PHP：如何在数组中保存递归函数的结果？

Question

I have changed version of this recursive function... http://www.phpbuilder.com/articles/databases/mysql/handling-hierarchical-data-in-mysql-and-php.html

What I need is a way to save the returned value of this function in an array so that I can reverse the order of array elements. The function works well for me, but I need a way to save values. Here is the code...

function display_children($category_id, $level) {
  global $database;
  $result = mysql_query("SELECT * FROM parents WHERE id_roditelja='$category_id'") or die(mysql_error());
  $niz = array();
  while ($row = mysql_fetch_array($result)) {
    echo str_repeat('  ', $level) . $row['naziv'] . "<br/>";
    array_push($niz, display_children($row['parent_id'], $level + 1));
//this is one way I tried, and I get $niz with exact number of elements but each is null
//in this $niz array I need to store values of recursion
    var_dump($niz);
  }
}

Answer 1

I think you want this:

function display_children/* <- this must be the same */($category_id, $level) {
  global $database;
  $result = mysql_query("SELECT * FROM parents WHERE id_roditelja='$category_id'") or     die(mysql_error());
  $niz = array();
  while ($row = mysql_fetch_array($result)) {
    $niz[] = str_repeat('  ', $level) . $row['naziv'] . "<br/>"; // we need to save this
    $niz = array_merge($niz, /* as this -> */display_children($row['parent_id'], $level + 1)); // array_merge doesn't take a reference so we need to store its result in $niz
  }
  return $niz;
}

if you want a tree like structure use array_push instead of array_merge. As noone seems to notice: His function can't return anything without a return statement !