Default sorting by first member variable of class

Question

As class has all the member variables of int type and C++ knows how to sort int types, why can't class sorting work without < operator ?

Try uncommening sort statement and it will throw errors

In other words , we have vector<vector<int>> , then C++ by default sorts outer vector based on first element of inner vector.

Why this non uniformity
https://sololearn.com/compiler-playground/cvj2h8MyefIL/?ref=app

Answer 1

maybe because the default behavior is ascending sort, so it needs an overload for < for custom types.

Answer 2

Let it do ascending or descending. I was expecting it to not ask for any operator like it is not asking for vector of vector.