NAME¶

std::atomic::fetch_sub - std::atomic::fetch_sub

Synopsis¶

member only of atomic<Integral>(C++11) and atomic<Floating>(C++20)
template specializations
T fetch_sub( T arg,
std::memory_order order = std::memory_order_seq_cst ) noexcept;
T fetch_sub( T arg,
std::memory_order order = std::memory_order_seq_cst ) volatile noexcept;
member only of atomic<T*> template specialization (1)
T* fetch_sub( std::ptrdiff_t arg,
std::memory_order order = std::memory_order_seq_cst ) noexcept; (2)
T* fetch_sub( std::ptrdiff_t arg,
std::memory_order order = std::memory_order_seq_cst ) volatile noexcept;

Atomically replaces the current value with the result of arithmetic subtraction of
the value and arg. That is, it performs atomic post-decrement. The operation is
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 T* types, the result may be an undefined address, but the operation otherwise
has no undefined behavior. The program is ill-formed if T is not an object type.

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 (since C++20)
operation otherwise has no undefined behavior.

The volatile-qualified versions are deprecated if
std::atomic<T>::is_always_lock_free is false.

Parameters¶

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

Return value¶

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

Defect reports

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

DR Applied to Behavior as published Correct behavior
P0558R1 C++11 arithmetic permitted on pointers to cv void or made ill-formed
function

See also¶

atomic_fetch_sub subtracts a non-atomic value from an atomic object and
atomic_fetch_sub_explicit obtains the previous value of the atomic
(C++11) (function template)
(C++11)
operator++
operator++(int) increments or decrements the atomic value by one
operator-- (public member function)
operator--(int)