std::atomic_ref<T>::exchange

value_type exchange( value_type desired,
                     std::memory_order order =
                         std::memory_order_seq_cst ) const noexcept;

(constexpr since C++26)

Atomically replaces the value of the referenced object with desired. The operation is a read-modify-write operation. Memory is affected according to the value of order.

This overload participates in overload resolution only if std::is_const_v<T> is false.

Parameters

desired	-	value to assign
order	-	memory order constraints to enforce

Return value

The value of the referenced object before the call.

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 3508 (P3323R1)	C++20	`exchange` was meaningless for constT	constrained to accept only non-const `T`

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/cpp/atomic/atomic_ref/exchange