Proposed resolution:

This wording is relative to N3936.

1. Change class template shared_ptr synopsis, [util.smartptr.shared], as indicated:

   constexpr shared_ptr(nullptr_t) noexcept : shared_ptr() { }
   

[ 2014-03-26 Library reflector vote ]

The issue has been identified as Tentatively Ready based on six votes in favour.

The declaration and definition of shared_ptr::shared_ptr(nullptr_t), given in [util.smartptr.shared], is

constexpr shared_ptr(nullptr_t) : shared_ptr() { }

The intention seems clear: this constructor should have the same semantics of the default constructor. However, contrarily to the default constructor, this one is not noexcept. In contrast, unique_ptr::unique_ptr(nullptr_t) is noexcept, as per [unique.ptr.single]:

constexpr unique_ptr(nullptr_t) noexcept : unique_ptr() { }

Both libstdc++ and libc++ have added noexcept to shared_ptr::shared_ptr(nullptr_t). Microsoft's STL has not.