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

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<refentry xml:id="function.uniqid" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>uniqid</refname>
  <refpurpose>Generate a unique ID</refpurpose>
 </refnamediv>
 
 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>string</type><methodname>uniqid</methodname>
   <methodparam choice="opt"><type>string</type><parameter>prefix</parameter><initializer>""</initializer></methodparam>
   <methodparam choice="opt"><type>bool</type><parameter>more_entropy</parameter><initializer>false</initializer></methodparam>
  </methodsynopsis>
  <para>
   Gets a prefixed unique identifier based on the current time in
   microseconds. 
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>prefix</parameter></term>
     <listitem>
      <para>
       Can be useful, for instance, if you generate identifiers
       simultaneously on several hosts that might happen to generate the
       identifier at the same microsecond.
      </para>
      <para>
       With an empty <parameter>prefix</parameter>, the returned string will
       be 13 characters long.  If <parameter>more_entropy</parameter> is
       &true;, it will be 23 characters.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>more_entropy</parameter></term>
     <listitem>
      <para>
       If set to &true;, <function>uniqid</function> will add additional
       entropy (using the combined linear congruential generator) at the end
       of the return value, which increases the likelihood that the result
       will be unique.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns the unique identifier, as a string.
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>uniqid</function> Example</title>
    <programlisting role="php">
<![CDATA[
<?php
/* A uniqid, like: 4b3403665fea6 */
printf("uniqid(): %s\r\n", uniqid());

/* We can also prefix the uniqid, this the same as 
 * doing:
 *
 * $uniqid = $prefix . uniqid();
 * $uniqid = uniqid($prefix);
 */
printf("uniqid('php_'): %s\r\n", uniqid('php_'));

/* We can also activate the more_entropy parameter, which is 
 * required on some systems, like Cygwin. This makes uniqid()
 * produce a value like: 4b340550242239.64159797
 */
printf("uniqid('', true): %s\r\n", uniqid('', true));
?>
]]>
    </programlisting>
   </example>
  </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>5.0.0</entry>
       <entry>
        The <parameter>prefix</parameter> parameter was made optional.
       </entry>
      </row>
      <row>
       <entry>4.3.1</entry>
       <entry>
        The limit of 114 characters long for <parameter>prefix</parameter>
        was raised.
       </entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>
  </para>
 </refsect1>

 <refsect1 role="notes">
  &reftitle.notes;
  <caution>
   <para>
    This function does not generate cryptographically secure tokens, 
    in fact without being passed any additional parameters the return 
    value is little different from <function>microtime</function>. If 
    you need to generate cryptographically secure tokens use 
    <function>openssl_random_pseudo_bytes</function>.
   </para>
  </caution>
  <note>
   <para>
    Under Cygwin, the <parameter>more_entropy</parameter> must be set 
    to &true; for this function to work.
   </para>
  </note>

 </refsect1>

</refentry>

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