std::atomic_ref<T>::operator+=,-=
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< cpp | atomic | atomic ref
C++
Concurrency support library
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std::atomic_ref
| Member functions | ||||
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(C++26)
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Operations for arithmetic types (except bool and pointer-to-object)
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atomic_ref::operator+=atomic_ref::operator-= | ||||
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Operations for integral types (except bool and pointer-to-object)
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(C++26)
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(C++26)
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| Operations for integral types (except bool) | ||||
| Constants | ||||
Provided only when T is an arithmetic type other than cv bool or a pointer-to-object type |
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value_type operator+
=
( difference_type arg )
const
noexcept
;
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(1) | (constexpr since C++26) |
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value_type operator-
=
( difference_type arg )
const
noexcept
;
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(2) | (constexpr since C++26) |
Atomically replaces the current value referenced by
*
ptr
with the result of computation involving the previous value and arg
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
- For pointer types, the result may be an undefined address, but the operation otherwise has no undefined behavior.
- If std::remove_pointer_t <T>
These overloads participate in overload resolution only if std::is_const_v<T> is false
Parameters
| arg | - | the argument for the arithmetic operation |
Return value
The resulting value (that is, the result of applying the corresponding binary operator to the value referenced by
*
ptr
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.
Example
| This section is incomplete Reason: no example |
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
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See also
| atomically adds the argument to the value stored in the referenced object and obtains the value held previously (public member function) |
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| atomically subtracts the argument from the value stored in the referenced object and obtains the value held previously (public member function) |
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| atomically increments or decrements the referenced object by one (public member function) |
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| atomically performs bitwise AND, OR, XOR with the referenced value (public member function) |