unset

PHP 4, PHP 5, PHP 7, PHP 8
unset - Unset a given variable
Manual
Code Examples

unset( mixed$var, ... mixed$vars ): void

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

To unset a global variable inside of a function, then 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.

vars

Further variables.

Return Values

No value is returned.

Notes

Note:

Because this is a language construct and not a function, it cannot be called using variable functions, or named arguments.

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.

Note:

When using unset on inaccessible object properties, the __unset() overloading method will be called, if declared.

Related Functions

Example of unset

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