title: c++ boost::posix_time::ptime default value
body: <p>I have a member variable in my class:</p>
  
  <pre><code>class Foo
  {
  // ...
  private:
    boost::posix_time::ptime t;
  }
  </code></pre>
  
  <p>I want to initialize it in the constructor to a well known value such that I know it hasn't been set by the program yet:</p>
  
  <pre><code>Foo::Foo()
     : t(NULL) // doesnt work
  {}
  </code></pre>
  
  <p>But setting it to NULL doesn't work because its not a pointer.</p>
  
  <p>How do I initialize <code>boost::posix_time::ptime</code> to a well known value?</p>