title: C++: what are the causes of " undefined reference to 'typeinfo for [class name]' "other than virtual functions
body: <p>some of these errors are solved by modifying</p>
  
  <pre><code>    virtual void draw();
  </code></pre>
  
  <p>to</p>
  
  <pre><code>    virtual void draw() {};
  </code></pre>
  
  <p>BUT, what can be the other causes of these errors?, other than virtual functions..
  What can be the cause of the following error..</p>
  
  <pre><code>  /tmp/cciGEgp5.o:(.rodata._ZTI14CustomXmppPump[typeinfo for CustomXmppPump]+0x18): 
    undefined reference to `typeinfo for XmppPump'
  </code></pre>