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

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  <refentry id="function.unpack">
   <refnamediv>
    <refname>unpack</refname>
    <refpurpose>Unpack data from binary string</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
     <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>
     <function>unpack</function> from binary string into array
     according to <parameter>format</parameter>. Returns array
     containing unpacked elements of binary string.
    </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 /.
     <example>
      <title><function>unpack</function> example</title>
      <programlisting role="php">
<![CDATA[
$array = unpack("c2chars/nint", $binarydata);
]]>
      </programlisting>
      <para>
       The resulting array will contain the entries "chars1",
       "chars2" and "int".
      </para>
     </example>
    </para>
    <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>
    <para>
     See also <function>pack</function> for an explanation of the format
     codes.
    </para>
   </refsect1>
  </refentry>

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