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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 > specializations

and atomic<Floating > specializations

*(since C++20)*

T fetch_sub( T arg, std::memory_order order = **(1)** *(since C++11)*

std::memory_order_seq_cst ) noexcept;

T fetch_sub( T arg, std::memory_order order =

std::memory_order_seq_cst ) volatile **(2)** *(since C++11)*

noexcept;

member only of atomic<T*> partial specialization

T* fetch_sub( std::ptrdiff_t arg,

std::memory_order order = **(3)** *(since C++11)*

std::memory_order_seq_cst ) noexcept;

T* fetch_sub( std::ptrdiff_t arg,

std::memory_order order = **(4)** *(since C++11)*

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.

1,2) 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
*(since C++20)*

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.

3,4) The result may be an undefined address, but the operation otherwise has
no

undefined behavior.

If T is not a complete object type, the program is ill-formed.

It is deprecated if std::atomic<T>::is_always_lock_free is false and
*(since C++20)*

overload **(2)** or **(4)** participates in overload resolution.

# 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 (possibly made ill-formed

cv-qualified) void or 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)

2024.06.10 | http://cppreference.com |