我如何使用Gravity Forms的GFAPI类？

How do I use the GFAPI class from Gravity Forms? I want to get all the entries from a given form. But nothing seems to work.. Do I need to import/include/require the class?

<?php

getEntries();

function getEntries() {
    $form_id = 73;
    $search_criteria = array();
    $entries = GFAPI::get_entries($form_id, $search_criteria);
    exit(var_dump($entries));
}

When I open the file, it doens't work, and I have a feeling it's because it can't find the class.

In the GF docs, it says: "The API Functions are automatically included when Gravity Forms loads and they will be available by the time add-ons load. The API class is called GFAPI and it can be found in /plugins/gravityforms/includes/api.php.".