From: "daniel åkerud" <daniel.akerud@...>
Date: 2009-10-28T16:55:36+09:00
Subject: Ruby FFI: fixed size char array inside struct

(I dind't find an official Ruby FFI mailing-list so I try here)

I have a char array baked into a struct (not a pointer), and I have
problems describing it in a layout.

struct {
  uint8 Value;
  uint8 String[SIZE_OF_ARRAY];
} MyArray_t;

The only thing I've come up with is to have a dummy variable at the end.

class MyArray_t < FFI::Struct
  layout  :Value,  :uint8,
          :String, :char_array,
          :Dummy,  :uint8, SIZE_OF_ARRAY+1 # TODO TODO
end

And I use it something like this:

arr = MyArray_t.new
c_function(arr.pointer) # calls a c function that fills the string
str_ptr = arr.pointer + arr.offset_of(:String)
puts str_ptr.read_string()

I need the dummy otherwise there wont be enough bytes allocated and
c_function overwrites the heap.
Any and all help appreciated. (Note that it's a legacy API,
redesigning the C-interface is not possible.)

/D