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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<sect1 xml:id="language.types.boolean">
<title>Booleans</title>
<simpara>
The <type>bool</type> type only has two values, and is used to express
a truth value. It can be either &true; or &false;.
</simpara>
<sect2 xml:id="language.types.boolean.syntax">
<title>Syntax</title>
<para>
To specify a <type>bool</type> literal, use the constants &true; or
&false;. Both are case-insensitive.
</para>
<informalexample>
<programlisting role="php">
<![CDATA[
<?php
$foo = True; // assign the value TRUE to $foo
?>
]]>
</programlisting>
</informalexample>
<para>
Typically, the result of an <link linkend="language.operators">operator</link>
which returns a <type>bool</type> value is passed on to a
<link linkend="language.control-structures">control structure</link>.
</para>
<informalexample>
<programlisting role="php">
<![CDATA[
<?php
// == is an operator which tests
// equality and returns a boolean
if ($action == "show_version") {
echo "The version is 1.23";
}
// this is not necessary...
if ($show_separators == TRUE) {
echo "<hr>\n";
}
// ...because this can be used with exactly the same meaning:
if ($show_separators) {
echo "<hr>\n";
}
?>
]]>
</programlisting>
</informalexample>
</sect2>
<sect2 xml:id="language.types.boolean.casting">
<title>Converting to boolean</title>
<simpara>
To explicitly convert a value to <type>bool</type>, use the
<literal>(bool)</literal> cast. Generally this is not necessary because when
a value is used in a logical context it will be automatically interpreted
as a value of type <type>bool</type>. For more information see the
<link linkend="language.types.type-juggling">Type Juggling</link> page.
</simpara>
<para>
When converting to <type>bool</type>, the following values are considered
&false;:
</para>
<itemizedlist>
<listitem>
<simpara>
the <link linkend="language.types.boolean">boolean</link> &false; itself
</simpara>
</listitem>
<listitem>
<simpara>
the <link linkend="language.types.integer">integer</link>
<literal>0</literal> (zero)
</simpara>
</listitem>
<listitem>
<simpara>
the <link linkend="language.types.float">float</link>s
<literal>0.0</literal> and <literal>-0.0</literal> (zero)
</simpara>
</listitem>
<listitem>
<simpara>
the empty <link linkend="language.types.string">string</link> <literal>""</literal>,
and the <link linkend="language.types.string">string</link> <literal>"0"</literal>
</simpara>
</listitem>
<listitem>
<simpara>
an <link linkend="language.types.array">array</link> with zero elements
</simpara>
</listitem>
<listitem>
<simpara>
the unit type <link linkend="language.types.null">NULL</link> (including
unset variables)
</simpara>
</listitem>
<listitem>
<simpara>
Internal objects that overload their casting behaviour to bool.
For example: <link linkend="ref.simplexml">SimpleXML</link> objects
created from empty elements without attributes.
</simpara>
</listitem>
</itemizedlist>
<para>
Every other value is considered &true;
(including <link linkend="language.types.resource">resource</link>
and <constant>NAN</constant>).
</para>
<warning>
<simpara>
<literal>-1</literal> is considered &true;, like any other non-zero
(whether negative or positive) number!
</simpara>
</warning>
<informalexample>
<programlisting role="php">
<![CDATA[
<?php
var_dump((bool) ""); // bool(false)
var_dump((bool) "0"); // bool(false)
var_dump((bool) 1); // bool(true)
var_dump((bool) -2); // bool(true)
var_dump((bool) "foo"); // bool(true)
var_dump((bool) 2.3e5); // bool(true)
var_dump((bool) array(12)); // bool(true)
var_dump((bool) array()); // bool(false)
var_dump((bool) "false"); // bool(true)
?>
]]>
</programlisting>
</informalexample>
</sect2>
</sect1>
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