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26 <div class=
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27 <a name=
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28 </h2></div></div></div>
29 <div class=
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30 <dt><span class=
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"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=
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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>
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
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>
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>
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
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>
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>
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
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>
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>
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>
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>
106 <span class=
"identifier">cvs
</span><span class=
"special">.
</span><span class=
"identifier">drawXXX
</span><span class=
"special">(..);
</span>
107 <span class=
"special">}
</span>
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>
112 <span class=
"keyword">private
</span> <span class=
"special">:
</span>
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>
116 <span class=
"special">};
</span>
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>
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>
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 Krzemie
ński
<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>)
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