mirror of
https://github.com/sigmasternchen/php-doc-en
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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@146503 c90b9560-bf6c-de11-be94-00142212c4b1
128 lines
3.4 KiB
XML
128 lines
3.4 KiB
XML
<?xml version="1.0" encoding="iso-8859-1"?>
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<!-- $Revision: 1.12 $ -->
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<!-- splitted from ./en/functions/var.xml, last change in rev 1.2 -->
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<refentry id="function.isset">
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<refnamediv>
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<refname>isset</refname>
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<refpurpose>Determine whether a variable is set</refpurpose>
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</refnamediv>
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<refsect1>
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<title>Description</title>
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<methodsynopsis>
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<type>bool</type><methodname>isset</methodname>
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<methodparam><type>mixed</type><parameter>var</parameter></methodparam>
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<methodparam choice="opt"><type>mixed</type><parameter>var</parameter></methodparam>
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<methodparam choice="opt"><parameter>...</parameter></methodparam>
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</methodsynopsis>
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<simpara>
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Returns &true; if <parameter>var</parameter> exists; &false; otherwise.
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</simpara>
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<para>
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If a variable has been unset with <function>unset</function>, it will no
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longer be set. <function>isset</function> will
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return &false; if testing a variable that has been set to &null;. Also
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note that a &null; byte (<literal>"\0"</literal>) is not equivalent to
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the PHP &null; constant.
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</para>
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<note>
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<title>Warning</title>
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<para>
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<function>isset</function> only works with variables as passing anything
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else will result in a parse error. For checking if
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<link linkend="language.constants">constants</link> are set use the
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<function>defined</function> function.
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</para>
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</note>
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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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$var = '';
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// This will evaluate to &true; so the text will be printed.
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if (isset($var)) {
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echo "This var is set set so I will print.";
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}
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// In the next examples we'll use var_dump to output
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// the return value of isset().
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$a = "test";
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$b = "anothertest";
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var_dump(isset($a)); // TRUE
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var_dump(isset($a, $b)); // TRUE
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unset ($a);
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var_dump(isset($a)); // FALSE
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var_dump(isset($a, $b)); // FALSE
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$foo = NULL;
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var_dump(isset($foo)); // FALSE
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?>
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]]>
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</programlisting>
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</informalexample>
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</para>
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<para>
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This also work for elements in arrays:
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<informalexample>
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<programlisting role="php">
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<![CDATA[
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<?php
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$a = array ('test' => 1, 'hello' => NULL);
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var_dump(isset($a['test'])); // TRUE
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var_dump(isset($a['foo'])); // FALSE
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var_dump(isset($a['hello'])); // FALSE
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// The key 'hello' equals NULL so is considered unset
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// If you want to check for NULL key values then try:
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var_dump(array_key_exists('hello', $a)); // TRUE
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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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¬e.language-construct;
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<simpara>
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See also <function>empty</function>,
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<function>unset</function>,
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<function>defined</function>,
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<link linkend="types.comparisons">the type comparison tables</link>,
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<function>array_key_exists</function>,
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and the error control
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<link linkend="language.operators.errorcontrol">@</link> operator.
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</simpara>
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</refsect1>
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</refentry>
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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:"../../../../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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