std::atomic<T>::operator++,++(int),--,--(int)

 

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

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

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

atomic_notify_one (C++20)

atomic_notify_all (C++20)

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)

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)

Initialization

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

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

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

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

atomic::wait (C++20)

atomic::notify_one (C++20)

atomic::notify_all (C++20)

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^=

 

T operator++() noexcept; T operator++() volatile noexcept;	(1)	(member only of atomic<Integral> template specialization) (since C++11)
T* operator++() noexcept; T* operator++() volatile noexcept;	(1)	(member only of atomic<T*> template specialization) (since C++11)
T operator++( int ) noexcept; T operator++( int ) volatile noexcept;	(2)	(member only of atomic<Integral> template specialization) (since C++11)
T* operator++( int ) noexcept; T* operator++( int ) volatile noexcept;	(2)	(member only of atomic<T*> template specialization) (since C++11)
T operator--() noexcept; T operator--() volatile noexcept;	(3)	(member only of atomic<Integral> template specialization) (since C++11)
T* operator--() noexcept; T* operator--() volatile noexcept;	(3)	(member only of atomic<T*> template specialization) (since C++11)
T operator--( int ) noexcept; T operator--( int ) volatile noexcept;	(4)	(member only of atomic<Integral> template specialization) (since C++11)
T* operator--( int ) noexcept; T* operator--( int ) volatile noexcept;	(4)	(member only of atomic<T*> template specialization) (since C++11)

Atomically increments or decrements the current value. The operation is read-modify-write operation.

1) Performs atomic pre-increment. Equivalent to fetch_add(1)+1.

2) Performs atomic post-increment. Equivalent to fetch_add(1).

3) Performs atomic pre-decrement. Equivalent to fetch_sub(1)-1

4) Performs atomic post-decrement. Equivalent to fetch_sub(1).

For signed Integral types, arithmetic is defined to use two’s complement representation. There are no undefined results.

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.

The volatile-qualified versions are deprecated if std::atomic<T>::is_always_lock_free is false.

(since C++20)

Parameters

(none)

Return value

1,3) The value of the atomic variable after the modification. Formally, the result of incrementing/decrementing the value immediately preceding the effects of this function in the modification order of *this.

2,4) The value of the atomic variable before the modification. Formally, the value immediately preceding the effects of this function in the modification order of *this.

Notes

Unlike most pre-increment and pre-decrement operators, the pre-increment and pre-decrement operators for atomic types do not return a reference to the modified object. 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

fetch_add	atomically adds the argument to the value stored in the atomic object and obtains the value held previously (public member function)
fetch_sub	atomically subtracts the argument from the value stored in the atomic object and obtains the value held previously (public member function)
operator+=operator-=operator&=operator|=operator^=	adds, subtracts, or performs bitwise AND, OR, XOR with the atomic value (public member function)