std::atomic<T>::atomic
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std::atomic
atomic::atomic
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(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.
This overload participates in overload resolution only if std::is_default_constructible_v <T> is true.
(since C++20)2) Initializes the underlying object with desired. The initialization is not atomic.
3) Atomic variables are not CopyConstructible.
[edit] Parameters
desired
-
value to initialize with
[edit] 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.
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 4169 | C++20 | std::is_default_constructible_v could report false positive | the default constructor is constrained |