File Handling: Reading/Writing .txt Files in C#

Working with files is a fundamental skill for many C# applications — whether saving user data, loading configurations, or processing logs. This session covers how to read from and write to plain text files (.txt) safely and efficiently using C#.

You’ll get hands-on with the most common file operations and understand best practices to avoid common pitfalls.

📂 What Is File Handling?

File handling means working with files on disk — opening, reading, writing, and closing them — to persist data beyond the lifetime of a program.

🔹 Reading Text Files

The easiest way to read a text file in C# is using File.ReadAllText() or File.ReadAllLines():

string content = File.ReadAllText("example.txt");
Console.WriteLine(content);

string[] lines = File.ReadAllLines("example.txt");
foreach (string line in lines)
{
    Console.WriteLine(line);
}

🔸 Writing Text Files

To write text to a file, use File.WriteAllText() or File.AppendAllText():

string textToWrite = "Hello, this is a test.";
File.WriteAllText("output.txt", textToWrite); // Overwrites existing content

File.AppendAllText("output.txt", "\nAppending this line."); // Adds to file

⚙️ Working with Streams for Large Files or More Control

For reading/writing large files or streaming data, use StreamReader and StreamWriter:

using (StreamReader reader = new StreamReader("example.txt"))
{
    string line;
    while ((line = reader.ReadLine()) != null)
    {
        Console.WriteLine(line);
    }
}

using (StreamWriter writer = new StreamWriter("output.txt"))
{
    writer.WriteLine("Writing line by line.");
    writer.WriteLine("Another line.");
}

🧠 Why Learn File Handling?

• Enables data persistence between program runs
• Useful for logs, configs, reports, and more
• Foundation for more advanced file/database operations

🧪 Practice Exercise

Create a program that:

• Reads a .txt file line by line and counts the number of words per line
• Writes the word counts to a new output file
• Handles missing file exceptions gracefully

📚 Summary

📬 Want help applying file handling in your projects or need examples for complex scenarios? Reach out — I’m here to help you master professional C# file operations.