PHP 4 OOP problem

[Nicholas Sherlock]

Hey all,

I wrote a class to represent a node in a site navigation tree which
contains methods for building the tree from the database. I also wrote
some routines to print out the whole tree, starting from the root.

This malfunctions in a weird way in PHP 4 (I get a truncated tree). In
desperation, I downloaded the trial of PHPEdit to use the debugger, and
the program worked flawlessly! I suspect that the difference is that
PHPEdit uses PHP 5 while my testing server and my production server are
using PHP 4 (Both were operating on the exact same data).

Can anyone spot any obvious problems?

//Display code, starting from node with id 7:

function display_tree($root, $indent)
{
for ($i=0; $i<$indent; $i++) {
echo "&nbsp;";
}

echo $root->name."<br>\n";

for ($i=0; $i<$root->count(); $i++) {
display_tree($root->getchild($i),$indent+1);
}
}

$tree=new NavNode();
$tree->buildtree(7,null);
while ($tree->level()>0) {
$tree=$tree->parent;
}

display_tree($tree,0);

// The tree code:

//the highest node
$nav_rootnode=null;

//represents a node in a navigation tree
class NavNode {

var $children;
var $parent, $parentid, $id;
var $pageid;
var $name;

function count()
{
return count($this->children);
}

function getchild($index)
{
return $this->children[$index];
}

function level()
{
if (isset($this->parent)) {
return $this->parent->level()+1;
} else {
return 0;
}
}

function NavNode()
{
$this->children=array();
}

function buildup($id, &$childnode)
{
//find out who our parents are
$result=mysql_query("SELECT parent,pageid,name,flags FROM
structure WHERE id=".$id) or die("Buildup: ".mysql_error());

if (mysql_num_rows($result)==0) {
exit;
//we don't actually exist
}

$row=mysql_fetch_row($result);
$this->id=$id;
$this->parentid=$row[0];
$this->pageid=$row[1];
$this->name=$row[2];

//build our parent
if ($this->parentid != 0) {
$this->parent=new NavNode();
global $nav_rootnode;
$nav_rootnode=$this->parent;
$this->parent->buildup($this->parentid,$this);
}
$this->builddown($childnode);
}

function builddown(&$childnode)
{
//build our children
$result=mysql_query("SELECT id,pageid,name,flags FROM structure
WHERE parent=".$this->id) or die("Build down: ".mysql_error());
while ($row=mysql_fetch_row($result)) {
//we've already built and been provided with this child
if (isset($childnode) && ($childnode->id==$row[0])) {
array_push($this->children,$childnode);
continue;
}
$child=new NavNode();
$child->id=$row[0];
$child->pageid=$row[1];
$child->name=$row[2];
if ($row[3]=="expandall") {
$child->builddown(null);
}
array_push($this->children,$child);
}
}

function buildtree($id,$childnode)
{
$this->buildup($id,$childnode);
}

}

function buildlinkbox($node, $level)
{
for ($i=0; $i<$node->count(); $i++) {

for ($s=0; $s<$level; $s++) {
echo " ";
}
$child=$node->getchild($i);
echo "<a
href='".$_SERVER['PHP_SELF']."?id=".$child->id."'>".$child->name."</a><br>\n";
buildlinkbox($child,$level+1);
}
}
Thanks so much if anyone can help me out here.

Cheers,
Nicholas Sherlock

[Nicholas Sherlock]

Nicholas Sherlock wrote:

This malfunctions in a weird way in PHP 4 (I get a truncated tree). In
desperation, I downloaded the trial of PHPEdit to use the debugger, and
the program worked flawlessly! I suspect that the difference is that
PHPEdit uses PHP 5 while my testing server and my production server are
using PHP 4 (Both were operating on the exact same data).

I finally tracked it down to the stupid way that PHP 4 makes a copy of
an object unless you explicitly pass it by reference with the '&'
character. I thought that I had it covered, I sprinkled & everywhere it
would go when I worked with my tree. I eventually tracked the problem
down to the code I used for adding a child to the list of child nodes:

function builddown(&$childnode)
{
array_push($this->children,$childnode);
}

This results in a copy of $childnode being pushed on to the array, not a
reference to $childnode. Array_push doesn't take a reference for the
object being pushed. Solution:

array_push($this->children,null);
$this->children[count($this->children)-1]=&$childnode;

(There is probably a neater way of doing that)

If you want OOP, don't use PHP 4. I wish I had the choice.

Cheers,
Nicholas Sherlock

[Chung Leong]

Do $this->children[] =& $childnode instead.

Tree structures are pretty tricky to deal with in PHP, even in version
5. I usually try to flatten the structure to a hash table instead. You
can usually get away with that because you usually only present the
tree once.