title: Difference between 'using' and 'using namespace'
body: <p>In the boost libraries, there are often examples of including the library like:  </p>
  
  <pre><code>#pragma once
  #include &lt;boost/property_tree/ptree.hpp&gt;
  using boost::property_tree::ptree;
  </code></pre>
  
  <p>Throughout my program I have been importing namespaces like this:</p>
  
  <pre><code>#include "../MyClass.h"
  using namespace MyClassNamespace;
  </code></pre>
  
  <p>Can someone please explain: </p>
  
  <ol>
  <li>The difference between <code>using</code> and <code>using namespace</code>;</li>
  <li>What the advantage of negating the use of <code>using namespace</code> in favour of <code>using</code>;</li>
  <li>The differences in forward declaring <code>using</code> and <code>using namespace</code>;</li>
  </ol>
  
  <p>Thanks</p>