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std::atomic::fetch_add

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< cpp‎ | atomic‎ | atomic
Revision as of 06:23, 28 May 2014 by Cubbi (Talk | contribs)

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(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.

Contents

[edit] Parameters

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

[edit] Return value

The value of the atomic variable before the call.

[edit] Exceptions

noexcept specification:  
noexcept
  

[edit] 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:

Result:5

[edit] See also

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