title: How to append a Qstring using "%" operand
body: <p>I am trying to <code>.append</code> my QString with two <code>double</code> values using the <code>%</code> operand. I saw the following example in the QString class reference documentation for using <code>arg</code> with double, but the example doesn't include appending the str:</p>
  
  <pre><code>double d = 12.34;
  QString str = QString("delta: %1").arg(d);
  </code></pre>
  
  <p>here is my code. it does not include any run-time error but it doesn't place my doubles where the <code>%</code> operand is, instead it include my %1 and %2 as normal strings too:</p>
  
  <pre><code>double d1 = 0.5,d2 = 30.0
  QString str  = "abc";
  str.append("%1 def %2").arg(d1).arg(d2);
  </code></pre>
  
  <p>thank you </p>