How do I restart my loop with get_next_post()?

get_next_post doesn’t really know what the “beginning” is. get_next_post uses get_adjacent_posts. If you look at the source, you can see that that function runs its own query to determine the next (or previous) post relative to the current post. It doesn’t loop through a list.

To get the “first” post, you will need to run a new query based on whatever parameters that you decide meet the condition of returning the first post. Something like this:

while (have_posts()) {
  the_post();
  the_title();
  $next_post = get_next_post();
  if (empty($next_post)) {
    echo 'empty'; 
    $args = array(
      'posts_per_page' => 1,
    );
    $first = new WP_Query($args);
    var_dump($first->post);
  }
  echo '<br>';
}

Also, “next” and “previous” are relative to sort order with “next” meaning closest newer post. In an ordinary default archive Loop, the first post in the list will not have a “next” post. I suspect you actually want to be using previous_post_link but that is a guess.

Related Posts: