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<title>Create or open shared memory block</title>
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<h1 class="refname">shmop_open</h1>
<p class="verinfo">(PHP 4 >= 4.0.4, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">shmop_open</span> — <span class="dc-title">Create or open shared memory block</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.shmop-open-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">resource</span> <span class="methodname"><strong>shmop_open</strong></span>
( <span class="methodparam"><span class="type">int</span> <code class="parameter">$key</code></span>
, <span class="methodparam"><span class="type">string</span> <code class="parameter">$flags</code></span>
, <span class="methodparam"><span class="type">int</span> <code class="parameter">$mode</code></span>
, <span class="methodparam"><span class="type">int</span> <code class="parameter">$size</code></span>
)</div>
<p class="para rdfs-comment">
<span class="function"><strong>shmop_open()</strong></span> can create or open a shared memory block.
</p>
</div>
<div class="refsect1 parameters" id="refsect1-function.shmop-open-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<code class="parameter">key</code></dt>
<dd>
<p class="para">
System's id for the shared memory block.
Can be passed as a decimal or hex.
</p>
</dd>
<dt>
<code class="parameter">flags</code></dt>
<dd>
<p class="para">
The flags that you can use:
<ul class="itemizedlist">
<li class="listitem">
<span class="simpara">
"a" for access (sets SHM_RDONLY for shmat)
use this flag when you need to open an existing shared memory
segment for read only
</span>
</li>
<li class="listitem">
<span class="simpara">
"c" for create (sets IPC_CREATE)
use this flag when you need to create a new shared memory segment
or if a segment with the same key exists, try to open it for read
and write
</span>
</li>
<li class="listitem">
<span class="simpara">
"w" for read & write access
use this flag when you need to read and write to a shared memory
segment, use this flag in most cases.
</span>
</li>
<li class="listitem">
<span class="simpara">
"n" create a new memory segment (sets IPC_CREATE|IPC_EXCL)
use this flag when you want to create a new shared memory segment
but if one already exists with the same flag, fail. This is useful
for security purposes, using this you can prevent race condition
exploits.
</span>
</li>
</ul>
</p>
</dd>
<dt>
<code class="parameter">mode</code></dt>
<dd>
<p class="para">
The permissions that you wish to assign to your memory segment, those
are the same as permission for a file. Permissions need to be passed
in octal form, like for example <em>0644</em>
</p>
</dd>
<dt>
<code class="parameter">size</code></dt>
<dd>
<p class="para">
The size of the shared memory block you wish to create in bytes
</p>
</dd>
</dl>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
Note: the 3rd and 4th should be entered as 0 if you are opening an
existing memory segment.
</p>
</p></blockquote>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.shmop-open-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
On success <span class="function"><strong>shmop_open()</strong></span> will return an resource that you can
use to access the shared memory segment you've created. <strong><code>FALSE</code></strong> is
returned on failure.
</p>
</div>
<div class="refsect1 changelog" id="refsect1-function.shmop-open-changelog">
<h3 class="title">Changelog</h3>
<table class="doctable informaltable">
<thead>
<tr>
<th>Version</th>
<th>Description</th>
</tr>
</thead>
<tbody class="tbody">
<tr>
<td>7.0.0</td>
<td>
The return type of <span class="function"><strong>shmop_open()</strong></span> has been changed from
<span class="type"><a href="language.types.integer.html" class="type int">int</a></span> to <span class="type"><a href="language.types.resource.html" class="type resource">resource</a></span>.
</td>
</tr>
</tbody>
</table>
</div>
<div class="refsect1 examples" id="refsect1-function.shmop-open-examples">
<h3 class="title">Examples</h3>
<p class="para">
<div class="example" id="example-4586">
<p><strong>Example #1 Create a new shared memory block</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$shm_key </span><span style="color: #007700">= </span><span style="color: #0000BB">ftok</span><span style="color: #007700">(</span><span style="color: #0000BB">__FILE__</span><span style="color: #007700">, </span><span style="color: #DD0000">'t'</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$shm_id </span><span style="color: #007700">= </span><span style="color: #0000BB">shmop_open</span><span style="color: #007700">(</span><span style="color: #0000BB">$shm_key</span><span style="color: #007700">, </span><span style="color: #DD0000">"c"</span><span style="color: #007700">, </span><span style="color: #0000BB">0644</span><span style="color: #007700">, </span><span style="color: #0000BB">100</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="para">
This example opened a shared memory block with a system id returned by
<span class="function"><a href="function.ftok.html" class="function">ftok()</a></span>.
</p>
</div>
<div class="refsect1 seealso" id="refsect1-function.shmop-open-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member"><span class="function"><a href="function.shmop-close.html" class="function" rel="rdfs-seeAlso">shmop_close()</a> - Close shared memory block</span></li>
<li class="member"><span class="function"><a href="function.shmop-delete.html" class="function" rel="rdfs-seeAlso">shmop_delete()</a> - Delete shared memory block</span></li>
</ul>
</p>
</div>
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