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Home Interviews How do you read a file asynchronously in C#? – MindStick
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1 Answers

ICSM Computer
ICSM Computer 08 May 2025
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In C#, you can read a file asynchronously using methods like File.ReadAllTextAsync, File.ReadAllLinesAsync, or by using StreamReader.ReadLineAsync() in an async loop. Asynchronous file I/O is useful for keeping your app responsive, especially in UI or web apps.

Example 1: Read the entire file as a string

using System;
using System.IO;
using System.Threading.Tasks;

class Program
{
    static async Task Main()
    {
        string filePath = @"C:\example.txt";

        try
        {
            string content = await File.ReadAllTextAsync(filePath);
            Console.WriteLine(content);
        }
        catch (Exception ex)
        {
            Console.WriteLine("Error: " + ex.Message);
        }
    }
}

Example 2: Read file line-by-line asynchronously

using System;
using System.IO;
using System.Threading.Tasks;

class Program
{
    static async Task Main()
    {
        string filePath = @"C:\example.txt";

        try
        {
            using (StreamReader reader = new StreamReader(filePath))
            {
                string? line;
                while ((line = await reader.ReadLineAsync()) != null)
                {
                    Console.WriteLine(line);
                }
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine("Error: " + ex.Message);
        }
    }
}

Other async file reading methods:

  1. File.ReadAllLinesAsync(path) – returns a string[]
  2. File.ReadBytesAsync(path) – returns a byte[] (for binary files)
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