How to Concatenate Two Vectors in C++?

Concatenation of two vectors refers to the process of adding the elements of one vector at the end of another vector. In this article, we will learn how to concatenate two vectors in C++.

The simplest method to concatenate the two vectors is by using the vector insert() method. Let’s take a look at an example:

#include <bits/stdc++.h>
using namespace std;

int main() {
    vector<int> v1 = {1, 4, 7};
    vector<int> v2 = {6, 5, 9};

    // Concatenate v2 to v1
    v1.insert(v1.end(), v2.begin(), v2.end());

    for (int i : v1)
        cout << i << " ";
    return 0;
}

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Explanation: The vector insert() method allows us to insert a range of elements at the given position in the vector. To concatenate, we define the range as the entire second vector and set the position to the end of the first vector.

Apart from the method shown above, C++ also provides a few other methods to concatenate the two vector. Some of them are as follows:

Using copy()

The copy() function can be used to copy one vector at the end of another vector.

#include <bits/stdc++.h>
using namespace std;

int main() {
    vector<int> v1 = {1, 4, 7};
    vector<int> v2 = {6, 5, 9};

    // Concatenate v2 to v1
    copy(v2.begin(), v2.end(), back_inserter(v1));

    for (int i : v1)
        cout << i << " ";
    return 0;
}

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Explanation: We have to use back_insertor() function as the v1 does not have enough space to store the new element. This function creates the space and append the incoming elements at the end.

Using Loop with vector push_back()

Iterate through the second vector and insert all the elements one by one at the end of first vector using vector push_back() method.

#include <bits/stdc++.h>
using namespace std;

int main() {
    vector<int> v1 = {1, 4, 7};
    vector<int> v2 = {6, 5, 9};

    // Insert all elements of second vector
    // into first vector
    for (auto i : v2)
        v1.push_back(i);

    for (int i : v1)
        cout << i << " ";
    return 0;
}

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