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<title>async_read (3 of 4 overloads)</title>
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<div class="titlepage"><div><div><h4 class="title">
<a name="asio.reference.async_read.overload3"></a><a class="link" href="overload3.html" title="async_read (3 of 4 overloads)"> async_read (3
of 4 overloads)</a>
</h4></div></div></div>
<p>
Start an asynchronous operation to read a certain amount of data from a
stream.
</p>
<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span>
<span class="keyword">typename</span> <a class="link" href="../AsyncReadStream.html" title="Buffer-oriented asynchronous read stream requirements">AsyncReadStream</a><span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">Allocator</span><span class="special">,</span>
<span class="keyword">typename</span> <a class="link" href="../ReadHandler.html" title="Read handler requirements">ReadHandler</a><span class="special">></span>
<span class="keyword">void</span> <span class="identifier">async_read</span><span class="special">(</span>
<span class="identifier">AsyncReadStream</span> <span class="special">&</span> <span class="identifier">s</span><span class="special">,</span>
<span class="identifier">basic_streambuf</span><span class="special"><</span> <span class="identifier">Allocator</span> <span class="special">></span> <span class="special">&</span> <span class="identifier">b</span><span class="special">,</span>
<span class="identifier">ReadHandler</span> <span class="identifier">handler</span><span class="special">);</span>
</pre>
<p>
This function is used to asynchronously read a certain number of bytes
of data from a stream. The function call always returns immediately. The
asynchronous operation will continue until one of the following conditions
is true:
</p>
<div class="itemizedlist"><ul type="disc"><li>
An error occurred.
</li></ul></div>
<p>
This operation is implemented in terms of zero or more calls to the stream's
async_read_some function.
</p>
<a name="asio.reference.async_read.overload3.parameters"></a><h6>
<a name="id720045"></a>
<a class="link" href="overload3.html#asio.reference.async_read.overload3.parameters">Parameters</a>
</h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">s</span></dt>
<dd><p>
The stream from which the data is to be read. The type must support
the AsyncReadStream concept.
</p></dd>
<dt><span class="term">b</span></dt>
<dd><p>
A basic_streambuf object into which the data will be read. Ownership
of the streambuf is retained by the caller, which must guarantee that
it remains valid until the handler is called.
</p></dd>
<dt><span class="term">handler</span></dt>
<dd>
<p>
The handler to be called when the read operation completes. Copies
will be made of the handler as required. The function signature of
the handler must be:
</p>
<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">handler</span><span class="special">(</span>
<span class="keyword">const</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&</span> <span class="identifier">error</span><span class="special">,</span> <span class="comment">// Result of operation.
</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_transferred</span> <span class="comment">// Number of bytes copied into the
</span> <span class="comment">// buffers. If an error occurred,
</span> <span class="comment">// this will be the number of
</span> <span class="comment">// bytes successfully transferred
</span> <span class="comment">// prior to the error.
</span><span class="special">);</span>
</pre>
<p>
Regardless of whether the asynchronous operation completes immediately
or not, the handler will not be invoked from within this function.
Invocation of the handler will be performed in a manner equivalent
to using asio::io_service::post().
</p>
</dd>
</dl>
</div>
<a name="asio.reference.async_read.overload3.remarks"></a><h6>
<a name="id720230"></a>
<a class="link" href="overload3.html#asio.reference.async_read.overload3.remarks">Remarks</a>
</h6>
<p>
This overload is equivalent to calling:
</p>
<pre class="programlisting"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_read</span><span class="special">(</span>
<span class="identifier">s</span><span class="special">,</span> <span class="identifier">b</span><span class="special">,</span>
<span class="identifier">asio</span><span class="special">::</span><span class="identifier">transfer_all</span><span class="special">(),</span>
<span class="identifier">handler</span><span class="special">);</span>
</pre>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="right"><div class="copyright-footer">Copyright 2003 - 2008 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>)
</p>
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