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std::atomic_ref<T>:: fetch_sub

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std::atomic_ref
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atomic_ref::fetch_sub
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Constants
Provided only when T is an arithmetic type other than cv bool or a pointer-to-object type
value_type fetch_sub ( difference_type arg,

std:: memory_order order =

std:: memory_order_seq_cst ) const noexcept ;
(constexpr since C++26)

Atomically replaces the current value of the referenced object with the result of arithmetic subtraction of the value and arg . This operation is a read-modify-write operation. Memory is affected according to the value of order .

  • For signed integral types, arithmetic is defined to use two’s complement representation. There are no undefined results.
  • For floating-point types, the floating-point environment in effect may be different from the calling thread's floating-point environment. The operation need not be conform to the corresponding std::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.
  • For pointer types, the result may be an undefined address, but the operation otherwise has no undefined behavior.

This overload participates in overload resolution only if std:: is_const_v < T > is false .

Contents

Parameters

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

Return value

The value referenced by * ptr , immediately preceding the effects of this function.

Example

This section is incomplete
Reason: no example

Defect reports

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

DR Applied to Behavior as published Correct behavior
LWG 3508
( P3323R1 ) 		C++20 fetch_sub was meaningless for const T constrained to accept only non-const T