I can understand people used to a HLL running into this. It's useful to read the documentation: https://en.cppreference.com/w/cpp/container/vector/insert https

I can understand people used to a HLL running into this. It's useful to read the documentation: https://en.cppreference.com/w/cpp/container/vector/insert https://en.cppreference.com/w/cpp/container/vector/insert mentions that references/iterators may be invalidated. I'm not going to pretend that I understand everything on that site (particularly anything about complex templates and things like SFINAE) but often there's comprehensible stuff in there. It can be really helpful.