The std::map subscript operator is a convenience, but a potentially dangerous one
https://blogs.msdn.microsoft.com/oldnewthing/20190227-00/?p=101045 [blogs.msdn.microsoft.com]
2019-02-27 21:21
The [] operator doesn’t know whether you’re going to read from or write to the result, so it has to come up with some sort of compromise. And sometimes the result of a compromise is something both sides dislike.
source: L