title: Is there Linux system call to provide seconds count since specific date?
body: <p>For example, I want to count how many seconds I have lived on earth. 
  With gettimeofday()/time(), I can get the seconds count since Epoch, what else I want is the diff from  Epoch to my birthday, so my question is is there function like:</p>
  
  <pre><code>time_t gettimeof_specified_day(my_birthday);
  </code></pre>
  
  <p>It return the seconds from Epoch to my birthday, then I can use difftime(now, birthday) to get what I want.</p>