# std::atomic_flag::atomic_flag

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< cpp‎ | atomic‎ | atomic flag

Defined in header `<atomic>` |  |
| (1) |
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

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

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