how to check if a constant exists in php
<p>So im using a php framework called <strong>fuelphp</strong>, and I have this page that is a <strong>html</strong> file so i can't use php in it, and I have another file that has a top bar in it, which my html file will call though ajax. And I was just asking, how do we check if a constant exists in php? aka  (the fuelphp framework file locations)</p>

<p>so these are constants I need to check (well I only have to check one of them)</p>

<pre><code>define('DOCROOT', __DIR__.DIRECTORY_SEPARATOR);
    define('APPPATH', realpath(__DIR__.'/fuel/app/').DIRECTORY_SEPARATOR);
    define('PKGPATH', realpath(__DIR__.'/fuel/packages/').DIRECTORY_SEPARATOR);
    define('COREPATH', realpath(__DIR__.'/fuel/core/').DIRECTORY_SEPARATOR);                    
    require APPPATH.'bootstrap.php';
</code></pre>

<p><strong>edit:</strong><br />
I realised that these aren't variables they are constants...</p>
