title: C++ Exceptions questions on rethrow of original exception
body: <p>Will the following append() in the catch cause the rethrown exception to see the effect of append() being called?</p>
  
  <pre><code>try {
    mayThrowMyErr();
  } catch (myErr &amp;err) {
    err.append("Add to my message here");
    throw; // Does the rethrow exception reflect the call to append()?
  }
  </code></pre>
  
  <p>Similarly, if I rewrite it this way, will bit slicing occur if the actual exception is derived by myErr?</p>
  
  <pre><code>try {
    mayThrowObjectDerivedFromMyErr();
  } catch (myErr &amp;err) {
    err.append("Add to my message's base class here");
    throw err; // Do I lose the derived class exception and only get myErr?
  }
  </code></pre>