std::atomic::fetch_add
From cppreference.com
                    
                                        
                    
                    
                                                            
                    | (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
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
[edit] See also
| (C++11)(C++11) | adds a non-atomic value to an atomic object and obtains the previous value of the atomic (function template) | 


