Boost.Unordered

Boost.Unordered offers a catalog of hash containers with different standards compliance levels, performances and intented usage scenarios:

boost::unordered_set boost::unordered_map boost::unordered_multiset boost::unordered_multimap

std::unordered_[multi](set|map)

try_emplace

contains

boost::unordered_flat_set boost::unordered_flat_map

The fastest of the lot. Based on open addressing, these containers slightly deviate from the standard in exchange for top performance.

boost::unordered_node_set boost::unordered_node_map

boost::unordered_flat_(set|map)

boost::concurrent_flat_set boost::concurrent_flat_map

High performance for multithreaded scenarios. Introducing a new non-standard, iterator-free API.

boost::concurrent_node_set boost::concurrent_node_map

boost::concurrent_flat_(set|map)

Learn about Boost.Unordered

Boost.Unordered can be installed in a number of ways:

Download Boost and you're ready to go (this is a header-only library requiring no building).
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 1.86):

[requires]
boost/[>=1.86.0]

If you're not using any compiled Boost library, the following will skip building altogether:

[options]
boost:header_only=True

vcpkg install boost-unordered

Using CMake: Boost CMake support infrastructure allows you to use CMake directly to download, build and consume all of Boost or some specific libraries.

Join the #boost-unordered discussion group at cpplang.slack.com (ask for an invite if you’re not a member of this workspace yet)
Ask in the Boost Users mailing list (add the [unordered] tag at the beginning of the subject line)
File an issue

Pull requests 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.