How do I create a variable that contains the html of a site using file_get_contents()?

Based on http://php.net/manual/en/function.file-get-contents.php, I've tried many variations of this short script with no joy.
PHP Code:
<?php
$homepage 
file_get_contents('http://www.example.com');
$txt fopen($homepage,'r');
?>
How do I avoid the warning and create a variable that I can fopen using file_get_contents()?