mirror of
https://github.com/sigmasternchen/php-doc-en
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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@343899 c90b9560-bf6c-de11-be94-00142212c4b1
143 lines
3.9 KiB
XML
143 lines
3.9 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<refentry xml:id="function.uniqid" xmlns="http://docbook.org/ns/docbook">
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<refnamediv>
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<refname>uniqid</refname>
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<refpurpose>Generate a unique ID</refpurpose>
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</refnamediv>
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<refsect1 role="description">
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&reftitle.description;
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<methodsynopsis>
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<type>string</type><methodname>uniqid</methodname>
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<methodparam choice="opt"><type>string</type><parameter>prefix</parameter><initializer>""</initializer></methodparam>
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<methodparam choice="opt"><type>bool</type><parameter>more_entropy</parameter><initializer>&false;</initializer></methodparam>
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</methodsynopsis>
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<para>
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Gets a prefixed unique identifier based on the current time in
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microseconds.
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</para>
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&caution.cryptographically-insecure;
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<warning>
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<para>
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This function does not guarantee uniqueness of return
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value. Since most systems adjust system clock by NTP or like,
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system time is changed constantly. Therefore, it is possible that
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this function does not return unique ID for the
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process/thread. Use <parameter>more_entropy</parameter> to
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increase likelihood of uniqueness.
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</para>
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</warning>
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</refsect1>
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<refsect1 role="parameters">
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&reftitle.parameters;
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<para>
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<variablelist>
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<varlistentry>
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<term><parameter>prefix</parameter></term>
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<listitem>
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<para>
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Can be useful, for instance, if you generate identifiers
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simultaneously on several hosts that might happen to generate the
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identifier at the same microsecond.
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</para>
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<para>
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With an empty <parameter>prefix</parameter>, the returned string will
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be 13 characters long. If <parameter>more_entropy</parameter> is
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&true;, it will be 23 characters.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>more_entropy</parameter></term>
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<listitem>
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<para>
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If set to &true;, <function>uniqid</function> will add additional
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entropy (using the combined linear congruential generator) at the end
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of the return value, which increases the likelihood that the result
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will be unique.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect1>
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<refsect1 role="returnvalues">
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&reftitle.returnvalues;
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<para>
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Returns timestamp based unique identifier as a string.
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</para>
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<warning>
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<para>
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This function tries to create unique identifier, but it does not
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guarantee 100% uniqueness of return value.
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</para>
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</warning>
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</refsect1>
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<refsect1 role="examples">
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&reftitle.examples;
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<para>
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<example>
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<title><function>uniqid</function> Example</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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/* A uniqid, like: 4b3403665fea6 */
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printf("uniqid(): %s\r\n", uniqid());
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/* We can also prefix the uniqid, this the same as
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* doing:
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*
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* $uniqid = $prefix . uniqid();
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* $uniqid = uniqid($prefix);
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*/
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printf("uniqid('php_'): %s\r\n", uniqid('php_'));
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/* We can also activate the more_entropy parameter, which is
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* required on some systems, like Cygwin. This makes uniqid()
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* produce a value like: 4b340550242239.64159797
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*/
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printf("uniqid('', true): %s\r\n", uniqid('', true));
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?>
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]]>
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</programlisting>
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</example>
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</para>
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</refsect1>
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<refsect1 role="notes">
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&reftitle.notes;
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<note>
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<para>
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Under Cygwin, the <parameter>more_entropy</parameter> must be set
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to &true; for this function to work.
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</para>
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</note>
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</refsect1>
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</refentry>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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indent-tabs-mode:nil
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sgml-parent-document:nil
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sgml-default-dtd-file:"~/.phpdoc/manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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