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# Boost.Unordered
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[](https://www.boost.org/users/license.html) < img alt = "C++11 required" src = "https://img.shields.io/badge/standard-C%2b%2b11-blue.svg" > < img alt = "Header-only library" src = "https://img.shields.io/badge/build-header--only-blue.svg" >
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Boost.Unordered offers a catalog of hash containers with different standards compliance levels, performances and intented usage scenarios:
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**`boost::unordered_set` `boost::unordered_map` `boost::unordered_multiset` `boost::unordered_multimap` **
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< ul > Fully conformant implementations of < code > std::unordered_[multi ](set|map )</ code > ,
but faster and up to the latest revisions of the standard even if you're working in an older version of C++ (heterogeneous lookup,
< code > try_emplace< / code > , < code > contains< / code > , etc.)< / ul >
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**`boost::unordered_flat_set` `boost::unordered_flat_map` **
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< ul > The fastest of the lot. Based on open addressing, these containers slightly
deviate from the standard in exchange for top performance.< / ul >
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**`boost::unordered_node_set` `boost::unordered_node_map` **
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< ul > Variations of < code > boost::unordered_flat_(set|map)< / code > providing pointer stability.< / ul >
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**`boost::concurrent_flat_set` `boost::concurrent_flat_map` **
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< ul > High performance for multithreaded scenarios. Introducing a new non-standard, iterator-free API.< / ul >
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## Learn about Boost.Unordered
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* [Online documentation ](https://boost.org/libs/unordered )
* [Some benchmarks ](https://github.com/boostorg/boost_unordered_benchmarks )
* Technical articles on Boost.Unordered internal design:
* [Advancing the state of the art for `std::unordered_map` implementations ](https://bannalia.blogspot.com/2022/06/advancing-state-of-art-for.html )
* [Inside `boost::unordered_flat_map` ](https://bannalia.blogspot.com/2022/11/inside-boostunorderedflatmap.html )
* [Inside `boost::concurrent_flat_map` ](https://bannalia.blogspot.com/2023/07/inside-boostconcurrentflatmap.html )
* [Bulk visitation in `boost::concurrent_flat_map` ](https://bannalia.blogspot.com/2023/10/bulk-visitation-in-boostconcurrentflatm.html )
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## Get the library
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Boost.Unordered can be installed in a number of ways:
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* [Download Boost ](https://www.boost.org/users/download/ ) and you're ready to go (this is a header-only library requiring no building).
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* Using Conan 2: In case you don't have it yet, add an entry for Boost in your `conanfile.txt` (the example requires at least Boost 1.83):
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```
[requires]
boost/[>=1.83.0]
```
< ul > If you're not using any compiled Boost library, the following will skip building altogether:< / ul >
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```
[options]
boost:header_only=True
```
* Using vcpkg: Execute the command
```
vcpkg install boost-unordered
```
* Using CMake: [Boost CMake support infrastructure ](https://github.com/boostorg/cmake )
allows you to use CMake directly to download, build and consume all of Boost or
some specific libraries.
## Support
* Join the ** #boost -unordered** discussion group at [cpplang.slack.com ](https://cpplang.slack.com/ )
([ask for an invite ](https://cppalliance.org/slack/ ) if you’
* Ask in the [Boost Users mailing list ](https://lists.boost.org/mailman/listinfo.cgi/boost-users )
(add the `[unordered]` tag at the beginning of the subject line)
* [File an issue ](https://github.com/boostorg/unordered/issues )
## Contribute
* [Pull requests ](https://github.com/boostorg/unordered/pulls ) against **develop** branch are most welcome.
Note that by submitting patches you agree to license your modifications under the [Boost Software License, Version 1.0 ](http://www.boost.org/LICENSE_1_0.txt ).
