A Simple FFI example on OS X

ffi_example.rb

#"" An FFI example on Mac 10.5.8
#
# % gcc --version
# i686-apple-darwin9-gcc-4.0.1 (GCC) 4.0.1 (Apple Inc. build 5465)

#
# Setup a source file
#

require 'fileutils'

Dir.glob("circle.*").each {|file| FileUtils.rm(file)}
File.open("circle.c", "w") do |file|
  file << %q{
double circularArea( double r )
{
  const double pi = 3.14159;
  return pi * r * r;
}}
end

#
# Build the dynamic library
# (on mac -dynamiclib is required instead of -shared)
#
def sh(cmd); puts cmd; system(cmd) end

puts "Building:"
sh "gcc -c circle.c"
sh "gcc -dynamiclib -o circle.dylib circle.c"

#
# Load the library with FFI
#

# using ffi 0.5.0
require 'ffi'

module Circle
  extend FFI::Library
  ffi_lib "circle.dylib"
  attach_function :circularArea, [:double ], :double
end

puts
puts "Test:"
puts "area(3) = #{Circle.circularArea(3)}"