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<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.12 $ -->
<!-- splitted from ./en/functions/var.xml, last change in rev 1.2 -->
<refentry id="function.unset">
<refnamediv>
<refname>unset</refname>
<refpurpose>Unset a given variable</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<methodsynopsis>
<type>void</type><methodname>unset</methodname>
<methodparam><type>mixed</type><parameter>var</parameter></methodparam>
<methodparam choice="opt"><type>mixed</type><parameter>var</parameter></methodparam>
<methodparam choice="opt"><type>mixed</type><parameter>...</parameter></methodparam>
</methodsynopsis>
<para>
<function>unset</function> destroys the specified variables. Note
that in PHP 3, <function>unset</function> will always return &true;
(actually, the integer value 1). In PHP 4, however,
<function>unset</function> is no longer a true function: it is
now a statement. As such no value is returned, and attempting to
take the value of <function>unset</function> results in a parse
error.
</para>
<para>
<example>
<title><function>unset</function> example</title>
<programlisting role="php">
<![CDATA[
<?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);
?>
]]>
</programlisting>
</example>
</para>
<para>
The behavior of <function>unset</function> inside of a function
can vary depending on what type of variable you are attempting to
destroy.
</para>
<para>
If a globalized variable is <function>unset</function> inside of
a function, only the local variable is destroyed. The variable
in the calling environment will retain the same value as before
<function>unset</function> was called.
<informalexample>
<programlisting role="php">
<![CDATA[
<?php
function destroy_foo()
{
global $foo;
unset($foo);
}
$foo = 'bar';
destroy_foo();
echo $foo;
?>
]]>
</programlisting>
</informalexample>
</para>
&example.outputs;
<para>
<informalexample>
<screen>
<![CDATA[
bar
]]>
</screen>
</informalexample>
</para>
<para>
If a variable that is PASSED BY REFERENCE is
<function>unset</function> inside of a function, only the local
variable is destroyed. The variable in the calling environment
will retain the same value as before <function>unset</function>
was called.
<informalexample>
<programlisting role="php">
<![CDATA[
<?php
function foo(&$bar)
{
unset($bar);
$bar = "blah";
}
$bar = 'something';
echo "$bar\n";
foo($bar);
echo "$bar\n";
?>
]]>
</programlisting>
</informalexample>
</para>
&example.outputs;
<para>
<informalexample>
<screen>
<![CDATA[
something
something
]]>
</screen>
</informalexample>
</para>
<para>
If a static variable is <function>unset</function> inside of a
function, <function>unset</function> destroys the variable and all
its references.
<informalexample>
<programlisting role="php">
<![CDATA[
<?php
function foo()
{
static $a;
$a++;
echo "$a\n";
unset($a);
}
foo();
foo();
foo();
?>
]]>
</programlisting>
</informalexample>
</para>
&example.outputs;
<para>
<informalexample>
<screen>
<![CDATA[
1
2
3
]]>
</screen>
</informalexample>
</para>
<para>
If you would like to <function>unset</function> a global variable
inside of a function, you can use
the <varname>$GLOBALS</varname> array to do so:
<informalexample>
<programlisting role="php">
<![CDATA[
<?php
function foo()
{
unset($GLOBALS['bar']);
}
$bar = "something";
foo();
?>
]]>
</programlisting>
</informalexample>
</para>
¬e.language-construct;
<para>
See also <function>isset</function>,
<function>empty</function>, and
<function>array_splice</function>.
</para>
</refsect1>
</refentry>
<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-omittag:t
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
indent-tabs-mode:nil
sgml-parent-document:nil
sgml-default-dtd-file:"../../../../manual.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:nil
sgml-local-ecat-files:nil
End:
vim600: syn=xml fen fdm=syntax fdl=2 si
vim: et tw=78 syn=sgml
vi: ts=1 sw=1
-->
|
