PHP Send no-cache Headers

<?php
function PHP_DO_NOT_CACHE_HEADERS()
{
      if (!headers_sent()) //Check if header has already been sent
      {
            header('Expires: Mon, 26 Jul 1997 05:00:00 GMT');
            header('Last-Modified: ' . gmdate( 'D, d M Y H:i:s' ) . ' GMT');
            header('Cache-Control: no-store, no-cache, must-revalidate');
            header('Cache-Control: post-check=0, pre-check=0', false);
            header('Pragma: no-cache');
            return true;
      }
      else
      {
            return false; //Do nothing since it has already been sent
      }
}
//How to call the above function
PHP_DO_NOT_CACHE_HEADERS();
?>