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////
Copyright 2005-2008 Daniel James
Copyright 2022 Christian Mazakas
Copyright 2022 Peter Dimov
Distributed under the Boost Software License, Version 1.0.
https://www.boost.org/LICENSE_1_0.txt
////
[#tutorial]
= Tutorial
:idprefix: tutorial_
When using a Boost container such as
link:../../../unordered/index.html[Boost.Unordered], you don't need to do
anything to use `boost::hash` as it's the default. To find out how to use
a user-defined type, read the <<user,section on extending boost::hash
for user types>>.
If you wish to use `boost::hash` with the standard unordered associative
containers, pass it as a template parameter:
[source]
----
std::unordered_multiset<int, boost::hash<int> >
set_of_ints;
std::unordered_set<std::pair<int, int>, boost::hash<std::pair<int, int> > >
set_of_pairs;
std::unordered_map<int, std::string, boost::hash<int> > map_int_to_string;
----
To use `boost::hash` directly, create an instance and call it as a function:
[source]
----
#include <boost/container_hash/hash.hpp>
int main()
{
boost::hash<std::string> string_hash;
std::size_t h = string_hash("Hash me");
}
----
or alternatively:
[source]
----
#include <boost/container_hash/hash.hpp>
int main()
{
std::size_t h = boost::hash<std::string>()("Hash me");
}
----
For an example of generic use, here is a function to generate a vector
containing the hashes of the elements of a container:
[source]
----
template <class Container>
std::vector<std::size_t> get_hashes(Container const& x)
{
std::vector<std::size_t> hashes;
std::transform(x.begin(), x.end(), std::back_inserter(hashes),
boost::hash<typename Container::value_type>());
return hashes;
}
----
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