php-doc-en/reference/session/functions/session-name.xml

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<refentry xml:id="function.session-name" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>session_name</refname>
  <refpurpose>Get and/or set the current session name</refpurpose>
 </refnamediv>
 
 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type class="union"><type>string</type><type>false</type></type><methodname>session_name</methodname>
   <methodparam choice="opt"><type class="union"><type>string</type><type>null</type></type><parameter>name</parameter><initializer>&null;</initializer></methodparam>
  </methodsynopsis>
  <para>
   <function>session_name</function> returns the name of the current
   session. If <parameter>name</parameter> is given,
   <function>session_name</function> will update the session name and return
   the <emphasis>old</emphasis> session name.
  </para>
  <para>
   If a new session <parameter>name</parameter> is
   supplied, <function>session_name</function> modifies the HTTP cookie
   (and output content when <literal>session.transid</literal> is
   enabled). Once the HTTP cookie is
   sent, <function>session_name</function> raises error.
   <function>session_name</function> must be called
   before <function>session_start</function> for the session to work
   properly.
  </para>
  <para>
   The session name is reset to the default value stored in
   <literal>session.name</literal> at request startup time. Thus, you need to
   call <function>session_name</function> for every request (and before
   <function>session_start</function> is called).
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>name</parameter></term>
     <listitem>
      <para>
       The session name references the name of the session, which is 
       used in cookies and URLs (e.g. <literal>PHPSESSID</literal>). It
       should contain only alphanumeric characters; it should be short and
       descriptive (i.e. for users with enabled cookie warnings).
       If <parameter>name</parameter> is specified and not &null;, the name of the current
       session is changed to its value.
      </para>
      <para>
       <warning>
        <para>
         The session name can't consist of digits only, at least one letter
         must be present. Otherwise a new session id is generated every time.
        </para>
       </warning>
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns the name of the current session. If <parameter>name</parameter> is given
   and function updates the session name, name of the <emphasis>old</emphasis> session
   is returned, &return.falseforfailure;.
  </para>
 </refsect1>

 <refsect1 role="changelog">
  &reftitle.changelog;
  <para>
   <informaltable>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>&Version;</entry>
       <entry>&Description;</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry>8.0.0</entry>
       <entry>
        <parameter>name</parameter> is nullable now.
       </entry>
      </row>
      <row>
       <entry>7.2.0</entry>
       <entry>
        <function>session_name</function> checks session status,
        previously it only checked cookie status. Therefore,
        older <function>session_name</function> allows to
        call <function>session_name</function>
        after <function>session_start</function> which may crash PHP
        and may result in misbehaviors.
       </entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>session_name</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php

/* set the session name to WebsiteID */

$previous_name = session_name("WebsiteID");

echo "The previous session name was $previous_name<br />";
?>
]]>
    </programlisting>
   </example>
  </para>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member>
     The <link linkend="ini.session.name">session.name</link> configuration
     directive
    </member>
   </simplelist>
  </para>
 </refsect1>

</refentry>
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