How to capture file not found exception in C#?

The FileNotFoundException is thrown when you try to access a file that does not exist on the system. This commonly occurs when using classes like StreamReader, File.ReadAllText(), or other file I/O operations with an incorrect file path.

Syntax

Following is the syntax for handling FileNotFoundException using try-catch −

try {
   // File operation that might throw FileNotFoundException
} catch (FileNotFoundException ex) {
   // Handle the exception
   Console.WriteLine("File not found: " + ex.Message);
}

Using StreamReader with Exception Handling

When using StreamReader to read a file that doesn't exist, a FileNotFoundException is thrown. Here's how to handle it properly −

using System;
using System.IO;

class Program {
   public static void Main() {
      try {
         using (StreamReader sReader = new StreamReader("new.txt")) {
            string content = sReader.ReadToEnd();
            Console.WriteLine("File content: " + content);
         }
      } catch (FileNotFoundException ex) {
         Console.WriteLine("File Not Found!");
         Console.WriteLine("Error: " + ex.Message);
      }
   }
}

The output of the above code is −

File Not Found!
Error: Could not find file 'C:\path\to\current\directory\new.txt'.

Using File.ReadAllText() with Exception Handling

The File.ReadAllText() method also throws FileNotFoundException when the specified file doesn't exist −

using System;
using System.IO;

class Program {
   public static void Main() {
      try {
         string content = File.ReadAllText("nonexistent.txt");
         Console.WriteLine("File content: " + content);
      } catch (FileNotFoundException ex) {
         Console.WriteLine("The specified file was not found.");
         Console.WriteLine("File name: " + ex.FileName);
      }
   }
}

The output of the above code is −

The specified file was not found.
File name: nonexistent.txt

Comprehensive File Exception Handling

In real applications, you should handle multiple types of exceptions that can occur during file operations −

using System;
using System.IO;

class Program {
   public static void Main() {
      string fileName = "data.txt";
      
      try {
         using (StreamReader reader = new StreamReader(fileName)) {
            string line;
            while ((line = reader.ReadLine()) != null) {
               Console.WriteLine(line);
            }
         }
      } catch (FileNotFoundException ex) {
         Console.WriteLine($"File '{ex.FileName}' not found.");
      } catch (DirectoryNotFoundException ex) {
         Console.WriteLine("Directory not found: " + ex.Message);
      } catch (UnauthorizedAccessException ex) {
         Console.WriteLine("Access denied: " + ex.Message);
      } catch (IOException ex) {
         Console.WriteLine("I/O error occurred: " + ex.Message);
      }
   }
}

The output of the above code is −

File 'data.txt' not found.

Checking File Existence Before Access

To prevent FileNotFoundException, you can check if a file exists before attempting to read it −

using System;
using System.IO;

class Program {
   public static void Main() {
      string fileName = "example.txt";
      
      if (File.Exists(fileName)) {
         try {
            string content = File.ReadAllText(fileName);
            Console.WriteLine("File content: " + content);
         } catch (IOException ex) {
            Console.WriteLine("Error reading file: " + ex.Message);
         }
      } else {
         Console.WriteLine($"File '{fileName}' does not exist.");
         Console.WriteLine("Creating a sample file...");
         File.WriteAllText(fileName, "Sample content for demonstration.");
         Console.WriteLine("File created successfully.");
      }
   }
}

The output of the above code is −

File 'example.txt' does not exist.
Creating a sample file...
File created successfully.

Conclusion

The FileNotFoundException occurs when attempting to access non-existent files. Use try-catch blocks to handle this exception gracefully, and consider checking file existence with File.Exists() before performing file operations to provide better user experience.