title: are copy and move constructors automatic friends?
body: <p>We can access private variables of another class when we define copy or move constructors. Does C++ make them <code>friend</code> to each other automatically? </p>
  
  <p>For example:</p>
  
  <pre><code>my_str::my_str(my_str&amp;&amp; m) 
  {
      size_ = m.size_; //accessing private variable another my_str class
      buff_ = m.buff_; //accessing private variable another my_str class
      m.buff_ = nullptr;
      m.size_ = 0;
  }
  </code></pre>