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144 lines
4.2 KiB
HTML
<HTML>
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<!--
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-- Copyright (c) Jeremy Siek, Lie-Quan Lee, and Andrew Lumsdaine 2000
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--
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-- Permission to use, copy, modify, distribute and sell this software
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-- and its documentation for any purpose is hereby granted without fee,
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-- provided that the above copyright notice appears in all copies and
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-- that both that copyright notice and this permission notice appear
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-- in supporting documentation. We make no
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-- representations about the suitability of this software for any
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-- purpose. It is provided "as is" without express or implied warranty.
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-->
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<Head>
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<Title>Boost Tie</Title>
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<BODY BGCOLOR="#ffffff" LINK="#0000ee" TEXT="#000000" VLINK="#551a8b"
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ALINK="#ff0000">
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<IMG SRC="../../c++boost.gif"
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ALT="C++ Boost" width="277" height="86">
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<BR Clear>
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<H1><A NAME="sec:tie"></A>
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<TT>tie</TT>
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</H1>
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<h3>
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[This version of tie has been removed from the utility.hpp
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header. There is a new, more general version of <a
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href="../tuple/doc/tuple_users_guide.html#tiers">tie</a> in the Boost
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Tuples Library. The more general version handles an (almost) arbitrary
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number of arguments, instead of just two. The version in utility.hpp
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had to be removed to avoid name clashes.]</h3>
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<PRE>
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template <class A, class B>
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tied<A,B> tie(A& a, B& b);
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</PRE>
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<P>
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This is a utility function that makes it more convenient to work with
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a function which returns a std::pair<>. The effect of the <TT>tie()</TT>
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function is to allow the assignment of the two values of the pair to
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two separate variables. The idea for this comes from Jaakko
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Järvi's Binders [<A
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HREF="../graph/doc/bibliography.html#jaakko_tuple_assign">1</A>].
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<P>
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<H3>Where Defined</H3>
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<P>
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<a href="../../boost/utility.hpp"><TT>boost/utility.hpp</TT></a>
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<P>
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<H3>Example</H3>
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<P>
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An example of using the <TT>tie()</TT> function with the
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<TT>vertices()</TT> function, which returns a pair of
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type <TT>std::pair<vertex_iterator,vertex_iterator></TT>. The
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pair of iterators is assigned to the iterator variables <TT>i</TT> and
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<TT>end</TT>.
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<P>
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<PRE>
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graph_traits< adjacency_list<> >::vertex_iterator i, end;
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for(tie(i,end) = vertices(G); i != end; ++i)
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// ...
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</PRE>
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<P>
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Here is another example that uses <TT>tie()</TT> for handling operations with <a
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href="http://www.sgi.com/tech/stl/set.html"><TT>std::set</TT></a>.
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<P>
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<PRE>
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#include <set>
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#include <algorithm>
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#include <iostream>
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#include <boost/utility.hpp>
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int
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main(int, char*[])
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{
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{
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typedef std::set<int> SetT;
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SetT::iterator i, end;
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bool inserted;
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int vals[5] = { 5, 2, 4, 9, 1 };
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SetT s(vals, vals + 5);
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// Using tie() with a return value of pair<iterator,bool>
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int new_vals[2] = { 3, 9 };
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for (int k = 0; k < 2; ++k) {
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boost::tie(i,inserted) = s.insert(new_vals[k]);
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if (!inserted)
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std::cout << *i << " was already in the set." << std::endl;
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else
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std::cout << *i << " successfully inserted." << std::endl;
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}
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}
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{
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int* i, *end;
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int vals[6] = { 5, 2, 4, 4, 9, 1 };
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std::sort(vals, vals + 6);
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// Using tie() with a return value of pair<iterator,iterator>
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boost::tie(i,end) = std::equal_range(vals, vals + 6, 4);
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std::cout << "There were " << std::distance(i,end)
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<< " occurrences of " << *i << "." << std::endl;
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// Footnote: of course one would normally just use std::count()
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// to get this information, but that would spoil the example :)
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}
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return 0;
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}
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</PRE>
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The output is:
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<PRE>
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3 successfully inserted.
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9 was already in the set.
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There were 2 occurrences of 4.
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</PRE>
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<br>
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<HR>
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<TABLE>
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<TR valign=top>
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<TD nowrap>Copyright © 2000</TD><TD>
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<a HREF="../../people/jeremy_siek.htm">Jeremy Siek</a>,
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Univ.of Notre Dame (<A
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HREF="mailto:jsiek@lsc.nd.edu">jsiek@lsc.nd.edu</A>)<br>
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<A HREF=http://www.lsc.nd.edu/~llee1>Lie-Quan Lee</A>, Univ.of Notre Dame (<A HREF="mailto:llee1@lsc.nd.edu">llee1@lsc.nd.edu</A>)<br>
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<A HREF=http://www.lsc.nd.edu/~lums>Andrew Lumsdaine</A>,
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Univ.of Notre Dame (<A
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HREF="mailto:lums@lsc.nd.edu">lums@lsc.nd.edu</A>)
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</TD></TR></TABLE>
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</BODY>
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</HTML>
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