Defined in header <atomic> | ||
|---|---|---|
#define ATOMIC_FLAG_INIT /* implementation-defined */ | (since C++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 | (until C++20) |
| This macro is no longer needed since default constructor of | (since C++20) |
#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
}The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 3659 | C++20 | ATOMIC_FLAG_INIT was deprecated, but needed in C on some platforms | it is undeprecated |
|
(C++11) | the lock-free boolean atomic type (class) |
C documentation for ATOMIC_FLAG_INIT |
|
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