Thanks Wayne,

you are correct, after doing what you just described everything works
in both ruby 1.8.7 and 1.9.2

best,

--Alex

On Wed, Apr 20, 2011 at 6:25 PM, Wayne Meissner <wmeissner@gmail.com> wrote:

>
> I suspect the problem is this:
>   - pointer to result size (int)
>
>
>
> You should allocate it thusly:
>     a3 = FFI::MemoryPointer.new(:int, 1, false)
>     a3.write_int(a2.size)
> If that C function is doing a conversion from an input string to an output
> string, the 'result size' probably needs to be initialized to the maximum
> size of the output string, and after the function is called, it will contain
> the actual number of bytes used in the output buffer.  Thats a pretty common
> idiom, and one of the most common things people get wrong.
> The reason why it sometimes worked, and sometimes did not was because the
> 'output size' was full of random garbage, since you were not initializing
> the a3 memory, so occasionally it would contain a positive integer value.
>
>