james.c

#include "person.h"

int main(int argc, const char *argv[])
{
        person_t james = {"James", "Newton", 21};

        person_print(james);

        return 0;
}

james.rb

require './person'

class James
  include Person

  def initialize(first_name, last_name, age)
    @first_name = first_name
    @last_name  = last_name
    @age        = age
  end

  def old_enough_to_drink?
    @age > 18
  end
end

james = James.new('James', 'Newton', 21)
james.full_name            #=> "James Newton"
james.old_enough_to_drink? #=> true

person.c

#include "person.h"

void person_print(person_t person)
{
        printf("Name: %s %s\n", person.first_name, person.last_name);
        printf("Age:  %i\n", person.age);
}

person.h

#include <stdio.h>

typedef struct {
        char *first_name;
        char *last_name;
        int  age;
} person_t;

extern void person_print(person_t person);

person.rb

module Person
  def full_name
    "#{@first_name} #{@last_name}"
  end
end