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  25 </div>
  26 <div class="section">
  27 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  28 <a name="boost_process.tutorial"></a><a class="link" href="tutorial.html" title="Tutorial">Tutorial</a>
  29 </h2></div></div></div>
  30 <div class="toc"><dl class="toc">
  31 <dt><span class="section"><a href="tutorial.html#boost_process.tutorial.starting_a_process">Starting a
  32       process</a></span></dt>
  33 <dt><span class="section"><a href="tutorial.html#boost_process.tutorial.launch_mode">Launch functions</a></span></dt>
  34 <dt><span class="section"><a href="tutorial.html#boost_process.tutorial.error_handling">Error</a></span></dt>
  35 <dt><span class="section"><a href="tutorial.html#boost_process.tutorial.io">Synchronous I/O</a></span></dt>
  36 <dt><span class="section"><a href="tutorial.html#boost_process.tutorial.async_io">Asynchronous I/O</a></span></dt>
  37 <dt><span class="section"><a href="tutorial.html#boost_process.tutorial.group">Groups</a></span></dt>
  38 <dt><span class="section"><a href="tutorial.html#boost_process.tutorial.env">Environment</a></span></dt>
  39 </dl></div>
  40 <p>
  41       In this section we will go step by step through the different features of boost.process.
  42       For a full description see the <a class="link" href="../process/reference.html" title="Reference">reference</a>
  43       and the <a class="link" href="concepts.html" title="Concepts">concepts</a> sections.
  44     </p>
  45 <div class="section">
  46 <div class="titlepage"><div><div><h3 class="title">
  47 <a name="boost_process.tutorial.starting_a_process"></a><a class="link" href="tutorial.html#boost_process.tutorial.starting_a_process" title="Starting a process">Starting a
  48       process</a>
  49 </h3></div></div></div>
  50 <p>
  51         We want to start a process, so let's start with a simple process. We will
  52         invoke the gcc compiler to compile a simple program.
  53       </p>
  54 <p>
  55         With the standard library this looks like this.
  56       </p>
  57 <p>
  58 </p>
  59 <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">result</span> <span class="special">=</span> <a href="http://en.cppreference.com/w/cpp/utility/program/system" target="_top">std::system</a><span class="special">(</span><span class="string">"g++ main.cpp"</span><span class="special">);</span>
  60 </pre>
  61 <p>
  62       </p>
  63 <p>
  64         Which we can write exactly like this in boost.process.
  65       </p>
  66 <p>
  67 </p>
  68 <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">bp</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">process</span><span class="special">;</span> <span class="comment">//we will assume this for all further examples</span>
  69 <span class="keyword">int</span> <span class="identifier">result</span> <span class="special">=</span> <code class="computeroutput"><a class="link" href="../boost/process/system.html" title="Function template system">bp::system</a></code><span class="special">(</span><span class="string">"g++ main.cpp"</span><span class="special">);</span>
  70 </pre>
  71 <p>
  72       </p>
  73 <p>
  74         If a single string (or the explicit form <code class="computeroutput">bp::cmd</code>),
  75         it will be interpreted as a command line. That will cause the execution function
  76         to search the <code class="computeroutput"><span class="identifier">PATH</span></code> variable
  77         to find the executable. The alternative is the <code class="computeroutput"><span class="identifier">exe</span><span class="special">-</span><span class="identifier">args</span></code> style,
  78         where the first string will be interpreted as a filename (including the path),
  79         and the rest as arguments passed to said function.
  80       </p>
  81 <div class="note"><table border="0" summary="Note">
  82 <tr>
  83 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td>
  84 <th align="left">Note</th>
  85 </tr>
  86 <tr><td align="left" valign="top"><p>
  87           For more details on the <code class="computeroutput"><span class="identifier">cmd</span></code>/<code class="computeroutput"><span class="identifier">exe</span><span class="special">-</span><span class="identifier">args</span></code> style look <a class="link" href="design.html#boost_process.design.arg_cmd_style" title="Arguments/Command Style">here</a>
  88         </p></td></tr>
  89 </table></div>
  90 <p>
  91         So as a first step, we'll use the <code class="computeroutput"><span class="identifier">exe</span><span class="special">-</span><span class="identifier">args</span></code> style.
  92       </p>
  93 <p>
  94 </p>
  95 <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">result</span> <span class="special">=</span> <code class="computeroutput"><a class="link" href="../boost/process/system.html" title="Function template system">bp::system</a></code><span class="special">(</span><span class="string">"/usr/bin/g++"</span><span class="special">,</span> <span class="string">"main.cpp"</span><span class="special">);</span>
  96 </pre>
  97 <p>
  98       </p>
  99 <p>
 100         With that syntax we still have "g++" hard-coded, so let's assume
 101         we get the string from an external source as <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">filesystem</span><span class="special">::</span><span class="identifier">path</span></code>,
 102         we can do this too.
 103       </p>
 104 <p>
 105 </p>
 106 <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">filesystem</span><span class="special">::</span><span class="identifier">path</span> <span class="identifier">p</span> <span class="special">=</span> <span class="string">"/usr/bin/g++"</span><span class="special">;</span> <span class="comment">//or get it from somewhere else.</span>
 107 <span class="keyword">int</span> <span class="identifier">result</span> <span class="special">=</span> <code class="computeroutput"><a class="link" href="../boost/process/system.html" title="Function template system">bp::system</a></code><span class="special">(</span><span class="identifier">p</span><span class="special">,</span> <span class="string">"main.cpp"</span><span class="special">);</span>
 108 </pre>
 109 <p>
 110       </p>
 111 <p>
 112         Now we might want to find the <code class="computeroutput"><span class="identifier">g</span><span class="special">++</span></code> executable in the <code class="computeroutput"><span class="identifier">PATH</span></code>-variable,
 113         as the <code class="computeroutput"><span class="identifier">cmd</span></code> syntax would do.
 114         <code class="computeroutput"><span class="identifier">Boost</span><span class="special">.</span><span class="identifier">process</span></code> provides a function to this end:
 115         <code class="computeroutput"><a class="link" href="../boost/process/search_path.html" title="Function search_path">bp::search_path</a></code>.
 116       </p>
 117 <p>
 118 </p>
 119 <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">filesystem</span><span class="special">::</span><span class="identifier">path</span> <span class="identifier">p</span> <span class="special">=</span> <code class="computeroutput"><a class="link" href="../boost/process/search_path.html" title="Function search_path">bp::search_path</a></code><span class="special">(</span><span class="string">"g++"</span><span class="special">);</span> <span class="comment">//or get it from somewhere else.</span>
 120 <span class="keyword">int</span> <span class="identifier">result</span> <span class="special">=</span> <code class="computeroutput"><a class="link" href="../boost/process/system.html" title="Function template system">bp::system</a></code><span class="special">(</span><span class="identifier">p</span><span class="special">,</span> <span class="string">"main.cpp"</span><span class="special">);</span>
 121 </pre>
 122 <p>
 123       </p>
 124 <div class="note"><table border="0" summary="Note">
 125 <tr>
 126 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td>
 127 <th align="left">Note</th>
 128 </tr>
 129 <tr><td align="left" valign="top"><p>
 130           <code class="computeroutput"><a class="link" href="../boost/process/search_path.html" title="Function search_path">search_path</a></code>
 131           will search for any executable with that name. This also includes to add
 132           a file suffix on windows, such as <code class="computeroutput"><span class="special">.</span><span class="identifier">exe</span></code> or <code class="computeroutput"><span class="special">.</span><span class="identifier">bat</span></code>.
 133         </p></td></tr>
 134 </table></div>
 135 </div>
 136 <div class="section">
 137 <div class="titlepage"><div><div><h3 class="title">
 138 <a name="boost_process.tutorial.launch_mode"></a><a class="link" href="tutorial.html#boost_process.tutorial.launch_mode" title="Launch functions">Launch functions</a>
 139 </h3></div></div></div>
 140 <p>
 141         Given that our example used the <code class="computeroutput"><a class="link" href="../boost/process/system.html" title="Function template system">system</a></code>
 142         function, our program will wait until the child process is completed. This
 143         may be unwanted, especially since compiling can take a while.
 144       </p>
 145 <p>
 146         In order to avoid that, boost.process provides several ways to launch a process.
 147         Besides the already mentioned <code class="computeroutput"><a class="link" href="../boost/process/system.html" title="Function template system">system</a></code>
 148         function and its asynchronous version <code class="computeroutput"><a class="link" href="../boost/process/async_system.html" title="Function template async_system">async_system</a></code>,
 149         we can also use the <code class="computeroutput"><a class="link" href="../boost/process/spawn.html" title="Function template spawn">spawn</a></code>
 150         function or the <code class="computeroutput"><a class="link" href="../boost/process/child.html" title="Class child">child</a></code>
 151         class.
 152       </p>
 153 <p>
 154         The <code class="computeroutput"><a class="link" href="../boost/process/spawn.html" title="Function template spawn">spawn</a></code> function
 155         launches a process and immediately detaches it, so no handle will be returned
 156         and the process will be ignored. This is not what we need for compiling,
 157         but maybe we want to entertain the user, while compiling:
 158       </p>
 159 <p>
 160 </p>
 161 <pre class="programlisting"><code class="computeroutput"><a class="link" href="../boost/process/spawn.html" title="Function template spawn">bp::spawn</a></code><span class="special">(</span><code class="computeroutput"><a class="link" href="../boost/process/search_path.html" title="Function search_path">bp::search_path</a></code><span class="special">(</span><span class="string">"chrome"</span><span class="special">),</span> <a href="../www.boost.org" target="_top">"www.boost.org"</a><span class="special">);</span>
 162 </pre>
 163 <p>
 164       </p>
 165 <p>
 166         Now for the more sensible approach for compiling: a non-blocking execution.
 167         To implement that, we directly call the constructor of <code class="computeroutput"><a class="link" href="../boost/process/child.html" title="Class child">child</a></code>.
 168       </p>
 169 <p>
 170 </p>
 171 <pre class="programlisting"><code class="computeroutput"><a class="link" href="../boost/process/child.html" title="Class child">bp::child</a></code> <span class="identifier">c</span><span class="special">(</span><code class="computeroutput"><a class="link" href="../boost/process/search_path.html" title="Function search_path">bp::search_path</a></code><span class="special">(</span><span class="string">"g++"</span><span class="special">),</span> <span class="string">"main.cpp"</span><span class="special">);</span>
 172
 173 <span class="keyword">while</span> <span class="special">(</span><span class="identifier">c</span><span class="special">.</span><code class="computeroutput"><a class="link" href="../boost/process/child.html#idm45170605253472-bb">running</a></code><span class="special">())</span>
 174     <span class="identifier">do_some_stuff</span><span class="special">();</span>
 175
 176 <span class="identifier">c</span><span class="special">.</span><code class="computeroutput"><a class="link" href="../boost/process/child.html#idm45170605250176-bb">wait</a></code><span class="special">();</span> <span class="comment">//wait for the process to exit   </span>
 177 <span class="keyword">int</span> <span class="identifier">result</span> <span class="special">=</span> <span class="identifier">c</span><span class="special">.</span><code class="computeroutput"><a class="link" href="../boost/process/child.html#idm45170605257888-bb">exit_code</a></code><span class="special">();</span>
 178 </pre>
 179 <p>
 180       </p>
 181 <p>
 182         So we launch the process, by calling the child constructor. Then we check
 183         and do other things while the process is running and afterwards get the exit
 184         code. The call to <code class="computeroutput"><a class="link" href="../boost/process/child.html#idm45170605250176-bb">wait</a></code>
 185         is necessary, to obtain it and tell the operating system, that no one is
 186         waiting for the process anymore.
 187       </p>
 188 <div class="note"><table border="0" summary="Note">
 189 <tr>
 190 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td>
 191 <th align="left">Note</th>
 192 </tr>
 193 <tr><td align="left" valign="top"><p>
 194           You can also wait for a time span or a until a time point with <code class="computeroutput"><a class="link" href="../boost/process/child.html#idm45170605246880-bb">wait_for</a></code> and <code class="computeroutput"><a class="link" href="../boost/process/child.html#idm45170605240496-bb">wait_until</a></code>
 195         </p></td></tr>
 196 </table></div>
 197 <div class="warning"><table border="0" summary="Warning">
 198 <tr>
 199 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../doc/src/images/warning.png"></td>
 200 <th align="left">Warning</th>
 201 </tr>
 202 <tr><td align="left" valign="top"><p>
 203           If you don't call wait on a child object, it will be terminated on destruction.
 204           This can be avoided by calling <code class="computeroutput"><a class="link" href="../boost/process/child.html#idm45170605262864-bb">detach</a></code>
 205           beforehand
 206         </p></td></tr>
 207 </table></div>
 208 </div>
 209 <div class="section">
 210 <div class="titlepage"><div><div><h3 class="title">
 211 <a name="boost_process.tutorial.error_handling"></a><a class="link" href="tutorial.html#boost_process.tutorial.error_handling" title="Error">Error</a>
 212 </h3></div></div></div>
 213 <p>
 214         Until now, we have assumed that everything works out, but it is not impossible,
 215         that "g++" is not present. That will cause the launch of the process
 216         to fail. The default behaviour of all functions is to throw a <a href="http://en.cppreference.com/w/cpp/error/system_error" target="_top">std::system_error</a>
 217         on failure. As with many other functions in this library, passing an <a href="http://en.cppreference.com/w/cpp/error/error_code" target="_top">std::error_code</a>
 218         will change the behaviour, so that instead of throwing an exception, the
 219         error will be assigned to the error code.
 220       </p>
 221 <p>
 222 </p>
 223 <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">error_code</span> <span class="identifier">ec</span><span class="special">;</span>
 224 <code class="computeroutput"><a class="link" href="../boost/process/system.html" title="Function template system">bp::system</a></code><span class="special">(</span><span class="string">"g++ main.cpp"</span><span class="special">,</span> <span class="identifier">ec</span><span class="special">);</span>
 225 </pre>
 226 <p>
 227       </p>
 228 </div>
 229 <div class="section">
 230 <div class="titlepage"><div><div><h3 class="title">
 231 <a name="boost_process.tutorial.io"></a><a class="link" href="tutorial.html#boost_process.tutorial.io" title="Synchronous I/O">Synchronous I/O</a>
 232 </h3></div></div></div>
 233 <p>
 234         In the examples given above, we have only started a program, but did not
 235         consider the output. The default depends on the system, but usually this
 236         will just write it to the same output as the launching process. If this shall
 237         be guaranteed, the streams can be explicitly forwarded like this.
 238       </p>
 239 <p>
 240 </p>
 241 <pre class="programlisting"><code class="computeroutput"><a class="link" href="../boost/process/system.html" title="Function template system">bp::system</a></code><span class="special">(</span><span class="string">"g++ main.cpp"</span><span class="special">,</span> <code class="computeroutput"><a class="link" href="../boost/process/std_out.html" title="Global std_out">bp::std_out</a></code> <span class="special">&gt;</span> <span class="identifier">stdout</span><span class="special">,</span> <code class="computeroutput"><a class="link" href="../boost/process/std_err.html" title="Global std_err">bp::std_err</a></code> <span class="special">&gt;</span> <span class="identifier">stderr</span><span class="special">,</span> <code class="computeroutput"><a class="link" href="../boost/process/std_in.html" title="Global std_in">bp::std_in</a></code> <span class="special">&lt;</span> <span class="identifier">stdin</span><span class="special">);</span>
 242 </pre>
 243 <p>
 244       </p>
 245 <p>
 246         Now for the first example, we might want to just ignore the output, which
 247         can be done by redirecting it to the null-device. This can be achieved this
 248         way:
 249       </p>
 250 <p>
 251 </p>
 252 <pre class="programlisting"><code class="computeroutput"><a class="link" href="../boost/process/system.html" title="Function template system">bp::system</a></code><span class="special">(</span><span class="string">"g++ main.cpp"</span><span class="special">,</span> <code class="computeroutput"><a class="link" href="../boost/process/std_out.html" title="Global std_out">bp::std_out</a></code> <span class="special">&gt;</span> <code class="computeroutput"><a class="link" href="../boost/process/null.html" title="Global null">bp::null</a></code><span class="special">);</span>
 253 </pre>
 254 <p>
 255       </p>
 256 <p>
 257         Alternatively we can also easily redirect the output to a file:
 258       </p>
 259 <p>
 260 </p>
 261 <pre class="programlisting"><code class="computeroutput"><a class="link" href="../boost/process/system.html" title="Function template system">bp::system</a></code><span class="special">(</span><span class="string">"g++ main.cpp"</span><span class="special">,</span> <code class="computeroutput"><a class="link" href="../boost/process/std_out.html" title="Global std_out">bp::std_out</a></code> <span class="special">&gt;</span> <span class="string">"gcc_out.log"</span><span class="special">);</span>
 262 </pre>
 263 <p>
 264       </p>
 265 <p>
 266         Now, let's take a more visual example for reading data. <a href="http://pubs.opengroup.org/onlinepubs/009696699/utilities/nm.html" target="_top">nm</a>
 267         is a tool on posix, which reads the outline, i.e. a list of all entry points,
 268         of a binary. Every entry point will be put into a single line, and we will
 269         use a pipe to read it. At the end an empty line is appended, which we use
 270         as the indication to stop reading. Boost.process provides the pipestream
 271         (<code class="computeroutput"><a class="link" href="../process/reference.html#boost.process.ipstream">ipstream</a></code>, <code class="computeroutput"><a class="link" href="../process/reference.html#boost.process.opstream">opstream</a></code>, <code class="computeroutput"><a class="link" href="../process/reference.html#boost.process.pstream">pstream</a></code>)
 272         to wrap around the <code class="computeroutput"><a class="link" href="../process/reference.html#boost.process.pipe">pipe</a></code>
 273         and provide an implementation of the <a href="http://en.cppreference.com/w/cpp/io/basic_istream" target="_top">std::istream</a>,
 274         <a href="http://en.cppreference.com/w/cpp/io/basic_ostream" target="_top">std::ostream</a>
 275         and <a href="http://en.cppreference.com/w/cpp/io/basic_iostream" target="_top">std::iostream</a>
 276         interface.
 277       </p>
 278 <p>
 279 </p>
 280 <pre class="programlisting"><a href="http://en.cppreference.com/w/cpp/container/vector" target="_top">std::vector</a><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;</span> <span class="identifier">read_outline</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">&amp;</span> <span class="identifier">file</span><span class="special">)</span>
 281 <span class="special">{</span>
 282     <code class="computeroutput"><a class="link" href="../process/reference.html#boost.process.ipstream">bp::ipstream</a></code> <span class="identifier">is</span><span class="special">;</span> <span class="comment">//reading pipe-stream</span>
 283     <code class="computeroutput"><a class="link" href="../boost/process/child.html" title="Class child">bp::child</a></code> <span class="identifier">c</span><span class="special">(</span><code class="computeroutput"><a class="link" href="../boost/process/search_path.html" title="Function search_path">bp::search_path</a></code><span class="special">(</span><span class="string">"nm"</span><span class="special">),</span> <span class="identifier">file</span><span class="special">,</span> <code class="computeroutput"><a class="link" href="../boost/process/std_out.html" title="Global std_out">bp::std_out</a></code> <span class="special">&gt;</span> <span class="identifier">is</span><span class="special">);</span>
 284
 285     <a href="http://en.cppreference.com/w/cpp/container/vector" target="_top">std::vector</a><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;</span> <span class="identifier">data</span><span class="special">;</span>
 286     <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">line</span><span class="special">;</span>
 287
 288     <span class="keyword">while</span> <span class="special">(</span><span class="identifier">c</span><span class="special">.</span><code class="computeroutput"><a class="link" href="../boost/process/child.html#idm45170605253472-bb">running</a></code><span class="special">()</span> <span class="special">&amp;&amp;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">getline</span><span class="special">(</span><span class="identifier">is</span><span class="special">,</span> <span class="identifier">line</span><span class="special">)</span> <span class="special">&amp;&amp;</span> <span class="special">!</span><span class="identifier">line</span><span class="special">.</span><span class="identifier">empty</span><span class="special">())</span>
 289         <span class="identifier">data</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">line</span><span class="special">);</span>
 290
 291     <span class="identifier">c</span><span class="special">.</span><code class="computeroutput"><a class="link" href="../boost/process/child.html#idm45170605250176-bb">wait</a></code><span class="special">();</span>
 292
 293     <span class="keyword">return</span> <span class="identifier">data</span><span class="special">;</span>
 294 <span class="special">}</span>
 295 </pre>
 296 <p>
 297       </p>
 298 <p>
 299         What this does is redirect the <code class="computeroutput"><span class="identifier">stdout</span></code>
 300         of the process into a pipe and we read this synchronously.
 301       </p>
 302 <div class="note"><table border="0" summary="Note">
 303 <tr>
 304 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td>
 305 <th align="left">Note</th>
 306 </tr>
 307 <tr><td align="left" valign="top"><p>
 308           You can do the same thing with <code class="computeroutput"><a class="link" href="../boost/process/std_err.html" title="Global std_err">std_err</a></code>
 309         </p></td></tr>
 310 </table></div>
 311 <p>
 312         Now we get the name from <code class="computeroutput"><span class="identifier">nm</span></code>
 313         and we might want to demangle it, so we use input and output. <code class="computeroutput"><span class="identifier">nm</span></code> has a demangle option, but for the sake
 314         of the example, we'll use <a href="https://sourceware.org/binutils/docs/binutils/c_002b_002bfilt.html" target="_top">c++filt</a>
 315         for this.
 316       </p>
 317 <p>
 318 </p>
 319 <pre class="programlisting"><code class="computeroutput"><a class="link" href="../process/reference.html#boost.process.opstream">bp::opstream</a></code> <span class="identifier">in</span><span class="special">;</span>
 320 <code class="computeroutput"><a class="link" href="../process/reference.html#boost.process.ipstream">bp::ipstream</a></code> <span class="identifier">out</span><span class="special">;</span>
 321
 322 <code class="computeroutput"><a class="link" href="../boost/process/child.html" title="Class child">bp::child</a></code> <span class="identifier">c</span><span class="special">(</span><span class="string">"c++filt"</span><span class="special">,</span> <span class="identifier">std_out</span> <span class="special">&gt;</span> <span class="identifier">out</span><span class="special">,</span> <span class="identifier">std_in</span> <span class="special">&lt;</span> <span class="identifier">in</span><span class="special">);</span>
 323
 324 <span class="identifier">in</span> <span class="special">&lt;&lt;</span> <span class="string">"_ZN5boost7process8tutorialE"</span> <span class="special">&lt;&lt;</span> <span class="identifier">endl</span><span class="special">;</span>
 325 <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">value</span><span class="special">;</span>
 326 <span class="identifier">out</span> <span class="special">&gt;&gt;</span> <span class="identifier">value</span><span class="special">;</span>
 327
 328 <span class="identifier">c</span><span class="special">.</span><code class="computeroutput"><a class="link" href="../boost/process/child.html#idm45170605226736-bb">terminate</a></code><span class="special">();</span>
 329 </pre>
 330 <p>
 331       </p>
 332 <p>
 333         Now you might want to forward output from one process to another processes
 334         input.
 335       </p>
 336 <p>
 337 </p>
 338 <pre class="programlisting"><a href="http://en.cppreference.com/w/cpp/container/vector" target="_top">std::vector</a><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;</span> <span class="identifier">read_demangled_outline</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">&amp;</span> <span class="identifier">file</span><span class="special">)</span>
 339 <span class="special">{</span>
 340     <code class="computeroutput"><a class="link" href="../process/reference.html#boost.process.pipe">bp::pipe</a></code> <span class="identifier">p</span><span class="special">;</span>
 341     <code class="computeroutput"><a class="link" href="../process/reference.html#boost.process.ipstream">bp::ipstream</a></code> <span class="identifier">is</span><span class="special">;</span>
 342
 343     <a href="http://en.cppreference.com/w/cpp/container/vector" target="_top">std::vector</a><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;</span> <span class="identifier">outline</span><span class="special">;</span>
 344
 345     <span class="comment">//we just use the same pipe, so the </span>
 346     <code class="computeroutput"><a class="link" href="../boost/process/child.html" title="Class child">bp::child</a></code> <span class="identifier">nm</span><span class="special">(</span><code class="computeroutput"><a class="link" href="../boost/process/search_path.html" title="Function search_path">bp::search_path</a></code><span class="special">(</span><span class="string">"nm"</span><span class="special">),</span> <span class="identifier">file</span><span class="special">,</span>  <code class="computeroutput"><a class="link" href="../boost/process/std_out.html" title="Global std_out">bp::std_out</a></code> <span class="special">&gt;</span> <span class="identifier">p</span><span class="special">);</span>
 347     <code class="computeroutput"><a class="link" href="../boost/process/child.html" title="Class child">bp::child</a></code> <span class="identifier">filt</span><span class="special">(</span><code class="computeroutput"><a class="link" href="../boost/process/search_path.html" title="Function search_path">bp::search_path</a></code><span class="special">(</span><span class="string">"c++filt"</span><span class="special">),</span> <code class="computeroutput"><a class="link" href="../boost/process/std_in.html" title="Global std_in">bp::std_in</a></code> <span class="special">&lt;</span> <span class="identifier">p</span><span class="special">,</span> <code class="computeroutput"><a class="link" href="../boost/process/std_out.html" title="Global std_out">bp::std_out</a></code> <span class="special">&gt;</span> <span class="identifier">is</span><span class="special">);</span>
 348
 349     <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">line</span><span class="special">;</span>
 350     <span class="keyword">while</span> <span class="special">(</span><span class="identifier">filt</span><span class="special">.</span><span class="identifier">running</span><span class="special">()</span> <span class="special">&amp;&amp;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">getline</span><span class="special">(</span><span class="identifier">is</span><span class="special">,</span> <span class="identifier">line</span><span class="special">))</span> <span class="comment">//when nm finished the pipe closes and c++filt exits</span>
 351         <span class="identifier">outline</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">line</span><span class="special">);</span>
 352
 353     <span class="identifier">nm</span><span class="special">.</span><code class="computeroutput"><a class="link" href="../boost/process/child.html#idm45170605250176-bb">wait</a></code><span class="special">();</span>
 354     <span class="identifier">filt</span><span class="special">.</span><span class="identifier">wait</span><span class="special">();</span>
 355 <span class="special">}</span>
 356 </pre>
 357 <p>
 358       </p>
 359 <p>
 360         This forwards the data from <code class="computeroutput"><span class="identifier">nm</span></code>
 361         to <code class="computeroutput"><span class="identifier">c</span><span class="special">++</span><span class="identifier">filt</span></code> without your process needing to do
 362         anything.
 363       </p>
 364 </div>
 365 <div class="section">
 366 <div class="titlepage"><div><div><h3 class="title">
 367 <a name="boost_process.tutorial.async_io"></a><a class="link" href="tutorial.html#boost_process.tutorial.async_io" title="Asynchronous I/O">Asynchronous I/O</a>
 368 </h3></div></div></div>
 369 <p>
 370         Boost.process allows the usage of boost.asio to implement asynchronous I/O.
 371         If you are familiar with <a href="http://www.boost.org/doc/libs/release/libs/asio/" target="_top">boost.asio</a>
 372         (which we highly recommend), you can use <code class="computeroutput"><a class="link" href="../boost/process/async_pipe.html" title="Class async_pipe">async_pipe</a></code>
 373         which is implemented as an I/O-Object and can be used like <code class="computeroutput"><a class="link" href="../process/reference.html#boost.process.pipe">pipe</a></code>
 374         as shown above.
 375       </p>
 376 <p>
 377         Now we get back to our compiling example. <code class="computeroutput"><span class="identifier">nm</span></code>
 378         we might analyze it line by line, but the compiler output will just be put
 379         into one large buffer.
 380       </p>
 381 <p>
 382         With <a href="http://www.boost.org/doc/libs/release/libs/asio/" target="_top">boost.asio</a>
 383         this is what it looks like.
 384       </p>
 385 <p>
 386 </p>
 387 <pre class="programlisting"><a href="http://www.boost.org/doc/libs/release/doc/html/boost_asio/reference/io_service.html" target="_top">boost::asio::io_service</a> <span class="identifier">ios</span><span class="special">;</span>
 388 <a href="http://en.cppreference.com/w/cpp/container/vector" target="_top">std::vector</a><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt;</span> <span class="identifier">buf</span><span class="special">(</span><span class="number">4096</span><span class="special">);</span>
 389
 390 <code class="computeroutput"><a class="link" href="../boost/process/async_pipe.html" title="Class async_pipe">bp::async_pipe</a></code> <span class="identifier">ap</span><span class="special">(</span><span class="identifier">ios</span><span class="special">);</span>
 391
 392 <code class="computeroutput"><a class="link" href="../boost/process/child.html" title="Class child">bp::child</a></code> <span class="identifier">c</span><span class="special">(</span><code class="computeroutput"><a class="link" href="../boost/process/search_path.html" title="Function search_path">bp::search_path</a></code><span class="special">(</span><span class="string">"g++"</span><span class="special">),</span> <span class="string">"main.cpp"</span><span class="special">,</span> <code class="computeroutput"><a class="link" href="../boost/process/std_out.html" title="Global std_out">bp::std_out</a></code> <span class="special">&gt;</span> <span class="identifier">ap</span><span class="special">);</span>
 393
 394 <a href="http://www.boost.org/doc/libs/release/doc/html/boost_asio/reference/async_read.html" target="_top">boost::asio::async_read</a><span class="special">(</span><span class="identifier">ap</span><span class="special">,</span> <a href="http://www.boost.org/doc/libs/release/doc/html/boost_asio/reference/buffer.html" target="_top">boost::asio::buffer</a><span class="special">(</span><span class="identifier">buf</span><span class="special">),</span>
 395                 <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">&amp;</span><span class="identifier">ec</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">size</span><span class="special">){});</span>
 396
 397 <span class="identifier">ios</span><span class="special">.</span><span class="identifier">run</span><span class="special">();</span>
 398 <span class="keyword">int</span> <span class="identifier">result</span> <span class="special">=</span> <span class="identifier">c</span><span class="special">.</span><span class="identifier">exit_code</span><span class="special">();</span>
 399 </pre>
 400 <p>
 401       </p>
 402 <p>
 403         To make it easier, boost.process provides simpler interface for that, so
 404         that the buffer can be passed directly, provided we also pass a reference
 405         to an <a href="http://www.boost.org/doc/libs/release/doc/html/boost_asio/reference/io_service.html" target="_top">boost::asio::io_service</a>.
 406       </p>
 407 <p>
 408 </p>
 409 <pre class="programlisting"><a href="http://www.boost.org/doc/libs/release/doc/html/boost_asio/reference/io_service.html" target="_top">boost::asio::io_service</a> <span class="identifier">ios</span><span class="special">;</span>
 410 <a href="http://en.cppreference.com/w/cpp/container/vector" target="_top">std::vector</a><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt;</span> <span class="identifier">buf</span><span class="special">(</span><span class="number">4096</span><span class="special">);</span>
 411
 412 <code class="computeroutput"><a class="link" href="../boost/process/child.html" title="Class child">bp::child</a></code> <span class="identifier">c</span><span class="special">(</span><code class="computeroutput"><a class="link" href="../boost/process/search_path.html" title="Function search_path">bp::search_path</a></code><span class="special">(</span><span class="string">"g++"</span><span class="special">),</span> <span class="string">"main.cpp"</span><span class="special">,</span> <code class="computeroutput"><a class="link" href="../boost/process/std_out.html" title="Global std_out">bp::std_out</a></code> <span class="special">&gt;</span> <a href="http://www.boost.org/doc/libs/release/doc/html/boost_asio/reference/buffer.html" target="_top">boost::asio::buffer</a><span class="special">(</span><span class="identifier">buf</span><span class="special">),</span> <span class="identifier">ios</span><span class="special">);</span>
 413
 414 <span class="identifier">ios</span><span class="special">.</span><span class="identifier">run</span><span class="special">();</span>
 415 <span class="keyword">int</span> <span class="identifier">result</span> <span class="special">=</span> <span class="identifier">c</span><span class="special">.</span><span class="identifier">exit_code</span><span class="special">();</span>
 416 </pre>
 417 <p>
 418       </p>
 419 <div class="note"><table border="0" summary="Note">
 420 <tr>
 421 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td>
 422 <th align="left">Note</th>
 423 </tr>
 424 <tr><td align="left" valign="top"><p>
 425           Passing an instance of <a href="http://www.boost.org/doc/libs/release/doc/html/boost_asio/reference/io_service.html" target="_top">boost::asio::io_service</a>
 426           to the launching function automatically cause it to wait asynchronously
 427           for the exit, so no call of <code class="computeroutput"><a class="link" href="../boost/process/child.html#idm45170605250176-bb">wait</a></code>
 428           is needed
 429         </p></td></tr>
 430 </table></div>
 431 <p>
 432         To make it even easier, you can use <a href="http://en.cppreference.com/w/cpp/thread/future" target="_top">std::future</a>
 433         for asynchronous operations (you will still need to pass a reference to a
 434         <a href="http://www.boost.org/doc/libs/release/doc/html/boost_asio/reference/io_service.html" target="_top">boost::asio::io_service</a>)
 435         to the launching function, unless you use <code class="computeroutput"><a class="link" href="../boost/process/system.html" title="Function template system">bp::system</a></code>
 436         or <code class="computeroutput"><a class="link" href="../boost/process/async_system.html" title="Function template async_system">bp::async_system</a></code>.
 437       </p>
 438 <p>
 439         Now we will revisit our first example and read the compiler output asynchronously:
 440       </p>
 441 <p>
 442 </p>
 443 <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><a href="http://www.boost.org/doc/libs/release/doc/html/boost_asio/reference/io_service.html" target="_top">boost::asio::io_service</a> <span class="identifier">ios</span><span class="special">;</span>
 444
 445 <span class="identifier">std</span><span class="special">::</span><span class="identifier">future</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;</span> <span class="identifier">data</span><span class="special">;</span>
 446
 447 <span class="identifier">child</span> <span class="identifier">c</span><span class="special">(</span><span class="string">"g++"</span><span class="special">,</span> <span class="string">"main.cpp"</span><span class="special">,</span> <span class="comment">//set the input</span>
 448         <code class="computeroutput"><a class="link" href="../boost/process/std_in.html" title="Global std_in">bp::std_in</a></code><span class="special">.</span><span class="identifier">close</span><span class="special">(),</span>
 449         <code class="computeroutput"><a class="link" href="../boost/process/std_out.html" title="Global std_out">bp::std_out</a></code> <span class="special">&gt;</span> <code class="computeroutput"><a class="link" href="../boost/process/null.html" title="Global null">bp::null</a></code><span class="special">,</span> <span class="comment">//so it can be written without anything</span>
 450         <code class="computeroutput"><a class="link" href="../boost/process/std_err.html" title="Global std_err">bp::std_err</a></code> <span class="special">&gt;</span> <span class="identifier">data</span><span class="special">,</span>
 451         <span class="identifier">ios</span><span class="special">);</span>
 452
 453
 454 <span class="identifier">ios</span><span class="special">.</span><span class="identifier">run</span><span class="special">();</span> <span class="comment">//this will actually block until the compiler is finished</span>
 455
 456 <span class="keyword">auto</span> <span class="identifier">err</span> <span class="special">=</span>  <span class="identifier">data</span><span class="special">.</span><span class="identifier">get</span><span class="special">();</span>
 457 </pre>
 458 <p>
 459       </p>
 460 </div>
 461 <div class="section">
 462 <div class="titlepage"><div><div><h3 class="title">
 463 <a name="boost_process.tutorial.group"></a><a class="link" href="tutorial.html#boost_process.tutorial.group" title="Groups">Groups</a>
 464 </h3></div></div></div>
 465 <p>
 466         When launching several processes, processes can be grouped together. This
 467         will also apply for a child process, that launches other processes, if they
 468         do not modify the group membership. E.g. if you call <code class="computeroutput"><span class="identifier">make</span></code>
 469         which launches other processes and call terminate on it, it will not terminate
 470         all the child processes of the child unless you use a group.
 471       </p>
 472 <p>
 473         The two main reasons to use groups are:
 474       </p>
 475 <div class="orderedlist"><ol class="orderedlist" type="1">
 476 <li class="listitem">
 477             Being able to terminate child processes of the child process
 478           </li>
 479 <li class="listitem">
 480             Grouping several processes into one, just so they can be terminated at
 481             once
 482           </li>
 483 </ol></div>
 484 <p>
 485         If we have program like <code class="computeroutput"><span class="identifier">make</span></code>,
 486         which does launch its own child processes, a call of <code class="computeroutput"><a class="link" href="../boost/process/child.html#idm45170605226736-bb">terminate</a></code>
 487         might not suffice. I.e. if we have a makefile launching <code class="computeroutput"><span class="identifier">gcc</span></code>
 488         and use the following code, the <code class="computeroutput"><span class="identifier">gcc</span></code>
 489         process will still run afterwards:
 490       </p>
 491 <p>
 492 </p>
 493 <pre class="programlisting"><code class="computeroutput"><a class="link" href="../boost/process/child.html" title="Class child">bp::child</a></code> <span class="identifier">c</span><span class="special">(</span><span class="string">"make"</span><span class="special">);</span>
 494 <span class="keyword">if</span> <span class="special">(!</span><span class="identifier">c</span><span class="special">.</span><code class="computeroutput"><a class="link" href="../boost/process/child.html#idm45170605246880-bb">wait_for</a></code><span class="special">(</span><a href="http://en.cppreference.com/w/cpp/chrono/duration" target="_top">std::chrono::seconds</a><span class="special">(</span><span class="number">10</span><span class="special">))</span> <span class="comment">//give it 10 seconds</span>
 495     <span class="identifier">c</span><span class="special">.</span><code class="computeroutput"><a class="link" href="../boost/process/child.html#idm45170605226736-bb">terminate</a></code><span class="special">();</span> <span class="comment">//then terminate</span>
 496 </pre>
 497 <p>
 498       </p>
 499 <p>
 500         So in order to also terminate <code class="computeroutput"><span class="identifier">gcc</span></code>
 501         we can use a group.
 502       </p>
 503 <p>
 504 </p>
 505 <pre class="programlisting"><code class="computeroutput"><a class="link" href="../boost/process/group.html" title="Class group">bp::group</a></code> <span class="identifier">g</span><span class="special">;</span>
 506 <code class="computeroutput"><a class="link" href="../boost/process/child.html" title="Class child">bp::child</a></code> <span class="identifier">c</span><span class="special">(</span><span class="string">"make"</span><span class="special">,</span> <span class="identifier">g</span><span class="special">);</span>
 507 <span class="keyword">if</span> <span class="special">(!</span><span class="identifier">g</span><span class="special">.</span><code class="computeroutput"><a class="link" href="../boost/process/group.html#idm45170604717728-bb">wait_for</a></code><span class="special">(</span><a href="http://en.cppreference.com/w/cpp/chrono/duration" target="_top">std::chrono::seconds</a><span class="special">(</span><span class="number">10</span><span class="special">))</span>
 508     <span class="identifier">g</span><span class="special">.</span><code class="computeroutput"><a class="link" href="../boost/process/group.html#idm45170604697552-bb">terminate</a></code><span class="special">();</span>
 509
 510 <span class="identifier">c</span><span class="special">.</span><code class="computeroutput"><a class="link" href="../boost/process/child.html#idm45170605250176-bb">wait</a></code><span class="special">();</span> <span class="comment">//to avoid a zombie process &amp; get the exit code</span>
 511 </pre>
 512 <p>
 513       </p>
 514 <p>
 515         Now given the example, we still call <code class="computeroutput"><a class="link" href="../boost/process/child.html#idm45170605250176-bb">wait</a></code>
 516         to avoid a zombie process. An easier solution for that might be to use <code class="computeroutput"><a class="link" href="../boost/process/spawn.html" title="Function template spawn">spawn</a></code>.
 517       </p>
 518 <p>
 519         To put two processes into one group, the following code suffices. Spawn already
 520         launches a detached process (i.e. without a child-handle), but they can be
 521         grouped, to that in the case of a problem, RAII is still a given.
 522       </p>
 523 <p>
 524 </p>
 525 <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">f</span><span class="special">()</span>
 526 <span class="special">{</span>
 527     <code class="computeroutput"><a class="link" href="../boost/process/group.html" title="Class group">bp::group</a></code> <span class="identifier">g</span><span class="special">;</span>
 528     <code class="computeroutput"><a class="link" href="../boost/process/spawn.html" title="Function template spawn">bp::spawn</a></code><span class="special">(</span><span class="string">"foo"</span><span class="special">,</span> <span class="identifier">g</span><span class="special">);</span>
 529     <code class="computeroutput"><a class="link" href="../boost/process/spawn.html" title="Function template spawn">bp::spawn</a></code><span class="special">(</span><span class="string">"bar"</span><span class="special">,</span> <span class="identifier">g</span><span class="special">);</span>
 530
 531     <span class="identifier">do_something</span><span class="special">();</span>
 532
 533     <span class="identifier">g</span><span class="special">.</span><code class="computeroutput"><a class="link" href="../boost/process/group.html#idm45170604721232-bb">wait</a></code><span class="special">();</span>
 534 <span class="special">};</span>
 535 </pre>
 536 <p>
 537       </p>
 538 <p>
 539         In the example, it will wait for both processes at the end of the function
 540         unless an exception occurs. I.e. if an exception is thrown, the group will
 541         be terminated.
 542       </p>
 543 <p>
 544         Please see the <code class="computeroutput"><a class="link" href="../process/reference.html#header.boost.process.group_hpp" title="Header &lt;boost/process/group.hpp&gt;">reference</a></code>
 545         for more information.
 546       </p>
 547 </div>
 548 <div class="section">
 549 <div class="titlepage"><div><div><h3 class="title">
 550 <a name="boost_process.tutorial.env"></a><a class="link" href="tutorial.html#boost_process.tutorial.env" title="Environment">Environment</a>
 551 </h3></div></div></div>
 552 <p>
 553         This library provides access to the environment of the current process and
 554         allows setting it for the child process.
 555       </p>
 556 <p>
 557 </p>
 558 <pre class="programlisting"><span class="comment">//get a handle to the current environment</span>
 559 <span class="keyword">auto</span> <span class="identifier">env</span> <span class="special">=</span> <code class="computeroutput"><a class="link" href="../process/reference.html#boost.this_process.environment">boost::this_process:deadlock :environment</a></code><span class="special">();</span>
 560 <span class="comment">//add a variable to the current environment</span>
 561 <span class="identifier">env</span><span class="special">[</span><span class="string">"VALUE_1"</span><span class="special">]</span> <span class="special">=</span> <span class="string">"foo"</span><span class="special">;</span>
 562
 563 <span class="comment">//copy it into an environment separate to the one of this process</span>
 564 <code class="computeroutput"><a class="link" href="../boost/process/basic_environment.html" title="Class template basic_environment">bp::environment</a></code> <span class="identifier">env_</span> <span class="special">=</span> <span class="identifier">env</span><span class="special">;</span>
 565 <span class="comment">//append two values to a variable in the new env</span>
 566 <span class="identifier">env_</span><span class="special">[</span><span class="string">"VALUE_2"</span><span class="special">]</span> <span class="special">+=</span> <span class="special">{</span><span class="string">"bar1"</span><span class="special">,</span> <span class="string">"bar2"</span><span class="special">};</span>
 567
 568 <span class="comment">//launch a process with `env_`</span>
 569 <code class="computeroutput"><a class="link" href="../boost/process/system.html" title="Function template system">bp::system</a></code><span class="special">(</span><span class="string">"stuff"</span><span class="special">,</span> <span class="identifier">env_</span><span class="special">);</span>
 570 </pre>
 571 <p>
 572       </p>
 573 <p>
 574         A more convenient way to modify the environment for the child is the <code class="computeroutput"><a class="link" href="../boost/process/env.html" title="Global env">env</a></code> property, which the example as
 575         following:
 576       </p>
 577 <p>
 578 </p>
 579 <pre class="programlisting"><code class="computeroutput"><a class="link" href="../boost/process/system.html" title="Function template system">bp::system</a></code><span class="special">(</span><span class="string">"stuff"</span><span class="special">,</span> <code class="computeroutput"><a class="link" href="../boost/process/env.html" title="Global env">bp::env</a></code><span class="special">[</span><span class="string">"VALUE_1"</span><span class="special">]=</span><span class="string">"foo"</span><span class="special">,</span> <code class="computeroutput"><a class="link" href="../boost/process/env.html" title="Global env">bp::env</a></code><span class="special">[</span><span class="string">"VALUE_2"</span><span class="special">]+={</span><span class="string">"bar1"</span><span class="special">,</span> <span class="string">"bar2"</span><span class="special">});</span>
 580 </pre>
 581 <p>
 582       </p>
 583 <p>
 584         Please see to the <code class="computeroutput"><a class="link" href="../process/reference.html#header.boost.process.environment_hpp" title="Header &lt;boost/process/environment.hpp&gt;">reference</a></code>
 585         for more information.
 586       </p>
 587 </div>
 588 </div>
 589 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 590 <td align="left"></td>
 591 <td align="right"><div class="copyright-footer">Copyright &#169; 2006-2012 Julio M. Merino Vidal, Ilya Sokolov,
 592       Felipe Tanus, Jeff Flinn, Boris Schaeling<br>Copyright &#169; 2016 Klemens D. Morgenstern<p>
 593         Distributed under the Boost Software License, Version 1.0. (See accompanying
 594         file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 595       </p>
 596 </div></td>
 597 </tr></table>
 598 <hr>
 599 <div class="spirit-nav">
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