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<div class="refentry">
<a name="boost.process.std_in"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2><span class="refentrytitle">Global std_in</span></h2>
<p>boost::process::std_in</p>
</div>
<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: <<a class="link" href="../../process/reference.html#header.boost.process.io_hpp" title="Header <boost/process/io.hpp>">boost/process/io.hpp</a>>
</span><span class="emphasis"><em><span class="identifier">unspecified</span></em></span> std_in<span class="special">;</span></pre></div>
<div class="refsect1">
<a name="id-1.3.31.9.15.18.4"></a><h2>Description</h2>
<p>This property allows to set the input stream for the child process.</p>
<div class="sect1">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="namespaceboost_1_1process_1stdin_details"></a>Details</h2></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="sect2"><a href="std_in.html#namespaceboost_1_1process_1stdin_file">File Input</a></span></dt>
<dt><span class="sect2"><a href="std_in.html#namespaceboost_1_1process_1stdin_pipe">Pipe Input</a></span></dt>
<dt><span class="sect2"><a href="std_in.html#namespaceboost_1_1process_1stdin_async_pipe">Asynchronous Pipe Input</a></span></dt>
<dt><span class="sect2"><a href="std_in.html#namespaceboost_1_1process_1stdin_close">Close</a></span></dt>
<dt><span class="sect2"><a href="std_in.html#namespaceboost_1_1process_1stdin_null">Null</a></span></dt>
</dl></div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="namespaceboost_1_1process_1stdin_file"></a>File Input</h3></div></div></div>
<p>The file I/O simple redirects the stream to a file, for which the possible types are</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p><code class="computeroutput">boost::filesystem::path</code></p></li>
<li class="listitem"><p><code class="computeroutput">std::basic_string<char_type></code></p></li>
<li class="listitem"><p><code class="computeroutput">const char_type*</code></p></li>
<li class="listitem"><p><code class="computeroutput">FILE*</code></p></li>
</ul></div>
<p>
</p>
<p>with <code class="computeroutput">char_type</code> being either <code class="computeroutput">char</code> or <code class="computeroutput">wchar_t</code>.</p>
<p>FILE* is explicitly added, so the process can easily redirect the output stream of the child to another output stream of the process. That is:</p>
<pre class="programlisting"><span class="identifier">system</span><span class="special">(</span><span class="string">"ls"</span><span class="special">,</span> <span class="identifier">std_in</span> <span class="special"><</span> <span class="identifier">stdin</span><span class="special">)</span><span class="special">;</span>
</pre>
<div class="warning"><table border="0" summary="Warning">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../../doc/src/images/warning.png"></td>
<th align="left">Warning</th>
</tr>
<tr><td align="left" valign="top"><p>If the launching and the child process use the input, this leads to undefined behaviour.</p></td></tr>
</table></div>
<p>
A syntax like <code class="computeroutput">system("ls", std_out > std::cerr)</code> is not possible, due to the C++ implementation not providing access to the handle.</p>
<p>The valid expressions for this property are</p>
<pre class="programlisting"><span class="identifier">std_in</span> <span class="special"><</span> <span class="identifier">file</span><span class="special">;</span>
<span class="identifier">std_in</span> <span class="special">=</span> <span class="identifier">file</span><span class="special">;</span>
</pre>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="namespaceboost_1_1process_1stdin_pipe"></a>Pipe Input</h3></div></div></div>
<p>As explained in the corresponding section, the boost.process library provides a <a class="link" href="async_pipe.html" title="Class async_pipe">async_pipe</a> class which can be used to communicate with child processes.</p>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>Technically the <a class="link" href="async_pipe.html" title="Class async_pipe">async_pipe</a> works synchronous here, since no asio implementation is used by the library here. The async-operation will then however not end if the process is finished, since the pipe remains open. You can use the async_close function with on_exit to fix that.</p></td></tr>
</table></div>
<p>
Valid expressions with pipes are these:</p>
<pre class="programlisting"><span class="identifier">std_in</span> <span class="special"><</span> <span class="identifier">pipe</span><span class="special">;</span>
<span class="identifier">std_in</span> <span class="special">=</span> <span class="identifier">pipe</span><span class="special">;</span>
</pre>
<p>Where the valid types for <code class="computeroutput">pipe</code> are the following:</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p><code class="computeroutput"><a class="link" href="basic_pipe.html" title="Class template basic_pipe">basic_pipe</a></code></p></li>
<li class="listitem"><p><code class="computeroutput"><a class="link" href="async_pipe.html" title="Class async_pipe">async_pipe</a></code></p></li>
<li class="listitem"><p><code class="computeroutput"><a class="link" href="basic_opstream.html" title="Class template basic_opstream">basic_opstream</a></code></p></li>
<li class="listitem"><p><code class="computeroutput"><a class="link" href="basic_pstream.html" title="Class template basic_pstream">basic_pstream</a></code></p></li>
</ul></div>
<p>
</p>
<p>Note that the pipe may also be used between several processes, like this:</p>
<pre class="programlisting"><span class="identifier">pipe</span> <span class="identifier">p</span><span class="special">;</span>
<span class="identifier">child</span> <span class="identifier">c1</span><span class="special">(</span><span class="string">"nm"</span><span class="special">,</span> <span class="string">"a.out"</span><span class="special">,</span> <span class="identifier">std_out</span><span class="special">></span><span class="identifier">p</span><span class="special">)</span><span class="special">;</span>
<span class="identifier">child</span> <span class="identifier">c2</span><span class="special">(</span><span class="string">"c++filt"</span><span class="special">,</span> <span class="identifier">std_in</span><span class="special"><</span><span class="identifier">p</span><span class="special">)</span><span class="special">;</span>
</pre>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="namespaceboost_1_1process_1stdin_async_pipe"></a>Asynchronous Pipe Input</h3></div></div></div>
<p>Asynchronous Pipe I/O classifies communication which has automatically handling of the asynchronous operations by the process library. This means, that a pipe will be constructed, the async_read/-write will be automatically started, and that the end of the child process will also close the pipe.</p>
<p>Valid types for pipe I/O are the following:</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p><code class="computeroutput">boost::asio::const_buffer</code> <a href="#ftn.id-1.3.31.9.15.18.4.3.4.4.1.1.1.2" class="footnote" name="id-1.3.31.9.15.18.4.3.4.4.1.1.1.2"><sup class="footnote">[28]</sup></a> </p></li>
<li class="listitem"><p><code class="computeroutput">boost::asio::mutable_buffer</code> <a href="#ftn.id-1.3.31.9.15.18.4.3.4.4.1.2.1.2" class="footnote" name="id-1.3.31.9.15.18.4.3.4.4.1.2.1.2"><sup class="footnote">[29]</sup></a> </p></li>
<li class="listitem"><p><code class="computeroutput">boost::asio::streambuf</code></p></li>
</ul></div>
<p>
</p>
<p>Valid expressions with pipes are these:</p>
<pre class="programlisting"><span class="identifier">std_in</span> <span class="special"><</span> <span class="identifier">buffer</span><span class="special">;</span>
<span class="identifier">std_in</span> <span class="special">=</span> <span class="identifier">buffer</span><span class="special">;</span>
<span class="identifier">std_out</span> <span class="special">></span> <span class="identifier">buffer</span><span class="special">;</span>
<span class="identifier">std_out</span> <span class="special">=</span> <span class="identifier">buffer</span><span class="special">;</span>
<span class="identifier">std_err</span> <span class="special">></span> <span class="identifier">buffer</span><span class="special">;</span>
<span class="identifier">std_err</span> <span class="special">=</span> <span class="identifier">buffer</span><span class="special">;</span>
<span class="special">(</span><span class="identifier">std_out</span> <span class="special">&</span> <span class="identifier">std_err</span><span class="special">)</span> <span class="special">></span> <span class="identifier">buffer</span><span class="special">;</span>
<span class="special">(</span><span class="identifier">std_out</span> <span class="special">&</span> <span class="identifier">std_err</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">buffer</span><span class="special">;</span>
</pre>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top">
<p>It is also possible to get a future for std_in, by chaining another <code class="computeroutput">std::future<void></code> onto it, so you can wait for the input to be completed. It looks like this: </p>
<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">future</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span> <span class="identifier">fut</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">io_context</span> <span class="identifier">ios</span><span class="special">;</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">data</span><span class="special">;</span>
<span class="identifier">child</span> <span class="identifier">c</span><span class="special">(</span><span class="string">"prog"</span><span class="special">,</span> <span class="identifier">std_in</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="special">></span> <span class="identifier">fut</span><span class="special">,</span> <span class="identifier">ios</span><span class="special">)</span><span class="special">;</span>
<span class="identifier">fut</span><span class="special">.</span><span class="identifier">get</span><span class="special">(</span><span class="special">)</span><span class="special">;</span>
</pre>
<p><code class="computeroutput">boost::asio::buffer</code> is also available in the <code class="computeroutput">boost::process</code> namespace.</p>
</td></tr>
</table></div>
<p>
</p>
<div class="warning"><table border="0" summary="Warning">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../../doc/src/images/warning.png"></td>
<th align="left">Warning</th>
</tr>
<tr><td align="left" valign="top"><p>This feature requires <code class="computeroutput">boost/process/async.hpp</code> to be included and a reference to <code class="computeroutput">boost::asio::io_context</code> to be passed to the launching function.</p></td></tr>
</table></div>
<p>
</p>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="namespaceboost_1_1process_1stdin_close"></a>Close</h3></div></div></div>
<p>The input stream can be closed, so it cannot be read from. This will lead to an error when attempted.</p>
<p>This can be achieved by the following syntax.</p>
<pre class="programlisting"><span class="identifier">std_in</span> <span class="special"><</span> <span class="identifier">close</span><span class="special">;</span>
<span class="identifier">std_in</span> <span class="special">=</span> <span class="identifier">close</span><span class="special">;</span>
<span class="identifier">std_in</span><span class="special">.</span><span class="identifier">close</span><span class="special">(</span><span class="special">)</span><span class="special">;</span>
</pre>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="namespaceboost_1_1process_1stdin_null"></a>Null</h3></div></div></div>
<p>The input stream can be redirected to read from the null-device, which means that only <code class="computeroutput">EOF</code> is read.</p>
<p>The syntax to achieve that has the following variants:</p>
<pre class="programlisting"><span class="identifier">std_in</span> <span class="special"><</span> <span class="identifier">null</span><span class="special">;</span>
<span class="identifier">std_in</span> <span class="special">=</span> <span class="identifier">null</span><span class="special">;</span>
<span class="identifier">std_in</span><span class="special">.</span><span class="identifier">null</span><span class="special">(</span><span class="special">)</span><span class="special">;</span>
</pre>
<p> </p>
</div>
</div>
</div>
<div class="footnotes">
<br><hr style="width:100; text-align:left;margin-left: 0">
<div id="ftn.id-1.3.31.9.15.18.4.3.4.4.1.1.1.2" class="footnote"><p><a href="#id-1.3.31.9.15.18.4.3.4.4.1.1.1.2" class="para"><sup class="para">[28] </sup></a> Constructed with <code class="computeroutput">boost::asio::buffer</code></p></div>
<div id="ftn.id-1.3.31.9.15.18.4.3.4.4.1.2.1.2" class="footnote"><p><a href="#id-1.3.31.9.15.18.4.3.4.4.1.2.1.2" class="para"><sup class="para">[29] </sup></a> Constructed with <code class="computeroutput">boost::asio::buffer</code></p></div>
</div>
</div>
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<td align="right"><div class="copyright-footer">Copyright © 2006-2012 Julio M. Merino Vidal, Ilya Sokolov,
Felipe Tanus, Jeff Flinn, Boris Schaeling<br>Copyright © 2016 Klemens D. Morgenstern<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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