title: Threadsafe way to convert time between timezones
body: <p>I am writing a application to convert utc-time to different timezones, now I can use something like this</p>
  
  <pre><code>putenv("TZ=TIMEZONE1"); 
  tzset()
  ...
  do time conversions
  </code></pre>
  
  <p>but I don't think it is thread safe, so is there any C/C++ library which can do timezone conversion by taking timezone as argument to function instead of being some global </p>