How to return array from recursive function

Question

I couldn't find solution for this and I don't have much time for this. So what I want is to make function that I give category ID and it returns all ID's of categories which are it's child categories.

function getID($var) {
    $categories = array();

    function getChildren($id) {
        $result = mysql_query("SELECT * FROM categories WHERE parentID = '$id'");
        echo "<ul>";
        while ($row = mysql_fetch_array($result)) {
            echo "<li><a>{$row['ID']}</a>";
            $categories[] = $row['ID'];
            getChildren($row['ID']);
            echo "</li>";
        }
        echo "</ul>";
    }

    getChildren($var);
    return $categories;
}

I wan't to store everything in $categories array. $var is category ID which I give to function. When I call this function it prints list of exactly what I want't but array is empty.

it prints list of exactly what I want't but array is empty it prints and its empty!?!? — Vimalnath
– Vimalnath, Commented Mar 15, 2013 at 8:05
echo "<li><a>{$row['ID']}</a>" this line outputs ID what I want but when I try to print_r($categories) it doesn't output anything. — LaKaede
– LaKaede, Commented Mar 15, 2013 at 8:07
Do you want to return a flat list or a tree that represents the children? — Gerald Schneider
– Gerald Schneider, Commented Mar 15, 2013 at 8:08

fredrik · Accepted Answer · 2013-03-15 08:16:19Z

12

It seems you have a scope problem. Try this:

function getChildren(&$categories, $id) {
  $result = mysql_query("SELECT * FROM categories WHERE parentID = '$id'");
  echo "<ul>";
  while ($row = mysql_fetch_array($result)) {
    echo "<li><a>{$row['ID']}</a>";
    $categories[] = $row['ID'];
    getChildren($categories, $row['ID']);
    echo "</li>";
  }
  echo "</ul>";
}

function getID($var) {
  $categories = array();

  getChildren($categories, $var);
  return $categories;
}

Here is the PHP reference page describing how to pass by reference instead of by value. Basically it says that any function parameter which has a & in front of it will be passed by reference instead of by value.

edited Mar 15, 2013 at 8:16

answered Mar 15, 2013 at 8:07

fredrik

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3 Comments

Gerald Schneider Over a year ago

Same problem as with Naryls answer, if you do it this way you have to pass a reference to the original array (as fabs answer suggests)

LaKaede Over a year ago

oh, thanks. It works! Only one thing getChildren($categories, $var); should be $this->getChildren($categories, $var);

fredrik Over a year ago

Oh, you have it in a class - that was not in the question. If course then you need the $this-> as well.

Fabian Schmengler · Accepted Answer · 2013-03-15 08:09:45Z

1

$categories only exists in the scope of get children. You could either pass it by reference as second parameter or create get children as a closure with use (&$categories)

answered Mar 15, 2013 at 8:09

Fabian Schmengler

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Comments

Naryl · Accepted Answer · 2013-03-15 08:06:46Z

0

function getChildren($id, $categories)

should work.

The array was out of scope, so the function didn't touch the one you are returning. It created a new local $categories inside the function.

answered Mar 15, 2013 at 8:06

Naryl

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1 Comment

Gerald Schneider Over a year ago

This will return an empty array as well. The function getChildren() will work with a copy of the empty array, the original array will not be touched. If you want the function to add to the original array you have tu use function getChildren($id, &$categories);.

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