Join two arrays in C++

This post will discuss how to join two arrays into a new array in C++. The new array should contain elements of the first array, followed by elements of the second array in the same order.

1. Write our own routine

A naive solution is to create a new array of size enough to accommodate all elements of both arrays and fill it with all elements of the first array, followed by all elements of the second array.

#include <iostream>

#include <algorithm>

int main()

{

int X[] = { 1, 2, 3 };

int Y[] = { 4, 5, 6 };

int m = sizeof(X)/sizeof(X[0]);

int n = sizeof(Y)/sizeof(Y[0]);

int arr[m + n];

for (int i = 0; i < m + n; i++)

{

if (i < m) {

arr[i] = X[i];

}

else {

arr[i] = Y[i - m];

}

for (int i = 0; i < m + n; i++) {

std::cout << arr[i] << ' ';

}

return 0;

}

Download Run Code

Output:

1 2 3 4 5 6

2. Using `std::copy` function

The recommended approach is to use the std::copy from <algorithm> header, as shown below:

#include <iostream>

#include <algorithm>

int main()

{

int X[] = { 1, 2, 3 };

int Y[] = { 4, 5, 6 };

int m = sizeof(X)/sizeof(X[0]);

int n = sizeof(Y)/sizeof(Y[0]);

int arr[m + n];

std::copy(X, X + m, arr);

std::copy(Y, Y + n, arr + m);

// or, use

// std::copy(Y, Y + n, std::copy(X, X + m, arr));