Can't change class data in $SESSION

larry1301

A simplifed code snipped of a problem thats driving me crazy is below. I have created a class, initialized it in the constructor and save an instance of the class in a $_SESSION variable. The ID variable is initialized in the constructor to 1. I can retrieve the class data fine but I can't change it. In the snippet below I call a class function to change the ID variable to 2 and it shows it changing fine, but when I list the contents of the $SESSION variable it shows it not being changed. Further, if I list the object contents using the class intstance that was returned, it shows the ID with the changed value of 2.

I can't figure this out. Am I making some kind of newbie error. It seems like I have two instances of the class. I have shown the code, output and the session portion of phpinfo(); My php version is 4.3.8 on XP Pro.

Code

<?php
session_start();
class Store
{
	var $ZipCode;
	var $ID;

function Store() 
{
	$this->ZipCode     = "99999";
	$this->ID = 1;
}
function SetID( $ID ) 
{
	$this->ID = $ID;
	echo "<br>Set ID in Class = ";
	echo $this->ID;
}
function ShowID( ) 
{	
	echo "<br>Show ID = in Class = ";
	echo $this->ID;
}
}
function print_vars($obj) 
{
    $arr = get_object_vars($obj);
    while (list($prop, $val) = each($arr))
        echo "\t$prop = $val\n";
	echo "<br>";

}
function  ShowSessionVariables ( )
{
    echo "<br>******_SESSION*****************<br>";
    while(list($key, $value) = each($_SESSION)) 
    { 
        echo "$key = $value<br>"; 
		print_vars ( $value );
    }
	reset ( $_SESSION );
}

$st = new Store();
echo "After Constructor";
$_SESSION [ 'st' ] = $st;
ShowSessionVariables ( );
echo "Print Vars";
print_vars ( $st );


$st->SetID ( 2 );
echo "<br>After Changing ID ";
ShowSessionVariables ( );
echo "Print Vars";
print_vars ( $st );
echo $st->ID;
echo $st->ShowID();
ShowSessionVariables ( );
?>

OUTPUT with comments

After Constructor
***_SESSION**************
st = Object
ZipCode = 99999 ID = 1
Print Vars ZipCode = 99999 ID = 1
// All fine to this point

// Set ID to 2
Set ID in Class = 2
After Changing ID
***SESSION***********
st = Object
ZipCode = 99999 ID = 1 // Session vars still show it as 1
Print Vars ZipCode = 99999 ID = 2 Print vars show it changed
2

Show ID = in Class = 2 Call to class function show it changed
SESSION**************
st = Object
ZipCode = 99999 ID = 1 // $SESSION variable not changed

php.ini variables

Session Support enabled

Registered save handlers files user

Directive Local Value Master Value
session.auto_start Off Off
session.bug_compat_42 On On
session.bug_compat_warn On On
session.cache_expire 180 180
session.cache_limiter nocache nocache
session.cookie_domain no value no value
session.cookie_lifetime 0 0
session.cookie_path / /
session.cookie_secure Off Off
session.entropy_file no value no value
session.entropy_length 0 0
session.gc_divisor 100 100
session.gc_maxlifetime 1440 1440
session.gc_probability 1 1
session.name PHPSESSID PHPSESSID
session.referer_check no value no value
session.save_handler files files
session.save_path /tmp /tmp
session.serialize_handler php php
session.use_cookies On On
session.use_only_cookies Off Off
session.use_trans_sid Off Off😕 😕

sneakyimp

as best i can tell, you assigned a session variable to point at an object and then changed the object. I'm not sure how objects are dealt with in PHP but i suspect you could do this and it would work just fine:

$_SESSION [ 'st' ]->SetID ( 2 );

either that OR after you've done this:

$st->SetID ( 2 );

then do this:

$_SESSION [ 'st' ] = $st;

seems plain enough to me. is there some kind of byval/byref thing that's over my head on this?

larry1301

I think I have it now. When you do:

$_SESSION [ 'st' ] = $st;

php makes a byte COPY of $st and places it in the $SESSION variable. anything done to the local copy of $st doesn't affect the $SESSION version of it. Coming from C++, I had assumed (wrongly) that it created an reference, not a copy.

So instead of the code I had:

$st->SetID ( 2 ); // changes local copy only

I should have had

$SESSION [ 'st' ]->SetID ( 2 ); // changes $SESSION copy but not local copy

$s = $SESSION [ 'st' ];
$s->SetID(2); // changes $SESSION copy but not local copy

The moral is not to use the local copy after it is copied to a $_SESSION variable

Thanks

sneakyimp

i think that'll work, but i'm no expert. be sure to test it.

jazz_snob

sneakyimp is again correct.

I use this type of code frequently:
$SESSION[ 'cart' ] =& new Cart();
$SESSION[ 'cart' ] -> addItem( $item, $qty, $price );

😉

bosshoff

I just wanted to say how very much this post helped me out. I was pulling my hair for about three days straight trying to figure out why in the hell nothing was getting altered. Now I fixed the problem, and I have a better understanding of session variables. Well done men!