Append Vector to Vector in C++

1. Use the insert Function to Append Vector to Vector in C++
2. Use insert Function to Add Elements in Vector in C++

This article will explain several methods of how to append a vector to another vector in C++.

Use the insert Function to Append Vector to Vector in C++

The insert method is a built-in function of the std::vector container that can add multiple elements to the vector objects. As the first example, we show how to append a given range from one vector to another. If we specify three iterators as arguments, the insert function will add elements from the last two arguments’ range before the iterator passed as the first parameter. Since we pass the end iterator of the first vector object in the following code example, the function is essentially doing appending of two vectors.

#include <iostream>
#include <vector>

using std::cout; using std::cin;
using std::endl; using std::string;
using std::vector;

template<typename T>
void printVectorElements(vector<T> &vec)
{
    for (auto i = 0; i < vec.size(); ++i) {
        cout << vec.at(i) << "; ";
    }
    cout << endl;
}

int main() {
    vector<int> i_vec1 = {12, 32, 43, 53, 23, 65, 84};
    vector<int> i_vec2 = {121, 321, 431, 531, 231, 651, 841};

    cout << "i_vec1           : ";
    printVectorElements(i_vec1);
    i_vec1.insert(i_vec1.end(), i_vec2.begin(), i_vec2.end());
    cout << "i_vec1 (inserted): ";
    printVectorElements(i_vec1);
    cout << endl;

    return EXIT_SUCCESS;
}

Output:

i_vec1           : 12; 32; 43; 53; 23; 65; 84;
i_vec1 (inserted): 12; 32; 43; 53; 23; 65; 84; 121; 321; 431; 531; 231; 651; 841;

Alternatively, we can specify the iterators using std::end/std::begin methods, implementing a more generic way of passing arguments to the insert function:

#include <iostream>
#include <vector>

using std::cout; using std::cin;
using std::endl; using std::string;
using std::vector;

template<typename T>
void printVectorElements(vector<T> &vec)
{
    for (auto i = 0; i < vec.size(); ++i) {
        cout << vec.at(i) << "; ";
    }
    cout << endl;
}

int main() {
    vector<int> i_vec1 = {12, 32, 43, 53, 23, 65, 84};
    vector<int> i_vec2 = {121, 321, 431, 531, 231, 651, 841};

    cout << "i_vec1           : ";
    printVectorElements(i_vec1);
    i_vec1.insert(std::end(i_vec1), std::begin(i_vec2), std::end(i_vec2));
    cout << "i_vec1 (inserted): ";
    printVectorElements(i_vec1);
    cout << endl;

    return EXIT_SUCCESS;
}

Use insert Function to Add Elements in Vector in C++

Another common way of using the insert method is to add a range of elements with a given value to the vector. For example, we can insert zeros at the first 4 positions of the integer vector. Note that the first argument is the position of the element before which the elements are added. The insert method can be utilized even if the vector elements are allocated manually using new call;

#include <iostream>
#include <vector>

using std::cout; using std::cin;
using std::endl; using std::string;
using std::vector;

template<typename T>
void printVectorElements(vector<T> &vec)
{
    for (auto i = 0; i < vec.size(); ++i) {
        cout << vec.at(i) << "; ";
    }
    cout << endl;
}

int main() {
    vector<int> i_vec1 = {12, 32, 43, 53, 23, 65, 84};

    cout << "i_vec1           : ";
    printVectorElements(i_vec1);
    i_vec1.insert(i_vec1.begin(), 4, 0);
    cout << "i_vec1 (inserted): ";
    printVectorElements(i_vec1);
    cout << endl;

    return EXIT_SUCCESS;
}

Output:

i_vec1           : 12; 32; 43; 53; 23; 65; 84;
i_vec1 (inserted): 0; 0; 0; 0; 12; 32; 43; 53; 23; 65; 84;

The insert method can also be applied when two vectors of strings need to be concatenated. The following example demonstrates the given case with almost the same syntax as used with the integer vectors.

#include <iostream>
#include <vector>

using std::cout; using std::cin;
using std::endl; using std::string;
using std::vector;

template<typename T>
void printVectorElements(vector<T> &vec)
{
    for (auto i = 0; i < vec.size(); ++i) {
        cout << vec.at(i) << "; ";
    }
    cout << endl;
}

int main() {
    vector<string> str_vec1 = {"doordash", "dribble",
                              "renode", "xilinx"};
    vector<string> str_vec2 = {"airbus", "sikorsky"};

    str_vec1.insert(str_vec1.end(), str_vec2.begin(), str_vec2.end());
    printVectorElements(str_vec1);
    cout << endl;

    return EXIT_SUCCESS;
}

Output:

doordash; dribble; renode; xilinx; airbus; sikorsky;

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