Convert a C-style array into a std::array container in C++

This post will discuss how to convert a C-style array into a std::array container in C++.

C++ doesn’t provide any straight conversion from an array to std::array. This is because the std::array class comprises aggregate types and has no custom constructors. So std::array can be constructed using the class member functions such as copy, move, or by using initializer lists, otherwise each of the elements will be default-initialized.

1. Using `std::copy` or `std::n_copy` function

The idea is to copy all elements from the given array to std::array using standard algorithms std::copy or std::n_copy from the algorithm header. This is demonstrated below:

#include <iostream>

#include <array>

#include <algorithm>

void printContainer(const auto &A)

{

for (auto i: A) {

std::cout << i << ' ';

}

std::cout << std::endl;

}

int main()

{

int arr[] = { 1, 2, 3, 4, 5};

const int n = sizeof(arr) / sizeof(arr[0]);

std::array<int, n> first, second;

// 1. Using `std::copy`

std::copy(std::begin(arr), std::end(arr), first.begin());

printContainer(first);

// 2. Using `std::copy_n`

std::copy_n(std::begin(arr), n, std::begin(second));

printContainer(second);

return 0;

}

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2. Using `std::move` function

We can also use std::move in place of std::copy. This is demonstrated below:

#include <iostream>

#include <array>

#include <algorithm>

int main()

{

int arr[] = { 1, 2, 3, 4, 5};

const int n = sizeof(arr) / sizeof(arr[0]);

std::array<int, n> A;

std::move(std::begin(arr), std::end(arr), A.begin());

// print the container

return 0;

}

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3. Using `reinterpret_cast` function

Another way to copy all elements from the given array to std::array is to use the reinterpret_cast. We should best avoid this function as C++ standard offers very few guarantees about reinterpret_cast behavior.

The following code works because a std::array class is POD (Plain Old Data) type and its memory layout requirements match with that of a standard array.

#include <iostream>

#include <array>

#include <algorithm>

void printContainer(const auto &A)

{

for (auto i: A) {

std::cout << i << ' ';

}

int main()

{

int arr[] = { 1, 2, 3, 4, 5};

const int n = sizeof(arr) / sizeof(arr[0]);

// `std::array` is a POD

// std::cout << std::is_pod<std::array<int, 5>>::value << std::endl;

std::array<int, n> &A = reinterpret_cast<std::array<int, n>&>(arr);

printContainer(A);

return 0;

}

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That’s all about converting a C-style array into a std::array container in C++.

Convert a C-style array into a std::array container in C++

1. Using std::copy or std::n_copy function

2. Using std::move function

3. Using reinterpret_cast function

Share this:

1. Using `std::copy` or `std::n_copy` function

2. Using `std::move` function

3. Using `reinterpret_cast` function