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49 lines
1.4 KiB
Plaintext
49 lines
1.4 KiB
Plaintext
[#tutorial]
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= Tutorial
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:idprefix: tutorial_
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When using a hash index with link:../../../multi_index/index.html[Boost.MultiIndex], you don't need to do anything to use `boost::hash` as it uses it by default. To find out how to use a user-defined type, read the <<custom,section on extending boost::hash for a custom data type>>.
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If your standard library supplies its own implementation of the unordered associative containers and you wish to use `boost::hash`, just use an extra template parameter:
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[source]
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----
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std::unordered_multiset<int, boost::hash<int> >
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set_of_ints;
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std::unordered_set<std::pair<int, int>, boost::hash<std::pair<int, int> > >
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set_of_pairs;
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std::unordered_map<int, std::string, boost::hash<int> > map_int_to_string;
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----
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To use `boost::hash` directly, create an instance and call it as a function:
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[source]
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----
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#include <boost/container_hash/hash.hpp>
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int main()
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{
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boost::hash<std::string> string_hash;
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std::size_t h = string_hash("Hash me");
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}
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----
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For an example of generic use, here is a function to generate a vector containing the hashes of the elements of a container:
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[source]
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----
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template <class Container>
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std::vector<std::size_t> get_hashes(Container const& x)
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{
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std::vector<std::size_t> hashes;
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std::transform(x.begin(), x.end(), std::back_inserter(hashes),
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boost::hash<typename Container::value_type>());
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return hashes;
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}
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----
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