File I/O (Input/Output) in C# allows you to read from and write to files on the filesystem. The System.IO namespace contains classes for working with files and directories. Below are detailed examples of common file I/O operations in C#.

1. File

• Description: Provides static methods for file operations.
• Notable Methods:
  • Create()
  • Copy()
  • Delete()
  • Exists()
  • Open()
  • ReadAllText()
  • WriteAllText()

2. FileInfo

• Description: Provides instance methods for file operations.
• Notable Methods:
  • CopyTo()
  • Delete()
  • Exists()
  • MoveTo()
  • Open()
  • OpenRead()
  • OpenText()
  • Refresh()

3. Directory

• Description: Provides static methods for directory operations.
• Notable Methods:
  • CreateDirectory()
  • Delete()
  • Exists()
  • GetFiles()
  • GetDirectories()
  • GetCurrentDirectory()

4. DirectoryInfo

• Description: Provides instance methods for directory operations.
• Notable Methods:
  • Create()
  • Delete()
  • GetFiles()
  • GetDirectories()
  • MoveTo()
  • Refresh()

5. FileStream

• Description: Provides a stream for file operations.
• Notable Methods:
  • Read()
  • Write()
  • Seek()
  • Flush()
  • Close()
  • SetLength()

6. StreamReader

• Description: Reads characters from a byte stream.
• Notable Methods:
  • Read()
  • ReadLine()
  • ReadToEnd()
  • Peek()
  • Close()

7. StreamWriter

• Description: Writes characters to a stream.
• Notable Methods:
  • Write()
  • WriteLine()
  • Flush()
  • Close()
  • Dispose()

8. BinaryReader

• Description: Reads primitive types as binary values.
• Notable Methods:
  • ReadInt32()
  • ReadString()
  • ReadBytes()
  • ReadBoolean()
  • Close()

9. BinaryWriter

• Description: Writes primitive types in binary format.
• Notable Methods:
  • Write()
  • Flush()
  • Close()
  • WriteInt32()
  • WriteString()

10. MemoryStream

• Description: Provides a stream that uses memory as its backing store.
• Notable Methods:
  • Read()
  • Write()
  • ToArray()
  • SetLength()
  • GetBuffer()

11. Path

• Description: Provides methods for processing file and directory paths.
• Notable Methods:
  • Combine()
  • GetFileName()
  • GetExtension()
  • GetDirectoryName()
  • ChangeExtension()

12. FileSystemWatcher

• Description: Watches for changes in the file system.
• Notable Methods:
  • Start()
  • Stop()
  • Dispose()
  • WaitForChanged()

13. TextReader

• Description: Base class for reading characters from a stream.
• Notable Methods:
  • Read()
  • ReadLine()
  • ReadToEnd()
  • Close()
  • Peek()

14. TextWriter

• Description: Base class for writing characters to a stream.
• Notable Methods:
  • Write()
  • WriteLine()
  • Flush()
  • Close()
  • Dispose()

1. Writing to a File

You can write text to a file using StreamWriter, File.WriteAllText, or File.AppendAllText. Here’s an example using StreamWriter.

Example: Writing to a File

csharp
1using System;
2using System.IO;
3
4class Program
5{
6    static void Main()
7    {
8        string filePath = "example.txt";
9
10        // Using StreamWriter to write to a file
11        using (StreamWriter writer = new StreamWriter(filePath))
12        {
13            writer.WriteLine("Hello, World!");
14            writer.WriteLine("Welcome to C# File I/O.");
15            writer.WriteLine("This is a sample text file.");
16        }
17
18        Console.WriteLine($"Data written to {filePath}");
19    }
20}

2. Reading from a File

To read text from a file, you can use StreamReader, File.ReadAllText, or File.ReadAllLines. Here’s an example using StreamReader.

Example: Reading from a File

csharp
1using System;
2using System.IO;
3
4class Program
5{
6    static void Main()
7    {
8        string filePath = "example.txt";
9
10        // Using StreamReader to read from a file
11        using (StreamReader reader = new StreamReader(filePath))
12        {
13            string line;
14            while ((line = reader.ReadLine()) != null)
15            {
16                Console.WriteLine(line);
17            }
18        }
19    }
20}

3. Checking if a File Exists

Before performing operations on a file, you may want to check if the file exists using File.Exists.

Example: Checking if a File Exists

csharp
1using System;
2using System.IO;
3
4class Program
5{
6    static void Main()
7    {
8        string filePath = "example.txt";
9
10        if (File.Exists(filePath))
11        {
12            Console.WriteLine($"{filePath} exists.");
13        }
14        else
15        {
16            Console.WriteLine($"{filePath} does not exist.");
17        }
18    }
19}

4. Appending to a File

You can append text to an existing file using StreamWriter with the append parameter set to true.

Example: Appending to a File

csharp
1using System;
2using System.IO;
3
4class Program
5{
6    static void Main()
7    {
8        string filePath = "example.txt";
9
10        // Appending text to a file
11        using (StreamWriter writer = new StreamWriter(filePath, true))
12        {
13            writer.WriteLine("This line is appended to the file.");
14        }
15
16        Console.WriteLine("Data appended to the file.");
17    }
18}

5. Deleting a File

You can delete a file using File.Delete.

Example: Deleting a File

csharp
1using System;
2using System.IO;
3
4class Program
5{
6    static void Main()
7    {
8        string filePath = "example.txt";
9
10        if (File.Exists(filePath))
11        {
12            File.Delete(filePath);
13            Console.WriteLine($"{filePath} has been deleted.");
14        }
15        else
16        {
17            Console.WriteLine($"{filePath} does not exist.");
18        }
19    }
20}

6. Working with Directories

You can also create, delete, and check for directories using the Directory class.

Example: Creating and Deleting a Directory

csharp
1using System;
2using System.IO;
3
4class Program
5{
6    static void Main()
7    {
8        string directoryPath = "exampleDir";
9
10        // Create a directory
11        if (!Directory.Exists(directoryPath))
12        {
13            Directory.CreateDirectory(directoryPath);
14            Console.WriteLine($"Directory {directoryPath} created.");
15        }
16
17        // Delete the directory
18        if (Directory.Exists(directoryPath))
19        {
20            Directory.Delete(directoryPath);
21            Console.WriteLine($"Directory {directoryPath} deleted.");
22        }
23    }
24}

7. Copying and Moving Files

You can copy and move files using File.Copy and File.Move.

Example: Copying and Moving Files

csharp
1using System;
2using System.IO;
3
4class Program
5{
6    static void Main()
7    {
8        string sourceFile = "example.txt";
9        string copyFile = "example_copy.txt";
10        string moveFile = "example_moved.txt";
11
12        // Copying a file
13        if (File.Exists(sourceFile))
14        {
15            File.Copy(sourceFile, copyFile, true); // true to overwrite if exists
16            Console.WriteLine($"File copied to {copyFile}");
17        }
18
19        // Moving a file
20        if (File.Exists(copyFile))
21        {
22            File.Move(copyFile, moveFile);
23            Console