std::atomic::fetch_add

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

 

Atomic operations library

Types

atomic (C++11)

atomic_is_lock_free (C++11)

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 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

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^=

 

	(1)	(since C++11) (member only of atomic<Integral> template specialization)
T fetch_add( T arg,              memory_order = std::memory_order_seq_cst );
T fetch_add( T arg,              memory_order = std::memory_order_seq_cst ) volatile;
			(2)	(since C++11) (member only of atomic<T*> template specialization)
T* fetch_add( std::ptrdiff_t arg,               memory_order = std::memory_order_seq_cst );
T* fetch_add( std::ptrdiff_t arg,               memory_order = std::memory_order_seq_cst ) volatile;

Atomically replaces the current value with the result of arithmetic addition of the value and arg. The operation is read-modify-write operation. Memory is affected according to the value of memory_order.

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.

Parameters

arg	-	the other argument of arithmetic addition
memory_order	-	memory order constraints to enforce

Return value

The value of the atomic variable before the call.

Exceptions

noexcept specification:  

noexcept

  

Example

Run this code

#include <iostream>
#include <thread>
#include <atomic>
 
std::atomic<long long> data;
void do_work()
{
    data.fetch_add(1, std::memory_order_relaxed);
}
 
int main()
{
    std::thread th1(do_work);
    std::thread th2(do_work);
    std::thread th3(do_work);
    std::thread th4(do_work);
    std::thread th5(do_work);
 
    th1.join();
    th2.join();
    th3.join();
    th4.join();
    th5.join();
 
    std::cout << "Result:" << data << '\n';
}

Output:

Result:5

See also

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

adds a non-atomic value to an atomic object and obtains the previous value of the atomic (function template)