hash table


A Hash Table (or dictonary, associative array) is a datastructure that maps keys to values.

It’s name derived from the fact that the keys or pointers to them are hashed (often with some collision resolution strategy) and stored in a table with the associated values (the hash indicates where the value is stored).

Useful for caches to speed up data-access, sets, indexing, uniqueness (dictonary, unique string lookups). A hash-table is also used for Objects in dynamic languages, where one object is a hash-table with names of members and methods are the keys and the values are pointer to the methods and members. Or a Combination of an array and a hash for instance variables ([1] ruby)

map and unordered map

If you have a reason to use a different container, other than std::array or std::vector [2], use std::unordered_map [3] or if the keys have to be sorted: std::map.

Example a “string” to “string” map:

std::unordered_map<std::string, std::string> colors = {

A gist of an unordered map with string as key and variable array (vector) of strings as value: unordered_map <string, vector<string>> dict;:

  1. don’t @ me
  2. c++ guidelins on vector
  3. cppreference/unordered_map
Written on August 13, 2020
[ c++  data-structures  ]