Tom Hughes writes:
On 06/08/2019 09:37, Miroslav Lichvar wrote:Ok, but does that mean the program has to abort? Could gcc do anything dangerous here? If we were actually trying to catch undefined behavior (e.g. with -fsanitize=undefined), I suspect Fedora wouldn't even boot without a crash.Well of course the program doesn't have to abort - we have chosen to compile in a mode where it does. We do that because by default this is invoking the nasal daemons clause and the compiler is allowed to do absolutely anything it feels like.
Earlier in the thread I posted some conflicting references from the standard, related to the additional requirements of contiguous containers, and the specification of the "*" operator, that leaves some room open for interpretation, here.
If you go by the formal specification of container and iterator requirements, this is undefined behavior. But std::vector is also specified as having "additional" requirements of a "contiguous container", whose semantics are specified in terms of std::addressof behavior, and that rabbit hole goes in a slightly different direction.
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