Simple look how PHP Reference works<?php/* Imagine this is memory map ______________________________|pointer | value | variable              | -----------------------------------|   1     |  NULL  |         ---           ||   2     |  NULL  |         ---           ||   3     |  NULL  |         ---           ||   4     |  NULL  |         ---           ||   5     |  NULL  |         ---           |------------------------------------Create some variables   */$a=10;$b=20;$c=array ('one'=>array (1, 2, 3));/* Look at memory _______________________________|pointer | value |       variable's       | -----------------------------------|   1     |  10     |       $a               ||   2     |  20     |       $b               ||   3     |  1       |      $c['one'][0]   ||   4     |  2       |      $c['one'][1]   ||   5     |  3       |      $c['one'][2]   |------------------------------------do  */$a=&$c['one'][2];/* Look at memory _______________________________|pointer | value |       variable's       | -----------------------------------|   1     |  NULL  |       ---              |  //value of  $a is destroyed and pointer is free|   2     |  20     |       $b               ||   3     |  1       |      $c['one'][0]   ||   4     |  2       |      $c['one'][1]   ||   5     |  3       |  $c['one'][2]  ,$a | // $a is now here------------------------------------do  */$b=&$a;  // or  $b=&$c['one'][2]; result is same as both "$c['one'][2]" and "$a" is at same pointer./* Look at memory _________________________________|pointer | value |       variable's           | --------------------------------------|   1     |  NULL  |       ---                  |  |   2     |  NULL  |       ---                  |  //value of  $b is destroyed and pointer is free|   3     |  1       |      $c['one'][0]       ||   4     |  2       |      $c['one'][1]       ||   5     |  3       |$c['one'][2]  ,$a , $b |  // $b is now here---------------------------------------next do */unset($c['one'][2]);/* Look at memory _________________________________|pointer | value |       variable's           | --------------------------------------|   1     |  NULL  |       ---                  |  |   2     |  NULL  |       ---                  |  |   3     |  1       |      $c['one'][0]       ||   4     |  2       |      $c['one'][1]       ||   5     |  3       |      $a , $b              | // $c['one'][2]  is  destroyed not in memory, not in array---------------------------------------next do   */$c['one'][2]=500;    //now it is in array/* Look at memory _________________________________|pointer | value |       variable's           | --------------------------------------|   1     |  500    |      $c['one'][2]       |  //created it lands on any(next) free pointer in memory|   2     |  NULL  |       ---                  |  |   3     |  1       |      $c['one'][0]       ||   4     |  2       |      $c['one'][1]       ||   5     |  3       |      $a , $b              | //this pointer is in use---------------------------------------lets tray to return $c['one'][2] at old pointer an remove reference $a,$b.  */$c['one'][2]=&$a;unset($a);unset($b);   /* look at memory _________________________________|pointer | value |       variable's           | --------------------------------------|   1     |  NULL  |       ---                  |  |   2     |  NULL  |       ---                  |  |   3     |  1       |      $c['one'][0]       ||   4     |  2       |      $c['one'][1]       ||   5     |  3       |      $c['one'][2]       | //$c['one'][2] is returned, $a,$b is destroyed--------------------------------------- ?>I hope this helps.

<?php//if you do:$a = "hihaha";$b = &$a;$c = "eita";$b = $c;echo $a; // shows "eita"$a = "hihaha";$b = &$a;$c = "eita";$b = &$c;echo $a; // shows "hihaha"$a = "hihaha";$b = &$a;$b = null;echo $a; // shows nothing (both are set to null)$a = "hihaha";$b = &$a;unset($b);echo $a; // shows "hihaha"$a = "hihaha";$b = &$a;$c = "eita";$a = $c;echo $b; // shows "eita"$a = "hihaha";$b = &$a;$c = "eita";$a = &$c;echo $b; // shows "hihaha"$a = "hihaha";$b = &$a;$a = null;echo $b; // shows nothing (both are set to null)$a = "hihaha";$b = &$a;unset($a);echo $b; // shows "hihaha"?>I tested each case individually on PHP 4.3.10.

Here's an example of unsetting a reference without losing an ealier set reference<?php$foo = 'Bob';              // Assign the value 'Bob' to $foo$bar = &$foo;              // Reference $foo via $bar.$bar = "My name is $bar";  // Alter $bar...echo $bar;echo $foo;                 // $foo is altered too.$foo = "I am Frank";       // Alter $foo and $bar because of the referenceecho $bar;                 // output: I am Frankecho $foo;                 // output: I am Frank$foobar = &$bar;           // create a new reference between $foobar and $bar$foobar = "hello $foobar"; // alter $foobar and with that $bar and $fooecho $foobar;              //output : hello I am Frankunset($bar);               // unset $bar and destroy the reference$bar = "dude!";            // assign $bar/* even though the reference between $bar and $foo is destroyed, and also the reference between $bar and $foobar is destroyed, there is still a reference between $foo and $foobar. */echo $foo;                 // output : hello I am Frankecho $bar;                 // output : due!?>

Your idea about unsetting all referenced variables at once is right,just a tiny note that you changed NULL with unset()...again, unset affects only one name and NULL affects the data,which is kept by all the three names...<?php$a = 1;$b =& $a;$b = NULL; ?>This does also work!<?php$a = 1;$b =& $a;$c =& $b;$b = NULL; ?>

A little quirk on unset() when using references that may help someone.If you want to delete the element of a reference to an array, you need to have the reference point to the parent of the key that you want to delete.<?php$arr = array('foo' => array('foo_sub1' => 'hey', 'foo_sub2' => 'you'), 'bar' => array('bar_sub1' => 'good', 'bar_sub2' => 'bye'));$parref =  &$arr['foo'];$childref = &$parref['foo_sub1'];unset($childref);                   // this will simply unset the reference to childunset($parref['foo_sub1']);   // this will actually unset the data in $arr;$parref['foo_sub1'] = NULL;  // this will set the element to NULL, but not delete it.  If you run it after unset(), it add the key back and set it to NULL?>This is nice to use for passing something dynamically to a function by reference without copying the entire array to the function, but you want to do some maintenance on the array.

it's my way to remember.<?php// the var $a is point to the value 1, as a line connect to value 1$a = 1;      // the var $b point to the value which the var $a point to, as a new line connect to value 1$b =& $a;  // cut the line of the var $a to value 1,now $a is freedom,it's nothing point to. so the value of $a is nullunset($a);?>         $a--------> 1                           ↑                            |                            |                           $b

clerca at inp-net dot eu dot org"If you have a lot of references linked to the same contents, maybe it could be useful to do this : <?php$a = 1;$b = & $a;$c = & $b; // $a, $b, $c reference the same content '1'$b = NULL; // All variables $a, $b or $c are unset?>"------------------------NULL will not result in unseting the variables.Its only change the value to "null" for all the variables.becouse they all points to the same "part" in the memory.