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  26 <div class="refentry">
  27 <a name="boost.process.std_in"></a><div class="titlepage"></div>
  28 <div class="refnamediv">
  29 <h2><span class="refentrytitle">Global std_in</span></h2>
  30 <p>boost::process::std_in</p>
  31 </div>
  32 <h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
  33 <div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../../process/reference.html#header.boost.process.io_hpp" title="Header &lt;boost/process/io.hpp&gt;">boost/process/io.hpp</a>&gt;
  34
  35 </span><span class="emphasis"><em><span class="identifier">unspecified</span></em></span> std_in<span class="special">;</span></pre></div>
  36 <div class="refsect1">
  37 <a name="id-1.3.31.9.16.18.4"></a><h2>Description</h2>
  38 <p>This property allows to set the input stream for the child process.</p>
  39 <div class="sect1">
  40 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  41 <a name="namespaceboost_1_1process_1stdin_details"></a>Details</h2></div></div></div>
  42 <div class="toc"><dl class="toc">
  43 <dt><span class="sect2"><a href="std_in.html#namespaceboost_1_1process_1stdin_file">File Input</a></span></dt>
  44 <dt><span class="sect2"><a href="std_in.html#namespaceboost_1_1process_1stdin_pipe">Pipe Input</a></span></dt>
  45 <dt><span class="sect2"><a href="std_in.html#namespaceboost_1_1process_1stdin_async_pipe">Asynchronous Pipe Input</a></span></dt>
  46 <dt><span class="sect2"><a href="std_in.html#namespaceboost_1_1process_1stdin_close">Close</a></span></dt>
  47 <dt><span class="sect2"><a href="std_in.html#namespaceboost_1_1process_1stdin_null">Null</a></span></dt>
  48 </dl></div>
  49 <div class="sect2">
  50 <div class="titlepage"><div><div><h3 class="title">
  51 <a name="namespaceboost_1_1process_1stdin_file"></a>File Input</h3></div></div></div>
  52 <p>The file I/O simple redirects the stream to a file, for which the possible types are</p>
  53 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  54 <li class="listitem"><p><code class="computeroutput">boost::filesystem::path</code></p></li>
  55 <li class="listitem"><p><code class="computeroutput">std::basic_string&lt;char_type&gt;</code></p></li>
  56 <li class="listitem"><p><code class="computeroutput">const char_type*</code></p></li>
  57 <li class="listitem"><p><code class="computeroutput">FILE*</code></p></li>
  58 </ul></div>
  59 <p>
  60 </p>
  61 <p>with <code class="computeroutput">char_type</code> being either <code class="computeroutput">char</code> or <code class="computeroutput">wchar_t</code>.</p>
  62 <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>
  63 <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">&lt;</span> <span class="identifier">stdin</span><span class="special">)</span><span class="special">;</span>
  64 </pre>
  65 <div class="warning"><table border="0" summary="Warning">
  66 <tr>
  67 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../../doc/src/images/warning.png"></td>
  68 <th align="left">Warning</th>
  69 </tr>
  70 <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>
  71 </table></div>
  72 <p>
  73 A syntax like <code class="computeroutput">system("ls", std_out &gt; std::cerr)</code> is not possible, due to the C++ implementation not providing access to the handle.</p>
  74 <p>The valid expressions for this property are</p>
  75 <pre class="programlisting"><span class="identifier">std_in</span> <span class="special">&lt;</span> <span class="identifier">file</span><span class="special">;</span>
  76 <span class="identifier">std_in</span> <span class="special">=</span> <span class="identifier">file</span><span class="special">;</span>
  77 </pre>
  78 </div>
  79 <div class="sect2">
  80 <div class="titlepage"><div><div><h3 class="title">
  81 <a name="namespaceboost_1_1process_1stdin_pipe"></a>Pipe Input</h3></div></div></div>
  82 <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>
  83 <div class="note"><table border="0" summary="Note">
  84 <tr>
  85 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../doc/src/images/note.png"></td>
  86 <th align="left">Note</th>
  87 </tr>
  88 <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>
  89 </table></div>
  90 <p>
  91 Valid expressions with pipes are these:</p>
  92 <pre class="programlisting"><span class="identifier">std_in</span> <span class="special">&lt;</span> <span class="identifier">pipe</span><span class="special">;</span>
  93 <span class="identifier">std_in</span> <span class="special">=</span> <span class="identifier">pipe</span><span class="special">;</span>
  94 </pre>
  95 <p>Where the valid types for <code class="computeroutput">pipe</code> are the following:</p>
  96 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  97 <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>
  98 <li class="listitem"><p><code class="computeroutput"><a class="link" href="async_pipe.html" title="Class async_pipe">async_pipe</a></code></p></li>
  99 <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>
 100 <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>
 101 </ul></div>
 102 <p>
 103 </p>
 104 <p>Note that the pipe may also be used between several processes, like this:</p>
 105 <pre class="programlisting"><span class="identifier">pipe</span> <span class="identifier">p</span><span class="special">;</span>
 106 <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">&gt;</span><span class="identifier">p</span><span class="special">)</span><span class="special">;</span>
 107 <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">&lt;</span><span class="identifier">p</span><span class="special">)</span><span class="special">;</span>
 108 </pre>
 109 </div>
 110 <div class="sect2">
 111 <div class="titlepage"><div><div><h3 class="title">
 112 <a name="namespaceboost_1_1process_1stdin_async_pipe"></a>Asynchronous Pipe Input</h3></div></div></div>
 113 <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>
 114 <p>Valid types for pipe I/O are the following:</p>
 115 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 116 <li class="listitem"><p><code class="computeroutput">boost::asio::const_buffer</code> <a href="#ftn.id-1.3.31.9.16.18.4.3.4.4.1.1.1.2" class="footnote" name="id-1.3.31.9.16.18.4.3.4.4.1.1.1.2"><sup class="footnote">[30]</sup></a> </p></li>
 117 <li class="listitem"><p><code class="computeroutput">boost::asio::mutable_buffer</code> <a href="#ftn.id-1.3.31.9.16.18.4.3.4.4.1.2.1.2" class="footnote" name="id-1.3.31.9.16.18.4.3.4.4.1.2.1.2"><sup class="footnote">[31]</sup></a> </p></li>
 118 <li class="listitem"><p><code class="computeroutput">boost::asio::streambuf</code></p></li>
 119 </ul></div>
 120 <p>
 121 </p>
 122 <p>Valid expressions with pipes are these:</p>
 123 <pre class="programlisting"><span class="identifier">std_in</span> <span class="special">&lt;</span> <span class="identifier">buffer</span><span class="special">;</span>
 124 <span class="identifier">std_in</span> <span class="special">=</span> <span class="identifier">buffer</span><span class="special">;</span>
 125 <span class="identifier">std_out</span> <span class="special">&gt;</span> <span class="identifier">buffer</span><span class="special">;</span>
 126 <span class="identifier">std_out</span> <span class="special">=</span> <span class="identifier">buffer</span><span class="special">;</span>
 127 <span class="identifier">std_err</span> <span class="special">&gt;</span> <span class="identifier">buffer</span><span class="special">;</span>
 128 <span class="identifier">std_err</span> <span class="special">=</span> <span class="identifier">buffer</span><span class="special">;</span>
 129 <span class="special">(</span><span class="identifier">std_out</span> <span class="special">&amp;</span> <span class="identifier">std_err</span><span class="special">)</span> <span class="special">&gt;</span> <span class="identifier">buffer</span><span class="special">;</span>
 130 <span class="special">(</span><span class="identifier">std_out</span> <span class="special">&amp;</span> <span class="identifier">std_err</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">buffer</span><span class="special">;</span>
 131 </pre>
 132 <div class="note"><table border="0" summary="Note">
 133 <tr>
 134 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../doc/src/images/note.png"></td>
 135 <th align="left">Note</th>
 136 </tr>
 137 <tr><td align="left" valign="top">
 138 <p>It is also possible to get a future for std_in, by chaining another <code class="computeroutput">std::future&lt;void&gt;</code> onto it, so you can wait for the input to be completed. It looks like this: </p>
 139 <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">future</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="identifier">fut</span><span class="special">;</span>
 140 <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>
 141 <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">data</span><span class="special">;</span>
 142 <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">&lt;</span> <span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">)</span> <span class="special">&gt;</span>  <span class="identifier">fut</span><span class="special">,</span> <span class="identifier">ios</span><span class="special">)</span><span class="special">;</span>
 143 <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>
 144 </pre>
 145 </td></tr>
 146 </table></div>
 147 <p>
 148 </p>
 149 <div class="note"><table border="0" summary="Note">
 150 <tr>
 151 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../doc/src/images/note.png"></td>
 152 <th align="left">Note</th>
 153 </tr>
 154 <tr><td align="left" valign="top"><p><code class="computeroutput">boost::asio::buffer</code> is also available in the <code class="computeroutput">boost::process</code> namespace.</p></td></tr>
 155 </table></div>
 156 <p>
 157 </p>
 158 <div class="warning"><table border="0" summary="Warning">
 159 <tr>
 160 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../../doc/src/images/warning.png"></td>
 161 <th align="left">Warning</th>
 162 </tr>
 163 <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>
 164 </table></div>
 165 <p>
 166 </p>
 167 </div>
 168 <div class="sect2">
 169 <div class="titlepage"><div><div><h3 class="title">
 170 <a name="namespaceboost_1_1process_1stdin_close"></a>Close</h3></div></div></div>
 171 <p>The input stream can be closed, so it cannot be read from. This will lead to an error when attempted.</p>
 172 <p>This can be achieved by the following syntax.</p>
 173 <pre class="programlisting"><span class="identifier">std_in</span> <span class="special">&lt;</span> <span class="identifier">close</span><span class="special">;</span>
 174 <span class="identifier">std_in</span> <span class="special">=</span> <span class="identifier">close</span><span class="special">;</span>
 175 <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>
 176 </pre>
 177 </div>
 178 <div class="sect2">
 179 <div class="titlepage"><div><div><h3 class="title">
 180 <a name="namespaceboost_1_1process_1stdin_null"></a>Null</h3></div></div></div>
 181 <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>
 182 <p>The syntax to achieve that has the following variants:</p>
 183 <pre class="programlisting"><span class="identifier">std_in</span> <span class="special">&lt;</span> <span class="identifier">null</span><span class="special">;</span>
 184 <span class="identifier">std_in</span> <span class="special">=</span> <span class="identifier">null</span><span class="special">;</span>
 185 <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>
 186 </pre>
 187 <p> </p>
 188 </div>
 189 </div>
 190 </div>
 191 <div class="footnotes">
 192 <br><hr style="width:100; text-align:left;margin-left: 0">
 193 <div id="ftn.id-1.3.31.9.16.18.4.3.4.4.1.1.1.2" class="footnote"><p><a href="#id-1.3.31.9.16.18.4.3.4.4.1.1.1.2" class="para"><sup class="para">[30] </sup></a> Constructed with <code class="computeroutput">boost::asio::buffer</code></p></div>
 194 <div id="ftn.id-1.3.31.9.16.18.4.3.4.4.1.2.1.2" class="footnote"><p><a href="#id-1.3.31.9.16.18.4.3.4.4.1.2.1.2" class="para"><sup class="para">[31] </sup></a> Constructed with <code class="computeroutput">boost::asio::buffer</code></p></div>
 195 </div>
 196 </div>
 197 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 198 <td align="left"></td>
 199 <td align="right"><div class="copyright-footer">Copyright &#169; 2006-2012 Julio M. Merino Vidal, Ilya Sokolov,
 200       Felipe Tanus, Jeff Flinn, Boris Schaeling<br>Copyright &#169; 2016 Klemens D. Morgenstern<p>
 201         Distributed under the Boost Software License, Version 1.0. (See accompanying
 202         file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 203       </p>
 204 </div></td>
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