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<title>Unset a given variable</title>
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<div class="refnamediv">
<h1 class="refname">unset</h1>
<p class="verinfo">(PHP 4, PHP 5)</p><p class="refpurpose"><span class="refname">unset</span> — <span class="dc-title">Unset a given variable</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.unset-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type"><span class="type void">void</span></span> <span class="methodname"><strong>unset</strong></span>
( <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <code class="parameter">$var</code></span>
[, <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <code class="parameter">$...</code></span>
] )</div>
<p class="para rdfs-comment">
<span class="function"><strong>unset()</strong></span> destroys the specified variables.
</p>
<p class="para">
The behavior of <span class="function"><strong>unset()</strong></span> inside of a function
can vary depending on what type of variable you are attempting to
destroy.
</p>
<p class="para">
If a globalized variable is <span class="function"><strong>unset()</strong></span> inside of
a function, only the local variable is destroyed. The variable
in the calling environment will retain the same value as before
<span class="function"><strong>unset()</strong></span> was called.
<div class="informalexample">
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">destroy_foo</span><span style="color: #007700">() <br />{<br /> global </span><span style="color: #0000BB">$foo</span><span style="color: #007700">;<br /> unset(</span><span style="color: #0000BB">$foo</span><span style="color: #007700">);<br />}<br /><br /></span><span style="color: #0000BB">$foo </span><span style="color: #007700">= </span><span style="color: #DD0000">'bar'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">destroy_foo</span><span style="color: #007700">();<br />echo </span><span style="color: #0000BB">$foo</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="para">The above example will output:</p>
<p class="para">
<div class="informalexample">
<div class="example-contents screen">
<div class="cdata"><pre>
bar
</pre></div>
</div>
</div>
</p>
<p class="para">
To <span class="function"><strong>unset()</strong></span> a global variable
inside of a function, then use
the <var class="varname"><var class="varname"><a href="reserved.variables.globals.html" class="classname">$GLOBALS</a></var></var> array to do so:
<div class="informalexample">
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">foo</span><span style="color: #007700">() <br />{<br /> unset(</span><span style="color: #0000BB">$GLOBALS</span><span style="color: #007700">[</span><span style="color: #DD0000">'bar'</span><span style="color: #007700">]);<br />}<br /><br /></span><span style="color: #0000BB">$bar </span><span style="color: #007700">= </span><span style="color: #DD0000">"something"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">foo</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="para">
If a variable that is PASSED BY REFERENCE is
<span class="function"><strong>unset()</strong></span> inside of a function, only the local
variable is destroyed. The variable in the calling environment
will retain the same value as before <span class="function"><strong>unset()</strong></span>
was called.
<div class="informalexample">
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">foo</span><span style="color: #007700">(&</span><span style="color: #0000BB">$bar</span><span style="color: #007700">) <br />{<br /> unset(</span><span style="color: #0000BB">$bar</span><span style="color: #007700">);<br /> </span><span style="color: #0000BB">$bar </span><span style="color: #007700">= </span><span style="color: #DD0000">"blah"</span><span style="color: #007700">;<br />}<br /><br /></span><span style="color: #0000BB">$bar </span><span style="color: #007700">= </span><span style="color: #DD0000">'something'</span><span style="color: #007700">;<br />echo </span><span style="color: #DD0000">"</span><span style="color: #0000BB">$bar</span><span style="color: #DD0000">\n"</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">foo</span><span style="color: #007700">(</span><span style="color: #0000BB">$bar</span><span style="color: #007700">);<br />echo </span><span style="color: #DD0000">"</span><span style="color: #0000BB">$bar</span><span style="color: #DD0000">\n"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="para">The above example will output:</p>
<p class="para">
<div class="informalexample">
<div class="example-contents screen">
<div class="cdata"><pre>
something
something
</pre></div>
</div>
</div>
</p>
<p class="para">
If a static variable is <span class="function"><strong>unset()</strong></span> inside of a
function, <span class="function"><strong>unset()</strong></span> destroys the variable only in the
context of the rest of a function. Following calls will restore the
previous value of a variable.
<div class="informalexample">
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">foo</span><span style="color: #007700">()<br />{<br /> static </span><span style="color: #0000BB">$bar</span><span style="color: #007700">;<br /> </span><span style="color: #0000BB">$bar</span><span style="color: #007700">++;<br /> echo </span><span style="color: #DD0000">"Before unset: </span><span style="color: #0000BB">$bar</span><span style="color: #DD0000">, "</span><span style="color: #007700">;<br /> unset(</span><span style="color: #0000BB">$bar</span><span style="color: #007700">);<br /> </span><span style="color: #0000BB">$bar </span><span style="color: #007700">= </span><span style="color: #0000BB">23</span><span style="color: #007700">;<br /> echo </span><span style="color: #DD0000">"after unset: </span><span style="color: #0000BB">$bar</span><span style="color: #DD0000">\n"</span><span style="color: #007700">;<br />}<br /><br /></span><span style="color: #0000BB">foo</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">foo</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">foo</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="para">The above example will output:</p>
<p class="para">
<div class="informalexample">
<div class="example-contents screen">
<div class="cdata"><pre>
Before unset: 1, after unset: 23
Before unset: 2, after unset: 23
Before unset: 3, after unset: 23
</pre></div>
</div>
</div>
</p>
</div>
<div class="refsect1 parameters" id="refsect1-function.unset-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<span class="term"><em><code class="parameter">var</code></em></span>
<dd>
<p class="para">
The variable to be unset.
</p>
</dd>
</dt>
<dt>
<span class="term"><em><code class="parameter">...</code></em></span>
<dd>
<p class="para">
Another variable ...
</p>
</dd>
</dt>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.unset-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
No value is returned.
</p>
</div>
<div class="refsect1 changelog" id="refsect1-function.unset-changelog">
<h3 class="title">Changelog</h3>
<p class="para">
<table class="doctable informaltable">
<thead>
<tr>
<th>Version</th>
<th>Description</th>
</tr>
</thead>
<tbody class="tbody">
<tr>
<td>4.0.1</td>
<td>
Added support for multiple arguments.
</td>
</tr>
</tbody>
</table>
</p>
</div>
<div class="refsect1 examples" id="refsect1-function.unset-examples">
<h3 class="title">Examples</h3>
<p class="para">
<div class="example" id="example-5276">
<p><strong>Example #1 <span class="function"><strong>unset()</strong></span> example</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">// destroy a single variable<br /></span><span style="color: #007700">unset(</span><span style="color: #0000BB">$foo</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">// destroy a single element of an array<br /></span><span style="color: #007700">unset(</span><span style="color: #0000BB">$bar</span><span style="color: #007700">[</span><span style="color: #DD0000">'quux'</span><span style="color: #007700">]);<br /><br /></span><span style="color: #FF8000">// destroy more than one variable<br /></span><span style="color: #007700">unset(</span><span style="color: #0000BB">$foo1</span><span style="color: #007700">, </span><span style="color: #0000BB">$foo2</span><span style="color: #007700">, </span><span style="color: #0000BB">$foo3</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
<div class="example" id="example-5277">
<p><strong>Example #2 Using <em>(unset)</em> casting</strong></p>
<div class="example-contents"><p>
<em>(unset)</em> casting is often confused with the
<span class="function"><strong>unset()</strong></span> function. <em>(unset)</em>
casting serves only as a <em>NULL</em>-type cast, for
completeness. It does not alter the variable it's casting.
</p></div>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$name </span><span style="color: #007700">= </span><span style="color: #DD0000">'Felipe'</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">((unset) </span><span style="color: #0000BB">$name</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">$name</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
<div class="example-contents"><p>The above example will output:</p></div>
<div class="example-contents screen">
<div class="cdata"><pre>
NULL
string(6) "Felipe"
</pre></div>
</div>
</div>
</p>
</div>
<div class="refsect1 notes" id="refsect1-function.unset-notes">
<h3 class="title">Notes</h3>
<blockquote class="note"><p><strong class="note">Note</strong>: <span class="simpara">Because this is a
language construct and not a function, it cannot be called using
<a href="functions.variable-functions.html" class="link">variable functions</a>.</span>
</p></blockquote>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
It is possible to unset even object properties visible in current context.
</p>
</p></blockquote>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
It is not possible to unset <em>$this</em> inside an object
method since PHP 5.
</p>
</p></blockquote>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
When using <span class="function"><strong>unset()</strong></span> on inaccessible object properties,
the <a href="language.oop5.overloading.html#object.unset" class="link">__unset()</a>
overloading method will be called, if declared.
</p>
</p></blockquote>
</div>
<div class="refsect1 seealso" id="refsect1-function.unset-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member"> <span class="function"><a href="function.isset.html" class="function" rel="rdfs-seeAlso">isset()</a> - Determine if a variable is set and is not NULL</span></li>
<li class="member"> <span class="function"><a href="function.empty.html" class="function" rel="rdfs-seeAlso">empty()</a> - Determine whether a variable is empty</span></li>
<li class="member"><a href="language.oop5.overloading.html#object.unset" class="link">__unset()</a></li>
<li class="member"> <span class="function"><a href="function.array-splice.html" class="function" rel="rdfs-seeAlso">array_splice()</a> - Remove a portion of the array and replace it with something else</span></li>
</ul>
</p>
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