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std::atomic::fetch_sub(3) | C++ Standard Libary | std::atomic::fetch_sub(3) |

# 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)

2022.07.31 | http://cppreference.com |