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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision: 297028 $ -->
<chapter xml:id="language.types" xmlns="http://docbook.org/ns/docbook">
<title>Types</title>
<sect1 xml:id="language.types.intro">
<title>Introduction</title>
<simpara>
PHP supports eight primitive types.
</simpara>
<para>
Four scalar types:
</para>
<itemizedlist>
<listitem>
<simpara>
<type>boolean</type>
</simpara>
</listitem>
<listitem>
<simpara>
<type>integer</type>
</simpara>
</listitem>
<listitem>
<simpara>
<type>float</type> (floating-point number, aka <type>double</type>)
</simpara>
</listitem>
<listitem>
<simpara>
<type>string</type>
</simpara>
</listitem>
</itemizedlist>
<para>
Two compound types:
</para>
<itemizedlist>
<listitem>
<simpara>
<type>array</type>
</simpara>
</listitem>
<listitem>
<simpara>
<type>object</type>
</simpara>
</listitem>
</itemizedlist>
<para>
And finally two special types:
</para>
<itemizedlist>
<listitem>
<simpara>
<type>resource</type>
</simpara>
</listitem>
<listitem>
<simpara>
<type>NULL</type>
</simpara>
</listitem>
</itemizedlist>
<para>
This manual also introduces some
<link linkend="language.pseudo-types">pseudo-types</link> for readability
reasons:
</para>
<itemizedlist>
<listitem>
<simpara>
<type>mixed</type>
</simpara>
</listitem>
<listitem>
<simpara>
<type>number</type>
</simpara>
</listitem>
<listitem>
<simpara>
<type>callback</type>
</simpara>
</listitem>
</itemizedlist>
<para>
And the pseudo-variable <parameter>$...</parameter>.
</para>
<simpara>
Some references to the type "double" may remain in the manual. Consider
double the same as float; the two names exist only for historic reasons.
</simpara>
<simpara>
The type of a variable is not usually set by the programmer; rather, it is
decided at runtime by PHP depending on the context in which that variable is
used.
</simpara>
<note>
<simpara>
To check the type and value of an
<link linkend="language.expressions">expression</link>, use the
<function>var_dump</function> function.
</simpara>
<para>
To get a human-readable representation of a type for debugging, use the
<function>gettype</function> function. To check for a certain type, do
<emphasis>not</emphasis> use <function>gettype</function>, but rather the
<literal>is_<replaceable>type</replaceable></literal> functions. Some
examples:
</para>
<informalexample>
<programlisting role="php">
<![CDATA[
<?php
$a_bool = TRUE; // a boolean
$a_str = "foo"; // a string
$a_str2 = 'foo'; // a string
$an_int = 12; // an integer
echo gettype($a_bool); // prints out: boolean
echo gettype($a_str); // prints out: string
// If this is an integer, increment it by four
if (is_int($an_int)) {
$an_int += 4;
}
// If $bool is a string, print it out
// (does not print out anything)
if (is_string($a_bool)) {
echo "String: $a_bool";
}
?>
]]>
</programlisting>
</informalexample>
</note>
<simpara>
To forcibly convert a variable to a certain type, either
<link linkend="language.types.typecasting">cast</link> the variable or use
the <function>settype</function> function on it.
</simpara>
<simpara>
Note that a variable may be evaluated with different values in certain
situations, depending on what type it is at the time. For more information,
see the section on <link linkend="language.types.type-juggling">Type
Juggling</link>. <link linkend="types.comparisons">The type comparison
tables</link> may also be useful, as they show examples of various
type-related comparisons.
</simpara>
</sect1>
&language.types.boolean;
&language.types.integer;
&language.types.float;
&language.types.string;
&language.types.array;
&language.types.object;
&language.types.resource;
&language.types.null;
&language.types.pseudo-types;
&language.types.type-juggling;
</chapter>
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