uniqid.xml

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<refentry xml:id="function.uniqid" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>uniqid</refname>
  <refpurpose>Generate a time-based identifier</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 an identifier based on the current time with microsecond precision,
   prefixed with the given <parameter>prefix</parameter> and optionally
   appending a randomly generated value.
  </para>
  &caution.cryptographically-insecure;
  <warning>
    <para>
     This function does not guarantee the uniqueness of the return
     value because the value is based on the current time in microseconds
     or the current time with a small amount of random data appended
     if <parameter>more_entropy</parameter> is &true;.
    </para>
  </warning>
 </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 could generate the
       same identifier at the same microsecond. (This can happen
       even on a single host if the system clock is moved backwards,
       such as by an NTP adjustment.)
      </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 timestamp based identifier as a string.
  </para>
  <warning>
   <para>
     This function does not guarantee the uniqueness of the return value.
   </para>
  </warning>
 </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="notes">
  &reftitle.notes;
  <note>
   <para>
    Under Cygwin, the <parameter>more_entropy</parameter> must be set 
    to &true; for this function to work.
   </para>
  </note>

 </refsect1>
 <refsect1 role="seealso">
  &reftitle.seealso;
  <simplelist>
   <member><function>random_bytes</function></member>
  </simplelist>
 </refsect1>
</refentry>

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