Thank you for this bug report. To properly diagnose the problem, we
need a short but complete example script to be able to reproduce
this bug ourselves. 

A proper reproducing script starts with <?php and ends with ?>,
is max. 10-20 lines long and does not require any external 
resources such as databases, etc.

If possible, make the script source available online and provide
an URL to it here. Try to avoid embedding huge scripts into the report.

I did not experience any problems with Apache/1.3.29 (Unix) PHP/5.0.4 on Debian stable.
Code:
<?php
  $_SESSION['one'] = 1;
  $_SESSION['two'] = 2;
  $_SESSION['three'] = 3;

  print_r($_SESSION);

  foreach ($_SESSION as $key_session => $session)
        unset($_SESSION[$key_session]);

  print_r($_SESSION);
?>

Result is as expected:
Array ( [DF_debug] => 1 [one] => 1 [two] => 2 [three] => 3 ) Array ( )

I can confirm this problem with Windows Server 2003, PHP 5.0.4.  Sample code:

<?php
function unsetSessionVariables($session_name) {
    foreach ($_SESSION as $session_key => $session_variable) {
        if (strstr($session_key, $session_name)) {
            // Neither of these work as intended.
            unset($GLOBALS[_SESSION][$session_key]);
            unset($_SESSION[$session_key]);
        }
    }
}

unsetSessionVariables("session_name");
?>

I have verified that the same problem exists in the latest 5.1 snap (php5-win32-200504041430) on the same platform.

More information:
This "problem" does not exist with 5.0.2 on Windows 2003 (IIS6).

duh at dowebwedo dot com's method does work within the execution of that one script, but the unset variables are not persistent.  The $_SESSION variables are restored on each subsequent page load even after they have been unset which leads to problems with session fixation and the inability to clean-up session values that are no longer needed.

No feedback was provided for this bug for over a week, so it is
being suspended automatically. If you are able to provide the
information that was originally requested, please do so and change
the status of the bug back to "Open".

In this testcase the "write" function is not called. If you comment line with "unset", the write function is called properly. If you delete whole foreach cycle and use 
"unset($_SESSION['A']);" instead, the "write" function si also called - as expected. This bug appear only when you call "unset" inside foreach cycle.

My environment: 
MS Windows Server 2003 SE (Windows NT 5.2 build 3790)
Apache/2.0.53 (Win32) PHP/5.0.4
I can provide more information if you ask for them.

<?php
function foo(){
  return(true);
}
function read($id){
  return 'A|s:1:"a";B|s:1:"b";';
}
function write($id, $sess_data){
  print "I'm writing this data: \n";
  print_r($sess_data);
  return true;
}

header('Content-Type: text/plain');
session_set_save_handler("foo", "foo", "read", "write", "foo", "foo");
session_start();
print_r($_SESSION);
foreach($_SESSION as $lsKey => $lsVal){
  if($lsKey != 'A'){
    unset($_SESSION[$lsKey]);  //<<<<<<<< if you comment this line, the write function is called properly
  }
}
print_r($_SESSION);
print("finished\n");

?>

This problem is duplicating on WinXP Pro (SP2) Apache 1.3.33 PHP 5.0.4

register_globals = Off
register_long_arrays= Off

If you have 3 php pages with the following code:
1.php:
<?php 
@session_start();
$_SESSION['var1'] = 'val1';
$_SESSION['var2'] = 'val2';
$_SESSION['var3'] = 'val3';
var_dump($_SESSION);
?>
click <a href="2.php">here</a> for page 2

2.php:
<?php 
@session_start();
foreach($_SESSION as $k=>$v){
   unset($_SESSION[$k]);
}
var_dump($_SESSION);
?>
click <a href="3.php">here</a> for page 3

3.php:
<?php 
@session_start();
var_dump($_SESSION);
?>
Finish!

The results in the browser will be:

1.php:


array(3) { ["var1"]=> string(4) "val1" ["var2"]=> string(4) "val2" ["var3"]=> string(4) "val3" } 
click here for page 2 

2.php:

array(0) { } 
click here for page 3 

3.php:

array(3) { ["var1"]=> string(4) "val1" ["var2"]=> string(4) "val2" ["var3"]=> string(4) "val3" } Finish! 

Now, if you turn On the register_long_arrays this will work as expected having on page 3 an empty session.

Also if you execute outside a foreach loop the unset is working as well.

Contact me if you need more details.

is this bug fixed in the latest PHP versions? I see the bug report is still not closed..

Regards,
Ionut

Year 2008, this bug is still here. Simple recrusion function:

<?php
function recrusion($array, &$return, $pid=0, $level=0){
	foreach($array as $id=>$parent){
		if( $parent===$pid ){
			$return[$id]= $level;
			unset($array[$id]); /* remove this to get correct results */
			recrusion(&$array, &$return, $id, $level+1);
		}
	}
}
$return= array();
$array= array(1=>0,2=>1,3=>2,4=>3,5=>2,6=>2,7=>6,8=>6,9=>0,10=>0);
recrusion($array, &$return);
var_dump( $return );
?>

Result:
array(6) { [1]=> int(0) [2]=> int(1) [3]=> int(2) [4]=> int(3) [9]=> int(0) [10]=> int(0) } 
Should be:
array(10) { [1]=> int(0) [2]=> int(1) [3]=> int(2) [4]=> int(3) [5]=> int(2) [6]=> int(2) [7]=> int(3) [8]=> int(3) [9]=> int(0) [10]=> int(0) } 

Tested with PHP 5.2.6 on Debian-40r3-amd64 and Windows Vista 32


It DOES work with bigger/deeper array though!