std::atomic_ref<T>::operator++,++(int),--,--(int)
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                    < cpp | atomic | atomic ref
                    
                                                            
                    |   member of  atomic_ref<Integral> specializationsand atomic_ref<T*> partial specialization | 
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|   value_type operator++() const noexcept;  | 
(1) | (since C++20) | 
|   value_type operator++( int ) const noexcept;  | 
(2) | (since C++20) | 
|   value_type operator--() const noexcept;  | 
(3) | (since C++20) | 
|   value_type operator--( int ) const noexcept;  | 
(4) | (since C++20) | 
Atomically increments or decrements the current value of the referenced object. These operations are read-modify-write operations.
1) Performs atomic pre-increment. Equivalent to return fetch_add(1) + 1;.
2) Performs atomic post-increment. Equivalent to return fetch_add(1);.
3) Performs atomic pre-decrement. Equivalent to return fetch_sub(1) - 1;
4) Performs atomic post-decrement. Equivalent to return fetch_sub(1);.
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. The program is ill-formed if T is not an object type.
Return value
1,3) The value of the referenced object after the modification.
2,4) The value of the referenced object before the modification.
Notes
Unlike most pre-increment and pre-decrement operators, the pre-increment and pre-decrement operators for atomic_ref do not return a reference to the modified object. They return a copy of the stored value instead.
See also
|   atomically adds the argument to the value stored in the referenced object and obtains the value held previously  (public member function)  | |
|   atomically subtracts the argument from the value stored in the referenced object and obtains the value held previously  (public member function)  | |
|   atomically adds to or subtracts from the referenced value  (public member function)  | |
|   atomically performs bitwise AND, OR, XOR with the referenced value  (public member function)  |