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      std::atomic<T>::operator+=,-=

      From cppreference.com
      <cpp‎ |atomic‎ |atomic
       
       
      Concurrency support library
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      member only ofatomic<Integral > specializations
      andatomic<Floating > specializations(since C++20)
      T operator+=( T arg)noexcept;
      		 (1)(since C++11)
      T operator+=( T arg)volatilenoexcept;
      		 (2)(since C++11)
      T operator-=( T arg)noexcept;
      		 (3)(since C++11)
      T operator-=( T arg)volatilenoexcept;
      		 (4)(since C++11)
      member only ofatomic<T*> partial specialization
      T* operator+=(std::ptrdiff_t arg)noexcept;
      		 (5)(since C++11)
      T* operator+=(std::ptrdiff_t arg)volatilenoexcept;
      		 (6)(since C++11)
      T* operator-=(std::ptrdiff_t arg)noexcept;
      		 (7)(since C++11)
      T* operator-=(std::ptrdiff_t arg)volatilenoexcept;
      		 (8)(since C++11)

      Atomically replaces the current value with the result of computation involving the previous value andarg. The operation is read-modify-write operation.

      • operator+= performs atomic addition. Equivalent toreturn fetch_add(arg)+ arg;.
      • operator-= performs atomic subtraction. Equivalent toreturn fetch_sub(arg)- arg;.
      1-4) For signed integral types, arithmetic is defined to use two’s complement representation. There are no undefined results.

      For floating-point types, thefloating-point environment in effect may be different from the calling thread's floating-point environment. The operation need not be conform to the correspondingstd::numeric_limits traits but is encouraged to do so. If the result is not a representable value for its type, the result is unspecified but the operation otherwise has no undefined behavior.

      		(since C++20)
      5-8) The result may be an undefined address, but the operations otherwise have no undefined behavior.
      IfT is not a complete object type, the program is ill-formed.


      It is deprecated ifstd::atomic<T>::is_always_lock_free isfalse and anyvolatile overload participates in overload resolution.

      		(since C++20)

      Contents

      [edit]Parameters

      arg - the argument for the arithmetic operation

      [edit]Return value

      The resulting value (that is, the result of applying the corresponding binary operator to the value immediately preceding the effects of the corresponding member function in themodification order of*this).

      [edit]Notes

      Unlike most compound assignment operators, the compound assignment operators for atomic types do not return a reference to their left-hand arguments. They return a copy of the stored value instead.

      [edit]Defect reports

      The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

      DRApplied toBehavior as publishedCorrect behavior
      P0558R1C++11arithmetic permitted on pointers to (possibly cv-qualified)void or functionmade ill-formed

      [edit]See also

      atomically adds the argument to the value stored in the atomic object and obtains the value held previously
      (public member function)[edit]
      atomically subtracts the argument from the value stored in the atomic object and obtains the value held previously
      (public member function)[edit]
      increments or decrements the atomic value by one
      (public member function)[edit]
      performs bitwise AND, OR, XOR with the atomic value
      (public member function)[edit]
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