1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>IO operators</title> 5<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../index.html" title="Boost.Optional"> 8<link rel="up" href="../../optional/tutorial.html" title="Tutorial"> 9<link rel="prev" href="relational_operators.html" title="Relational operators"> 10<link rel="next" href="optional_references.html" title="Optional references"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="relational_operators.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="optional_references.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 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 © 2014-2018 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> 80</div></td> 81</tr></table> 82<hr> 83<div class="spirit-nav"> 84<a accesskey="p" href="relational_operators.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="optional_references.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 85</div> 86</body> 87</html> 88
