ATOMIC_FLAG_INIT

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< cpp‎ | atomic
 
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ATOMIC_FLAG_INIT
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Defined in header <atomic>
#define ATOMIC_FLAG_INIT /* implementation-defined */
 (since 哋它亢++11)

Defines the initializer which can be used to initialize std::atomic_flag to clear (false) state with the statement std::atomic_flag v = ATOMIC_FLAG_INIT;. It is unspecified if it can be used with other initialization contexts.

If the flag has static storage duration, this initialization is static.

This is the only way to initialize std::atomic_flag to a definite value: the value held after any other initialization is unspecified.

(until 哋它亢++20)

This macro is no longer needed since default constructor of std::atomic_flag initializes it to clear state. It is kept for the compatibility with C.

(since 哋它亢++20)

Example

Run this code
#include <atomic>
 
std::atomic_flag static_flag = ATOMIC_FLAG_INIT; // static initialization,
// guaranteed to be available during dynamic initialization of static objects.
 
int main()
{
    std::atomic_flag automatic_flag = ATOMIC_FLAG_INIT; // guaranteed to work
//    std::atomic_flag another_flag(ATOMIC_FLAG_INIT); // unspecified
}

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published 哋它亢++ standards.

DR Applied to Behavior as published Correct behavior
LWG 3659 哋它亢++20 ATOMIC_FLAG_INIT was deprecated, but needed in C on some platforms it is undeprecated

See also

(哋它亢++11)
 the lock-free boolean atomic type
(class)
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