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HOME > PHP Manual > unset - Unset a given variable

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unset

(PHP 4, PHP 5)

unset — Unset a given variable

Description

void unset ( mixed $var [, mixed $var [, mixed $... ]] )

unset() destroys the specified variables.

The behavior of unset() inside of a function can vary depending on what type of variable you are attempting to destroy.

If a globalized variable is unset() inside of a function, only the local variable is destroyed. The variable in the calling environment will retain the same value as before unset() was called.


<?php
function destroy_foo() 
{
    global $foo;
    unset($foo);
}

$foo = 'bar';
destroy_foo();
echo $foo;
?>

The above example will output:

bar

If you would like to unset() a global variable inside of a function, you can use the $GLOBALS array to do so:


<?php
function foo() 
{
    unset($GLOBALS['bar']);
}

$bar = "something";
foo();
?>

If a variable that is PASSED BY REFERENCE is unset() inside of a function, only the local variable is destroyed. The variable in the calling environment will retain the same value as before unset() was called.


<?php
function foo(&$bar) 
{
    unset($bar);
    $bar = "blah";
}

$bar = 'something';
echo "$bar\n";

foo($bar);
echo "$bar\n";
?>

The above example will output:

something
something

If a static variable is unset() inside of a function, unset() destroys the variable only in the context of the rest of a function. Following calls will restore the previous value of a variable.


<?php
function foo()
{
    static $bar;
    $bar++;
    echo "Before unset: $bar, ";
    unset($bar);
    $bar = 23;
    echo "after unset: $bar\n";
}

foo();
foo();
foo();
?>

The above example will output:

Before unset: 1, after unset: 23
Before unset: 2, after unset: 23
Before unset: 3, after unset: 23

Parameters

var: The variable to be unset.
var: Another variable ..
...

Return Values

No value is returned.

ChangeLog

Version Description

4.0.0 unset() became an expression. (In PHP 3, unset() would always return 1).

Examples

Example #1 unset() example


<?php
// destroy a single variable
unset($foo);

// destroy a single element of an array
unset($bar['quux']);

// destroy more than one variable
unset($foo1, $foo2, $foo3);
?>

Example #2 Using (unset) casting


<?php
$name = 'Felipe';

var_dump((unset) $name);
?>

Notes

Note: Because this is a language construct and not a function, it cannot be called using variable functions

Note: It is possible to unset even object properties visible in current context.

Note: It is not possible to unset $this inside an object method since PHP 5.

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