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C# - Files

Handling files in C# involves reading from, writing to, and manipulating files on disk. The .NET Framework and .NET Core provide a range of classes and methods for file operations, primarily within the System.IO namespace. Here’s a comprehensive guide to working with files in C#:

1. File Basics

The System.IO namespace provides classes for file operations:

  • File – Provides static methods for creating, copying, deleting, moving, and opening files.
  • FileInfo – Provides instance methods for file operations and properties to get file information.
  • StreamReader and StreamWriter – Used for reading from and writing to files.
  • FileStream – Provides a stream for file operations, allowing more granular control.

2. Reading Files

Using StreamReader

StreamReader is used to read text from files.

Example:

csharp
using System;
using System.IO;

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

        // Using StreamReader to read the entire file
        using (StreamReader reader = new StreamReader(path))
        {
            string content = reader.ReadToEnd();
            Console.WriteLine(content);
        }
    }
}

Reading Lines

To read a file line by line, you can use the ReadLine method.

csharp
using System;
using System.IO;

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

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

3. Writing Files

Using StreamWriter

StreamWriter is used to write text to files.

Example:

csharp
using System;
using System.IO;

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

        // Using StreamWriter to write text to a file
        using (StreamWriter writer = new StreamWriter(path))
        {
            writer.WriteLine("Hello, World!");
            writer.WriteLine("This is a new line.");
        }
    }
}

Appending Text

To append text to an existing file, use the File.AppendText method.

csharp
using System;
using System.IO;

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

        using (StreamWriter writer = File.AppendText(path))
        {
            writer.WriteLine("This line is appended.");
        }
    }
}

4. File Operations

File Creation and Deletion

You can create and delete files using the File class.

csharp
using System;
using System.IO;

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

        // Create a new file
        if (!File.Exists(path))
        {
            File.Create(path).Dispose(); // Dispose to close the file handle
        }

        // Delete the file
        if (File.Exists(path))
        {
            File.Delete(path);
        }
    }
}

File Copying and Moving

Copy and move files using the File class methods.

csharp
using System;
using System.IO;

class Program
{
    static void Main()
    {
        string sourcePath = "source.txt";
        string destinationPath = "destination.txt";

        // Copy the file
        if (File.Exists(sourcePath))
        {
            File.Copy(sourcePath, destinationPath, true); // Overwrite if exists
        }

        // Move the file
        if (File.Exists(destinationPath))
        {
            File.Move(destinationPath, "newDestination.txt");
        }
    }
}

5. File Information

To get information about a file, use the FileInfo class.

Example:

csharp
using System;
using System.IO;

class Program
{
    static void Main()
    {
        string path = "example.txt";
        FileInfo fileInfo = new FileInfo(path);

        if (fileInfo.Exists)
        {
            Console.WriteLine($"File Name: {fileInfo.Name}");
            Console.WriteLine($"File Size: {fileInfo.Length} bytes");
            Console.WriteLine($"Creation Time: {fileInfo.CreationTime}");
            Console.WriteLine($"Last Access Time: {fileInfo.LastAccessTime}");
        }
    }
}

6. Working with Directories

Creating and Deleting Directories

Use the Directory class to manage directories.

csharp
using System;
using System.IO;

class Program
{
    static void Main()
    {
        string dirPath = "exampleDir";

        // Create a new directory
        if (!Directory.Exists(dirPath))
        {
            Directory.CreateDirectory(dirPath);
        }

        // Delete the directory
        if (Directory.Exists(dirPath))
        {
            Directory.Delete(dirPath, true); // true to delete recursively
        }
    }
}

Listing Files and Directories

List files and directories using Directory methods.

csharp
using System;
using System.IO;

class Program
{
    static void Main()
    {
        string dirPath = "exampleDir";

        if (Directory.Exists(dirPath))
        {
            // List files
            string[] files = Directory.GetFiles(dirPath);
            foreach (string file in files)
            {
                Console.WriteLine(file);
            }

            // List directories
            string[] directories = Directory.GetDirectories(dirPath);
            foreach (string dir in directories)
            {
                Console.WriteLine(dir);
            }
        }
    }
}

7. Handling Exceptions

File operations can throw exceptions, such as FileNotFoundException, IOException, and UnauthorizedAccessException. Use try-catch blocks to handle these exceptions.

Example:

csharp
using System;
using System.IO;

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

        try
        {
            using (StreamReader reader = new StreamReader(path))
            {
                string content = reader.ReadToEnd();
                Console.WriteLine(content);
            }
        }
        catch (FileNotFoundException ex)
        {
            Console.WriteLine("File not found: " + ex.Message);
        }
        catch (IOException ex)
        {
            Console.WriteLine("I/O error: " + ex.Message);
        }
        catch (UnauthorizedAccessException ex)
        {
            Console.WriteLine("Access denied: " + ex.Message);
        }
    }
}

8. Asynchronous File Operations

For I/O-bound operations, consider using asynchronous methods to improve performance and responsiveness.

Example:

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

class Program
{
    static async Task Main()
    {
        string path = "example.txt";

        // Asynchronous file writing
        using (StreamWriter writer = new StreamWriter(path))
        {
            await writer.WriteLineAsync("Hello, asynchronous world!");
        }

        // Asynchronous file reading
        using (StreamReader reader = new StreamReader(path))
        {
            string content = await reader.ReadToEndAsync();
            Console.WriteLine(content);
        }
    }
}

Summary

Handling files in C# involves a variety of operations, including reading, writing, copying, moving, and deleting files, as well as managing directories. The System.IO namespace provides the necessary classes and methods to perform these operations. Understanding how to work with files effectively can help you manage data persistence and file-related tasks in your C# applications.