ATOMIC_VAR_INIT

Defined in header <stdatomic.h>
#define ATOMIC_VAR_INIT(value) /* unspecified */		(since C11) (deprecated in C17) (removed in C23)

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

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).

Notes

This macro was a part of early draft design for C11 atomic types. It is not needed in C11, and is deprecated in C17 and removed in C23.

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C standards.

DR	Applied to	Behavior as published	Correct behavior
DR 485	C11	the specification was redundant and contradictory to the core language	fixed

References

See also

ATOMIC_FLAG_INIT (C11)	initializes a new atomic_flag (macro constant)
C++ documentation for ATOMIC_VAR_INIT