Unset a given variable (original) (raw)

(PHP 4, PHP 5, PHP 7)

unset — Unset a given variable

Description

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

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 beforeunset() was called.

<?php function destroy_foo() { global $foo; unset($foo); }$foo = 'bar'; destroy_foo(); echo $foo; ?>

The above example will output:

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 isunset() 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:

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.

...

Another variable ...

Return Values

No value is returned.

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, <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>f</mi><mi>o</mi><mi>o</mi><mn>2</mn><mo separator="true">,</mo></mrow><annotation encoding="application/x-tex">foo2, </annotation></semantics></math>foo2,foo3); ?>

Example #2 Using (unset) casting

(unset) casting is often confused with theunset() function. (unset) casting serves only as a NULL-type cast, for completeness. It does not alter the variable it's casting. The (unset) cast is deprecated as of PHP 7.2.0.

<?php <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>n</mi><mi>a</mi><mi>m</mi><mi>e</mi><msup><mo>=</mo><mo mathvariant="normal" lspace="0em" rspace="0em">′</mo></msup><mi>F</mi><mi>e</mi><mi>l</mi><mi>i</mi><mi>p</mi><msup><mi>e</mi><mo mathvariant="normal" lspace="0em" rspace="0em">′</mo></msup><mo separator="true">;</mo><mi>v</mi><mi>a</mi><msub><mi>r</mi><mi>d</mi></msub><mi>u</mi><mi>m</mi><mi>p</mi><mo stretchy="false">(</mo><mo stretchy="false">(</mo><mi>u</mi><mi>n</mi><mi>s</mi><mi>e</mi><mi>t</mi><mo stretchy="false">)</mo></mrow><annotation encoding="application/x-tex">name = 'Felipe';var_dump((unset) </annotation></semantics></math>name=′Felipe′;vardump((unset)name); var_dump($name); ?>

The above example will output:

Notes

Note: Because this is a language construct and not a function, it cannot be called usingvariable 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.

Note:

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

Unset a given variable (original) (raw)

Description

Parameters

Return Values

Examples

Notes

See Also