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< 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 >
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< div class = "titlepage" >< div >< div >< h2 class = "title" style = "clear: both" >
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< a name = "boost_optional.examples" ></ a >< a class = "link" href = "examples.html" title = "Examples" > Examples</ a >
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< div class = "toc" >< dl class = "toc" >
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< dt >< span class = "section" >< a href = "examples.html#boost_optional.examples.optional_return_values" > Optional
return values</ a ></ span ></ dt >
< dt >< span class = "section" >< a href = "examples.html#boost_optional.examples.optional_local_variables" > Optional
local variables</ a ></ span ></ dt >
< dt >< span class = "section" >< a href = "examples.html#boost_optional.examples.optional_data_members" > Optional
data members</ a ></ span ></ dt >
< dt >< span class = "section" >< a href = "examples.html#boost_optional.examples.bypassing_expensive_unnecessary_default_construction" > Bypassing
expensive unnecessary default construction</ a ></ span ></ dt >
</ dl ></ div >
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< div class = "section" >
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< div class = "titlepage" >< div >< div >< h3 class = "title" >
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< 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
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return values</ a >
</ h3 ></ div ></ div ></ div >
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< 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 >
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< span class = "special" > {</ span >
< 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 >
< 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 >
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< 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 >
< span class = "special" > }</ span >
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< span class = "keyword" > void</ span > < span class = "identifier" > receive_async_message</ span >< span class = "special" > ()</ span >
< span class = "special" > {</ span >
< 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 >
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< span class = "comment" > // The safe boolean conversion from 'rcv' is used here.</ span >
< 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 >
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< span class = "identifier" > output</ span >< span class = "special" > (*</ span >< span class = "identifier" > rcv</ span >< span class = "special" > );</ span >
< span class = "special" > }</ span >
</ pre >
</ div >
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< div class = "section" >
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< div class = "titlepage" >< div >< div >< h3 class = "title" >
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< 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
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local variables</ a >
</ h3 ></ div ></ div ></ div >
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< 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 >
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< 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 >
< span class = "special" > {</ span >
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< 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 >
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< span class = "special" > }</ span >
< span class = "keyword" > else</ span >
< span class = "special" > {</ span >
< span class = "keyword" > if</ span > < span class = "special" > (</ span > < span class = "identifier" > can_ask_user</ span > < span class = "special" > )</ span >
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< 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 >
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< span class = "special" > }</ span >
< span class = "keyword" > if</ span > < span class = "special" > (</ span > < span class = "identifier" > name</ span > < span class = "special" > )</ span >
< span class = "identifier" > print</ span >< span class = "special" > (*</ span >< span class = "identifier" > name</ span >< span class = "special" > );</ span >
< 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 >
</ pre >
</ div >
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< div class = "section" >
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< div class = "titlepage" >< div >< div >< h3 class = "title" >
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< 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
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data members</ a >
</ h3 ></ div ></ div ></ div >
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< pre class = "programlisting" >< span class = "keyword" > class</ span > < span class = "identifier" > figure</ span >
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< span class = "special" > {</ span >
< span class = "keyword" > public</ span >< span class = "special" > :</ span >
< span class = "identifier" > figure</ span >< span class = "special" > ()</ span >
< span class = "special" > {</ span >
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< span class = "comment" > // data member 'm_clipping_rect' is uninitialized at this point.</ span >
< span class = "special" > }</ span >
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< 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 >
< span class = "special" > {</ span >
< span class = "special" > ....</ span >
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< 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 >
< span class = "special" > }</ span >
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< 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 >
< span class = "special" > {</ span >
< span class = "keyword" > if</ span > < span class = "special" > (</ span > < span class = "identifier" > m_clipping_rect</ span > < span class = "special" > )</ span >
< span class = "identifier" > do_clipping</ span >< span class = "special" > (*</ span >< span class = "identifier" > m_clipping_rect</ span >< span class = "special" > );</ span >
< span class = "identifier" > cvs</ span >< span class = "special" > .</ span >< span class = "identifier" > drawXXX</ span >< span class = "special" > (..);</ span >
< span class = "special" > }</ span >
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< span class = "comment" > // this can return NULL.</ span >
< 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 >
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< span class = "keyword" > private</ span > < span class = "special" > :</ span >
< 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 >
< span class = "special" > };</ span >
</ pre >
</ div >
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< div class = "section" >
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< div class = "titlepage" >< div >< div >< h3 class = "title" >
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< 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
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expensive unnecessary default construction</ a >
</ h3 ></ div ></ div ></ div >
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< 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 >
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< span class = "keyword" > class</ span > < span class = "identifier" > Fred</ span >
< span class = "special" > {</ span >
< 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 >
< 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 >
< span class = "special" > }</ span > < span class = "special" > ;</ span >
</ pre >
</ div >
</ div >
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< td align = "right" >< div class = "copyright-footer" > Copyright © 2003-2007 Fernando Luis Cacciola Carballal< br > Copyright © 2014 Andrzej Krzemień ski< p >
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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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