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<title>Handlers</title>
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<div class="section" title="Handlers">
<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"><span class="identifier">CopyConstructible</span></code>
types (C++ Std, 20.1.3).
</p>
<p>
In the table below, <code class="computeroutput"><span class="identifier">X</span></code> denotes
a handler class, <code class="computeroutput"><span class="identifier">h</span></code> denotes
a value of <code class="computeroutput"><span class="identifier">X</span></code>, <code class="computeroutput"><span class="identifier">p</span></code> denotes a pointer to a block of allocated
memory of type <code class="computeroutput"><span class="keyword">void</span><span class="special">*</span></code>,
<code class="computeroutput"><span class="identifier">s</span></code> denotes the size for a
block of allocated memory, and <code class="computeroutput"><span class="identifier">f</span></code>
denotes a function object taking no arguments.
</p>
<div class="table">
<a name="id627956"></a><p class="title"><b>Table 13. 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"><span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">;</span>
<span class="identifier">asio_handler_allocate</span><span class="special">(</span><span class="identifier">s</span><span class="special">,</span> <span class="special">&</span><span class="identifier">h</span><span class="special">);</span>
</pre>
<p>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="keyword">void</span><span class="special">*</span></code>
</p>
</td>
<td>
<p>
Returns a pointer to a block of memory of size <code class="computeroutput"><span class="identifier">s</span></code>.
The pointer must satisfy the same alignment requirements as a pointer
returned by <code class="computeroutput"><span class="special">::</span><span class="keyword">operator</span>
<span class="keyword">new</span><span class="special">()</span></code>.
Throws <code class="computeroutput"><span class="identifier">bad_alloc</span></code> on
failure.<br> <br> The <code class="computeroutput"><span class="identifier">asio_handler_allocate</span><span class="special">()</span></code> function is located using argument-dependent
lookup. The function <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">asio_handler_allocate</span><span class="special">()</span></code> serves as a default if no user-supplied
function is available.
</p>
</td>
</tr>
<tr>
<td>
<p>
</p>
<pre class="programlisting"><span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">;</span>
<span class="identifier">asio_handler_deallocate</span><span class="special">(</span><span class="identifier">p</span><span class="special">,</span> <span class="identifier">s</span><span class="special">,</span> <span class="special">&</span><span class="identifier">h</span><span class="special">);</span>
</pre>
<p>
</p>
</td>
<td>
<p>
</p>
</td>
<td>
<p>
Frees a block of memory associated with a pointer <code class="computeroutput"><span class="identifier">p</span></code>,
of at least size <code class="computeroutput"><span class="identifier">s</span></code>,
that was previously allocated using <code class="computeroutput"><span class="identifier">asio_handler_allocate</span><span class="special">()</span></code>.<br> <br> The <code class="computeroutput"><span class="identifier">asio_handler_deallocate</span><span class="special">()</span></code> function is located using argument-dependent
lookup. The function <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">asio_handler_deallocate</span><span class="special">()</span></code> serves as a default if no user-supplied
function is available.
</p>
</td>
</tr>
<tr>
<td>
<p>
</p>
<pre class="programlisting"><span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">;</span>
<span class="identifier">asio_handler_invoke</span><span class="special">(</span><span class="identifier">f</span><span class="special">,</span> <span class="special">&</span><span class="identifier">h</span><span class="special">);</span>
</pre>
<p>
</p>
</td>
<td>
<p>
</p>
</td>
<td>
<p>
Causes the function object <code class="computeroutput"><span class="identifier">f</span></code>
to be executed as if by calling <code class="computeroutput"><span class="identifier">f</span><span class="special">()</span></code>.<br> <br> The <code class="computeroutput"><span class="identifier">asio_handler_invoke</span><span class="special">()</span></code> function is located using argument-dependent
lookup. The function <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">asio_handler_invoke</span><span class="special">()</span></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 - 2010 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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