C++ Atomic Library - fetch add

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Description

It automically atomically adds the argument to the value stored in the atomic object and obtains the value held previously.

Declaration

Following is the declaration for std::atomic::fetch_add.

T fetch_add (T val, memory_order sync = memory_order_seq_cst) volatile noexcept;

C++11

T fetch_add (T val, memory_order sync = memory_order_seq_cst) noexcept;

Following is the declaration for std::atomic::fetch_add(member only of atomic template specialization).

T fetch_add (ptrdiff_t val, memory_order sync = memory_order_seq_cst) volatile noexcept;

C++11

T fetch_add (ptrdiff_t val, memory_order sync = memory_order_seq_cst) noexcept;

Parameters

• arg − It is used put the other argument of arithmetic addition.

• order − It is used enforce the memory order for the value.

Return Value

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

Exceptions

No-noexcept − this member function never throws exceptions.

Example

In below example for std::atomic::fetch_add.

#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 << "Ans:" << data << '\n';
}

The sample output should be like this −

Ans:5