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< a name = "boost_optional.examples" > < / a > < a class = "link" href = "examples.html" title = "Examples" > Examples< / a >
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< / h2 > < / div > < / div > < / div >
< div class = "toc" > < dl >
< 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 >
< table xmlns:rev = "http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width = "100%" > < tr >
< td align = "left" > < / td >
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< td align = "right" > < div class = "copyright-footer" > Copyright © 2003-2007 Fernando Luis Cacciola Carballal< 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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< 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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