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Efficiently Append Elements with std::back_inserter in C++

Are you a C++ programmer who is looking for a way to efficiently insert elements into a container? Look no further than std::back_inserter! This powerful tool allows for easy appending of elements at the end of a container, without the need for manual resizing or reallocation.

In this article, we’ll explore the basics of using std::back_inserter, its functionality as an iterator, and its applications with STL algorithms. Let’s get started!

Using std::back_inserter in C++:

std::back_inserter is a constructor that builds an iterator that allows for appending elements at the end of a container.

This iterator is known as an insert iterator – an iterator that is designed for element insertion. These iterators work by taking a container and a position in the container as arguments, and inserting elements at that position.

One of the most significant benefits of using insert iterators is that they allow for the use of STL algorithms with containers that do not provide an iterator for inserting elements at the end. For example, some containers might provide “push_front” functionality but not “push_back,” making it challenging to insert elements without manual resizing or reallocation.

However, with back inserters, programmers can easily append elements to the end of the container without worrying about these details. Back inserters and their use with containers that have a push_back member function are particularly useful in C++.

With push_back, elements can easily be appended to a container’s end, but it still requires manual resizing and reallocation. By using a back inserter, we can avoid these complexities, making insertion into a container much more straightforward, efficient, and less prone to errors.

Using std::back_inserter with algorithms:

Now that we’ve covered the basics of using std::back_inserter, let’s explore some of the ways that it can be used with STL algorithms. std::fill_n algorithm with std::back_inserter:

The std::fill_n algorithm allows the programmer to initialize a range of elements in a container with a specified value.

For example, suppose we have a vector of integers that we want to initialize with the value zero. We can use std::fill_n along with std::back_inserter to insert the elements at the end of the vector, like so:

std::vector myVector;

std::fill_n(std::back_inserter(myVector), 10, 0);

In this example, we are filling the vector with 10 elements, all initialized to zero.

Using std::back_inserter ensures that these elements are appended to the end of the vector without requiring us to manually resize or reallocate the vector. std::set_intersection algorithm with std::back_inserter:

The std::set_intersection algorithm allows the programmer to create a new container with the common elements between two existing containers.

Suppose we have two vectors of integers, and we want to create a new vector that contains only the common elements between them. We can use std::set_intersection, along with std::back_inserter, to create this new vector, like so:

std::vector myVector1 = {1, 2, 3, 4, 5};

std::vector myVector2 = {3, 4, 5, 6, 7};

std::vector commonElements;

std::set_intersection(myVector1.begin(), myVector1.end(),

myVector2.begin(), myVector2.end(),


In this example, we are finding the common elements between myVector1 and myVector2 and inserting them at the end of the commonElements vector using std::back_inserter.

Using std::back_inserter allows us to append these elements without needing to reserve space beforehand, making the code more efficient and less error-prone. std::set_union algorithm with std::back_inserter:

The std::set_union algorithm allows the programmer to create a new container that contains all elements from two existing containers, without duplication.

This algorithm can be used in combination with std::back_inserter to append portions of a string to another string object. For example, suppose we have two strings, and we want to concatenate them together without duplication.

We can use std::set_union and std::back_inserter to achieve this, like so:

std::string string1 = “hello”;

std::string string2 = “world”;

std::string concatenatedString;

std::set_union(string1.begin(), string1.end(),

string2.begin(), string2.end(),


In this example, we are using std::set_union to concatenate the two strings together without duplication. We achieve this by using std::back_inserter to append the elements to the end of the concatenatedString string object.


In conclusion, std::back_inserter is a powerful tool that allows for efficient appending of elements to the end of a container. It is particularly useful when used with STL algorithms, allowing for easy initialization, intersection, and concatenation of ranges of elements.

Whether you are a seasoned C++ programmer or just starting, std::back_inserter is a must-know tool that will make your coding easier, more efficient, and less prone to errors. We hope that this article has provided a starting point for exploring this powerful tool, and we encourage you to continue to seek out ways to incorporate it into your programming.

In conclusion, std::back_inserter makes inserting elements at the end of a container efficient and straightforward, particularly when used with STL algorithms. This tool is a must-know for any C++ programmer, eliminating the complexities of manual resizing and reallocation.

Its use with fill_n, set_intersection, and set_union algorithms highlights its flexibility and essential capabilities. As you continue to explore and incorporate std::back_inserter into your programming, remember the simplicity and efficiency it provides for successful code implementation.

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