std::atomic_ref<T>::operator+=,-=
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std::atomic_ref
(C++26)
atomic_ref::operator+=atomic_ref::operator-=
(C++26)
(C++26)
Provided only when
T is an arithmetic type other than cv bool or a pointer-to-object typevalue_type operator+=( difference_type arg ) const noexcept;
(1)
(constexpr since C++26)
value_type operator-=( difference_type arg ) const noexcept;
(2)
(constexpr since C++26)
Atomically replaces the current value referenced by *ptr with the result of computation involving the previous value and arg. These operations are read-modify-write operations.
1) operator+= performs atomic addition. Equivalent to return fetch_add(arg) + arg;.
2) operator-= performs atomic subtraction. Equivalent to return fetch_sub(arg) - arg;.
- 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.
These overloads participate in overload resolution only if std::is_const_v <T> is false.
[edit] Parameters
arg
-
the argument for the arithmetic operation
[edit] Return value
The resulting value (that is, the result of applying the corresponding binary operator to the value referenced by *ptr immediately preceding the effects of the corresponding member function).
[edit] Notes
Unlike most compound assignment operators, the compound assignment operators for atomic_ref return a copy of the stored value instead of a reference to arg.
[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 | compound assignment operators were meaningless for const T | constrained to accept only non-const T
|
[edit] See also
atomically adds the argument to the value stored in the referenced object and obtains the value held previously
(public member function) [edit]
(public member function) [edit]
atomically subtracts the argument from the value stored in the referenced object and obtains the value held previously
(public member function) [edit]
(public member function) [edit]