How to Read and Write Arrays to/from Files in C++?

Last Updated : 11 Mar, 2024

In C++, an array is a collection of elements of the same type placed in contiguous memory locations. A file is a container in a computer system for storing information. In this article, we will learn how to read and write arrays to/from files in C++.

Example:

Input: 
Array = {1, 2, 3, 4, 5}
Output: 
// Write the array to a file, then read the array from the file 
Array: 1 2 3 4 5

Reading and Writing Arrays to and from Files in C++

To read and write arrays to and from files in C++, we can use the file streams from the standard library, std::ifstream for reading from files and std::ofstream for writing to files. We can read and write the arrays in a similar way as any other data.

C++ Program to Read and Write Arrays to and from Files

The below example demonstrates how to read and write arrays to/from files in C++.

C++

// C++ program to demonstrate how to read and write arrays to/from files
#include <fstream>
#include <iostream>
using namespace std;

int main()
{
    // Creating an array of size 5
    int arr[] = { 1, 2, 3, 4, 5 };
    int size = sizeof(arr) / sizeof(arr[0]);

    // Opening the file in write mode
    ofstream outfile("array.txt");
    if (!outfile.is_open()) {
        cerr << "Failed to open file for writing.\n";
        return 1;
    }

    // Writing the array elements to the file
    for (int i = 0; i < size; ++i) {
        outfile << arr[i] << " ";
    }

    // Closing the file
    outfile.close();

    // Opening the file in read mode
    ifstream infile("array.txt");

    // Reading the array elements from the file
    for (int i = 0; i < size; ++i) {
        infile >> arr[i];
    }

    // Closing the file
    infile.close();

    // Displaying the array elements
    cout << "Array elements: ";
    for (int i = 0; i < 5; ++i) {
        cout << arr[i] << " ";
    }
    cout << endl;

    return 0;
}

Output

Array elements: 1 2 3 4 5

Time Complexity: O(N), here N is the size of the array.
Auxiliary Space: O(1)