File Reading and Writing Basics

In this lesson you will learn the basics of reading and writing files in C#, so a program can save and load text files. This is for anyone searching for "C# File.WriteAllText how to use".

File.WriteAllText writes to a file and File.ReadAllText reads one back. Saving configuration files and logs makes this a basic operation you will use often in practice.

The sample code saves the contents of a note with File.WriteAllText("memo.txt", ...), then immediately reads the same file back with File.ReadAllText("memo.txt") and prints it. Notice how a single line handles each direction.

A common stumbling block for beginners is error handling for a missing file or a lack of write permission. The asynchronous WriteAllTextAsync also handles large files efficiently.

In real-world development, combining this with exception handling for the missing-file case makes your file operations far more robust.

📖 Reference code

using System;
using System.IO;

class Program {
    static void Main() {
        File.WriteAllText("memo.txt", "Hello\nThis is line 2");
        string content = File.ReadAllText("memo.txt");
        Console.WriteLine(content);
    }
}

✍️ Your code

Type your code, then press "Run"

🧪 This site can't compile or run C# directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser — nothing is sent anywhere).