1 book.module book_prev($book_link)

Fetches the menu link for the previous page of the book.


$book_link: A fully loaded menu link that is part of the book hierarchy.

Return value

A fully loaded menu link for the page before the one represented in: $book_link.


core/modules/book/book.module, line 752
Allows users to create and organize related content in an outline.


function book_prev($book_link) {
  // If the parent is zero, we are at the start of a book.
  if ($book_link['plid'] == 0) {
    return NULL;
  $flat = book_get_flat_menu($book_link);
  $curr = NULL;
  do {
    $prev = $curr;
    $curr = current($flat);
    $key = key($flat);
  } while ($key && $key != $book_link['mlid']);

  if ($key == $book_link['mlid']) {
    // The previous page in the book may be a child of the previous visible link.
    if ($prev['depth'] == $book_link['depth'] && $prev['has_children']) {
      // The subtree will have only one link at the top level - get its data.
      $tree = book_menu_subtree_data($prev);
      $data = array_shift($tree);
      // The link of interest is the last child - iterate to find the deepest one.
      while ($data['below']) {
        $data = end($data['below']);

      return $data['link'];
    else {
      return $prev;