Reading binary files with a fixed struct

[Psychotron]

In C i've used to do a single fread passing a struct.
In ruby what is the best method?

I mean, without making subsequent reads, i've many fields of 2/4 bytes
each)

Thanks.

 

[ts]

P> In C i've used to do a single fread passing a struct.
P> In ruby what is the best method?

String#unpack ?

i.e. read xxx characters then use String#unpack

 

[Ross Bamford]

In C i've used to do a single fread passing a struct.
In ruby what is the best method?

I mean, without making subsequent reads, i've many fields of 2/4 bytes
each)

You probably want to look up String#unpack.

 

[Robert Klemme]

P> In C i've used to do a single fread passing a struct.
P> In ruby what is the best method?

String#unpack ?

i.e. read xxx characters then use String#unpack

And don't forget to open the file in binary mode.

robert

 

[Psychotron]

You probably want to look up String#unpack.

Thanks, now i have an Array with all my fields, but if i want these
values in a meaningful Hash?

I can put an Array (less verbose than an Hash with null values) :

keys = %w{field1 field2 field2} #many fields with a better name

then i take my values :

values = f.read(64).unpack('VVVVvvvvvvvvVvvvvVVVVVV')

I can create an Hash from two arrays without iterating all elements?

 

[Psychotron]

And don't forget to open the file in binary mode.

b flag i think is useful only in windows enviroment.
In unix is ok, but i've don't tested in windows for now.

<http://www.rubycentral.com/book/ref_c_io.html>

 

[Robert Klemme]

b flag i think is useful only in windows enviroment.
In unix is ok, but i've don't tested in windows for now.

It's useful on Unix as well - if only for documentation purposes. This
also prevents that your script suddenly breaks if transferred to another
platform.

Cheers

robert

 

[Ross Bamford]

Thanks, now i have an Array with all my fields, but if i want these
values in a meaningful Hash?

I can put an Array (less verbose than an Hash with null values) :

keys = %w{field1 field2 field2} #many fields with a better name

then i take my values :

values = f.read(64).unpack('VVVVvvvvvvvvVvvvvVVVVVV')

I can create an Hash from two arrays without iterating all elements?

You could try something like:

keys = [:a, :b, :c]
values = [1, 2, 3]

h = Hash[*keys.zip(values).flatten]
# => {:b=>2, :a=>1, :c=>3}

 

[Jeremy Henty]

Thanks, now i have an Array with all my fields, but if i want these
values in a meaningful Hash?

Are you sure you want a Hash ? Perhaps a Struct class would work
better. It's very easy to turn arrays into structs. Here's an
example where I created a Struct class with some named members, then
turned an array into a struct, then recovered the members of the
original array by examining the members of the struct.

$ irb
irb(main):001:0> class Foo < Struct.newx,:y,:z) ; end
=> nil
irb(main):002:0> arr = [ :foo, "bar", 23, ]
=> [:foo, "bar", 23]
irb(main):003:0> struct = Foo.new(*arr)
=> #<struct Foo x=:foo, y="bar", z=23>
irb(main):004:0> struct.x
=> :foo
irb(main):005:0> struct.y
=> "bar"
irb(main):006:0> struct.z
=> 23
irb(main):007:0>

You can also access struct members in the same way as Arrays and
Hashes: struct[:x] is the same as struct.x .

Hope this helps,

Jeremy Henty

 

[Psychotron]

You could try something like:

keys = [:a, :b, :c]
values = [1, 2, 3]

h = Hash[*keys.zip(values).flatten]
# => {:b=>2, :a=>1, :c=>3}

Thanks, ...and now i've found this :
<http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/122906>

Is a benchmark of many methods that create hashes from two arrays.

I'm going offtopic, thank you all!

 

[Psychotron]

Are you sure you want a Hash ? Perhaps a Struct class would work
better. It's very easy to turn arrays into structs. Here's an
example where I created a Struct class with some named members, then
turned an array into a struct, then recovered the members of the
original array by examining the members of the struct.

Not sure, but i agree with you. I'll try Struct in a second
implementation.

Thank you.