Open-addressed hash map in C++
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Open-addressed hash map implementation in C++

This is a cache friendly alternative to std::unordered_map. Inspired by Chandler Carruth's talk at CppCon.

#include <iostream>
#include <dict/dict.hpp>

int main() {
  io::dict<std::string, int> worldcups{{"Germany", 4}, {"Brazil", 5}, {"France", 1}};

  std::cout << worldcups["Germany"] << " stars for Germany!" << std::endl;

The interface is the same as for std::unordered_map besides the following list.

Interface Differences to std::unordered_map

  • resides in namespace io and is simply called dict
  • C++17 N4279 additional member functions
  • no erase(iterator first, iterator last)
  • erase doesn't offer the strong exception safety guarantee and invalidates all iterators
  • no bucket interface (Seriously, who uses that anyway?)
  • the load factor is a percentage - a float in the range of [0,1)

Everything else should be the same as in the standard unordered_map.

Follow these links for implementation and performance notes.

Using/Installing dict

dict is header only so you don't need to build anything. You can either add include/dict to your compiler include path(e.g.: -I/path/to/dict/include or put it to /usr/local/include) or copy the files to your local project.


The only dependency is a recent C++11 compiler and boost. So far we only use the iterator library from boost so the header only part is even enough. Simply install it via your favourite package manager

Supported Systems Build Status

Tested on:

  • Ubuntu 14.04LTS with default gcc(4.8) and default boost(1.54)
  • Fedora 21 with default gcc(4.9) and default boost(1.55)
  • Mac OSX with apple clang(3.5svn), clang3.5 and homebrew gcc(4.9) and homebrew boost(1.55)
  • Windows 8.1 with STL's mingw(4.9.1) + boost(1.56) pack(12.1)

Contributions and feedback highly appreciated.


There is also a branch (robinhood-ng) which implements the robinhood hashing scheme similar to the one in Rust's std::collections::HashMap.