title: what is difference between lock() and guard() after lock_guard
body: <p>Hi I'm up to code a circular buffer through c++ boost library. and I have come up with some questions that I can't understand.</p>
  
  <pre><code>boost::lock_guard&lt;boost::mutex&gt; guard( Mutex );
  boost::lock_guard&lt;boost::mutex&gt; lock( Mutex );
  </code></pre>
  
  <p>This is my first time using boost library so I don't really understand what is difference between these two. please help me </p>