title: diffrence of two time in c++
body: <p>At first I get a time by </p>
  
  <pre><code>time_t t1 = time(0) 
  </code></pre>
  
  <p>(is it right for getting current time?)
  then</p>
  
  <pre><code>time_t t2 = time(0)
  </code></pre>
  
  <p>now I want the find the difference between t1 and t2 in milliseconds
  I searched a lot but it didn't worked.
  lots of casting problems and unable to change it to milliseconds
  thanks for your help in advance</p>