< cpp‎ | atomic
Defined in header <atomic>
#define ATOMIC_VAR_INIT(value) /* implementation-defined */

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.


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.


#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

See also

non-atomic initialization of a default-constructed atomic object
(function template)
constructs an atomic object
(public member function of std::atomic)