https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67515
--- Comment #4 from Roger Orr <rogero at howzatt dot demon.co.uk> --- Ah - apologies -- I'd got the example by stripping down a call in boost::format and didn't do a full enough check that the code was well formed: I'll report that UB to boost. However as Markus says the seg fault remains troublesome.
