Source of: /manual/en/function.pack.php
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<div id="function.pack" class="refentry">
<div class="refnamediv">
<h1 class="refname">pack</h1>
<p class="verinfo">(PHP 4, PHP 5)</p><p class="refpurpose"><span class="refname">pack</span> — <span class="dc-title">Pack data into binary string</span></p>
</div>
<a name="function.pack.description"></a><div class="refsect1 description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">string</span> <span class="methodname"><b>pack</b></span>
( <span class="methodparam"><span class="type">string</span> <tt class="parameter">$format</tt></span>
[, <span class="methodparam"><span class="type"><a href="language.pseudo-types.php#language.types.mixed" class="type mixed">mixed</a></span> <tt class="parameter">$args</tt></span>
[, <span class="methodparam"><span class="type"><a href="language.pseudo-types.php#language.types.mixed" class="type mixed">mixed</a></span> <tt class="parameter">$...</tt></span>
]] )</div>
<p class="para rdfs-comment">
Pack given arguments into binary string according to
<i><tt class="parameter">format</tt></i>
.
</p>
<p class="para">
The idea for this function was taken from Perl and all formatting codes
work the same as in Perl. However, there are some formatting codes that are
missing such as Perl's "u" format code.
</p>
<p class="para">
Note that the distinction between signed and unsigned values only
affects the function <a href="function.unpack.php" class="function">unpack()</a>, where as
function <b>pack()</b> gives the same result for
signed and unsigned format codes.
</p>
<p class="para">
Also note that PHP internally stores <a href="language.types.integer.php" class="type integer">integer</a> 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
<a href="language.types.float.php" class="type float">float</a> which often yields an undesired result.
</p>
</div>
<a name="function.pack.parameters"></a><div class="refsect1 parameters">
<h3 class="title">Parameters</h3>
<p class="para">
</p><dl>
<dt class="varlistentry">
<span class="term"><i><tt class="parameter">format</tt></i>
</span>
</dt><dd class="listitem">
<p class="para">
The <i><tt class="parameter">format</tt></i>
string consists of format codes
followed by an optional repeater argument. The repeater argument can
be either an integer value or <i>*</i> 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.
</p>
<p class="para">
Currently implemented formats are:
</p><table class="doctable table">
<caption><b><b>pack()</b> format characters</b></caption>
<thead valign="middle">
<tr valign="middle">
<th>Code</th>
<th>Description</th>
</tr>
</thead>
<tbody valign="middle" class="tbody">
<tr valign="middle">
<td align="left">a</td>
<td align="left">NUL-padded string</td>
</tr>
<tr valign="middle">
<td align="left">A</td>
<td align="left">SPACE-padded string</td></tr>
<tr valign="middle">
<td align="left">h</td>
<td align="left">Hex string, low nibble first</td></tr>
<tr valign="middle">
<td align="left">H</td>
<td align="left">Hex string, high nibble first</td></tr>
<tr valign="middle"><td align="left">c</td><td align="left">signed char</td></tr>
<tr valign="middle">
<td align="left">C</td>
<td align="left">unsigned char</td></tr>
<tr valign="middle">
<td align="left">s</td>
<td align="left">signed short (always 16 bit, machine byte order)</td>
</tr>
<tr valign="middle">
<td align="left">S</td>
<td align="left">unsigned short (always 16 bit, machine byte order)</td>
</tr>
<tr valign="middle">
<td align="left">n</td>
<td align="left">unsigned short (always 16 bit, big endian byte order)</td>
</tr>
<tr valign="middle">
<td align="left">v</td>
<td align="left">unsigned short (always 16 bit, little endian byte order)</td>
</tr>
<tr valign="middle">
<td align="left">i</td>
<td align="left">signed integer (machine dependent size and byte order)</td>
</tr>
<tr valign="middle">
<td align="left">I</td>
<td align="left">unsigned integer (machine dependent size and byte order)</td>
</tr>
<tr valign="middle">
<td align="left">l</td>
<td align="left">signed long (always 32 bit, machine byte order)</td>
</tr>
<tr valign="middle">
<td align="left">L</td>
<td align="left">unsigned long (always 32 bit, machine byte order)</td>
</tr>
<tr valign="middle">
<td align="left">N</td>
<td align="left">unsigned long (always 32 bit, big endian byte order)</td>
</tr>
<tr valign="middle">
<td align="left">V</td>
<td align="left">unsigned long (always 32 bit, little endian byte order)</td>
</tr>
<tr valign="middle">
<td align="left">f</td>
<td align="left">float (machine dependent size and representation)</td>
</tr>
<tr valign="middle">
<td align="left">d</td>
<td align="left">double (machine dependent size and representation)</td>
</tr>
<tr valign="middle">
<td align="left">x</td>
<td align="left">NUL byte</td>
</tr>
<tr valign="middle">
<td align="left">X</td>
<td align="left">Back up one byte</td>
</tr>
<tr valign="middle">
<td align="left">@</td>
<td align="left">NUL-fill to absolute position</td>
</tr>
</tbody>
</table>
<p>
</p>
</dd>
<dt class="varlistentry">
<span class="term"><i><tt class="parameter">args</tt></i>
</span>
</dt><dd class="listitem">
<p class="para">
</p>
</dd>
</dl>
<p>
</p>
</div>
<a name="function.pack.returnvalues"></a><div class="refsect1 returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
Returns a binary string containing data.
</p>
</div>
<a name="function.pack.examples"></a><div class="refsect1 examples">
<h3 class="title">Examples</h3>
<p class="para">
</p><div class="example">
<p><b>Example #1 <b>pack()</b> example</b></p>
<div class="example-contents programlisting">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$binarydata </span><span style="color: #007700">= </span><span style="color: #0000BB">pack</span><span style="color: #007700">(</span><span style="color: #DD0000">"nvc*"</span><span style="color: #007700">, </span><span style="color: #0000BB">0x1234</span><span style="color: #007700">, </span><span style="color: #0000BB">0x5678</span><span style="color: #007700">, </span><span style="color: #0000BB">65</span><span style="color: #007700">, </span><span style="color: #0000BB">66</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
<div class="example-contents para"><p>
The resulting binary string will be 6 bytes long and contain
the byte sequence 0x12, 0x34, 0x78, 0x56, 0x41, 0x42.
</p></div>
</div><p>
</p>
</div>
<a name="function.pack.seealso"></a><div class="refsect1 seealso">
<h3 class="title">See Also</h3>
<p class="para">
</p><ul class="simplelist">
<li class="member"><a href="function.unpack.php" class="function" rel="rdfs-seeAlso">unpack()</a> - Unpack data from binary string</li>
</ul><p>
</p>
</div>
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