std::atomic::operator+=,-=,&=,|=,^=

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Atomic operations library

Types

atomic (C++11)

atomic_ref (C++20)

Functions

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_is_lock_free (C++11)

Atomic flags

atomic_flag (C++11)

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

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

Initialization

atomic_init (C++11)

ATOMIC_VAR_INIT (C++11)

ATOMIC_FLAG_INIT (C++11)

Memory ordering

memory_order (C++11)

kill_dependency (C++11)

atomic_thread_fence (C++11)

atomic_signal_fence (C++11)

 

std::atomic

Member functions

atomic::atomic

atomic::operator=

atomic::is_lock_free

atomic::store

atomic::load

atomic::operator T

atomic::exchange

atomic::compare_exchange_strongatomic::compare_exchange_weak

Constants

atomic::is_always_lock_free (C++17)

Specialized member functions

atomic::fetch_add

atomic::fetch_sub

atomic::fetch_and

atomic::fetch_or

atomic::fetch_xor

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

atomic::operator+=atomic::operator-=atomic::operator&=atomic::operator|=atomic::operator^=

 

member only of atomic<Integral>(C++11) and atomic<Floating>(C++20) template specializations
	(1)
T operator+=( T arg ) noexcept;
T operator+=( T arg ) volatile noexcept;
member only of atomic<T*> template specialization
		(1)
T* operator+=( std::ptrdiff_t arg ) noexcept;
T* operator+=( std::ptrdiff_t arg ) volatile noexcept;
member only of atomic<Integral>(C++11) and atomic<Floating>(C++20) template specializations
			(2)
T operator-=( T arg ) noexcept;
T operator-=( T arg ) volatile noexcept;
member only of atomic<T*> template specialization
				(2)
T* operator-=( std::ptrdiff_t arg ) noexcept;
T* operator-=( std::ptrdiff_t arg ) volatile noexcept;
member only of atomic<Integral> template specialization
					(3)
T operator&=( T arg ) noexcept;
T operator&=( T arg ) volatile noexcept;
						(4)
T operator|=( T arg ) noexcept;
T operator|=( T arg ) volatile noexcept;
							(5)
T operator^=( T arg ) noexcept;
T operator^=( T arg ) volatile noexcept;

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

1) Performs atomic addition. Equivalent to fetch_add(arg) + arg.

2) Performs atomic subtraction. Equivalent to fetch_sub(arg) - arg.

3) Performs atomic bitwise and. Equivalent to fetch_and(arg) & arg.

4) Performs atomic bitwise or. Equivalent to fetch_or(arg) | arg.

5) Performs atomic bitwise exclusive or. Equivalent to fetch_xor(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.

(since C++20)

For T* types, the result may be an undefined address, but the operations otherwise have no undefined behavior. The program is ill-formed if T is not an object type.

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

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.

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 cv void or function	made ill-formed

See also

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

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