what is the difference between using ATOMIC_FLAG_INIT and std::atomic_flag::clear
atomic, c++, c++11
Solution
`ATOMIC_FLAG_INIT` is an implementation defined macro that is guaranteed to work in expressions like the one you've posted. It comes in handy for initializing an `atomic_flag` that you may have defined at namespace scope, for instance. It also guarantees that the flag will be cleared and that if the flag itself has static storage duration, the initialization will also be static.
The second set of statements is initialization followed by clearing of the flag. Since the state of `atomic_flag` is unspecified post default construction, it does mean that the flag is in an unspecified state until the `clear()` has been executed.
Problem
Are the following two code snippets the same: ``` std::atomic_flag lock = ATOMIC_FLAG_INIT; ``` and ``` std::atomic_flag lock; lock.clear(); ``` It seems like the second can allow for lock to be in an unknown state for a few clicks Is the first code snippet always going to have a known state?