std::atomic::fetch_add

(1) (since C++11)
(member only of atomic<Integral> template specialization)

T fetch_add( T arg, 
             std::memory_order order = std::memory_order_seq_cst );

T fetch_add( T arg, 
             std::memory_order 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, 
              std::memory_order order = std::memory_order_seq_cst );

T* fetch_add( std::ptrdiff_t arg, 
              std::memory_order 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 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
order	-	memory order constraints to enforce

Return value

The value immediately preceding the effects of this function in the modification order of *this.

Exceptions

noexcept specification:

noexcept

Example

#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:

1	`Result:5`

std::atomic::fetch_add

Parameters

Return value

Exceptions

Example

See also