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50 lines
4.5 KiB
Markdown
50 lines
4.5 KiB
Markdown
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# Boost.Unordered
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Part of collection of the [Boost C++ Libraries](http://github.com/boostorg).
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For accessing data based on key lookup, the C++ standard library offers `std::set`, `std::map`, `std::multiset` and `std::multimap`.
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These are generally implemented using balanced binary trees so that lookup time has logarithmic complexity.
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That is generally okay, but in many cases a hash table can perform better, as accessing data has constant complexity, on average.
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The worst case complexity is linear, but that occurs rarely and with some care, can be avoided.
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Also, the existing containers require a 'less than' comparison object to order their elements.
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For some data types this is impossible to implement or isn’t practical.
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In contrast, a hash table only needs an equality function and a hash function for the key.
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With this in mind, unordered associative containers were added to the C++ standard.
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This is an implementation of the containers described in C++11, with some deviations from the standard in order to work with non-C++11 compilers and libraries.
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### License
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Distributed under the [Boost Software License, Version 1.0](http://www.boost.org/LICENSE_1_0.txt).
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### Properties
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* C++03
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* Header-Only
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### Build Status
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Branch | GH Actions | Appveyor | codecov.io | Deps | Docs | Tests |
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:-------------: | ---------- | -------- | ---------- | ---- | ---- | ----- |
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[`master`](https://github.com/boostorg/unordered/tree/master) | [](https://github.com/boostorg/unordered/actions/workflows/ci.yml) | [](https://ci.appveyor.com/project/danieljames/unordered-qtwe6/branch/master) | [](https://codecov.io/gh/boostorg/unordered/branch/master) | [](https://pdimov.github.io/boostdep-report/master/unordered.html) | [](https://www.boost.org/doc/libs/master/libs/unordered/doc/html/unordered.html) | [](http://www.boost.org/development/tests/master/developer/unordered.html)
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[`develop`](https://github.com/boostorg/unordered/tree/develop) | [](https://github.com/boostorg/unordered/actions/workflows/ci.yml) | [](https://ci.appveyor.com/project/danieljames/unordered-qtwe6/branch/develop) | [](https://codecov.io/gh/boostorg/unordered/branch/develop) | [](https://pdimov.github.io/boostdep-report/develop/unordered.html) | [](https://www.boost.org/doc/libs/develop/libs/unordered/doc/html/unordered.html) | [](http://www.boost.org/development/tests/develop/developer/unordered.html)
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### Directories
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| Name | Purpose |
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| ----------- | ------------------------------ |
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| `doc` | documentation |
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| `example` | examples |
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| `include` | headers |
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| `test` | unit tests |
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### More information
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* [Ask questions](http://stackoverflow.com/questions/ask?tags=c%2B%2B,boost,boost-unordered)
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* [Report bugs](https://github.com/boostorg/unordered/issues): Be sure to mention Boost version, platform and compiler you're using. A small compilable code sample to reproduce the problem is always good as well.
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* Submit your patches as pull requests against **develop** branch. 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).
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* Discussions about the library are held on the [Boost developers mailing list](http://www.boost.org/community/groups.html#main). Be sure to read the [discussion policy](http://www.boost.org/community/policy.html) before posting and add the `[unordered]` tag at the beginning of the subject line.
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