declaration.c

  MITIE_EXPORT char** mitie_tokenize (
        const char* text
    );
    /*!
        requires
            - text == a valid pointer to a NULL terminated C string
        ensures
            - returns an array that contains a tokenized copy of the input text.  
            - The returned array is an array of pointers to NULL terminated C strings.  The
              array itself is terminated with a NULL.  So for example, if text was "some text" 
              then the returned array, TOK, would contain:
                - TOK[0] == "some"
                - TOK[1] == "text"
                - TOK[2] == NULL
            - It is the responsibility of the caller to free the returned array.  You free
              it by calling mitie_free() once on the entire array.  So to use the above
              nomenclature, you call mitie_free(TOK).  DO NOT CALL FREE ON ELEMENTS OF TOK.
            - If something prevents this function from succeeding then a NULL is returned.
    !*/

test.rb

require 'ffi'

module FfiCustomTest
  extend FFI::Library
  ffi_lib 'c'
  ffi_lib '/Users/christinebooher/Sites/MITIE/mitielib/libmitie.so'
#  attach_function :mitie_get_num_possible_ner_tags, [:string], :string
  attach_function :mitie_tokenize, [:string], :string
end

puts FfiCustomTest.mitie_tokenize('this is a simple sentence, it should be tonkenizeable')

result:
➜ ffi ruby test.rb
��+��