How do you read and write files in C#?

Q: What class is used to read text files?

StreamReader is used to read text files in C#.

Q: How to write text to a file?

Use StreamWriter or File.WriteAllText to write text to files.

💡 Concept: File Reading and Writing

File handling in C# involves reading data from files and writing data to files using various classes and methods.

📘 Quick Intro

C# provides multiple APIs like StreamReader, StreamWriter, and File class to facilitate file I/O operations.

🧠 Analogy

Think of file handling like using a pen and paper — you can read what’s written or write new content.

🔧 Technical Explanation

📄 StreamReader reads text from a file sequentially.
✍️ StreamWriter writes text to a file, creating or overwriting it.
📁 The File class provides static methods for quick file operations.
⚙️ Supports synchronous and asynchronous methods for better performance.
🛠️ Proper disposal of streams is important to release resources.

🎯 Use Cases

✅ Reading configuration files.
✅ Logging application data.
✅ Processing large text files.
✅ Saving user data or reports.

💻 Code Example


using System;
using System.IO;

class Program {
    static void Main() {
        // Writing to a file
        using (StreamWriter writer = new StreamWriter(""example.txt"")) {
            writer.WriteLine(""Hello, World!"");
        }

        // Reading from a file
        using (StreamReader reader = new StreamReader(""example.txt"")) {
            string content = reader.ReadToEnd();
            Console.WriteLine(content);
        }
    }
}

❓ Interview Q&A

Q1: What class is used to read text files?
A: StreamReader.

Q2: How to write text to a file?
A: Using StreamWriter or File.WriteAllText.

Q3: How to ensure files are properly closed?
A: Use 'using' statement or call Dispose.

Q4: Can file operations be asynchronous?
A: Yes, using async methods.

Q5: What namespace contains file handling classes?
A: System.IO.

Q6: What happens if a file doesn't exist?
A: Reading throws exception; writing creates new file.

Q7: How to append text to an existing file?
A: Use StreamWriter with append parameter.

Q8: What is the difference between StreamReader and File.ReadAllText?
A: StreamReader reads streams; File.ReadAllText reads all content at once.

Q9: Can you read binary files with these classes?
A: No, use BinaryReader for binary data.

Q10: How to handle large files efficiently?
A: Read line by line or use buffering.

📝 MCQs

Q1. What class reads text files?

StreamWriter
File
StreamReader
BinaryReader

Q2. How to write text to file?

StreamReader
StreamWriter or File.WriteAllText
File.ReadAllText
Console.Write

Q3. How to ensure files close?

'using' statement
Close()
Dispose()
Flush()

Q4. Can file ops be async?

No
Yes
Sometimes
Never

Q5. Namespace for file handling?

System.Net
System.IO
System.Text
System.Threading

Q6. What if file missing?

Creates file
Exception when reading
Deletes file
Ignores

Q7. How to append text?

StreamReader append
StreamWriter append
File.ReadAllText append
Console.Write

Q8. StreamReader vs File.ReadAllText?

Same
StreamReader reads streams
File.ReadAllText reads streams
None

Q9. Read binary files?

Yes
No
Sometimes
Always

Q10. Handle large files?

Read all at once
Read line by line
Ignore
Skip

💡 Bonus Insight

Efficient file I/O is crucial for performance, especially with large datasets in C# applications.

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