< cpp‎ | atomic
Defined in header <atomic>
#define ATOMIC_VAR_INIT(value) /* implementation-defined */
(since C++11)
(deprecated in C++20)

Expands to an expression which can be used to initialize an std::atomic object that can be initialized from value. If the atomic object has static storage duration, this initialization is constant initialization.

[edit] Notes

Accessing the variable during initialization from another thread, even through an atomic operation, is a data race (it may happen if the address is immediately passed to another thread with a std::memory_order_relaxed operation)

This macro is primarily provided for compatibility with C; it behaves the same as the constructor of std::atomic.

[edit] Example

#include <atomic>
#include <iostream>
int main()
    std::atomic<int> a = ATOMIC_VAR_INIT(1);
    // std::atomic<int> a(1);   // C++-only alternative
    std::cout << "Initialized std::atomic<int> as: " << a << '\n';


Initialized std::atomic<int> as: 1

[edit] See also

(C++11)(deprecated in C++20)
non-atomic initialization of a default-constructed atomic object
(function template) [edit]
constructs an atomic object
(public member function of std::atomic<T>) [edit]
C documentation for ATOMIC_VAR_INIT