:

def loadgame(name, varstoload)
puts “Loading…”
loadgame = File.open(name + “.tsl”, “r”)
while varstoload.length != 0
# ?
end
loadgame.close
end

Where varstoload/varstosave is an array. Problem with the loading is
that I assumed there was a way to take the first variable name from the
array and actually use it as a variable. So, if the array is
["$intellect", “$strength”], I thought I would be able somehow to turn
a[0] into a variable object. It seems that there isn’t a way to do this,
so I was wondering if there was a better way to manage the
saving/loading.

  • Thanks in advance! :slight_smile:
2

On Sun, Nov 28, 2010 at 6:44 PM, Richard M.
[email protected] wrote:

Hey everyone,
It seems that there isn’t a way to do this,
so I was wondering if there was a better way to manage the
saving/loading.

Ruby 1.8.x ships with YAML, while Ruby 1.9.x includes JSON. Both
formats allow you to save variables to file, and reload them.

require “yaml”
require “json”

[1,2,3,4,].to_yaml
[1,2,3,4,].to_json

If you need something more complex, Marshall#dump and #load can be
useful.

All of this should be covered by the Ruby docs, too (at least YAML and
Marshall are, JSON at 1.9.x, as I’ve mentioned).

Mind, you still have to do the assignment and such yourself, but you
get the data back in a Ruby-friendly format. :wink:

–
Phillip G.

Though the folk I have met,
(Ah, how soon!) they forget
When I’ve moved on to some other place,
There may be one or two,
When I’ve played and passed through,
Who’ll remember my song or my face.

3

Phillip G. wrote in post #964503:

On Sun, Nov 28, 2010 at 6:44 PM, Richard M.
[email protected] wrote:

Hey everyone,
It seems that there isn’t a way to do this,
so I was wondering if there was a better way to manage the
saving/loading.

Ruby 1.8.x ships with YAML, while Ruby 1.9.x includes JSON. Both
formats allow you to save variables to file, and reload them.

Ah, exactly what I was looking for! Thanks a ton, I can’t believe I
didn’t know about that ^^
Thanks again! :smiley:
-Richard

4

On Nov 28, 5:44pm, Richard M. [email protected]
wrote:

while varstosave.length != 0
def loadgame(name, varstoload)
array and actually use it as a variable. So, if the array is
[“$intellect”, “$strength”], I thought I would be able somehow to turn
a[0] into a variable object. It seems that there isn’t a way to do this,
so I was wondering if there was a better way to manage the
saving/loading.

  • Thanks in advance! :slight_smile:

–
Posted viahttp://www.ruby-forum.com/.

Not sure if it helps, but here are a few tips.

First, if you simply want to dump all the data in a file and get it
back have a look at things like the YAML library: you can take your
objects, and just with one line of code dump it into a file. (you can
alternatively use Marshal but then the file will be written in binary
format: great if you need to save space but not if you want to be able
to open the file with a text editor to have a look).

Second, and possibly more relevant. :slight_smile:
A common way to do what you are trying to do would be to read a line
at a time from the file, analyse it and store the result. Here a
couple of useful functions may be:

File::read (it reads the whole file and returns a String object)
File::readlines (it reads the whole file and returns an Array of
String with one line of the file per element of the Array)

Note that in both cases these are class methods, similar to the
File.open you used.

A maybe more elegant method, and more similar to what you were trying
to do would be to use File#gets, which returns the “next” line. Then
you could modify your code so:

loadgame = File.open(name + “.tsl”, “r”)
while !loadgame.eof? # i.e. until it reaches the end of file
line = loadgame.gets

more code

end
loadgame.close

Now, assuming you manage to get a line, you need to parse it to get
the data you want. The most generic way would be to use a regexp, but
for simple cases you can simply split the line into smaller Strings
via the function String#split. This would make it easier to pick the
name and the value.

So far I’ve assumed that you want to load all the variables in the
file. If you only want to load some, i.e. only those in the Array
varstoload you can use Array#include, for example:

loadgame = File.open(name + “.tsl”, “r”)
while !loadgame.eof? # i.e. until it reaches the end of file
line = loadgame.gets
elements = line.split
if varstoload.include? elements[0]
# add elements[0] and elements[1] to some variable/object
end
end
loadgame.close

Hope that help.

Feel free if you have other questions.
Diego

5

On Nov 28, 11:44am, Richard M. [email protected]
wrote:

while varstosave.length != 0
def loadgame(name, varstoload)
array and actually use it as a variable. So, if the array is
[“$intellect”, “$strength”], I thought I would be able somehow to turn
a[0] into a variable object. It seems that there isn’t a way to do this,
so I was wondering if there was a better way to manage the
saving/loading.

Use a hash (associative array).

def save_game( name, hash )
open( name + “.tsl”, “w” ){|f|
f.puts hash.to_a.join( “\n” )
}
end

def load_game( name )
hash = {}
open( name + “.tsl”, “r” ){|f|
while key = f.gets
hash[ key.strip ] = f.gets.to_i
end
}
hash
end

status = {}
status[ ‘intellect’ ] = 140
status[ ‘strength’ ] = 120

save_game( ‘foo’, status )
p load_game( ‘foo’ )

6

On Sun, Nov 28, 2010 at 11:44 AM, Richard M. <
[email protected]> wrote:

def savegame(name, varstosave)
savegame = File.new(name + “.tsl”, “w”)
…
savegame.close
end

The preferred way to open a file is with the block syntax because it
ensures
the file gets closed after the block is evaluated, even if an error gets
raised.

File.open( name + ‘.tsl’ , ‘w’ ) do |savegame|
…
end

savegame.puts eval(varstosave[0]).to_s

For simple things like numbers and strings, this may work (you will
probably
have to do some conversions). But for more complex data, like objects,
you
will have difficulty because you aren’t using any well understood
representation of objects as Strings (others suggested yaml, json,
marshalling).

Use of eval is generally frowned upon because it is rarely necessary and
can
introduce security risks. In this case, it is enabling the bad practice
of
global variables (I’ll explain that a bit further down). Rather than
evaling
your global variable strings to get their value, try passing them in to
the
function. If you need to keep track of both the name of the variable,
and
its value, then try using a hash table.

def savegame(vars)
vars.each do |name,value|
puts “savegame has access to #{name} which has a value of #{value}”
end
end

intellect = 3
strength = 4

savegame ‘intellect’ => intellect , ‘strength’ => strength

output

>> savegame has access to intellect which has a value of 3

>> savegame has access to strength which has a value of 4

Where varstoload/varstosave is an array. Problem with the loading is
that I assumed there was a way to take the first variable name from the
array and actually use it as a variable. So, if the array is
["$intellect", “$strength”], I thought I would be able somehow to turn
a[0] into a variable object. It seems that there isn’t a way to do this,
so I was wondering if there was a better way to manage the
saving/loading.

Having a hard time understanding what you are looking for here (it
sounds
like you want it to return $intellect, the variable, rather than the
object
that the variable is pointing to – if that is the case, there is no way
to
do that)

I will just point out that variables that begin with dollar signs are
global
variables in Ruby. Here are the different kinds of variables you can
use:

The colon at the front of the results means that they are Symbols.

Symbols are basically immutable Strings. In earlier versions of Ruby,

this would have returned the results as Strings instead of Symbols.

search_pattern = /strength|intelligence/i

$strength = 3
$intelligence = 4
global_variables.grep(search_pattern) # => [:$strength, :$intelligence]

strength = 3
intelligence = 4
local_variables # => [:search_pattern, :strength, :intelligence]

@strength = 3
@intelligence = 4
instance_variables # => [:@strength, :@intelligence]

this one is a little weird since we are in the main object

@@strenght = 3
@@intelligence = 4
self.class.class_variables # => [:@@strenght, :@@intelligence]

STRENGTH = 3
INTELLIGENCE = 4
self.class.constants.grep(search_pattern) # => [:STRENGTH,
:INTELLIGENCE]