e.g.

  char tag[TOKEN_TAG_MAX];

instead of

  :tag, :string

it should be:

  :tag, [ :char, TOKEN_TAG_MAX ]

Similar for pattern, value1, value2.  Of course, you'll also need to define TOKEN_TAG_MAX and SYMBOL_MAX.

On Tuesday, May 8, 2012 3:55:35 AM UTC+10, Navaneeth KN wrote:

Hello,

I recently started using FFI and I have to say it is one of the best libraries I have ever used. Very neat syntax and performance. Thanks for such a great library.

Everything was working fine for me untill I got to iterate over a linked list. I am getting a segmentation fault when used from FFI. My C code works well and all tests are passing. My C function is like,

extern int
get_all_tokens(
    object *handle,
    int token_type,
    struct token **tokens
);

This function points the head of the linked list to "tokens" variable. Here is my FFI code.

  token_ptr = FFI::MemoryPointer.new :pointer
  done = Library.get_all_tokens($handle.get_pointer(0), 1, token_ptr);
  if done != 0
    error_message = Library.get_last_error($handle.get_pointer(0))
    error error_message
    return
  end

  ptr = token_ptr.read_pointer
 
  until ptr.null?
    item = Library::Token.new(ptr)
    puts item[:pattern] ----> Fails here
    ptr = item[:next]
  end

My C structure looks like,

struct token {
    int type, match_type;
    char tag[TOKEN_TAG_MAX];
    char pattern[SYMBOL_MAX];
    char value1[SYMBOL_MAX];
    char value2[SYMBOL_MAX];
    int children;
    struct token* next;
};

And here is the FFI equivalent one,

  class Token < FFI::Struct
    layout :type, :int,
           :match_type, :int,
           :tag, :string,
           :pattern, :string,
           :value1, :string,
           :value2, :string,
           :children, :int,
           :next,  :pointer
  end

When running this program, I am getting

[BUG] Segmentation fault
ruby 1.9.3p194 (2012-04-20 revision 35410) [x86_64-linux]

Any clue to resolve this issue would be helpful.

Thanks
Navaneeth