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

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<refentry xml:id="function.pack" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>pack</refname>
  <refpurpose>Pack data into binary string</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>string</type><methodname>pack</methodname>
   <methodparam><type>string</type><parameter>format</parameter></methodparam>
   <methodparam choice="opt"><type>mixed</type><parameter>args</parameter></methodparam>
   <methodparam choice="opt"><type>mixed</type><parameter>...</parameter></methodparam>
  </methodsynopsis>
  <para>
   Pack given arguments into binary string according to
   <parameter>format</parameter>. 
  </para>
  <para>
   The idea to this function was taken from Perl and all formatting codes
   work the same as there, however, there are some formatting codes that are
   missing such as Perl's "u" format code.
  </para>
  <para>
   Note that the distinction between signed and unsigned values only
   affects the function <function>unpack</function>, where as
   function <function>pack</function> gives the same result for
   signed and unsigned format codes.
  </para>
  <para>
   Also note that PHP internally stores <type>integer</type> values as
   signed values of a machine dependent size. If you give it an unsigned
   integer value too large to be stored that way it is converted to a
   <type>float</type> which often yields an undesired result.
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>format</parameter></term>
     <listitem>
      <para>
       The <parameter>format</parameter> string consists of format codes
       followed by an optional repeater argument. The repeater argument can
       be either an integer value or <literal>*</literal> for repeating to
       the end of the input data. For a, A, h, H the repeat count specifies
       how many characters of one data argument are taken, for @ it is the
       absolute position where to put the next data, for everything else the
       repeat count specifies how many data arguments are consumed and packed
       into the resulting binary string.
      </para>
      <para>
       Currently implemented formats are:
       <table>
        <title><function>pack</function> format characters</title>
        <tgroup cols="2">
         <thead>
          <row>
           <entry>Code</entry>
           <entry>Description</entry>
          </row>
         </thead>
         <tbody>
          <row>
           <entry>a</entry>
           <entry>NUL-padded string</entry>
          </row>
          <row>
           <entry>A</entry>
           <entry>SPACE-padded string</entry></row>
          <row>
           <entry>h</entry>
           <entry>Hex string, low nibble first</entry></row>
          <row>
           <entry>H</entry>
           <entry>Hex string, high nibble first</entry></row>
          <row><entry>c</entry><entry>signed char</entry></row>
          <row>
           <entry>C</entry>
           <entry>unsigned char</entry></row>
          <row>
           <entry>s</entry>
           <entry>signed short (always 16 bit, machine byte order)</entry>
          </row>
          <row>
           <entry>S</entry>
           <entry>unsigned short (always 16 bit, machine byte order)</entry>
          </row>
          <row>
           <entry>n</entry>
           <entry>unsigned short (always 16 bit, big endian byte order)</entry>
          </row>
          <row>
           <entry>v</entry>
           <entry>unsigned short (always 16 bit, little endian byte order)</entry>
          </row>
          <row>
           <entry>i</entry>
           <entry>signed integer (machine dependent size and byte order)</entry>
          </row>
          <row>
           <entry>I</entry>
           <entry>unsigned integer (machine dependent size and byte order)</entry>
          </row>
          <row>
           <entry>l</entry>
           <entry>signed long (always 32 bit, machine byte order)</entry>
          </row>
          <row>
           <entry>L</entry>
           <entry>unsigned long (always 32 bit, machine byte order)</entry>
          </row>
          <row>
           <entry>N</entry>
           <entry>unsigned long (always 32 bit, big endian byte order)</entry>
          </row>
          <row>
           <entry>V</entry>
           <entry>unsigned long (always 32 bit, little endian byte order)</entry>
          </row>
          <row>
           <entry>f</entry>
           <entry>float (machine dependent size and representation)</entry>
          </row>
          <row>
           <entry>d</entry>
           <entry>double (machine dependent size and representation)</entry>
          </row>
          <row>
           <entry>x</entry>
           <entry>NUL byte</entry>
          </row>
          <row>
           <entry>X</entry>
           <entry>Back up one byte</entry>
          </row>
          <row>
           <entry>@</entry>
           <entry>NUL-fill to absolute position</entry>
          </row>
         </tbody>
        </tgroup>
       </table>
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>args</parameter></term>
     <listitem>
      <para>
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns a binary string containing data.
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>pack</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php
$binarydata = pack("nvc*", 0x1234, 0x5678, 65, 66);
?>
]]>
    </programlisting>
    <para>
     The resulting binary string will be 6 bytes long and contain
     the byte sequence 0x12, 0x34, 0x78, 0x56, 0x41, 0x42.
    </para>
   </example>
  </para>
 </refsect1>

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

</refentry>

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