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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> | |
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