reference/misc/functions/uniqid.xml
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52c495140bdb84f45f186bfb1cccf09788b0121e
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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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<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 create random nor unpredictable strings.
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<emphasis>This function must not be used for security purposes.</emphasis>
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Use a cryptographically secure random function/generator and
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cryptographically secure hash functions to create unpredictable
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secure IDs.
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</para>
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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="returnvalues">
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&reftitle.returnvalues;
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<para>
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Returns the unique identifier, as a string.
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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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@@ -102,15 +110,6 @@ printf("uniqid('', true): %s\r\n", uniqid('', true));
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<refsect1 role="notes">
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&reftitle.notes;
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<caution>
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<para>
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This function does not generate cryptographically secure tokens,
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in fact without being passed any additional parameters the return
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value is little different from <function>microtime</function>. If
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you need to generate cryptographically secure tokens use
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<function>openssl_random_pseudo_bytes</function>.
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</para>
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</caution>
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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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</note>
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</refsect1>
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<refsect1 role="seealso">
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&reftitle.seealso;
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<simplelist>
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<member><function>random_bytes</function></member>
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</simplelist>
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</refsect1>
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</refentry>
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