What Is Dictionary Data Structure in C++?


Scott Campbell

A dictionary is a fundamental data structure in C++ that stores and organizes data in key-value pairs. It is also commonly referred to as a map or associative array. In this article, we will explore what a dictionary data structure is, how it works, and why it is essential in programming.

Understanding Dictionary Data Structure

A dictionary data structure allows us to store and retrieve values based on their associated keys. In other words, it provides a way to map unique keys to corresponding values. This makes it easier to search for and access specific data efficiently.

Key-Value Pairs

In a dictionary, each element consists of a key-value pair. The key is used as an identifier or index for the corresponding value. The value can be any data type, such as integers, strings, objects, or even other dictionaries.

To illustrate this concept, let’s consider an example:


#include <iostream>
#include <map>

int main() {
    std::map<std::string, int> studentGrades;

    // Adding key-value pairs
    studentGrades["Alice"] = 95;
    studentGrades["Bob"] = 87;
    studentGrades["Charlie"] = 91;

    // Retrieving values using keys
    std::cout << "Alice's grade: " << studentGrades["Alice"] << std::endl;
    std::cout << "Bob's grade: " << studentGrades["Bob"] << std::endl;
    std::cout << "Charlie's grade: " << studentGrades["Charlie"] << std::endl;

    return 0;
  • The above code snippet demonstrates the usage of a dictionary in C++.
  • We define a dictionary named studentGrades using the std::map data structure from the C++ Standard Library.
  • Key-value pairs are added to the dictionary using the square bracket notation.
  • We can retrieve the values associated with keys by using the same square bracket notation.

Advantages of Dictionary Data Structure

The dictionary data structure offers several benefits:

  • Fast Access: The dictionary allows direct access to values based on their keys, resulting in efficient retrieval and modification operations.
  • Flexibility: Dictionaries can store values of different types, making them versatile for various programming scenarios.
  • Data Organization: By associating keys with values, dictionaries provide a structured way to organize and manage data effectively.

C++ Dictionary Implementations

C++ offers multiple implementations for dictionaries or map-like structures. Some popular ones include:

  • std::map: This implementation provides an ordered dictionary based on a binary search tree, ensuring efficient search and retrieval operations.
  • std::unordered_map: This implementation uses a hash table to store key-value pairs. It offers faster average search and insertion times compared to std::map but does not maintain order.

Selecting the Right Implementation

The choice between std::map and std::unordered_map depends on the specific requirements of your program. If order is essential, or if you frequently perform range-based queries, std::map may be a better choice. However, if constant-time access is crucial and order does not matter, std::unordered_map can provide faster operations.


The dictionary data structure in C++ is a powerful tool for organizing and accessing data efficiently. By associating keys with values, dictionaries allow us to perform fast searches and retrievals based on specific identifiers. Understanding the different implementations available and selecting the appropriate one for your needs is key to leveraging the full potential of dictionaries in C++ programming.

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