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<title>Handlers</title>
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<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.reference.Handler"></a><a class="link" href="Handler.html" title="Handlers">Handlers</a>
</h3></div></div></div>
<p>
A handler must meet the requirements of <code class="computeroutput">MoveConstructible</code> types
(C++Std [moveconstructible]).
</p>
<p>
In the table below, <code class="computeroutput">X</code> denotes a handler class, <code class="computeroutput">h</code>
denotes a value of <code class="computeroutput">X</code>, <code class="computeroutput">p</code> denotes a pointer to a
block of allocated memory of type <code class="computeroutput">void*</code>, <code class="computeroutput">s</code> denotes
the size for a block of allocated memory, and <code class="computeroutput">f</code> denotes a function
object taking no arguments.
</p>
<div class="table">
<a name="boost_asio.reference.Handler.t0"></a><p class="title"><b>Table 17. Handler requirements</b></p>
<div class="table-contents"><table class="table" summary="Handler requirements">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
expression
</p>
</th>
<th>
<p>
return type
</p>
</th>
<th>
<p>
assertion/note<br> pre/post-conditions
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
</p>
<pre class="programlisting">using boost::asio::asio_handler_allocate;
asio_handler_allocate(s, &h);
</pre>
<p>
</p>
</td>
<td>
<p>
<code class="computeroutput">void*</code>
</p>
</td>
<td>
<p>
Returns a pointer to a block of memory of size <code class="computeroutput">s</code>.
The pointer must satisfy the same alignment requirements as a pointer
returned by <code class="computeroutput">::operator new()</code>. Throws <code class="computeroutput">bad_alloc</code>
on failure.<br> <br> The <code class="computeroutput">asio_handler_allocate()</code>
function is located using argument-dependent lookup. The function
<code class="computeroutput">boost::asio::asio_handler_allocate()</code> serves as a default
if no user-supplied function is available.
</p>
</td>
</tr>
<tr>
<td>
<p>
</p>
<pre class="programlisting">using boost::asio::asio_handler_deallocate;
asio_handler_deallocate(p, s, &h);
</pre>
<p>
</p>
</td>
<td>
</td>
<td>
<p>
Frees a block of memory associated with a pointer <code class="computeroutput">p</code>,
of at least size <code class="computeroutput">s</code>, that was previously allocated
using <code class="computeroutput">asio_handler_allocate()</code>.<br> <br> The <code class="computeroutput">asio_handler_deallocate()</code>
function is located using argument-dependent lookup. The function
<code class="computeroutput">boost::asio::asio_handler_deallocate()</code> serves as a
default if no user-supplied function is available.
</p>
</td>
</tr>
<tr>
<td>
<p>
</p>
<pre class="programlisting">using boost::asio::asio_handler_invoke;
asio_handler_invoke(f, &h);
</pre>
<p>
</p>
</td>
<td>
</td>
<td>
<p>
Causes the function object <code class="computeroutput">f</code> to be executed as if
by calling <code class="computeroutput">f()</code>.<br> <br> The <code class="computeroutput">asio_handler_invoke()</code>
function is located using argument-dependent lookup. The function
<code class="computeroutput">boost::asio::asio_handler_invoke()</code> serves as a default
if no user-supplied function is available.
</p>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2018 Christopher M. Kohlhoff<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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