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| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="boost_asio.reference.async_read.overload2"></a><a class="link" href="overload2.html" title="async_read (2 of 4 overloads)">async_read |
| (2 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> <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="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="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> |
| <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 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> |
| <a name="boost_asio.reference.async_read.overload2.parameters"></a><h6> |
| <a name="id871678"></a> |
| <a class="link" href="overload2.html#boost_asio.reference.async_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 AsyncReadStream 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. Although the buffers object may be copied as necessary, |
| ownership of the underlying memory blocks is retained by the caller, |
| which must guarantee that they remain valid until the handler is |
| called. |
| </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 async_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 async_read_some function. |
| </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">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">// 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 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">post</span><span class="special">()</span></code>. |
| </p> |
| </dd> |
| </dl> |
| </div> |
| <a name="boost_asio.reference.async_read.overload2.example"></a><h6> |
| <a name="id872061"></a> |
| <a class="link" href="overload2.html#boost_asio.reference.async_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">async_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> |
| <span class="identifier">handler</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> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <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>) |
| </p> |
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