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<title>Get and/or set the current session id</title>
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<div class="refnamediv">
<h1 class="refname">session_id</h1>
<p class="verinfo">(PHP 4, PHP 5)</p><p class="refpurpose"><span class="refname">session_id</span> — <span class="dc-title">Get and/or set the current session id</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.session-id-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">string</span> <span class="methodname"><strong>session_id</strong></span>
([ <span class="methodparam"><span class="type">string</span> <code class="parameter">$id</code></span>
] )</div>
<p class="para rdfs-comment">
<span class="function"><strong>session_id()</strong></span> is used to get or set the session id for
the current session.
</p>
<p class="para">
The constant <strong><code>SID</code></strong> can also be used to
retrieve the current name and session id as a string suitable for
adding to URLs. See also <a href="ref.session.html" class="link">Session
handling</a>.
</p>
</div>
<div class="refsect1 parameters" id="refsect1-function.session-id-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<span class="term"><em><code class="parameter">id</code></em></span>
<dd>
<p class="para">
If <em><code class="parameter">id</code></em> is specified, it will replace the current
session id. <span class="function"><strong>session_id()</strong></span> needs to be called before
<span class="function"><a href="function.session-start.html" class="function">session_start()</a></span> for that purpose. Depending on the
session handler, not all characters are allowed within the session id.
For example, the file session handler only allows characters in the
range <em>a-z A-Z 0-9 , (comma) and - (minus)</em>!
</p>
<blockquote class="note"><p><strong class="note">Note</strong>:
<span class="simpara">
When using session cookies, specifying an <em><code class="parameter">id</code></em>
for <span class="function"><strong>session_id()</strong></span> will always send a new cookie
when <span class="function"><a href="function.session-start.html" class="function">session_start()</a></span> is called, regardless if the
current session id is identical to the one being set.
</span>
</p></blockquote>
</dd>
</dt>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.session-id-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
<span class="function"><strong>session_id()</strong></span> returns the session id for the current
session or the empty string (<em>""</em>) if there is no current
session (no current session id exists).
</p>
</div>
<div class="refsect1 changelog" id="refsect1-function.session-id-changelog">
<h3 class="title">Changelog</h3>
<p class="para">
<table class="doctable informaltable">
<thead>
<tr>
<th>Version</th>
<th>Description</th>
</tr>
</thead>
<tbody class="tbody">
<tr>
<td>5.0.0</td>
<td>
The <em>,</em> (comma) and <em>-</em> (minus)
characters are allowed in the file session handler.
</td>
</tr>
</tbody>
</table>
</p>
</div>
<div class="refsect1 seealso" id="refsect1-function.session-id-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member"> <span class="function"><a href="function.session-regenerate-id.html" class="function" rel="rdfs-seeAlso">session_regenerate_id()</a> - Update the current session id with a newly generated one</span></li>
<li class="member"> <span class="function"><a href="function.session-start.html" class="function" rel="rdfs-seeAlso">session_start()</a> - Start new or resume existing session</span></li>
<li class="member"> <span class="function"><a href="function.session-set-save-handler.html" class="function" rel="rdfs-seeAlso">session_set_save_handler()</a> - Sets user-level session storage functions</span></li>
<li class="member">
<a href="session.configuration.html#ini.session.save-handler" class="link">session.save_handler</a>
</li>
</ul>
</p>
</div>
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