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<title>Start new or resume existing session</title>
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<div class="refnamediv">
<h1 class="refname">session_start</h1>
<p class="verinfo">(PHP 4, PHP 5)</p><p class="refpurpose"><span class="refname">session_start</span> — <span class="dc-title">Start new or resume existing session</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.session-start-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">bool</span> <span class="methodname"><strong>session_start</strong></span>
( <span class="methodparam">void</span>
)</div>
<p class="para rdfs-comment">
<span class="function"><strong>session_start()</strong></span> creates a session or resumes the
current one based on a session identifier passed via a GET or POST
request, or passed via a cookie.
</p>
<p class="para">
When <span class="function"><strong>session_start()</strong></span> is called or when a session auto starts,
PHP will call the open and read session save handlers. These will either be a built-in
save handler provided by default or by PHP extensions (such as SQLite or Memcached); or can be
custom handler as defined by <span class="function"><a href="function.session-set-save-handler.html" class="function">session_set_save_handler()</a></span>.
The read callback will retrieve any existing session data (stored in a special serialized format)
and will be unserialized and used to automatically populate the $_SESSION superglobal when the
read callback returns the saved session data back to PHP session handling.
</p>
<p class="para">
To use a named session, call
<span class="function"><a href="function.session-name.html" class="function">session_name()</a></span> before calling
<span class="function"><strong>session_start()</strong></span>.
</p>
<p class="para">
When <a href="session.configuration.html#ini.session.use-trans-sid" class="link">session.use_trans_sid</a>
is enabled, the <span class="function"><strong>session_start()</strong></span> function will
register an internal output handler for URL rewriting.
</p>
<p class="para">
If a user uses <em>ob_gzhandler</em> or similar with
<span class="function"><a href="function.ob-start.html" class="function">ob_start()</a></span>, the function order is important for
proper output. For example,
<em>ob_gzhandler</em> must be registered before starting the session.
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.session-start-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
This function returns <strong><code>TRUE</code></strong> if a session was successfully started,
otherwise <strong><code>FALSE</code></strong>.
</p>
</div>
<div class="refsect1 changelog" id="refsect1-function.session-start-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>5.3.0</td>
<td>
If a session fails to start, then <strong><code>FALSE</code></strong> is returned.
Previously <strong><code>TRUE</code></strong> was returned.
</td>
</tr>
<tr>
<td>4.3.3</td>
<td>
As of PHP 4.3.3, calling <span class="function"><strong>session_start()</strong></span>
after the session was previously started will result in an
error of level <strong><code>E_NOTICE</code></strong>. Also, the
second session start will simply be ignored.
</td>
</tr>
</tbody>
</table>
</p>
</div>
<div class="refsect1 examples" id="refsect1-function.session-start-examples">
<h3 class="title">Examples</h3>
<p class="para">
<div class="example" id="example-4772">
<p><strong>Example #1 A session example: <var class="filename">page1.php</var></strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">// page1.php<br /><br /></span><span style="color: #0000BB">session_start</span><span style="color: #007700">();<br /><br />echo </span><span style="color: #DD0000">'Welcome to page #1'</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">$_SESSION</span><span style="color: #007700">[</span><span style="color: #DD0000">'favcolor'</span><span style="color: #007700">] = </span><span style="color: #DD0000">'green'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$_SESSION</span><span style="color: #007700">[</span><span style="color: #DD0000">'animal'</span><span style="color: #007700">] = </span><span style="color: #DD0000">'cat'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$_SESSION</span><span style="color: #007700">[</span><span style="color: #DD0000">'time'</span><span style="color: #007700">] = </span><span style="color: #0000BB">time</span><span style="color: #007700">();<br /><br /></span><span style="color: #FF8000">// Works if session cookie was accepted<br /></span><span style="color: #007700">echo </span><span style="color: #DD0000">'<br /><a href="page2.php">page 2</a>'</span><span style="color: #007700">;<br /><br /></span><span style="color: #FF8000">// Or maybe pass along the session id, if needed<br /></span><span style="color: #007700">echo </span><span style="color: #DD0000">'<br /><a href="page2.php?' </span><span style="color: #007700">. </span><span style="color: #0000BB">SID </span><span style="color: #007700">. </span><span style="color: #DD0000">'">page 2</a>'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="para">
After viewing <var class="filename">page1.php</var>, the second page
<var class="filename">page2.php</var> will magically contain the session
data. Read the <a href="ref.session.html" class="link">session reference</a>
for information on <a href="session.idpassing.html" class="link">propagating
session ids</a> as it, for example, explains what the constant
<strong><code>SID</code></strong> is all about.
</p>
<p class="para">
<div class="example" id="example-4773">
<p><strong>Example #2 A session example: <var class="filename">page2.php</var></strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">// page2.php<br /><br /></span><span style="color: #0000BB">session_start</span><span style="color: #007700">();<br /><br />echo </span><span style="color: #DD0000">'Welcome to page #2<br />'</span><span style="color: #007700">;<br /><br />echo </span><span style="color: #0000BB">$_SESSION</span><span style="color: #007700">[</span><span style="color: #DD0000">'favcolor'</span><span style="color: #007700">]; </span><span style="color: #FF8000">// green<br /></span><span style="color: #007700">echo </span><span style="color: #0000BB">$_SESSION</span><span style="color: #007700">[</span><span style="color: #DD0000">'animal'</span><span style="color: #007700">]; </span><span style="color: #FF8000">// cat<br /></span><span style="color: #007700">echo </span><span style="color: #0000BB">date</span><span style="color: #007700">(</span><span style="color: #DD0000">'Y m d H:i:s'</span><span style="color: #007700">, </span><span style="color: #0000BB">$_SESSION</span><span style="color: #007700">[</span><span style="color: #DD0000">'time'</span><span style="color: #007700">]);<br /><br /></span><span style="color: #FF8000">// You may want to use SID here, like we did in page1.php<br /></span><span style="color: #007700">echo </span><span style="color: #DD0000">'<br /><a href="page1.php">page 1</a>'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
</div>
<div class="refsect1 notes" id="refsect1-function.session-start-notes">
<h3 class="title">Notes</h3>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
To use cookie-based sessions, <span class="function"><strong>session_start()</strong></span>
must be called before outputing anything to the browser.
</p>
</p></blockquote>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
Use of <a href="zlib.configuration.html#ini.zlib.output-compression" class="link">zlib.output_compression</a>
is recommended instead of <span class="function"><a href="function.ob-gzhandler.html" class="function">ob_gzhandler()</a></span>
</p>
</p></blockquote>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
This function sends out several HTTP headers depending on the
configuration. See <span class="function"><a href="function.session-cache-limiter.html" class="function">session_cache_limiter()</a></span> to
customize these headers.
</p>
</p></blockquote>
</div>
<div class="refsect1 seealso" id="refsect1-function.session-start-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member"><var class="varname"><var class="varname"><a href="reserved.variables.session.html" class="classname">$_SESSION</a></var></var></li>
<li class="member">
The <a href="session.configuration.html#ini.session.auto-start" class="link">session.auto_start</a>
configuration directive
</li>
<li class="member"> <span class="function"><a href="function.session-id.html" class="function" rel="rdfs-seeAlso">session_id()</a> - Get and/or set the current session id</span></li>
</ul>
</p>
</div>
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