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79 lines
2.6 KiB
HTML
79 lines
2.6 KiB
HTML
<HTML><HEAD><TITLE>Boost PREPROCESSOR library</TITLE><BODY bgcolor="#FFFFFF">
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<a href="index.htm"><IMG height=86 alt="c++boost.gif (8819 bytes)" src="../../../../c++boost.gif" width=277 align=center></a>
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<hr>
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<H1>#include <<a href="../../../../boost/preprocessor/empty.hpp">boost/preprocessor/empty.hpp</a>></H1>
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<hr>
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<H2><a name="BOOST_PP_EMPTY">#define BOOST_PP_EMPTY</a>()</H2>
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<P>Expands to nothing. Used with <a href="if.htm#BOOST_PP_IF">BOOST_PP_IF</a>() and as an unused parameter.</P>
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<P>Example usage as the implementation of <a href="comma_if.htm#BOOST_PP_COMMA_IF">BOOST_PP_COMMA_IF</a>(C):</P>
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<PRE>
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#define <a href="comma_if.htm#BOOST_PP_COMMA_IF">BOOST_PP_COMMA_IF</a>(C)\
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<a href="if.htm#BOOST_PP_IF">BOOST_PP_IF</a>(C,<a href="comma.htm#BOOST_PP_COMMA">BOOST_PP_COMMA</a>,<a href="empty.htm#BOOST_PP_EMPTY">BOOST_PP_EMPTY</a>)()
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</PRE>
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<P>Example usage as an unused macro parameter:</P>
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<PRE>
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#define BOOST_PP_DEF(CV)\
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template<class base>\
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CV() typename implement_subscript_using_begin_subscript<base>::value_type&\
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implement_subscript_using_begin_subscript<base>::operator[]\
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( index_type\
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i\
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) CV()\
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{ return base::begin()[i];\
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}
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BOOST_PP_DEF(<a href="empty.htm#BOOST_PP_EMPTY">BOOST_PP_EMPTY</a>)
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BOOST_PP_DEF(const <a href="empty.htm#BOOST_PP_EMPTY">BOOST_PP_EMPTY</a>)
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#undef BOOST_PP_DEF
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</PRE>
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<P>The above expands to:</P>
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<PRE>
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template<class base>
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typename implement_subscript_using_begin_subscript<base>::value_type&
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implement_subscript_using_begin_subscript<base>::operator[]
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( index_type
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i
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)
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{ return base::begin()[i];
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}
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template<class base>
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const typename implement_subscript_using_begin_subscript<base>::value_type&
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implement_subscript_using_begin_subscript<base>::operator[]
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( index_type
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i
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) const
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{ return base::begin()[i];
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}
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</PRE>
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<P>In case you wonder, the above code is part of a generalized layer for
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implementing the subscripting operators of a random access container.</P>
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<hr>
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<H2><a name="BOOST_PREPROCESSOR_EMPTY">#define BOOST_PREPROCESSOR_EMPTY</a>()</H2>
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<P>Obsolete. Use <a href="empty.htm#BOOST_PP_EMPTY">BOOST_PP_EMPTY</a>().</P>
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<hr>
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<p>(C) Copyright Housemarque Oy 2002</p>
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<p>Permission to copy, use, modify, sell and distribute this document is granted
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provided this copyright notice appears in all copies. This document is provided
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"as is" without express or implied warranty, and with no claim as to its suitability
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for any purpose.</p>
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<p>Generated: <!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %b %Y" startspan --><!--webbot bot="Timestamp" endspan i-checksum="15246" --></p>
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</BODY></HTML> |