Unsetting References

When you unset the reference, you just break the binding between variable name and variable content. This does not mean that variable content will be destroyed. For example:

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<?php

$a = 1;
$b =& $a;

unset($a); 
?>

won't unset $b, just $a.

Again, it might be useful to think about this as analogous to Unix unlink call.

Code Examples / Notes » language.references.unset

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; ?>

note that in the previous example all variables (or the one data item all variables point to) is set to NULL, what is interpreted as !isset(), but the linkage between the variables still exists, so <?php echo (isset($a)?"set":"unset")."\n"; $a=1; $b =& $a; echo (isset($b)?"set":"unset")."\n"; $a=null; echo (isset($b)?"set":"unset")."\n"; $a=1; echo (isset($b)?"set":"unset")."\n"; ?> shows: unset set unset set note that $b ist set again. So if you want to brake the linkage, you have to use unset()

If you wish to unset both variables, you will need to unset the last referenced variable of that condition. <?php $a = 1; $b =& $a; unset($b); ?> * These must be in a reference->copy hierarchy in order to unset; example: <?php $a = 1; $b =& $a; $c =& $b; unset($c); ?> This will not work: <?php $a = 1; $b =& $a; $c = $b; unset($c); ?> * Only $c is unset in the above example, meaning that both variables $b and $a are still assigned "1".

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 ?> I haven't test this trick a lot, but well, it seems to work greatly.

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 reference echo $bar; // output: I am Frank echo $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 $foo echo $foobar; //output : hello I am Frank unset($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 Frank echo $bar; // output : due! ?>

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.

<?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.

Unsetting References

Code Examples / Notes » language.references.unset

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