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<title>read (2 of 6 overloads)</title>
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<div class="section" title="read (2 of 6 overloads)">
<div class="titlepage"><div><div><h4 class="title">
<a name="boost_asio.reference.read.overload2"></a><a class="link" href="overload2.html" title="read (2 of 6 overloads)"> read (2 of 6
overloads)</a>
</h4></div></div></div>
<p>
Attempt to read a certain amount of data from a stream before returning.
</p>
<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span>
<span class="keyword">typename</span> <a class="link" href="../SyncReadStream.html" title="Buffer-oriented synchronous read stream requirements">SyncReadStream</a><span class="special">,</span>
<span class="keyword">typename</span> <a class="link" href="../MutableBufferSequence.html" title="Mutable buffer sequence requirements">MutableBufferSequence</a><span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">CompletionCondition</span><span class="special">></span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">read</span><span class="special">(</span>
<span class="identifier">SyncReadStream</span> <span class="special">&</span> <span class="identifier">s</span><span class="special">,</span>
<span class="keyword">const</span> <span class="identifier">MutableBufferSequence</span> <span class="special">&</span> <span class="identifier">buffers</span><span class="special">,</span>
<span class="identifier">CompletionCondition</span> <span class="identifier">completion_condition</span><span class="special">);</span>
</pre>
<p>
This function is used to read a certain number of bytes of data from a
stream. The call will block until one of the following conditions is true:
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
The supplied buffers are full. That is, the bytes transferred is equal
to the sum of the buffer sizes.
</li>
<li class="listitem">
The completion_condition function object returns 0.
</li>
</ul></div>
<p>
This operation is implemented in terms of zero or more calls to the stream's
read_some function.
</p>
<a name="boost_asio.reference.read.overload2.parameters"></a><h6>
<a name="id1061730"></a>
<a class="link" href="overload2.html#boost_asio.reference.read.overload2.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 SyncReadStream concept.
</p></dd>
<dt><span class="term">buffers</span></dt>
<dd><p>
One or more buffers into which the data will be read. The sum of the
buffer sizes indicates the maximum number of bytes to read from the
stream.
</p></dd>
<dt><span class="term">completion_condition</span></dt>
<dd>
<p>
The function object to be called to determine whether the read operation
is complete. The signature of the function object must be:
</p>
<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">completion_condition</span><span class="special">(</span>
<span class="comment">// Result of latest read_some operation.
</span> <span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</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">// Number of bytes transferred so far.
</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_transferred</span>
<span class="special">);</span>
</pre>
<p>
A return value of 0 indicates that the read operation is complete.
A non-zero return value indicates the maximum number of bytes to be
read on the next call to the stream's read_some function.
</p>
</dd>
</dl>
</div>
<a name="boost_asio.reference.read.overload2.return_value"></a><h6>
<a name="id1061916"></a>
<a class="link" href="overload2.html#boost_asio.reference.read.overload2.return_value">Return
Value</a>
</h6>
<p>
The number of bytes transferred.
</p>
<a name="boost_asio.reference.read.overload2.exceptions"></a><h6>
<a name="id1061942"></a>
<a class="link" href="overload2.html#boost_asio.reference.read.overload2.exceptions">Exceptions</a>
</h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">boost::system::system_error</span></dt>
<dd><p>
Thrown on failure.
</p></dd>
</dl>
</div>
<a name="boost_asio.reference.read.overload2.example"></a><h6>
<a name="id1061981"></a>
<a class="link" href="overload2.html#boost_asio.reference.read.overload2.example">Example</a>
</h6>
<p>
To read into a single data buffer use the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput"><span class="identifier">buffer</span></code></a> function as follows:
</p>
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">read</span><span class="special">(</span><span class="identifier">s</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">,</span> <span class="identifier">size</span><span class="special">),</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">transfer_at_least</span><span class="special">(</span><span class="number">32</span><span class="special">));</span>
</pre>
<p>
See the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput"><span class="identifier">buffer</span></code></a>
documentation for information on reading into multiple buffers in one go,
and how to use it with arrays, boost::array or std::vector.
</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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