>
> is it OK if the FilterBase * pointer is null? (maybe it means use no
> filter?).


Yes, that's fine.

That backtrace is odd... the line of code it's crashing on is:
 fprintf(f, "%s\n", ss.str().c_str());

The only thing I can think of that might crash it is if somehow the string
being passed is not null terminated, or if there's some memory corruption or
something.

Can you run the app in valgrind and see if it finds anything?

Josh