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<title>Generate a unique ID</title>
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<div class="refnamediv">
<h1 class="refname">uniqid</h1>
<p class="verinfo">(PHP 4, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">uniqid</span> — <span class="dc-title">Generate a unique ID</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.uniqid-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">string</span> <span class="methodname"><strong>uniqid</strong></span>
([ <span class="methodparam"><span class="type">string</span> <code class="parameter">$prefix</code><span class="initializer"> = ""</span></span>
[, <span class="methodparam"><span class="type">bool</span> <code class="parameter">$more_entropy</code><span class="initializer"> = <strong><code>FALSE</code></strong></span></span>
]] )</div>
<p class="para rdfs-comment">
Gets a prefixed unique identifier based on the current time in
microseconds.
</p>
<div class="caution"><strong class="caution">Caution</strong><p class="para">This function does not
generate cryptographically secure values, and should not be used for cryptographic purposes. If you need a
cryptographically secure value, consider using <span class="function"><a href="function.random-int.html" class="function">random_int()</a></span>, <span class="function"><a href="function.random-bytes.html" class="function">random_bytes()</a></span>, or
<span class="function"><a href="function.openssl-random-pseudo-bytes.html" class="function">openssl_random_pseudo_bytes()</a></span> instead.</p></div>
<div class="warning"><strong class="warning">Warning</strong>
<p class="para">
This function does not guarantee uniqueness of return
value. Since most systems adjust system clock by NTP or like,
system time is changed constantly. Therefore, it is possible that
this function does not return unique ID for the
process/thread. Use <code class="parameter">more_entropy</code> to
increase likelihood of uniqueness.
</p>
</div>
</div>
<div class="refsect1 parameters" id="refsect1-function.uniqid-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<code class="parameter">prefix</code></dt>
<dd>
<p class="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.
</p>
<p class="para">
With an empty <code class="parameter">prefix</code>, the returned string will
be 13 characters long. If <code class="parameter">more_entropy</code> is
<strong><code>TRUE</code></strong>, it will be 23 characters.
</p>
</dd>
<dt>
<code class="parameter">more_entropy</code></dt>
<dd>
<p class="para">
If set to <strong><code>TRUE</code></strong>, <span class="function"><strong>uniqid()</strong></span> 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.
</p>
</dd>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.uniqid-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
Returns timestamp based unique identifier as a string.
</p>
<div class="warning"><strong class="warning">Warning</strong>
<p class="para">
This function tries to create unique identifier, but it does not
guarantee 100% uniqueness of return value.
</p>
</div>
</div>
<div class="refsect1 examples" id="refsect1-function.uniqid-examples">
<h3 class="title">Examples</h3>
<p class="para">
<div class="example" id="example-4680">
<p><strong>Example #1 <span class="function"><strong>uniqid()</strong></span> Example</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">/* A uniqid, like: 4b3403665fea6 */<br /></span><span style="color: #0000BB">printf</span><span style="color: #007700">(</span><span style="color: #DD0000">"uniqid(): %s\r\n"</span><span style="color: #007700">, </span><span style="color: #0000BB">uniqid</span><span style="color: #007700">());<br /><br /></span><span style="color: #FF8000">/* We can also prefix the uniqid, this the same as <br /> * doing:<br /> *<br /> * $uniqid = $prefix . uniqid();<br /> * $uniqid = uniqid($prefix);<br /> */<br /></span><span style="color: #0000BB">printf</span><span style="color: #007700">(</span><span style="color: #DD0000">"uniqid('php_'): %s\r\n"</span><span style="color: #007700">, </span><span style="color: #0000BB">uniqid</span><span style="color: #007700">(</span><span style="color: #DD0000">'php_'</span><span style="color: #007700">));<br /><br /></span><span style="color: #FF8000">/* We can also activate the more_entropy parameter, which is <br /> * required on some systems, like Cygwin. This makes uniqid()<br /> * produce a value like: 4b340550242239.64159797<br /> */<br /></span><span style="color: #0000BB">printf</span><span style="color: #007700">(</span><span style="color: #DD0000">"uniqid('', true): %s\r\n"</span><span style="color: #007700">, </span><span style="color: #0000BB">uniqid</span><span style="color: #007700">(</span><span style="color: #DD0000">''</span><span style="color: #007700">, </span><span style="color: #0000BB">true</span><span style="color: #007700">));<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
</div>
<div class="refsect1 notes" id="refsect1-function.uniqid-notes">
<h3 class="title">Notes</h3>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
Under Cygwin, the <code class="parameter">more_entropy</code> must be set
to <strong><code>TRUE</code></strong> for this function to work.
</p>
</p></blockquote>
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