ATOMIC_FLAG_INIT

< cpp‎ | atomic
Defined in header <atomic>
#define ATOMIC_FLAG_INIT /* implementation-defined */
 (since C++11)
(deprecated in C++20)

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 C++20)

This macro is no longer needed and deprecated, since default constructor of std::atomic_flag initializes it to clear state.

 (since C++20)

Example

#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
}

See also

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