ruby c extension

clips.c

#include "ruby.h"
#include "foo_class.h"

VALUE CExtensionModule = Qnil;

void Init_c_extension()
{
        CExtensionModule = rb_define_module("CExtension");
        rb_init_foo_class();
}

extconf.rb

require 'mkmf'
create_makefile('c_extension')

foo_class.c

#include "foo_class.h"

VALUE FooClass = Qnil;
VALUE ExampleStructClass = Qnil;
extern VALUE CExtensionModule;
typedef struct example_struct {
        char *name;
        int struct_id;
} example_struct;

static VALUE rb_example_struct_init(VALUE self, VALUE name) {
        example_struct* p;

        Check_Type(name, T_STRING);

        Data_Get_Struct(self, example_struct, p);
        p->name = (char *)malloc(RSTRING_LEN(name) + 1);
        memcpy(p->name, StringValuePtr(name), RSTRING_LEN(name) + 1);

        return self;
}

static VALUE rb_example_struct_name(VALUE self) {
        example_struct* p;
        Data_Get_Struct(self, example_struct, p);

        return rb_str_new_cstr(p->name);
}

void rb_init_foo_class()
{
        FooClass = rb_define_class_under(CExtensionModule, "FooClass", rb_cObject);
        rb_define_method(FooClass, "say_hi", rb_foo_class_say_hi, 0);
        rb_define_method(FooClass, "say_hi_to", rb_foo_class_say_hi_to, 1);

        ExampleStructClass = rb_define_class_under(CExtensionModule, "ExampleStructClass", rb_cObject);
        rb_define_alloc_func(ExampleStructClass, rb_foo_class_struct_alloc);
        rb_define_method(ExampleStructClass, "initialize", rb_example_struct_init, 1);
        rb_define_method(ExampleStructClass, "name", rb_example_struct_name, 0);
}

VALUE rb_foo_class_say_hi(VALUE self)
{
        return rb_str_new2("Hello!");
}

VALUE rb_foo_class_say_hi_to(VALUE self, VALUE r_name)
{
        VALUE r_greeting = rb_str_new2("Hello, ");
        rb_str_append(r_greeting, r_name);

        return r_greeting;
}

void example_struct_free(example_struct * self) {
        if (self->name != NULL) {
                free(self->name);
        }
        ruby_xfree(self);
}

VALUE rb_foo_class_struct_alloc(VALUE self)
{
        return Data_Wrap_Struct(self, NULL, example_struct_free, ruby_xmalloc(sizeof(example_struct)));
}

foo_class.h

#include "ruby.h"
void rb_init_foo_class();
VALUE rb_foo_class_say_hi(VALUE self);
VALUE rb_foo_class_say_hi_to(VALUE self, VALUE r_name);
VALUE rb_foo_class_struct(VALUE self, VALUE r_bar);
VALUE rb_foo_class_struct_alloc(VALUE klass);

Rakefile

require "bundler/gem_tasks"
require "rake/testtask"
require "rake/extensiontask"

Rake::TestTask.new(:test) do |t|
  t.libs << "test"
  t.libs << "lib"
  t.test_files = FileList["test/**/*_test.rb"]
end

Rake::ExtensionTask.new("c_extension") do |ext|
  ext.lib_dir = "lib/c_extension"
end

task :default => :test

test.rb

require "test_helper"

class CExtensionTest < Minitest::Test
  def test_that_it_has_a_version_number
    refute_nil ::CExtension::VERSION
  end

  def test_it_says_hi
    assert "Hello!", CExtension::FooClass.new.say_hi
  end

  def test_it_says_hi_to_bob
    assert "Hello, Bob", CExtension::FooClass.new.say_hi_to("Bob")
  end

  def test_struct
    assert_equal 'a', CExtension::ExampleStructClass.new('a').name
  end
end