std::atomic_ref<T>::fetch_sub

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
• For pointer types, the result may be an undefined address, but the operation otherwise has no undefined behavior.
  • If std::remove_pointer_t <T>

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

Parameters

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

Return value

The value referenced by *ptr

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