ceph/src/boost/libs/optional/doc/html/boost_optional/tutorial/io_operators.html

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  26 <div class="titlepage"><div><div><h3 class="title">
  27 <a name="boost_optional.tutorial.io_operators"></a><a class="link" href="io_operators.html" title="IO operators">IO operators</a>
  28 </h3></div></div></div>
  29 <p>
  30         It is possible to use <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code>
  31         with IO streams, provided that <code class="computeroutput"><span class="identifier">T</span></code>
  32         can be used with streams. IOStream operators are defined in a separate header.
  33       </p>
  34 <p>
  35 </p>
  36 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
  37 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">optional</span><span class="special">/</span><span class="identifier">optional_io</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
  38
  39 <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
  40 <span class="special">{</span>
  41   <span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">o1</span> <span class="special">=</span> <span class="number">1</span><span class="special">,</span> <span class="identifier">oN</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span><span class="special">;</span>
  42   <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">o1</span><span class="special">;</span>
  43   <span class="identifier">std</span><span class="special">::</span><span class="identifier">cin</span> <span class="special">&gt;&gt;</span> <span class="identifier">oN</span><span class="special">;</span>
  44 <span class="special">}</span>
  45 </pre>
  46 <p>
  47       </p>
  48 <p>
  49         The current implementation does not guarantee any particular output. What
  50         it guarantees is that if streaming out and then back in <code class="computeroutput"><span class="identifier">T</span></code>
  51         gives the same value, then streaming out and then back in <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code>
  52         will also give back the same result:
  53       </p>
  54 <p>
  55 </p>
  56 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cassert</span><span class="special">&gt;</span>
  57 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">sstream</span><span class="special">&gt;</span>
  58 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">optional</span><span class="special">/</span><span class="identifier">optional_io</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
  59
  60 <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
  61 <span class="special">{</span>
  62   <span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">o1</span> <span class="special">=</span> <span class="number">1</span><span class="special">,</span> <span class="identifier">oN</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span><span class="special">;</span>
  63   <span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">x1</span><span class="special">,</span> <span class="identifier">x2</span><span class="special">;</span>
  64   <span class="identifier">std</span><span class="special">::</span><span class="identifier">stringstream</span> <span class="identifier">s</span><span class="special">;</span>
  65   <span class="identifier">s</span> <span class="special">&lt;&lt;</span> <span class="identifier">o1</span> <span class="special">&lt;&lt;</span> <span class="identifier">oN</span><span class="special">;</span>
  66   <span class="identifier">s</span> <span class="special">&gt;&gt;</span> <span class="identifier">x1</span> <span class="special">&gt;&gt;</span> <span class="identifier">x2</span><span class="special">;</span>
  67   <span class="identifier">assert</span> <span class="special">(</span><span class="identifier">o1</span> <span class="special">==</span> <span class="identifier">x1</span><span class="special">);</span>
  68   <span class="identifier">assert</span> <span class="special">(</span><span class="identifier">oN</span> <span class="special">==</span> <span class="identifier">x2</span><span class="special">);</span>
  69 <span class="special">}</span>
  70 </pre>
  71 <p>
  72       </p>
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  76 <td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014-2016 Andrzej Krzemie&#324;ski<p>
  77         Distributed under the Boost Software License, Version 1.0. (See accompanying
  78         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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