doc/html/boost_asio/reference/posix__stream_descriptor/async_read_some.html


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<div class="titlepage"><div><div><h4 class="title">
<a name="boost_asio.reference.posix__stream_descriptor.async_read_some"></a><a class="link" href="async_read_some.html" title="posix::stream_descriptor::async_read_some">posix::stream_descriptor::async_read_some</a>
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<p>
          <a class="indexterm" name="boost_asio.indexterm.posix__stream_descriptor.async_read_some"></a> 
Start
          an asynchronous read.
        </p>
<pre class="programlisting">template&lt;
    typename <a class="link" href="../MutableBufferSequence.html" title="Mutable buffer sequence requirements">MutableBufferSequence</a>,
    typename <a class="link" href="../ReadHandler.html" title="Read handler requirements">ReadHandler</a>&gt;
<a class="link" href="../asynchronous_operations.html#boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type"><span class="emphasis"><em>DEDUCED</em></span></a> async_read_some(
    const MutableBufferSequence &amp; buffers,
    ReadHandler &amp;&amp; handler);
</pre>
<p>
          This function is used to asynchronously read data from the stream descriptor.
          The function call always returns immediately.
        </p>
<h6>
<a name="boost_asio.reference.posix__stream_descriptor.async_read_some.h0"></a>
          <span class="phrase"><a name="boost_asio.reference.posix__stream_descriptor.async_read_some.parameters"></a></span><a class="link" href="async_read_some.html#boost_asio.reference.posix__stream_descriptor.async_read_some.parameters">Parameters</a>
        </h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl class="variablelist">
<dt><span class="term">buffers</span></dt>
<dd><p>
                One or more buffers into which the data will be read. 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">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">void handler(
  const boost::system::error_code&amp; error, // Result of operation.
  std::size_t bytes_transferred           // Number of bytes read.
);
</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">boost::asio::io_context::post()</code>.
              </p>
</dd>
</dl>
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<h6>
<a name="boost_asio.reference.posix__stream_descriptor.async_read_some.h1"></a>
          <span class="phrase"><a name="boost_asio.reference.posix__stream_descriptor.async_read_some.remarks"></a></span><a class="link" href="async_read_some.html#boost_asio.reference.posix__stream_descriptor.async_read_some.remarks">Remarks</a>
        </h6>
<p>
          The read operation may not read all of the requested number of bytes. Consider
          using the <a class="link" href="../async_read.html" title="async_read"><code class="computeroutput">async_read</code></a>
          function if you need to ensure that the requested amount of data is read
          before the asynchronous operation completes.
        </p>
<h6>
<a name="boost_asio.reference.posix__stream_descriptor.async_read_some.h2"></a>
          <span class="phrase"><a name="boost_asio.reference.posix__stream_descriptor.async_read_some.example"></a></span><a class="link" href="async_read_some.html#boost_asio.reference.posix__stream_descriptor.async_read_some.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">buffer</code></a>
          function as follows:
        </p>
<pre class="programlisting">descriptor.async_read_some(boost::asio::buffer(data, size), handler);
</pre>
<p>
          See the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput">buffer</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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        Distributed under the Boost Software License, Version 1.0. (See accompanying
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