Source of: /manual/en/language.types.null.php
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<div id="language.types.null" class="sect1">
<h2 class="title">NULL</h2>
<p class="para">
The special <b><tt class="constant">NULL</tt></b> value represents a variable with no value. <b><tt class="constant">NULL</tt></b> is the
only possible value of type <a href="language.types.null.php" class="type NULL">NULL</a>.
</p>
<blockquote><p><b class="note">Note</b>:
<span class="simpara">
The <a href="language.types.null.php" class="type null">null</a> type was introduced in PHP 4.
</span>
</p></blockquote>
<p class="para">
A variable is considered to be <a href="language.types.null.php" class="type null">null</a> if:
</p>
<ul class="itemizedlist">
<li class="listitem">
<p class="para">
it has been assigned the constant <b><tt class="constant">NULL</tt></b>.
</p>
</li>
<li class="listitem">
<p class="para">
it has not been set to any value yet.
</p>
</li>
<li class="listitem">
<p class="para">
it has been <a href="function.unset.php" class="function">unset()</a>.
</p>
</li>
</ul>
<div id="language.types.null.syntax" class="sect2">
<h3 class="title">Syntax</h3>
<p class="para">
There is only one value of type <a href="language.types.null.php" class="type null">null</a>, and that is the
case-insensitive keyword <b><tt class="constant">NULL</tt></b>.
</p>
<div class="informalexample">
<div class="example-contents programlisting">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$var </span><span style="color: #007700">= </span><span style="color: #0000BB">NULL</span><span style="color: #007700">; <br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
<p class="para">
See also the functions <a href="function.is-null.php" class="function">is_null()</a> and
<a href="function.unset.php" class="function">unset()</a>.
</p>
</div>
<div id="language.types.null.casting" class="sect2">
<h3 class="title">Casting to <i>NULL</i></h3>
<p class="para">
Casting a variable to <a href="language.types.null.php" class="type null">null</a> will remove the variable
and unset its value.
</p>
</div>
</div><?php manual_footer(); ?>
