title: QbyteArray data copy
body: <p>I have two <code>QByteArray</code>, <code>sData</code> and <code>dData</code>.</p>
  
  <p>I want to copy <code>n</code> bytes from location <code>x</code> in <code>dData</code> i.e. <code>&amp;dData[x]</code> to location <code>y</code> of <code>sData</code> i.e. <code>&amp;sData[y]</code>. </p>
  
  <p>In C, array copy is done by <code>memcpy(&amp;dData[x], &amp;sData[y], n);</code></p>
  
  <p>How could copying above data of <code>QByteArray</code> be done in Qt?</p>