How can I list all files in a directory sorted alphabetically using PHP?

I'm using the following PHP code to list all files and folders under the current directory:

<?php
    $dirname = ".";
    $dir = opendir($dirname);

    while(false != ($file = readdir($dir)))
        {
          if(($file != ".") and ($file != "..") and ($file != "index.php"))
             {
              echo("<a href='$file'>$file</a> <br />");
        }
    }
?>

The problem is list is not ordered alphabetically (perhaps it's sorted by creation date? I'm not sure).

How can I make sure it's sorted alphabetically?