Code:
...
Matrix3f m;
m << 1, 2, 3,
4, 5, 6,
7, 8, 9;
std::cout << m;
...
I have System.AccessViolationException: Attempted to read or write protected memory...

I have just copied the example Does anyone have any suggestions about the problem. It's new for me and I'm confused

strange, do you have a self contained example that triggers the issue, because such a code is known to work, so the issue probably comes from somewhere else...