Is there a Drupal API function to get the list of nodes by type?
Depending on the version of Drupal :

drupal 6:

$nodes = db_query('SELECT nid FROM {node} WHERE type="%s"', $type);

drupal 7: 

$nodes = node_load_multiple(array(), array('type' =&gt; $type));

drupal 8: 

$nids = \Drupal::entityQuery('node')
  -&gt;condition('type', 'NODETYPE')
  -&gt;execute();
$nodes = \Drupal::entityTypeManager()
  -&gt;getStorage('node')
  -&gt;loadMultiple($nids);