> 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

> You've got it almost right - the problem is your mapping of the struct
> token string fields.

> 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.