< cpp‎ | atomic‎ | atomic ref
member only of atomic_ref<Integral> and atomic_ref<Floating> template specializations
T fetch_add( T arg,
             std::memory_order order = std::memory_order_seq_cst ) const noexcept;
member only of atomic_ref<T*> template specialization
T* fetch_add( std::ptrdiff_t 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 addition 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 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.


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

Return value

The value of the referenced object, immediately preceding the effects of this function.