System.IO Namespace

Provides types that allow reading and writing files and data streams, and types that represent and manage different kinds of I/O operations.

Key Types

Class

File

Provides static methods for the creation, copying, deletion, moving, and opening of files.

Class

Path

Contains a set of static properties and instance methods that are useful for creating, manipulating, and converting directory and file path strings.

Class

Stream

Abstract base class and a representative of a stream of bytes. Provides a base for all streams.

Class

FileInfo

Provides properties and instance methods for the creation, deletion, moving, and opening of files.

Class

DirectoryInfo

Provides properties and instance methods for the creation, deletion, moving, and enumeration of directories and subdirectories.

Class

StreamWriter

Implements a TextWriter for writing characters to a stream in a particular encoding.

Class

StreamReader

Implements a TextReader that reads from a byte stream in a particular encoding.

Class

MemoryStream

Creates a stream that supports both reading and writing by using an array of bytes as the backing store.

Class

FileStream

Exposes a Stream around a file, supporting both synchronous and asynchronous read and write operations.

Common Operations

The System.IO namespace is fundamental for any application that interacts with the file system or network streams. Here are some common operations:

Reading from a Text File

using System;
using System.IO;

public class Example
{
    public static void Main(string[] args)
    {
        try
        {
            // Specify the path to the file.
            string path = @"C:\Users\Public\Documents\MyFile.txt";

            // Create a StreamReader object.
            using (StreamReader sr = new StreamReader(path))
            {
                string line;
                // Read line by line.
                while ((line = sr.ReadLine()) != null)
                {
                    Console.WriteLine(line);
                }
            }
        }
        catch (Exception e)
        {
            Console.WriteLine("The file could not be read:");
            Console.WriteLine(e.Message);
        }
    }
}

Writing to a Text File

using System;
using System.IO;

public class Example
{
    public static void Main(string[] args)
    {
        try
        {
            string path = @"C:\Users\Public\Documents\MyFile.txt";

            // Create a StreamWriter object.
            using (StreamWriter sw = new StreamWriter(path, append: true)) // append: true to add to the file
            {
                sw.WriteLine("This is a new line.");
                sw.WriteLine("Another line of text.");
            }
        }
        catch (Exception e)
        {
            Console.WriteLine("The file could not be written:");
            Console.WriteLine(e.Message);
        }
    }
}

Working with Directories

using System;
using System.IO;

public class Example
{
    public static void Main(string[] args)
    {
        string dirPath = @"C:\MyNewDirectory";

        // Create a directory
        if (!Directory.Exists(dirPath))
        {
            Directory.CreateDirectory(dirPath);
            Console.WriteLine($"Directory created: {dirPath}");
        }

        // Get all directories in the current path
        string[] directories = Directory.GetDirectories(@"C:\");
        Console.WriteLine("\nDirectories in C:\\:");
        foreach (string dir in directories)
        {
            Console.WriteLine(dir);
        }

        // Get all files in a directory
        string[] files = Directory.GetFiles(dirPath);
        Console.WriteLine($"\nFiles in {dirPath}:");
        if (files.Length == 0)
        {
            Console.WriteLine("(No files found)");
        }
        else
        {
            foreach (string file in files)
            {
                Console.WriteLine(file);
            }
        }
    }
}