title: Codeigniter: A fatal error occurs when using base_url() function to define a constant in "application/config/constants.php" file
body: <p>I'm using Codeigniter and right now I'm trying to define some constants to hold full paths to some folders like css, js, images, etc. and I've tried to define these constants in <code>application/config/constants.php</code> file like this:</p>
  
  <pre><code>define("PATH_TO_CSS_FOLDER", base_url("assets/css"));
  </code></pre>
  
  <p>but I've got this error:</p>
  
  <pre><code>Fatal error: Call to undefined function base_url() in D:\xampp\htdocs\demo\application\config\constants.php on line 44
  </code></pre>
  
  <p>so how can I define these constants without having to write the absolute path in the constants.php file like this:</p>
  
  <pre><code>define("PATH_TO_CSS_FOLDER", "http://my-website.com/assets/css");
  </code></pre>