title: QHash storing large amount of data
body: <p>I've 10,000,000 entry of type struct{int, int, int, int}. when I store them using <a href="http://doc.qt.io/qt-5/qhash.html" rel="nofollow noreferrer">QHash</a> or <a href="http://doc.qt.io/qt-5/qmap.html" rel="nofollow noreferrer">QMap</a>, it occupies large amount of memory, indeed it must take about </p>
  
  <pre><code>10,000,000 * 4 * 4 (sizeof integer) &lt;= 153 MB
  </code></pre>
  
  <p>but when I load my data it takes about 1.2 GB for both QHash and QMap, why this occurs and how can I optimize it for both speed and memory?(through any other data structure or some tricks to qmap and qhash)</p>