Defined in header <atomic>
atomic_flag() noexcept = default;
(since C++11)
(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 unspecified state. (until C++20)
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

initializes an std::atomic_flag to false
(macro constant)

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