title: mktime conversion
body: <p>I wanted to calculate the time difference for a GMT time and current time. For this I am converting tm time  (which is in GMT) to time_t format using mktime. and current time using time() api. </p>
  
  <pre><code>struct tm = x;  time_t t1, t2; 
  time(&amp;t1);
  /* here x  will get in GMT format */
  t2 = mktime(&amp;x);
  sec = difftime(t2 , t1);
  </code></pre>
  
  <p>In this for making the same time zone, is mktime() will  take care of converting to local time ? or shall I need to explicitly add  <code>sec = difftime(t2 , gmtime(&amp;t1);</code>
  Thanks</p>