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std::atomic<T>::operator+=,-=

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< cpp‎ | atomic‎ | atomic

Compiler support

Freestanding and hosted

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Diagnostics library

Memory management library

Metaprogramming library (C++11)

General utilities library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library (C++17)

Concurrency support library (C++11)

Execution control library (C++26)

Technical specifications

External libraries

Concurrency support library

(C++11)

(C++20)

hardware_destructive_interference_sizehardware_constructive_interference_size

(C++17)(C++17)

this_thread namespace

(C++11)

(C++11)

(C++11)

(C++11)

Cooperative cancellation

(C++20)

inplace_stop_token

(C++26)

never_stop_token

(C++26)

(C++20)

inplace_stop_source

(C++26)

(C++20)

inplace_stop_callback

(C++26)

stop_callback_for_t

(C++26)

stoppable_token

(C++26)

unstoppable_token

(C++26)

stoppable-source

(C++26)

stoppable-callback-for

(C++26)

Mutual exclusion

(C++11)

recursive_mutex

(C++11)

(C++17)

(C++11)

recursive_timed_mutex

(C++11)

shared_timed_mutex

(C++14)

Generic lock management

(C++11)

(C++11)

(C++17)

(C++11)

(C++14)

(C++11)

(C++11)

(C++11)

defer_locktry_to_lockadopt_lockdefer_lock_ttry_to_lock_tadopt_lock_t

(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)

Condition variables

condition_variable

(C++11)

condition_variable_any

(C++11)

notify_all_at_thread_exit

(C++11)

(C++11)

counting_semaphorebinary_semaphore

(C++20)(C++20)

Latches and Barriers

(C++20)

(C++20)

(C++11)

(C++11)

(C++11)

(C++11)

(C++11)

(C++11)

(C++11)

(C++11)

future_category

(C++11)

(C++11)

Safe reclamation

(C++26)

(C++26)

rcu_default_domain

(C++26)

rcu_synchronize

(C++26)

(C++26)

(C++26)

Hazard pointers

hazard_pointer_obj_base

(C++26)

(C++26)

make_hazard_pointer

(C++26)

(C++11)

(C++20)

(C++11)

Initialization of atomic types

(C++11)(deprecated in C++20)

ATOMIC_VAR_INIT

(C++11)(deprecated in C++20)

ATOMIC_FLAG_INIT

(C++11)

Memory ordering

(C++11)

kill_dependency

(C++11)(deprecated in C++26)

atomic_thread_fence

(C++11)

atomic_signal_fence

(C++11)

Free functions for atomic operations

atomic_storeatomic_store_explicit

(C++11)(C++11)

atomic_loadatomic_load_explicit

(C++11)(C++11)

atomic_exchangeatomic_exchange_explicit

(C++11)(C++11)

atomic_compare_exchange_weakatomic_compare_exchange_weak_explicitatomic_compare_exchange_strongatomic_compare_exchange_strong_explicit

(C++11)(C++11)(C++11)(C++11)

atomic_fetch_addatomic_fetch_add_explicit

(C++11)(C++11)

atomic_fetch_subatomic_fetch_sub_explicit

(C++11)(C++11)

atomic_fetch_andatomic_fetch_and_explicit

(C++11)(C++11)

atomic_fetch_oratomic_fetch_or_explicit

(C++11)(C++11)

atomic_fetch_xoratomic_fetch_xor_explicit

(C++11)(C++11)

atomic_fetch_maxatomic_fetch_max_explicit

(C++26)(C++26)

atomic_fetch_minatomic_fetch_min_explicit

(C++26)(C++26)

atomic_is_lock_free

(C++11)

atomic_waitatomic_wait_explicit

(C++20)(C++20)

atomic_notify_one

(C++20)

atomic_notify_all

(C++20)

Free functions for atomic flags

atomic_flag_test_and_setatomic_flag_test_and_set_explicit

(C++11)(C++11)

atomic_flag_clearatomic_flag_clear_explicit

(C++11)(C++11)

atomic_flag_testatomic_flag_test_explicit

(C++20)(C++20)

atomic_flag_waitatomic_flag_wait_explicit

(C++20)(C++20)

atomic_flag_notify_one

(C++20)

atomic_flag_notify_all

(C++20)

Member functions

atomic::operator=

atomic::is_lock_free

atomic::operator T

atomic::exchange

atomic::compare_exchange_strongatomic::compare_exchange_weak

(C++20)

atomic::notify_one

(C++20)

atomic::notify_all

(C++20)

atomic::is_always_lock_free

(C++17)

Specialized member functions

Specialized for integral,
floating-point (C++20)
and pointer types

atomic::fetch_add

atomic::fetch_sub

atomic::operator+=atomic::operator-=

Specialized for integral and
pointer types only

atomic::fetch_max

(C++26)

atomic::fetch_min

(C++26)

atomic::operator++atomic::operator++(int)atomic::operator--atomic::operator--(int)

Specialized for integral types only

atomic::fetch_and

atomic::fetch_or

atomic::fetch_xor

atomic::operator&=atomic::operator|=atomic::operator^=

member only of atomic<Integral > specializations
and atomic<Floating > specializations(since C++20)

T operator+=( T arg ) noexcept;

(1) (since C++11)

T operator+=( T arg ) volatile noexcept;

(2) (since C++11)

T operator-=( T arg ) noexcept;

(3) (since C++11)

T operator-=( T arg ) volatile noexcept;

(4) (since C++11)

member only of atomic<T*> partial specialization

T* operator+=( std::ptrdiff_t arg ) noexcept;

(5) (since C++11)

T* operator+=( std::ptrdiff_t arg ) volatile noexcept;

(6) (since C++11)

T* operator-=( std::ptrdiff_t arg ) noexcept;

(7) (since C++11)

T* operator-=( std::ptrdiff_t arg ) volatile noexcept;

(8) (since C++11)

Atomically replaces the current value with the result of computation involving the previous value and arg. The operation is read-modify-write operation.

operator+= performs atomic addition. Equivalent to return fetch_add(arg) + arg;.
operator-= performs atomic subtraction. Equivalent to return fetch_sub(arg) - arg;.

1-4) 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.

(since C++20)

5-8) The result may be an undefined address, but the operations otherwise have no undefined behavior.

If T is not a complete object type, the program is ill-formed.

It is deprecated if std::atomic <T>::is_always_lock_free is false and any volatile overload participates in overload resolution.

(since C++20)

Contents

[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 immediately preceding the effects of the corresponding member function in the modification order of *this).

[edit] Notes

Unlike most compound assignment operators, the compound assignment operators for atomic types do not return a reference to their left-hand arguments. They return a copy of the stored value instead.

[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
P0558R1	C++11	arithmetic permitted on pointers to (possibly cv-qualified) void or function	made ill-formed

[edit] See also

atomically adds the argument to the value stored in the atomic object and obtains the value held previously
(public member function) [edit]

atomically subtracts the argument from the value stored in the atomic object and obtains the value held previously
(public member function) [edit]

operator++operator++(int)operator--operator--(int)

increments or decrements the atomic value by one
(public member function) [edit]

operator&=operator|=operator^=

performs bitwise AND, OR, XOR with the atomic value
(public member function) [edit]

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