std::atomic::exchange
From cppreference.com
                    
                                        
                    
                    
                                                            
                    | (since C++11) | ||
| T exchange( T desired, std::memory_order order = std::memory_order_seq_cst ); | ||
| T exchange( T desired, std::memory_order order = std::memory_order_seq_cst ) volatile; | ||
Atomically replaces the underlying value with desired. The operation is read-modify-write operation. Memory is affected according to the value of order.
| Contents | 
[edit] Parameters
| desired | - | value to assign | 
| order | - | memory order constraints to enforce | 
[edit] Return value
The value of the atomic variable before the call.
[edit] Exceptions
noexcept specification:  
noexcept
  [edit] See also
| (C++11)(C++11) | atomically replaces the value of the atomic object with non-atomic argument and returns the old value of the atomic (function template) | 


