std::atomic_ref<T>::fetch_sub

value_type fetch_sub( difference_type arg,
                      std::memory_order order =
                          std::memory_order_seq_cst ) const noexcept;

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.
  • If std::remove_pointer_t<T> is not a complete object type, the program is ill-formed.

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

Parameters

Return value

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

Example

Defect reports

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