1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> 4<title>Examples</title> 5<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.78.1"> 7<link rel="home" href="../index.html" title="Chapter 1. Boost.Optional"> 8<link rel="up" href="../index.html" title="Chapter 1. Boost.Optional"> 9<link rel="prev" href="detailed_semantics.html" title="Detailed Semantics"> 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="detailed_semantics.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.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><h2 class="title" style="clear: both"> 27<a name="boost_optional.examples"></a><a class="link" href="examples.html" title="Examples">Examples</a> 28</h2></div></div></div> 29<div class="toc"><dl class="toc"> 30<dt><span class="section"><a href="examples.html#boost_optional.examples.optional_return_values">Optional 31 return values</a></span></dt> 32<dt><span class="section"><a href="examples.html#boost_optional.examples.optional_local_variables">Optional 33 local variables</a></span></dt> 34<dt><span class="section"><a href="examples.html#boost_optional.examples.optional_data_members">Optional 35 data members</a></span></dt> 36<dt><span class="section"><a href="examples.html#boost_optional.examples.bypassing_expensive_unnecessary_default_construction">Bypassing 37 expensive unnecessary default construction</a></span></dt> 38</dl></div> 39<div class="section"> 40<div class="titlepage"><div><div><h3 class="title"> 41<a name="boost_optional.examples.optional_return_values"></a><a class="link" href="examples.html#boost_optional.examples.optional_return_values" title="Optional return values">Optional 42 return values</a> 43</h3></div></div></div> 44<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">char</span><span class="special">></span> <span class="identifier">get_async_input</span><span class="special">()</span> 45<span class="special">{</span> 46 <span class="keyword">if</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">queue</span><span class="special">.</span><span class="identifier">empty</span><span class="special">()</span> <span class="special">)</span> 47 <span class="keyword">return</span> <span class="identifier">optional</span><span class="special"><</span><span class="keyword">char</span><span class="special">>(</span><span class="identifier">queue</span><span class="special">.</span><span class="identifier">top</span><span class="special">());</span> 48 <span class="keyword">else</span> <span class="keyword">return</span> <span class="identifier">optional</span><span class="special"><</span><span class="keyword">char</span><span class="special">>();</span> <span class="comment">// uninitialized</span> 49<span class="special">}</span> 50 51<span class="keyword">void</span> <span class="identifier">receive_async_message</span><span class="special">()</span> 52<span class="special">{</span> 53 <span class="identifier">optional</span><span class="special"><</span><span class="keyword">char</span><span class="special">></span> <span class="identifier">rcv</span> <span class="special">;</span> 54 <span class="comment">// The safe boolean conversion from 'rcv' is used here.</span> 55 <span class="keyword">while</span> <span class="special">(</span> <span class="special">(</span><span class="identifier">rcv</span> <span class="special">=</span> <span class="identifier">get_async_input</span><span class="special">())</span> <span class="special">&&</span> <span class="special">!</span><span class="identifier">timeout</span><span class="special">()</span> <span class="special">)</span> 56 <span class="identifier">output</span><span class="special">(*</span><span class="identifier">rcv</span><span class="special">);</span> 57<span class="special">}</span> 58</pre> 59</div> 60<div class="section"> 61<div class="titlepage"><div><div><h3 class="title"> 62<a name="boost_optional.examples.optional_local_variables"></a><a class="link" href="examples.html#boost_optional.examples.optional_local_variables" title="Optional local variables">Optional 63 local variables</a> 64</h3></div></div></div> 65<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">string</span><span class="special">></span> <span class="identifier">name</span> <span class="special">;</span> 66<span class="keyword">if</span> <span class="special">(</span> <span class="identifier">database</span><span class="special">.</span><span class="identifier">open</span><span class="special">()</span> <span class="special">)</span> 67<span class="special">{</span> 68 <span class="identifier">name</span> <span class="special">=</span> <span class="identifier">database</span><span class="special">.</span><span class="identifier">lookup</span><span class="special">(</span><span class="identifier">employer_name</span><span class="special">)</span> <span class="special">;</span> 69<span class="special">}</span> 70<span class="keyword">else</span> 71<span class="special">{</span> 72 <span class="keyword">if</span> <span class="special">(</span> <span class="identifier">can_ask_user</span> <span class="special">)</span> 73 <span class="identifier">name</span> <span class="special">=</span> <span class="identifier">user</span><span class="special">.</span><span class="identifier">ask</span><span class="special">(</span><span class="identifier">employer_name</span><span class="special">)</span> <span class="special">;</span> 74<span class="special">}</span> 75 76<span class="keyword">if</span> <span class="special">(</span> <span class="identifier">name</span> <span class="special">)</span> 77 <span class="identifier">print</span><span class="special">(*</span><span class="identifier">name</span><span class="special">);</span> 78<span class="keyword">else</span> <span class="identifier">print</span><span class="special">(</span><span class="string">"employer's name not found!"</span><span class="special">);</span> 79</pre> 80</div> 81<div class="section"> 82<div class="titlepage"><div><div><h3 class="title"> 83<a name="boost_optional.examples.optional_data_members"></a><a class="link" href="examples.html#boost_optional.examples.optional_data_members" title="Optional data members">Optional 84 data members</a> 85</h3></div></div></div> 86<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">figure</span> 87<span class="special">{</span> 88 <span class="keyword">public</span><span class="special">:</span> 89 90 <span class="identifier">figure</span><span class="special">()</span> 91 <span class="special">{</span> 92 <span class="comment">// data member 'm_clipping_rect' is uninitialized at this point.</span> 93 <span class="special">}</span> 94 95 <span class="keyword">void</span> <span class="identifier">clip_in_rect</span> <span class="special">(</span> <span class="identifier">rect</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rect</span> <span class="special">)</span> 96 <span class="special">{</span> 97 <span class="special">....</span> 98 <span class="identifier">m_clipping_rect</span> <span class="special">=</span> <span class="identifier">rect</span> <span class="special">;</span> <span class="comment">// initialized here.</span> 99 <span class="special">}</span> 100 101 <span class="keyword">void</span> <span class="identifier">draw</span> <span class="special">(</span> <span class="identifier">canvas</span><span class="special">&</span> <span class="identifier">cvs</span> <span class="special">)</span> 102 <span class="special">{</span> 103 <span class="keyword">if</span> <span class="special">(</span> <span class="identifier">m_clipping_rect</span> <span class="special">)</span> 104 <span class="identifier">do_clipping</span><span class="special">(*</span><span class="identifier">m_clipping_rect</span><span class="special">);</span> 105 106 <span class="identifier">cvs</span><span class="special">.</span><span class="identifier">drawXXX</span><span class="special">(..);</span> 107 <span class="special">}</span> 108 109 <span class="comment">// this can return NULL.</span> 110 <span class="identifier">rect</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">get_clipping_rect</span><span class="special">()</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">get_pointer</span><span class="special">(</span><span class="identifier">m_clipping_rect</span><span class="special">);</span> <span class="special">}</span> 111 112 <span class="keyword">private</span> <span class="special">:</span> 113 114 <span class="identifier">optional</span><span class="special"><</span><span class="identifier">rect</span><span class="special">></span> <span class="identifier">m_clipping_rect</span> <span class="special">;</span> 115 116<span class="special">};</span> 117</pre> 118</div> 119<div class="section"> 120<div class="titlepage"><div><div><h3 class="title"> 121<a name="boost_optional.examples.bypassing_expensive_unnecessary_default_construction"></a><a class="link" href="examples.html#boost_optional.examples.bypassing_expensive_unnecessary_default_construction" title="Bypassing expensive unnecessary default construction">Bypassing 122 expensive unnecessary default construction</a> 123</h3></div></div></div> 124<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">ExpensiveCtor</span> <span class="special">{</span> <span class="special">...</span> <span class="special">}</span> <span class="special">;</span> 125<span class="keyword">class</span> <span class="identifier">Fred</span> 126<span class="special">{</span> 127 <span class="identifier">Fred</span><span class="special">()</span> <span class="special">:</span> <span class="identifier">mLargeVector</span><span class="special">(</span><span class="number">10000</span><span class="special">)</span> <span class="special">{}</span> 128 129 <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">ExpensiveCtor</span><span class="special">></span> <span class="special">></span> <span class="identifier">mLargeVector</span> <span class="special">;</span> 130<span class="special">}</span> <span class="special">;</span> 131</pre> 132</div> 133</div> 134<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 135<td align="left"></td> 136<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014 Andrzej Krzemieński<p> 137 Distributed under the Boost Software License, Version 1.0. (See accompanying 138 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>) 139 </p> 140</div></td> 141</tr></table> 142<hr> 143<div class="spirit-nav"> 144<a accesskey="p" href="detailed_semantics.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.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> 145</div> 146</body> 147</html> 148
