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std::atomic<T>::atomic

(1) 
atomic() noexcept = default;
 (since C++11)
(until C++20)		 
constexpr atomic() noexcept(std::is_nothrow_default_constructible_v<T>);
 (since C++20) 
constexpr atomic( T desired ) noexcept;
 (2) (since C++11) 
atomic( const atomic& ) = delete;
 (3) (since C++11)

Constructs a new atomic variable.

1) The default constructor is trivial: no initialization takes place other than zero initialization of static and thread-local objects. std::atomic_init may be used to complete initialization. (until C++20)
1) Value-initializes the underlying object (i.e. with T()). The initialization is not atomic. The program is ill-formed if std::is_default_constructible_v<T> is false. (since C++20)
2) Initializes the underlying object with desired. The initialization is not atomic.
3) Atomic variables are not CopyConstructible.

Parameters

desired - value to initialize with

Notes

The default-initialized std::atomic<T> does not contain a T object, and its only valid uses are destruction and initialization by std::atomic_init, see LWG issue 2334.

 (until C++20)

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