std::atomic_ref<T>::fetch_sub
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std::atomic_ref
(C++26)
atomic_ref::fetch_sub
(C++26)
(C++26)
Provided only when
T is an arithmetic type other than cv bool or a pointer-to-object typevalue_type fetch_sub( difference_type arg,
(constexpr since C++26)
std::memory_order order =
Atomically replaces the current value of the referenced object with the result of arithmetic subtraction of the value and arg. This operation is a read-modify-write operation. Memory is affected according to the value of order.
- For signed integral types, arithmetic is defined to use two’s complement representation. There are no undefined results.
- For floating-point types, the floating-point environment in effect may be different from the calling thread's floating-point environment. The operation need not be conform to the corresponding std::numeric_limits traits but is encouraged to do so. If the result is not a representable value for its type, the result is unspecified but the operation otherwise has no undefined behavior.
- For pointer types, the result may be an undefined address, but the operation otherwise has no undefined behavior.
- If std::remove_pointer_t <T> is not a complete object type, the program is ill-formed.
This overload participates in overload resolution only if std::is_const_v <T> is false.
[edit] Parameters
arg
-
the other argument of arithmetic subtraction
order
-
memory order constraints to enforce
[edit] Return value
The value referenced by *ptr , immediately preceding the effects of this function.
[edit] Example
This section is incomplete
Reason: no example
Reason: no example
[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 3508 (P3323R1) |
C++20 | fetch_sub was meaningless for const T
|
constrained to accept only non-const T
|