php-doc-en/reference/misc/functions/unpack.xml

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<refentry xml:id="function.unpack" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>unpack</refname>
  <refpurpose>Unpack data from binary string</refpurpose>
 </refnamediv>
 
 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>array</type><methodname>unpack</methodname>
   <methodparam><type>string</type><parameter>format</parameter></methodparam>
   <methodparam><type>string</type><parameter>data</parameter></methodparam>
  </methodsynopsis>
  <para>
   Unpacks from a binary string into an array according to the given
   <parameter>format</parameter>. 
  </para>
  <para>
   <function>unpack</function> works slightly different from Perl as
   the unpacked data is stored in an associative array. To
   accomplish this you have to name the different format codes and
   separate them by a slash /.
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>format</parameter></term>
     <listitem>
      <para>
       See <function>pack</function> for an explanation of the format codes.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>data</parameter></term>
     <listitem>
      <para>
       The packed data.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns an associative array containing unpacked elements of binary
   string.
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>unpack</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php
$array = unpack("c2chars/nint", $binarydata);
?>
]]>
    </programlisting>
    <para>
     The resulting array will contain the entries "chars1",
     "chars2" and "int".
    </para>
   </example>
  </para>
 </refsect1>

 <refsect1 role="notes">
  &reftitle.notes;
  <caution>
   <para>
    Note that PHP internally stores integral values as signed. If you
    unpack a large unsigned long and it is of the same size as PHP
    internally stored values the result will be a negative number
    even though unsigned unpacking was specified.
   </para>
  </caution>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>pack</function></member>
   </simplelist>
  </para>
 </refsect1>

</refentry>

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