cpp/atomic/atomic ref/fetch add

Atomically replaces the current value of the referenced object with the result of arithmetic addition of the value and. This operation is a read-modify-write operation. Memory is affected according to the value of.

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 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 types, the result may be an undefined address, but the operation otherwise has no undefined behavior. The program is ill-formed if is not an object type.

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