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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision: 332733 $ -->
<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>
<warning>
<para>
This function does not create random nor unpredictable string.
<emphasis>This function must not be used for security purposes.</emphasis>
Use cryptographically secure random function/generator and
cryptographically secure hash functions to create unpredictable
secure ID.
</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 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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