Why do I get cannot load such file?

Question

I need to use the ffi gem to access native extensions. When I require 'ffi' in a simple ruby script, then it works fine. But when I require ffi in my Rails application, then I get: cannot load such file -- ffi Why?

gem env shows this:

RubyGems Environment:

• RUBYGEMS VERSION: 2.2.2
• RUBY VERSION: 1.9.3 (2012-04-20 patchlevel 194) [x86_64-linux]
• INSTALLATION DIRECTORY: /usr/lib/ruby/gems/1.9.1
• RUBY EXECUTABLE: /usr/bin/ruby1.9.1
• EXECUTABLE DIRECTORY: /usr/bin
• SPEC CACHE DIRECTORY: /home/adminuser/.gem/specs
• RUBYGEMS PLATFORMS:
  • ruby
  • x86_64-linux
  • GEM PATHS:
    • /usr/lib/ruby/gems/1.9.1
    • /home/adminuser/.gem/ruby/1.9.1

Answer 1

Add this line in your Gemfile:

gem 'ffi'

Next:

$ bundle install

Now:

require 'ffi'

You need to specify which gem you are going to use in your Gemfile in order to make it available for your Rails project with bundler.

UPDATE: I'd encourage you to checkout How does bundler bundle, how bundler require gems, and this railscast.