title: Subtracting a certain number of hours, days, months or years from date
body: <p>I'm trying to create a simple function which returns me a date with a certain number of subtracted days from now, so something like this but I dont know the date classes well:</p>
  
  <pre><code>&lt;?
  function get_offset_hours ($hours) {
      return date ("Y-m-d H:i:s", strtotime (date ("Y-m-d H:i:s") /*and now?*/));
  }
  
  function get_offset_days ($days) {
      return date ("Y-m-d H:i:s", strtotime (date ("Y-m-d H:i:s") /*and now?*/));
  }
  
  function get_offset_months ($months) {
      return date ("Y-m-d H:i:s", strtotime (date ("Y-m-d H:i:s") /*and now?*/));
  }
  
  function get_offset_years ($years) {
      return date ("Y-m-d H:i:s", strtotime (date ("Y-m-d H:i:s") + $years));
  }
  
  print get_offset_years (-30);
  ?&gt;
  </code></pre>
  
  <p>Is it possible to do something similar to this?
  this kind of function works for years, but how to do the same with other time types?</p>