ATOMIC_FLAG_FREE
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                    |   Defined in header <stdatomic.h>
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|   #define ATOMIC_FLAG_INIT /* unspecified */  | 
(since C11) | |
Expands to an expression that can be used to initialize atomic_flag type. The value atomic_flag that is not initialized using this macro is undefined.
[edit] See also
|    (C11)  | 
   initializes a new atomic object   (function macro)  |