Using Hinnant's C++11 stack allocator with std::basic_string is libstdc++ or libc++ correct?

Using a slightly modified version of Howard Hinnants's C++11 stack allocator which is documented here, with std::basic_string and libstdc++ (see it live ):

const unsigned int N = 200;

arena<N> a;
short_alloc<char, N> ac(a) ;

std::basic_string<char,std::char_traits<char>,short_alloc<char, N>> empty(ac);

gives the following error amongst others:

error: no matching function for call to 'short_alloc<char, 200ul>::short_alloc()'
   if (__n == 0 && __a == _Alloc())
                       ^

However it works without error when using libc++ (see it live ).

The stdlibc++ implementation of std::basic_string seems to expect the allocator to have a default constructor.

Does C++11 require allocators to be default constructible? Which implementation is correct?