php-doc-en/language/types.xml

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<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 ten primitive types.
  </simpara>
  
  <para>
   Four scalar types:
  </para>

  <itemizedlist>

   <listitem>
    <simpara>
     <type>bool</type>
    </simpara>
   </listitem>

   <listitem>
    <simpara>
     <type>int</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>
   Four compound types:
  </para>

  <itemizedlist>

   <listitem>
    <simpara>
     <type>array</type>
    </simpara>
   </listitem>

   <listitem>
    <simpara>
     <type>object</type>
    </simpara>
   </listitem>

   <listitem>
    <simpara>
     <type>callable</type>
    </simpara>
   </listitem>

   <listitem>
    <simpara>
     <type>iterable</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>

  <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 $a_bool is a string, print it out
// (does not print out anything)
if (is_string($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.numeric-strings;
 &language.types.array;
 &language.types.iterable;
 &language.types.object;
 &language.types.enumerations;
 &language.types.resource;
 &language.types.null;
 &language.types.callable;
 &language.types.declarations;
 &language.types.type-juggling;
 
</chapter>
 
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