Std::back_inserter in C++

C++ stands out as a potent programming language celebrated for its efficiency and adaptability. Within its arsenal of tools for working with containers, the Standard Template Library (STL) boasts an invaluable asset ? std::back_inserter. This back-insert iterator simplifies the task of inserting elements at a container's tail, making it an indispensable component of C++ programming. In this blog post, we'll delve into the capabilities of std::back_inserter, offering illustrative code examples and presenting the corresponding outputs.

What is a std::back_inserter?

Nestled within the <iterator> header in C++, std::back_inserter serves as a back-insert iterator, custom-tailored for effortlessly adding elements to the end of a container. It shines particularly bright when employed alongside algorithms generating or transforming elements, eliminating the need for manual resizing of containers.

Example:

Let's unpack the utility of std::back_inserter with a straightforward example. Suppose we have a vector of integers, and our goal is to copy elements from another container into this vector.

Code:

#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
 
int main() {
    // Source container
    std::vector<int> source = {1, 2, 3, 4, 5};
 
    // Destination container
    std::vector<int> destination;
 
    // Utilizing std::back_inserter to copy elements
    std::copy(source.begin(), source.end(), std::back_inserter(destination));
 
    // Displaying the contents of the destination container
    std::cout << "Destination container: ";
    for (const auto& elem : destination) {
        std::cout << elem << " ";
    }
 
    return 0;
}

Output:

Destination container: 1 2 3 4 5

Explanation:

In this instance, std::back_inserter(destination) creates a back-insert iterator tailored for the destination vector. The std::copy algorithm seamlessly transfers elements from the source vector to the destination vector, automatically adjusting the size of the destination vector to accommodate the new elements.

Dynamic Container Expansion:

A notable advantage of employing std::back_inserter lies in its capability to dynamically expand containers during insertion. It stands in contrast to the manual resizing of containers, a potentially error-prone and laborious process that std::back_inserter elegantly sidesteps.

Example:

Let's extend our example to showcase dynamic container expansion:
#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
 
int main() {
    // Source container
    std::vector<int> source = {1, 2, 3, 4, 5};
 
    // Destination container
    std::vector<int> destination;
 
    // Generate numbers from 6 to 10
    for (int i = 6; i <= 10; ++i) {
        // Leveraging std::back_inserter for dynamic expansion
        std::copy(source.begin(), source.end(), std::back_inserter(destination));
        destination.push_back(i);
 
        // Displaying the contents of the destination container
        std::cout << "Destination container: ";
        for (const auto& elem : destination) {
            std::cout << elem << " ";
        }
        std::cout << std::endl;
    }
 
    return 0;
}

Output:

Destination container: 1 2 3 4 5 6
Destination container: 1 2 3 4 5 6 1 2 3 4 5 6 7
Destination container: 1 2 3 4 5 6 1 2 3 4 5 6 7 1 2 3 4 5 6 7 8
Destination container: 1 2 3 4 5 6 1 2 3 4 5 6 7 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 9
Destination container: 1 2 3 4 5 6 1 2 3 4 5 6 7 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 10

Explanation:

As evident, the destination container dynamically adjusts its size to incorporate the new elements, streamlining the process by std::back_inserter.

Conclusion:

In summary, the adaptability of std::back_inserter in C++ offers a robust solution for dynamic manipulation of containers. This back-insert iterator, seamlessly integrated into the Standard Template Library, proves indispensable when the need arises for effortless insertion of elements at the end of containers. Its utility becomes particularly apparent when combined with algorithms designed for element generation or transformation, streamlining the process by automatically adjusting container sizes without manual intervention.

The provided examples simplify the sophistication of std::back_inserter in scenarios where dynamic expansion of containers is critical. Whether transferring elements between containers or incorporating dynamically generated elements, this iterator simplifies the code, enhancing both its clarity and efficiency.

By embracing std::back_inserter, C++ developers can enhance their programming practices, focusing more on algorithmic logic and less on the intricacies of container management. Positioned as a dependable ally in the C++ programmer's toolkit, std::back_inserter underscores the language's commitment to providing efficient, expressive, and user-friendly tools for managing intricate data structures.

Next TopicStd::allocator() in C++

← prev next →