StreamReader and StreamWriter in C#

What are StreamReader and StreamWriter in C#?

**StreamReader** and **StreamWriter** are classes in the System.IO namespace used for reading and writing text files in C#. These classes provide an efficient way to handle text-based file operations.

Key Features of StreamReader & StreamWriter

• StreamReader reads text files **line by line** or fully at once.
• StreamWriter writes text data to a file **efficiently**.
• Supports **buffering**, making read and write operations faster.
• Works well for handling **large text files**.

Writing to a File Using StreamWriter

The StreamWriter class allows writing text data to a file efficiently.

Example: Writing to a File Using StreamWriter

using System;
using System.IO;

class Program
{
    static void Main()
    {
        string filePath = "example.txt";

        using (StreamWriter writer = new StreamWriter(filePath))
        {
            writer.WriteLine("Hello, StreamWriter in C#!");
            writer.WriteLine("This is a test file.");
        }

        Console.WriteLine("Text written to file successfully.");
    }
}

// Output:
// Text written to file successfully.
        

The **using** statement ensures the file is properly closed after writing.

Appending Text Using StreamWriter

You can **append** text to an existing file by opening it in **append mode**.

Example: Appending Text to a File

using System;
using System.IO;

class Program
{
    static void Main()
    {
        string filePath = "example.txt";

        using (StreamWriter writer = new StreamWriter(filePath, true))
        {
            writer.WriteLine("Appending this line to the file.");
        }

        Console.WriteLine("Text appended to file successfully.");
    }
}

// Output:
// Text appended to file successfully.
        

The **true** parameter ensures the file is opened in **append mode** instead of overwriting its content.

Reading from a File Using StreamReader

The StreamReader class is used to **read text from a file line by line** or **fully**.

Example: Reading a File Using StreamReader

using System;
using System.IO;

class Program
{
    static void Main()
    {
        string filePath = "example.txt";

        using (StreamReader reader = new StreamReader(filePath))
        {
            string content = reader.ReadToEnd();
            Console.WriteLine("File Content:");
            Console.WriteLine(content);
        }
    }
}

// Output (depends on file content):
// File Content:
// Hello, StreamWriter in C#!
// This is a test file.
// Appending this line to the file.
        

The **ReadToEnd()** method reads the entire content of the file at once.

Reading a File Line by Line

You can read a file **line by line** using ReadLine().

Example: Reading a File Line by Line

using System;
using System.IO;

class Program
{
    static void Main()
    {
        string filePath = "example.txt";

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

// Output (depends on file content):
// Hello, StreamWriter in C#!
// This is a test file.
// Appending this line to the file.
        

The **ReadLine()** method reads the file one line at a time, reducing memory usage for large files.

Best Practices for Using StreamReader & StreamWriter

• Use **using statements** to ensure files are properly closed.
• Prefer **ReadLine()** for large files instead of **ReadToEnd()**.
• Check **file existence** using File.Exists() before reading.
• Use **buffering** for efficient file operations.