title: Passing vector by reference
body: <p>Using normal C arrays I'd do something like that:</p>
  
  <pre><code>void do_something(int el, int **arr)
  {
     *arr[0] = el;
     // do something else
  }
  </code></pre>
  
  <p>Now, I want to replace standard array with vector, and achieve the same results here:</p>
  
  <pre><code>void do_something(int el, std::vector&lt;int&gt; **arr)
  {
     *arr.push_front(el); // this is what the function above does
  }
  </code></pre>
  
  <p>But it displays "expression must have class type". How to do this properly?</p>