Standard Template Library (STL) in C++ (original) (raw)

Last Updated : 16 May, 2026

STL (Standard Template Library) is a collection of pre-built classes and functions in C++ used for efficient data handling and programming. It provides ready-to-use data structures and algorithms that simplify development.

• Includes containers like vectors, stacks, queues, and maps.
• Saves time and improves performance using reusable components.

Components of STL

The components of STL are the features provided by STL in C++ that can be classified into 3 types:

These components are designed to be efficient, flexible, and reusable, making them an integral part of modern C++ programming.

Containers

Containers are the data structures used to store objects and data according to the requirement. Each container is implemented as a template class that also contains the methods to perform basic operations on it. Every STL container is defined inside its own header file.

Containers can be further classified into 4 types:

• Sequence Containers :Vector, Deque, List, Forward List, Array
• Container Adaptors :Stack, Queue, Priority Queue
• Associative Containers :Set, Multiset, Map****,** Multimap
• Unordered Associative Containers :Unordered Set, Unordered Multiset, Unordered Map****,** Unordered Multimap

Instead of writing your own data structures (like linked lists or stacks), STL provides ready-made containers that are: Fast, Reliable, Easy-to-use and Type-Safe (work with any data type using templates).

Algorithms

STL algorithms offer a wide range of functions to perform common operations on data (mainly containers). These functions implement the most efficient version of the algorithm for tasks such as sorting, searching, modifying and manipulating data in containers, etc. Most STL algorithms are defined in and , while some specialized algorithms and utilities are available in other headers like , , and . Some of the most frequently used algorithms are:

• Sort : Arranges elements in ascending order (default).
• Binary Search : Checks whether a value exists in a sorted range.
• Find : Searches for the first occurrence of a given value.
• Count : Counts how many times a value appears in the given range.
• Reverse : Reverses the order of elements in the given range.
• Accumulate : Computes the sum of all elements in the range.
• Unique : Removes consecutive duplicate elements.
• Lower bound : Returns iterator to the first element ≥ value in a sorted range.
• Upper bound : Returns iterator to the first element > value in a sorted range.
• Replace : Replaces all occurrences of old value with new value in the given range.

**Iterators

Iterators are the pointer like objects that are used to point to the memory addresses of STL containers. They are one of the most important components that contributes the most in connecting the STL algorithms with the containers. Iterators are defined inside the ****** header file.

Benefits of C++ Standard Template Library (STL)

The key benefits of the STL is :

• Reliable and Tested
• Fast and Efficient
• Reusability
• Built-in Algorithms