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      std::atomic<T>::fetch_sub

      From cppreference.com
      <cpp‎ |atomic‎ |atomic
       
       
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      member only ofatomic<Integral > specializations
      andatomic<Floating > specializations(since C++20)
      T fetch_sub( T arg,std::memory_order order=
                             std::memory_order_seq_cst)noexcept;
      		 (1)(since C++11)
      T fetch_sub( T arg,std::memory_order order=
                             std::memory_order_seq_cst)volatilenoexcept;
      		 (2)(since C++11)
      member only ofatomic<T*> partial specialization
      T* fetch_sub(std::ptrdiff_t arg,

                   std::memory_order order=

                       std::memory_order_seq_cst)noexcept;
      		 (3)(since C++11)
      T* fetch_sub(std::ptrdiff_t arg,

                   std::memory_order order=

                       std::memory_order_seq_cst)volatilenoexcept;
      		 (4)(since C++11)

      Atomically replaces the current value with the result of arithmetic subtraction of the value andarg. That is, it performs atomic post-decrement. The operation is read-modify-write operation. Memory is affected according to the value oforder.

      1,2) 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)
      3,4) The result may be an undefined address, but the operation otherwise has 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 overload(2) or(4) participates in overload resolution.

      		(since C++20)

      Contents

      [edit]Parameters

      arg - the other argument of arithmetic subtraction
      order - memory order constraints to enforce

      [edit]Return value

      The value immediately preceding the effects of this function in themodification order of*this.

      [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

      subtracts a non-atomic value from an atomic object and obtains the previous value of the atomic
      (function template)[edit]
      increments or decrements the atomic value by one
      (public member function)[edit]
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