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| 24 | </div> | |
| 25 | <div class="section"> | |
| 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"><</span><span class="identifier">T</span><span class="special">></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"><</span><span class="identifier">iostream</span><span class="special">></span> | |
| 37 | <span class="preprocessor">#include</span> <span class="special"><</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">></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"><</span><span class="keyword">int</span><span class="special">></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"><<</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">>></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"><</span><span class="identifier">T</span><span class="special">></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"><</span><span class="identifier">cassert</span><span class="special">></span> | |
| 57 | <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">sstream</span><span class="special">></span> | |
| 58 | <span class="preprocessor">#include</span> <span class="special"><</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">></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"><</span><span class="keyword">int</span><span class="special">></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"><</span><span class="keyword">int</span><span class="special">></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"><<</span> <span class="identifier">o1</span> <span class="special"><<</span> <span class="identifier">oN</span><span class="special">;</span> | |
| 66 | <span class="identifier">s</span> <span class="special">>></span> <span class="identifier">x1</span> <span class="special">>></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> | |
| 73 | </div> | |
| 74 | <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> | |
| 75 | <td align="left"></td> | |
| 76 | <td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2016 Andrzej Krzemieński<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>) | |
| 79 | </p> | |
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