How to Write Our Own STL Container?

The Standard Template Library (STL) in C++ provides us with various data structures and algorithms. We have STL containers like vector, list, map, and set that we commonly use to store and manipulate data efficiently. However, there are situations where the existing STL containers may not meet our specific requirements, so we may want to create our own custom container to optimize for particular use cases.

In this article, we will learn the concept of STL containers, why we might need to write our own, and how to create a custom STL-like container from scratch.

STL containers are data structures that store collections of objects and provide various functionalities, including adding, removing, and accessing elements, iterating through the collection, and more. The most commonly used STL containers are:

• Sequence Containers: Such as vector, deque, and list, which maintains the order of elements.
• Associative Containers: Such as set, map, multiset, and multimap, which store elements in sorted order, typically for fast retrieval.
• Unordered Containers: Such as unordered_set,unordered_map, unordered_multiset, and unordered_multimap, which stores elements in an unordered manner for constant-time average lookup.

These containers are designed with generic programming in mind and can be used with any data type. They are highly optimized and cover most general use cases.

Why Write Our Own STL Container?

While STL containers are highly efficient and versatile, there might be scenarios where a custom container is more beneficial:

• When the problem at hand requires a data structure that is not provided by the standard library, such as a specific tree structure or a graph, creating a custom container may be necessary.
• In performance-critical applications, a custom container tailored to the specific needs of the application can provide better performance than the general-purpose STL containers.
• Writing our own STL container is a great way to deepen our understanding of C++ and how the standard library works.

Steps to Write a Custom STL Container

To creating a custom STL container we need to follow several steps, like defining the container class, implementing iterators, and providing necessary member functions. Below, we will outline a basic approach to writing a custom container in C++.

1. First define the container class template, specifying the type of elements it will store and any necessary member types, such as value_type, reference, const_reference, iterator, and const_iterator.
2. Implement the core functionality of the container includes managing memory allocation, adding and removing elements, and providing access to elements.
3. Next, implement Iterators that allows us to traverse and manipulate the elements within the container. The iterators should support the necessary operations like incrementing, dereferencing, and comparing.
4. Finally, test the custom container to ensure that the custom container behaves as expected. we can create a simple main function to test our container with different data types and operations.

C++ Program to Write Custom STL-Like Container

The below program demonstrate the implementation of custom STL-like container in C++.

Output

Container elements after push_back operations: 1 2 3 
Container elements after pop_back operation: 1 2 
Element at index 1: 2
Element at index 2: Error: Index out of range