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028513e94b
Also, simplify the first paragraph of 'Traditional assertions' in assert() docs git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@342126 c90b9560-bf6c-de11-be94-00142212c4b1
94 lines
1.9 KiB
XML
94 lines
1.9 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<sect1 xml:id="language.types.null">
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<title>NULL</title>
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<para>
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The special &null; value represents a variable with no value. &null; is the
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only possible value of type <type>null</type>.
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</para>
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<para>
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A variable is considered to be <type>null</type> if:
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</para>
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<itemizedlist>
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<listitem>
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<para>
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it has been assigned the constant &null;.
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</para>
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</listitem>
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<listitem>
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<para>
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it has not been set to any value yet.
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</para>
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</listitem>
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<listitem>
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<para>
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it has been <function>unset</function>.
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</para>
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</listitem>
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</itemizedlist>
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<sect2 xml:id="language.types.null.syntax">
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<title>Syntax</title>
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<para>
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There is only one value of type <type>null</type>, and that is the
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case-insensitive constant &null;.
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</para>
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<informalexample>
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<programlisting role="php">
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<![CDATA[
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<?php
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$var = NULL;
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?>
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]]>
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</programlisting>
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</informalexample>
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<para>
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See also the functions <function>is_null</function> and
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<function>unset</function>.
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</para>
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</sect2>
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<sect2 xml:id="language.types.null.casting">
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<title>Casting to &null;</title>
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<para>
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&warn.deprecated.feature-7-2-0;
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</para>
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<para>
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Casting a variable to <type>null</type> using <literal>(unset) $var</literal>
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will <emphasis>not</emphasis> remove the variable or unset its value.
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It will only return a &null; value.
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</para>
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</sect2>
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</sect1>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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indent-tabs-mode:nil
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sgml-parent-document:nil
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sgml-default-dtd-file:"~/.phpdoc/manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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