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unset

(PHP 3, 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

VersionDescription
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);
?>

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.

See Also

isset()
empty()
array_splice()

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