title: Function date_default_timezone_set() is not available
body: <p>As the title says, can anybody explain why the code</p>
  
  <pre><code>ini_set( 'date.timezone', 'Europe/Athens' );
  </code></pre>
  
  <p>works but</p>
  
  <pre><code>date_default_timezone_set( 'Europe/Athens' );
  </code></pre>
  
  <p>does not? It gives me this error:</p>
  
  <blockquote>
    <p>Fatal error: Call to undefined function date_default_timezone_set()</p>
  </blockquote>
  
  <p>I was looking for a solution to convert a timestamp and all I could find on the web was to use <code>date_default_timezone_set</code>. But the conversion had always 1 hour difference.</p>
  
  <p>Then I found this topic "<a href="https://stackoverflow.com/a/10503708/972773" title="strftime&#40;&#41; function showing incorrect time"><code>strftime()</code> function showing incorrect time</a>" which is using the init_set code (and afterwards I've RTM and found out that it's already mentioned in the documentation). I tried it and it worked.</p>
  
  <p>But I haven't found an answer why <code>date_default_timezone_set</code> is not working.</p>
  
  <p>Can anybody explain please?</p>