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<title>Stream-Oriented File Descriptors</title>
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<div class="titlepage"><div><div><h4 class="title">
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<a name="boost_asio.overview.posix.stream_descriptor"></a><a class="link" href="stream_descriptor.html" title="Stream-Oriented File Descriptors">Stream-Oriented
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File Descriptors</a>
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</h4></div></div></div>
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<p>
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Boost.Asio includes classes added to permit synchronous and asynchronous
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read and write operations to be performed on POSIX file descriptors, such
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as pipes, standard input and output, and various devices.
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</p>
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<p>
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These classes also provide limited support for regular files. This support
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assumes that the underlying read and write operations provided by the operating
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system never fail with <code class="computeroutput">EAGAIN</code> or <code class="computeroutput">EWOULDBLOCK</code>.
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(This assumption normally holds for buffered file I/O.) Synchronous and
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asynchronous read and write operations on file descriptors will succeed
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but the I/O will always be performed immediately. Wait operations, and
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operations involving <code class="computeroutput">boost::asio::null_buffers</code>, are not portably
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supported.
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</p>
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<p>
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For example, to perform read and write operations on standard input and
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output, the following objects may be created:
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</p>
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<pre class="programlisting">posix::stream_descriptor in(my_io_context, ::dup(STDIN_FILENO));
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posix::stream_descriptor out(my_io_context, ::dup(STDOUT_FILENO));
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</pre>
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<p>
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These are then used as synchronous or asynchronous read and write streams.
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This means the objects can be used with any of the <a class="link" href="../../reference/read.html" title="read">read()</a>,
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<a class="link" href="../../reference/async_read.html" title="async_read">async_read()</a>, <a class="link" href="../../reference/write.html" title="write">write()</a>, <a class="link" href="../../reference/async_write.html" title="async_write">async_write()</a>,
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<a class="link" href="../../reference/read_until.html" title="read_until">read_until()</a> or
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<a class="link" href="../../reference/async_read_until.html" title="async_read_until">async_read_until()</a>
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free functions.
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</p>
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<h6>
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<a name="boost_asio.overview.posix.stream_descriptor.h0"></a>
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<span class="phrase"><a name="boost_asio.overview.posix.stream_descriptor.see_also"></a></span><a class="link" href="stream_descriptor.html#boost_asio.overview.posix.stream_descriptor.see_also">See Also</a>
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</h6>
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<p>
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<a class="link" href="../../reference/posix__stream_descriptor.html" title="posix::stream_descriptor">posix::stream_descriptor</a>,
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<a class="link" href="../../examples/cpp03_examples.html#boost_asio.examples.cpp03_examples.chat">Chat example (C++03)</a>,
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<a class="link" href="../../examples/cpp11_examples.html#boost_asio.examples.cpp11_examples.chat">Chat example (C++11)</a>.
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</p>
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<h6>
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<a name="boost_asio.overview.posix.stream_descriptor.h1"></a>
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<span class="phrase"><a name="boost_asio.overview.posix.stream_descriptor.notes"></a></span><a class="link" href="stream_descriptor.html#boost_asio.overview.posix.stream_descriptor.notes">Notes</a>
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</h6>
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<p>
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POSIX stream descriptors are only available at compile time if supported
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by the target operating system. A program may test for the macro <code class="computeroutput">BOOST_ASIO_HAS_POSIX_STREAM_DESCRIPTOR</code>
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to determine whether they are supported.
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</p>
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<td align="left"></td>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2021 Christopher
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M. Kohlhoff<p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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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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