c++ - Iterator invalidity after calling erase

Question

I am confused a bit. What I have learned or been told is that an iterator of a vector becomes invalid if erase is called. But why the code below works. It is compiled using g++ and run in Linux.

#include <vector>
#include <iostream>

using namespace std;

int main() {
  vector<int> vec;
  vec.push_back(1);
  vec.push_back(2);
  vec.push_back(3);

  vector<int>::iterator it = vec.begin();
  ++it;
  vector<int>::iterator it2;

  it2 = vec.erase(it);
  cout << "it: " << *it << endl;
  cout << "it2: " << *it2 << endl;
}

Thanks for any feedbacks!

Answer 1

From http://www.cplusplus.com/reference/stl/vector/erase/ (not the world's best C++ reference):

This invalidates all iterator and references to position (or first) and its subsequent elements.

So it is invalid; using it results in undefined behaviour. The fact that you happen to get what you expect is pure bad luck.