std::atomic_flag::atomic_flag(3)

NAME
std::atomic_flag::atomic_flag - std::atomic_flag::atomic_flag

Synopsis
   Defined in header <atomic>
   atomic_flag() noexcept = default; (since C++11)
                        (1) (until C++20)
   constexpr atomic_flag() noexcept; (since C++20)
   atomic_flag( const atomic_flag& ) = delete; (2) (since C++11)
   Constructs a new std::atomic_flag.
   1) Trivial default constructor, initializes std::atomic_flag to (until C++20)
   unspecified state.
   1) Initializes std::atomic_flag to clear state. (since C++20)
   2) The copy constructor is deleted; std::atomic_flag is not copyable.
   In addition, std::atomic_flag can be value-initialized to clear state with the
   expression ATOMIC_FLAG_INIT. For an atomic_flag with static storage duration, this
   guarantees static initialization: the flag can be used in constructors of static
   objects.

See also
   ATOMIC_FLAG_INIT initializes an std::atomic_flag to false
   (C++11) (macro constant)