Ruby ffi examples

file_write.rb

require 'ffi'

module LibC
  extend FFI::Library
  ffi_lib FFI::Library::LIBC

  typedef :pointer, :FILE

  attach_function :fopen, [:string, :string], :FILE
  attach_function :fclose, [:FILE], :int
  attach_function :fputs, [:string, :FILE], :int
end

handle = LibC::fopen '/tmp/hogehoge', 'w'
LibC::fputs 'hogehoge', handle
LibC::fclose handle

Gemfile

source "https://rubygems.org"

gem 'ffi'

hello_world.rb

require 'ffi'

module LibC # <--- 1
  extend FFI::Library # <--- 1
  ffi_lib FFI::Library::LIBC
  attach_function :puts, [ :string ], :int
end

LibC::puts 'Hello World!!'

mp4_tag.rb

# Mp4v2 binding module
module Mp4v2
  module Native
    # Mp4v2 Tag struct
    class MP4Tags < FFI::Struct
      layout :__handle, :pointer,
             :name, :string,
             :artist, :string,
             :album_artist, :string,
             :album, :string,
             :grouping, :string,
             :composer, :string,
             :comments, :string,
             :genre, :string

      def self.keys
        [
          :name, :artist, :album_artist, :album,
          :grouping, :composer, :comments, :genre
        ]
      end
    end
  end
end