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

<?xml version="1.0" encoding="utf-8"?>
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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>
   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 /. If a repeater argument is present,
   then each of the array keys will have a sequence number behind
   the given name.
  </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="changelog"><!-- {{{ -->
  &reftitle.changelog;
  <para>
   <informaltable>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>&Version;</entry>
       <entry>&Description;</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry>5.5.0</entry>
       <entry>
        <para>
         Changes were made to bring this function into line with Perl:
        </para>
        <para>
         The "a" code now retains trailing NULL bytes.
        </para>
        <para>
         The "A" code now strips all trailing ASCII whitespace (spaces, tabs,
         newlines, carriage returns, and NULL bytes).
        </para>
        <para>
         The "Z" code was added for NULL-padded strings, and removes trailing
         NULL bytes.
        </para>
       </entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>
  </para>
 </refsect1><!-- }}} -->

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>unpack</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php
$binarydata = "\x04\x00\xa0\x00";
$array = unpack("cchars/nint", $binarydata);
?>
]]>
    </programlisting>
    <para>
     The resulting array will contain the entries "chars" with value
     <literal>4</literal> and "int" with <literal>160</literal>.
    </para>
   </example>
  </para>

  <para>
   <example>
    <title><function>unpack</function> example with a repeater</title>
    <programlisting role="php">
<![CDATA[
<?php
$binarydata = "\x04\x00\xa0\x00";
$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>
  <caution>
   <para>
    Be aware that if you do not name an element, an empty string is used.
    If you do not name more than one element, this means
    that some data is overwritten as the keys are the same such as in:
   </para>
   <para>
    <example>
     <title><function>unpack</function> example with unnamed keys</title>
     <programlisting role="php">
<![CDATA[
<?php
$binarydata = "\x32\x42\x00\xa0";
$array = unpack("c2/n", $binarydata);
var_dump($array);
?>
]]>
     </programlisting>
     <para>
      The resulting array will contain the entries "1" with value
      <literal>160</literal> and "2" with <literal>66</literal>. The
      first value from the <literal>c</literal> specifier is 
      overwritten by the first value from the <literal>n</literal>
      specifier.
     </para>
    </example>
   </para>
  </caution>
 </refsect1>

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

</refentry>

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