How do you know if a file has changed?

Question

Qt

without open/close cycles. using event

Answer 1

https://doc.qt.io/qt-5/qfilesystemwatcher.html

Answer 2

without open/close cycles. using event

The problem has no solution in pure C++.

Answer 3

Linux has inotify under Windows FindFirstChangeNotification.
Perhaps there is some kind of cross-platform library that can do this.