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<title>Creates or open a shared memory segment</title>
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<div class="refnamediv">
<h1 class="refname">shm_attach</h1>
<p class="verinfo">(PHP 4, PHP 5)</p><p class="refpurpose"><span class="refname">shm_attach</span> — <span class="dc-title">Creates or open a shared memory segment</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.shm-attach-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">resource</span> <span class="methodname"><strong>shm_attach</strong></span>
( <span class="methodparam"><span class="type">int</span> <code class="parameter">$key</code></span>
[, <span class="methodparam"><span class="type">int</span> <code class="parameter">$memsize</code></span>
[, <span class="methodparam"><span class="type">int</span> <code class="parameter">$perm</code><span class="initializer"> = 0666</span></span>
]] )</div>
<p class="para rdfs-comment">
<span class="function"><strong>shm_attach()</strong></span> returns an id that can be used to access
the System V shared memory with the given <em><code class="parameter">key</code></em>, the
first call creates the shared memory segment with
<em><code class="parameter">memsize</code></em> and the optional perm-bits
<em><code class="parameter">perm</code></em>.
</p>
<p class="para">
A second call to <span class="function"><strong>shm_attach()</strong></span> for the same
<em><code class="parameter">key</code></em> will return a different shared memory
identifier, but both identifiers access the same underlying
shared memory. <em><code class="parameter">memsize</code></em> and
<em><code class="parameter">perm</code></em> will be ignored.
</p>
</div>
<div class="refsect1 parameters" id="refsect1-function.shm-attach-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<span class="term"><em><code class="parameter">key</code></em></span>
<dd>
<p class="para">
A numeric shared memory segment ID
</p>
</dd>
</dt>
<dt>
<span class="term"><em><code class="parameter">memsize</code></em></span>
<dd>
<p class="para">
The memory size. If not provided, default to the
<em>sysvshm.init_mem</em> in the <var class="filename">php.ini</var>, otherwise 10000
bytes.
</p>
</dd>
</dt>
<dt>
<span class="term"><em><code class="parameter">perm</code></em></span>
<dd>
<p class="para">
The optional permission bits. Default to 0666.
</p>
</dd>
</dt>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.shm-attach-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
Returns a shared memory segment identifier.
</p>
</div>
<div class="refsect1 changelog" id="refsect1-function.shm-attach-changelog">
<h3 class="title">Changelog</h3>
<p class="para">
<table class="doctable informaltable">
<thead>
<tr>
<th>Version</th>
<th>Description</th>
</tr>
</thead>
<tbody class="tbody">
<tr>
<td>5.3.0</td>
<td>
This function now returns a <a href="language.types.resource.html" class="link">resource</a> instead of an
<a href="language.types.integer.html" class="link">integer</a>.
</td>
</tr>
</tbody>
</table>
</p>
</div>
<div class="refsect1 notes" id="refsect1-function.shm-attach-notes">
<h3 class="title">Notes</h3>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
This function used to return an integer value prior to
PHP 5.3.0. To achieve the same value in a portable manner, the
return value can be cast to an integer like:
</p>
<p class="para">
<div class="example" id="example-3721">
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">// Create a temporary file and return its path<br /></span><span style="color: #0000BB">$tmp </span><span style="color: #007700">= </span><span style="color: #0000BB">tempnam</span><span style="color: #007700">(</span><span style="color: #DD0000">'/tmp'</span><span style="color: #007700">, </span><span style="color: #DD0000">'PHP'</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">// Get the file token key<br /></span><span style="color: #0000BB">$key </span><span style="color: #007700">= </span><span style="color: #0000BB">ftok</span><span style="color: #007700">(</span><span style="color: #0000BB">$tmp</span><span style="color: #007700">, </span><span style="color: #DD0000">'a'</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">// Attach the SHM resource, notice the cast afterwards<br /></span><span style="color: #0000BB">$id </span><span style="color: #007700">= </span><span style="color: #0000BB">shm_attach</span><span style="color: #007700">(</span><span style="color: #0000BB">$key</span><span style="color: #007700">);<br /><br />if (</span><span style="color: #0000BB">$id </span><span style="color: #007700">=== </span><span style="color: #0000BB">false</span><span style="color: #007700">) {<br /> die(</span><span style="color: #DD0000">'Unable to create the shared memory segment'</span><span style="color: #007700">);<br />}<br /><br /></span><span style="color: #FF8000">// Cast to integer, since prior to PHP 5.3.0 the resource id <br />// is returned which can be exposed when casting a resource<br />// to an integer<br /></span><span style="color: #0000BB">$id </span><span style="color: #007700">= (integer) </span><span style="color: #0000BB">$id</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
</p></blockquote>
</div>
<div class="refsect1 seealso" id="refsect1-function.shm-attach-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member"> <span class="function"><a href="function.shm-detach.html" class="function" rel="rdfs-seeAlso">shm_detach()</a> - Disconnects from shared memory segment</span></li>
<li class="member"> <span class="function"><a href="function.ftok.html" class="function" rel="rdfs-seeAlso">ftok()</a> - Convert a pathname and a project identifier to a System V IPC key</span></li>
</ul>
</p>
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