title: Why is mktime returning -1 for my std::tm
body: <p>I have a <code>std::tm</code> that looks correct.</p>
  
  <p><img src="https://i.stack.imgur.com/RcmGt.png" alt="enter image description here"></p>
  
  <p>However when normalizing with <code>mktime</code> I am seeing a <code>-1</code></p>
  
  <p>According to <code>man mktime</code>:</p>
  
  <p><code>The mktime() function returns the
       specified calendar time; if the calendar time cannot be represented, it returns -1;</code></p>
  
  <p>However, looking at the screenshot I posted, I dont see what is wrong with what is being put in the <code>std::tm</code> Is there a problem with <code>tm_gmtoff</code> and <code>tm_zone</code>?</p>