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  26 <div class="section">
  27 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  28 <a name="boost_process.design"></a><a class="link" href="design.html" title="Design Rationale">Design Rationale</a>
  29 </h2></div></div></div>
  30 <div class="toc"><dl class="toc">
  31 <dt><span class="section"><a href="design.html#boost_process.design.scope">Scope</a></span></dt>
  32 <dt><span class="section"><a href="design.html#boost_process.design.interface_style">Interface Style</a></span></dt>
  33 <dt><span class="section"><a href="design.html#boost_process.design.arg_cmd_style">Arguments/Command
  34       Style</a></span></dt>
  35 <dt><span class="section"><a href="design.html#boost_process.design.plat_ext">Extensions</a></span></dt>
  36 </dl></div>
  37 <div class="section">
  38 <div class="titlepage"><div><div><h3 class="title">
  39 <a name="boost_process.design.scope"></a><a class="link" href="design.html#boost_process.design.scope" title="Scope">Scope</a>
  40 </h3></div></div></div>
  41 <p>
  42         This library is meant to give an wrapper around the different OS-specific
  43         methods to launch processes. Its aim is to provide all functionality that
  44         is available on those systems and allow the user to do all related things,
  45         which require using the OS APIs.
  46       </p>
  47 <p>
  48         <span class="bold"><strong>This library does not try to provide a full library
  49         for everything process related</strong></span> In many discussions the proposal
  50         was made to build boost.process into a DSEL <a href="#ftn.boost_process.design.scope.f0" class="footnote" name="boost_process.design.scope.f0"><sup class="footnote">[29]</sup></a> of some sort. This is not the goal, it rather provides the facilities
  51         to build such a DSEL-Library on top of it. Therefore the library also does
  52         <span class="bold"><strong>not</strong></span> force any particular use (such as only
  53         asynchronous communication) on its user. It rather could be integrated with
  54         such a library.
  55       </p>
  56 </div>
  57 <div class="section">
  58 <div class="titlepage"><div><div><h3 class="title">
  59 <a name="boost_process.design.interface_style"></a><a class="link" href="design.html#boost_process.design.interface_style" title="Interface Style">Interface Style</a>
  60 </h3></div></div></div>
  61 <p>
  62         Boost.Process does use a very particular style when constructing a process.
  63         This is because a process holds many properties, which are not members of
  64         the actual child class. Those properties are in many cases not accessible
  65         by the father process, for example when using environments. Here the child
  66         process can modify its own environment, but there is no way for the father
  67         process to know. That means, that a child process has properties that cannot
  68         be accessed in C++.
  69       </p>
  70 <p>
  71         This now leads to the two styles supported and mixed by this library. Overloading
  72         and properties. Consider that you may want to launch a process passing a
  73         number of arguments. This is supported in both styles, and would look like
  74         this:
  75       </p>
  76 <p>
  77 </p>
  78 <pre class="programlisting"><span class="identifier">system</span><span class="special">(</span><span class="string">"gcc"</span><span class="special">,</span> <span class="string">"--version"</span><span class="special">);</span> <span class="comment">//overloading</span>
  79 <span class="identifier">system</span><span class="special">(</span><span class="string">"gcc"</span><span class="special">,</span> <span class="identifier">args</span><span class="special">={</span><span class="string">"--version"</span><span class="special">});</span> <span class="comment">//property style.</span>
  80 </pre>
  81 <p>
  82       </p>
  83 <p>
  84         Both styles can also be mixed in some cases.
  85       </p>
  86 <p>
  87 </p>
  88 <pre class="programlisting"><span class="identifier">system</span><span class="special">(</span><span class="string">"gcc"</span><span class="special">,</span> <span class="string">"-c"</span><span class="special">,</span> <span class="identifier">args</span><span class="special">+={</span><span class="string">"main.cpp"</span><span class="special">});</span>
  89 </pre>
  90 <p>
  91       </p>
  92 <p>
  93         In the following section the avaible styles will be described. Note that
  94         the overload style is implemented via type traits, so the types will be listed.
  95       </p>
  96 <div class="caution"><table border="0" summary="Caution">
  97 <tr>
  98 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Caution]" src="../../../doc/src/images/caution.png"></td>
  99 <th align="left">Caution</th>
 100 </tr>
 101 <tr><td align="left" valign="top"><p>
 102           There is no guarantee in which order the arguments will be applied! There
 103           is however a guarantee for arguments belonging together, i.e. the string
 104           argument and the args property will be evaluated in the order given.
 105         </p></td></tr>
 106 </table></div>
 107 </div>
 108 <div class="section">
 109 <div class="titlepage"><div><div><h3 class="title">
 110 <a name="boost_process.design.arg_cmd_style"></a><a class="link" href="design.html#boost_process.design.arg_cmd_style" title="Arguments/Command Style">Arguments/Command
 111       Style</a>
 112 </h3></div></div></div>
 113 <p>
 114         When passing arguments to the process, two styles are provided, the cmd-style
 115         and the exe-/args-style.
 116       </p>
 117 <p>
 118         The cmd style will interpret the string as a sequence of the exe and arguments
 119         and parse them as such, while the exe-/args-style will interpret each string
 120         as an argument.
 121       </p>
 122 <div class="table">
 123 <a name="boost_process.design.arg_cmd_style.id"></a><p class="title"><b>Table&#160;30.1.&#160;Cmd vs Exe/Args</b></p>
 124 <div class="table-contents"><table class="table" summary="Cmd vs Exe/Args">
 125 <colgroup>
 126 <col>
 127 <col>
 128 <col>
 129 </colgroup>
 130 <thead><tr>
 131 <th>
 132                 <p>
 133                   String
 134                 </p>
 135               </th>
 136 <th>
 137                 <p>
 138                   Cmd
 139                 </p>
 140               </th>
 141 <th>
 142                 <p>
 143                   Exe/Args
 144                 </p>
 145               </th>
 146 </tr></thead>
 147 <tbody><tr>
 148 <td>
 149                 <p>
 150                   "gcc --version"
 151                 </p>
 152               </td>
 153 <td>
 154                 <p>
 155                   {"gcc", "--version"}
 156                 </p>
 157               </td>
 158 <td>
 159                 <p>
 160                   {"\"gcc --version\""}
 161                 </p>
 162               </td>
 163 </tr></tbody>
 164 </table></div>
 165 </div>
 166 <br class="table-break"><p>
 167         When using the overloading variant, a single string will result in a cmd
 168         interpretation, several strings will yield a exe-args interpretation. Both
 169         version can be set explicitly:
 170       </p>
 171 <p>
 172 </p>
 173 <pre class="programlisting"><span class="identifier">system</span><span class="special">(</span><span class="string">"grep -c false /etc/passwd"</span><span class="special">);</span> <span class="comment">//cmd style</span>
 174 <span class="identifier">system</span><span class="special">(</span><span class="string">"grep"</span><span class="special">,</span> <span class="string">"-c"</span><span class="special">,</span> <span class="string">"false"</span><span class="special">,</span> <span class="string">"/etc/passwd"</span><span class="special">);</span> <span class="comment">//exe-/args-</span>
 175
 176 <span class="identifier">system</span><span class="special">(</span><span class="identifier">cmd</span><span class="special">=</span><span class="string">"grep -c false /etc/passwd"</span><span class="special">);</span> <span class="comment">//cmd style</span>
 177 <span class="identifier">system</span><span class="special">(</span><span class="identifier">exe</span><span class="special">=</span><span class="string">"grep"</span><span class="special">,</span> <span class="identifier">args</span><span class="special">={</span><span class="string">"-c"</span><span class="special">,</span> <span class="string">"false"</span><span class="special">,</span> <span class="string">"/etc/passwd"</span><span class="special">});</span> <span class="comment">//exe-/args-</span>
 178 </pre>
 179 <p>
 180       </p>
 181 <div class="note"><table border="0" summary="Note">
 182 <tr>
 183 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td>
 184 <th align="left">Note</th>
 185 </tr>
 186 <tr><td align="left" valign="top"><p>
 187           If a '"' sign is used in the argument style, it will be passed as
 188           part of the argument. If the same effect it wanted with the cmd syntax,
 189           it ought to be escaped, i.e. '\"'.
 190         </p></td></tr>
 191 </table></div>
 192 <div class="note"><table border="0" summary="Note">
 193 <tr>
 194 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td>
 195 <th align="left">Note</th>
 196 </tr>
 197 <tr><td align="left" valign="top"><p>
 198           The <code class="computeroutput"><span class="identifier">PATH</span></code> variable will
 199           automatically be searched in the command style, but the one of the launching
 200           process, not the one passed to the child process.
 201         </p></td></tr>
 202 </table></div>
 203 </div>
 204 <div class="section">
 205 <div class="titlepage"><div><div><h3 class="title">
 206 <a name="boost_process.design.plat_ext"></a><a class="link" href="design.html#boost_process.design.plat_ext" title="Extensions">Extensions</a>
 207 </h3></div></div></div>
 208 <p>
 209         The simplest form to extend functionality is to provide another handler,
 210         which will be called on the respective events on process launching. The names
 211         are:
 212       </p>
 213 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 214 <li class="listitem">
 215             <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">process</span><span class="special">::</span><span class="identifier">on_setup</span></code>
 216           </li>
 217 <li class="listitem">
 218             <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">process</span><span class="special">::</span><span class="identifier">on_error</span></code>
 219           </li>
 220 <li class="listitem">
 221             <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">process</span><span class="special">::</span><span class="identifier">on_success</span></code>
 222           </li>
 223 </ul></div>
 224 <p>
 225         As an example:
 226       </p>
 227 <p>
 228 </p>
 229 <pre class="programlisting"><span class="identifier">child</span> <span class="identifier">c</span><span class="special">(</span><span class="string">"ls"</span><span class="special">,</span> <span class="identifier">on_setup</span><span class="special">([](){</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"On Setup"</span> <span class="special">&lt;&lt;</span> <span class="identifier">endl</span><span class="special">;});</span>
 230 </pre>
 231 <p>
 232       </p>
 233 <div class="note"><table border="0" summary="Note">
 234 <tr>
 235 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td>
 236 <th align="left">Note</th>
 237 </tr>
 238 <tr><td align="left" valign="top"><p>
 239           On posix all those callbacks will be handled by this process, not the created
 240           one. This is different for the posix extensions, which can be executed
 241           on the forked process.
 242         </p></td></tr>
 243 </table></div>
 244 </div>
 245 <div class="footnotes">
 246 <br><hr style="width:100; text-align:left;margin-left: 0">
 247 <div id="ftn.boost_process.design.scope.f0" class="footnote"><p><a href="#boost_process.design.scope.f0" class="para"><sup class="para">[29] </sup></a>
 248           Domain Specific Embedded Language
 249         </p></div>
 250 </div>
 251 </div>
 252 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 253 <td align="left"></td>
 254 <td align="right"><div class="copyright-footer">Copyright &#169; 2006-2012 Julio M. Merino Vidal, Ilya Sokolov,
 255       Felipe Tanus, Jeff Flinn, Boris Schaeling<br>Copyright &#169; 2016 Klemens D. Morgenstern<p>
 256         Distributed under the Boost Software License, Version 1.0. (See accompanying
 257         file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 258       </p>
 259 </div></td>
 260 </tr></table>
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