title: C++ Monitoring variable for changed value
body: <p>I'm converting a TradeStation EasyLanguage indicator code to a C++ DLL. Using the TradeStation API it's possible to access market data in the C++ DLL like so:</p>
  
  <pre><code>double currentBarDT = pELObject-&gt;DateTimeMD[iDataNumber]-&gt;AsDateTime[0];
  </code></pre>
  
  <p>My question is:</p>
  
  <p>Is it possible in C++ to somehow 'watch' or 'listen' for when the variable 'currentBarDT' has its value changed/updated?  I would like to use the changing of the value as a trigger to generate a signal with Boost.Signals2.</p>