help for back_inserter and end()

Hello,

The iterator adaptor "back_inserter" takes a container and returns a
iterator so that we can insert elements to the end of the container.
Out of curiosity, I tried to look at what element the returned
iterator refers to. Here is my code:

#include<iostream>
#include<vector>
#include<iterator>
#include<algorithm>

using namespace std;

int main(){
  vector<int> v;
  v.push_back(0);
  v.push_back(1);
  v.push_back(2);

  cout << (*(back_inserter(v)));
  return 0;
}

The code above couldn't compile. Since "back_inserter" returns an
iterator, then I would think I can dereference it. What's wrong with
it?

I also tried to copy containers using "copy", and instead of
"back_inserter", I used "end()". The code is:

#include<iostream>
#include<vector>
#include<iterator>
#include<algorithm>

using namespace std;

int main(){
  vector<int> v;
  v.push_back(0);
  v.push_back(1);
  v.push_back(2);

  vector<int> w;
  v.push_back(3);
  v.push_back(4);

  copy(w.begin(),w.end(),v.end()); //instead of back_inserter, I
used .end()

  for(vector<int>::const_iterator i = v.begin(); i != v.end(); i++)
    cout << (*i) << endl;

  return 0;
}

I was told the code above was wrong, but surprisingly, it compiled and
worked. I'm really puzzled by what "back_inserter" does and when I
can replace back_inserter by copy.

Thanks a lot!