gistfile1.c

// bar.c
#include <ruby.h>

static VALUE bar_init(int argc, VALUE* argv, VALUE self){
  VALUE v_func, v_proto, v_return, v_dll, v_array;
  int size;

  rb_scan_args(argc, argv, "13", &v_func, &v_proto, &v_return, &v_dll);

  v_array = rb_str_split(v_proto, "");

  // Segfault or bad behavior on Ruby 2.x
  if(RARRAY_LEN(v_array) > 5)
    rb_raise(rb_eArgError, "too many parameters: %li", RARRAY_LEN(v_array));

  size = RARRAY_LEN(v_array);
  printf("Size: %li\n", size);

  return self;
}

void Init_bar(){
  VALUE cBar;
  cBar = rb_define_class("Bar", rb_cObject);

  rb_define_method(cBar, "initialize", bar_init, -1);
}

# extconf.rb
require 'mkmf'
create_makefile('bar')

# test.rb
$:.unshift Dir.pwd
require 'bar'

Bar.new('test', 's' * 6, 'x', 'whatever')

# Ruby 1.9.x => test.rb:4:in `initialize': too many parameters: 6 (ArgumentError)
# Ruby 2.x => Segfault