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A libffi wrapper for Ruby.

Fiddle is an extension to translate a foreign function interface (FFI) with ruby.

It wraps libffi, a popular C library which provides a portable interface that allows code written in one language to call code written in another language.


Add this line to your application's Gemfile:

gem 'fiddle'

And then execute:

$ bundle

Or install it yourself as:

$ gem install fiddle


Here we will use Fiddle::Function to wrap floor(3) from libm

require 'fiddle'

libm = Fiddle.dlopen('/lib/')

floor =

puts #=> 3.0

Nested Structs

You can use hashes to create nested structs, where the hash keys are member names and the values are the nested structs:

StudentCollegeDetail = struct [
  'int college_id',
  'char college_name[50]'

StudentDetail = struct [
  'int id',
  'char name[20]',
  { clg_data: StudentCollegeDetail }

You can also specify an anonymous nested struct, like so:

StudentDetail = struct [
  'int id',
  'char name[20]',
    clg_data: struct([
                      'int college_id',
                      'char college_name[50]'

The position of a hash (and the order of the keys in the hash, in the case of a hash with multiple entries), dictate the offsets of the nested struct in memory. The following examples are both syntactically valid but will lay out the structs differently in memory:

# order of members in memory: position, id, dimensions
Rect = struct [ { position: struct(['float x', 'float y']) },
                'int id',
                { dimensions: struct(['float w', 'float h']) }

# order of members in memory: id, position, dimensions
Rect = struct [ 'int id',
                  position: struct(['float x', 'float y']),
                  dimensions: struct(['float w', 'float h'])


After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to


Bug reports and pull requests are welcome on GitHub at


The gem is available as open source under the terms of the BSD-2-Clause.