storing a reference to an object in a gl

[Anon]

hi,

it seems to be impossible to store a reference to a class object in a global variable.

i tried this:

<?
$g_test = null;

class CTest
{
var $m_iCount;

function CTest($iCount)
{
  $this->m_iCount = $iCount;
}

}

function test($iCount)
{
global $g_test;

if(isset($g_test))
{
  print("output 1: $g_test->m_iCount <br>");
}

$test = new CTest($iCount);
$g_test = &$test;

print("output 2: $g_test->m_iCount <br>");

}

test(0);
test(1);
test(2);
?>

the result was:
output 2: 0
output 2: 1
output 2: 2

this means that $g_test is never set when the function is entered. it is set temporary when we are inside of the function, this shows 'output 2: '.
don't ask me, why i don't use $g_test = $test instead of the reference, i don't want to store a copy of the new created object.

any idea???

matze

[[deleted]]

I guess the $g_test remains after you set it, but that which it references to gets unset when the function exits.

Sounds logical to me.
What exactly are you trying to achieve?

[Anon]

hello vincent,

i thought the same, but i can't understand, why then $g_test isn't undefined (the value doesn't exist), but contains the old value. that sounds ilogical.
you asked me, what i'm trying to archive:
i want to convert a xml-document into a tree of xml-elements, that store their childs in an array and a reference to their parent.
i wrote a short portion of executable code, that shows my problem:

<?
class CTreeElement
{
var $m_szName;
var $m_arSubElems;
var $m_parent;

	// constructor
	function CTreeElement($szName, &$parent)
{
  $this->m_szName = $szName;
  $this->m_arSubElems = array();
  $this->m_parent = &$parent;
}

function addSubElem(&$sub)
{
  array_push($this->m_arSubElems, &$sub);
}

}

$dummy = 0;
$g_curElem = &new CTreeElement('root', $dummy);
$g_newElem = null;

function addElem($name)
{
global $g_curElem;
global $g_newElem;

$g_newElem = &new CTreeElement($name, $g_curElem);
$g_curElem->addSubElem($g_newElem);
$g_curElem = &$g_newElem;

}

addElem('elem1');
print('cur elem: ' . $g_curElem->m_szName . ', array count: ' . count($g_curElem->m_arSubElems) . '<br>');
print('parent: ' . $g_curElem->m_parent->m_szName . ', array count: ' . count($g_curElem->m_parent->m_arSubElems) . '<br>');
?>

i declared $g_newElem as global, to prevent an undefined status of $g_curElem.

i expect the following output:

cur elem: elem1, array count 0
parent: root, array count 1

but the result is:
cur elem: root, array count: 1
parent: , array count: 0

this means, that $g_curElem wasn't assigned in addElem(). or more exactly, that it's only assigned to the new object inside of addElem().

i don't understand nothing and start desperating ...

matze

[[deleted]]

First, take out the ampersands in front of the \"new\" statements,
you don\'t want to make a reference here, you want to make a real new object.

Second, what you are trying to do sounds very \"recursive\"

and indeed, PHP thinks so too....
Try doing a \"print_r()\" on your objects after you work with them at the various functions.
This is what I found:

-- copied from my screen --
ctreeelement Object
(
[m_szName] => elem1
[m_arSubElems] => Array
(
)

[m_parent] => ctreeelement Object
    (
        [m_szName] => root
        [m_arSubElems] => Array
            (
                [0] => ctreeelement Object
                    (
                        [m_szName] => elem1
                        [m_arSubElems] => Array
                            (
                            )

                        [m_parent] =>  *RECURSION*
                    )

            )

        [m_parent] => 0
    )

)

-- end of copy ---

See the RECURSION notice? something is looping back into itself,
that\'s probably why it doesn\'t work.

Better re-think your code, I\'m too tired / lazy right now :-)

[Anon]

thank you very much for debugging my code and the tip with print_r(), i didn't knew this function and find it very helpfull.
you're right, what i'm trying is recursive, that's my intention. but naturally without confunding php ...

matze

[Anon]

hi,

i think the recursion that sees print_r() isn't an error. the subElems Array of the root object points to the child object, whichs parent reference is the root object ..., that's ok.
i changed the code a little bit to find the error:

<?
class CTreeElement
{
var $m_szName;
var $m_arSubElems;
var $m_parent;

	// constructor
	function CTreeElement($szName)
{
  $this->m_szName = $szName;
  $this->m_arSubElems = array();
}

function addSubElem(&$sub)
{
  $sub->m_parent = &$this;
  array_push($this->m_arSubElems, &$sub);
}

}

$g_curElem = new CTreeElement('root');
$g_newElem = null;

function addElem($name)
{
global $g_curElem;
global $g_newElem;

$g_newElem = new CTreeElement($name);
$g_curElem->addSubElem($g_newElem);

print_r($g_curElem);
print('<br>');

$g_curElem = &$g_newElem;

print_r($g_curElem);
print('<br>');

print('cur elem: ' . $g_curElem->m_szName . ', array count: ' . count($g_curElem->m_arSubElems) . '<br>');

}

addElem('elem1');
print('cur elem: ' . $g_curElem->m_szName . ', array count: ' . count($g_curElem->m_arSubElems) . '<br>');

print_r($g_curElem);
?>

the output of the two print_r() commands is imho correct. the first 'cur elem ...' line sa well, $g_curElem contains the correct value. the next 'cur elem ...' line i can't understand. i did nothing except returning of the function. NOTHING. what does php???
you told me i mustn't use $g_curElem = &$g_newElem. when i replace this with $g_curElem = $g_newElem i get a object 'elem1', which thinks it has a parent 'elem1', which thinks it has ... whyever.

sorry for posting so much code, i try to limit it, but don't know how to explain my problem in words.