What Data Structure Is STL Map?


Larry Thompson

What Data Structure Is STL Map?

STL Map is a powerful container in the Standard Template Library (STL) in C++. It is used to store data in key-value pairs, where each key is unique.

The map container is implemented as a self-balancing binary search tree, specifically a red-black tree. This data structure provides efficient search, insertion, and deletion operations with a time complexity of O(log n).

Key Features of STL Map

  • Ordered: One of the key features of the map container is that it maintains a strict ordering among its elements based on the keys. This allows for fast lookup and retrieval of elements based on their keys.
  • Unique Keys: Every key in the map is unique, which means you cannot have duplicate keys. If you try to insert an element with an existing key, it will simply update the value associated with that key.
  • Dynamic Size: The size of the map can change dynamically as elements are inserted or removed from it.

Working with STL Map

To use the STL Map container, you need to include the <map> header file in your C++ program. Once included, you can declare a map object using the following syntax:

#include <map>
std::map<KeyType, ValueType> mapName;

Where KeyType represents the type of the keys and ValueType represents the type of associated values.

Inserting Elements into STL Map

To insert elements into an STL Map, you can use either the insert function or the subscript operator ([]). Here’s an example of inserting key-value pairs into a map:

std::map<std::string, int> studentScores;
studentScores.insert(std::make_pair("John", 95));
studentScores["Alice"] = 87;

In the above code snippet, we insert two key-value pairs into the studentScores map. The first pair is inserted using the insert function, while the second pair is inserted using the subscript operator.

Accessing Elements in STL Map

You can access elements in an STL Map using their keys. To retrieve the value associated with a particular key, you can use the subscript operator ([]) or the at() function. Here’s an example:

// Accessing elements by key
int johnScore = studentScores["John"]; // returns 95

// Accessing elements using at()
int aliceScore = studentScores.at("Alice"); // returns 87

In this example, we access the values associated with the keys “John” and “Alice” from the studentScores map.

Removing Elements from STL Map

To remove elements from an STL Map, you can use the erase() function and specify either an iterator to the element or a key value to remove. Here’s an example:

// Removing elements by iterator
auto it = studentScores.find("John");
if (it != studentScores.end()) {

// Removing elements by key

In this code snippet, we remove an element from the studentScores map using both an iterator and a key.


In summary, the STL Map is a highly useful container in C++ for storing data in key-value pairs. It provides efficient operations for insertion, deletion, and retrieval of elements based on their keys. With its ordered nature and self-balancing binary search tree implementation, the map container is an excellent choice when you need to maintain a collection of unique keys with associated values.

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