c/atomic/ATOMIC VAR INIT

Expands to an expression that can be used to initialize an atomic variable of the same type as.

The initial value of atomic object of automatic storage duration that is not explicitly initialized is indeterminate. The default (zero) initialization of static and thread-local variables produces a valid value however.

When initializing an atomic variable, any concurrent access, even through an atomic operation, is a data race (it may happen if the address is immediately passed to another thread with a memory_order_relaxed operation).