NAME¶

std::atomic::operator+=,-=,&=,|=,^= - std::atomic::operator+=,-=,&=,|=,^=

Synopsis¶

member only of atomic<Integral>(C++11) and
atomic<Floating>(C++20) template specializations
T operator+=( T arg ) noexcept;
T operator+=( T arg ) volatile noexcept;
member only of atomic<T*> template specialization
T* operator+=( std::ptrdiff_t arg ) noexcept;
T* operator+=( std::ptrdiff_t arg ) volatile noexcept;
member only of atomic<Integral>(C++11) and
atomic<Floating>(C++20) template specializations
T operator-=( T arg ) noexcept;
T operator-=( T arg ) volatile noexcept;
member only of atomic<T*> template specialization (1)
T* operator-=( std::ptrdiff_t arg ) noexcept;
T* operator-=( std::ptrdiff_t arg ) volatile noexcept; (1)
member only of atomic<Integral> template
specialization (2)
T operator&=( T arg ) noexcept; (2)
T operator&=( T arg ) volatile noexcept;
T operator|=( T arg ) noexcept; (3)
T operator|=( T arg ) volatile noexcept; (4)
T operator^=( T arg ) noexcept; (5)
T operator^=( T arg ) volatile noexcept;

Atomically replaces the current value with the result of computation involving the
previous value and arg. The operation is read-modify-write operation.

1) Performs atomic addition. Equivalent to fetch_add(arg) + arg.
2) Performs atomic subtraction. Equivalent to fetch_sub(arg) - arg.
3) Performs atomic bitwise and. Equivalent to fetch_and(arg) & arg.
4) Performs atomic bitwise or. Equivalent to fetch_or(arg) | arg.
5) Performs atomic bitwise exclusive or. Equivalent to fetch_xor(arg) ^ arg.

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 operations otherwise
have 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 argument for the arithmetic operation

Return value¶

The resulting value (that is, the result of applying the corresponding binary
operator to the value immediately preceding the effects of the corresponding member
function in the modification order of *this).

Notes¶

Unlike most compound assignment operators, the compound assignment operators for
atomic types do not return a reference to their left-hand arguments. They return a
copy of the stored value instead.

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¶

operator++
operator++(int) increments or decrements the atomic value by one
operator-- (public member function)
operator--(int)