[Bug libstdc++/54388] New: std::array.at() const results in undefined behaviour

[lukeallardyce at yahoo dot co.uk]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54388

             Bug #: 54388
           Summary: std::array.at() const results in undefined behaviour
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: libstdc++
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: lukeallard...@yahoo.co.uk


array line 166:

#ifdef __EXCEPTIONS
      constexpr const_reference
      at(size_type __n) const
      {
    return __n < _Nm ? 
           _M_instance[__n] : throw out_of_range(__N("array::at"));
      }
#else
      const_reference
      at(size_type __n) const
      {
    return __n < _Nm ?
           _M_instance[__n] : __throw_out_of_range(__N("array::at"));
      }
#endif

Refer to

http://stackoverflow.com/questions/12136394/issue-with-bounds-checking-a-member-stdarray-inside-a-const-function

A conditional with a throw operand evaluates to a prvalue, which expires at the
end of the return statement.