Finally Block

Part of the Logic & Flow section of Coddy's C# journey — lesson 27 of 66.

The finally block contains code that always executes, whether an exception occurs or not, even if there's a return statement in the try or catch blocks.

Create a basic try-catch-finally structure:

try
{
    // Code that might throw an exception
    int result = 10 / 2;
    Console.WriteLine("Result: " + result);
}
catch (DivideByZeroException ex)
{
    // Code that handles the exception
    Console.WriteLine("Cannot divide by zero: " + ex.Message);
}
finally
{
    // Code that always executes
    Console.WriteLine("This always executes");
}

The finally block is useful for cleanup tasks like closing files or database connections:

System.IO.StreamReader file = null;
try
{
    file = new System.IO.StreamReader("data.txt");
    string content = file.ReadToEnd();
    Console.WriteLine(content);
}
catch (System.IO.FileNotFoundException)
{
    Console.WriteLine("File not found.");
}
finally
{
    // Always close the file, even if an exception occurred
    if (file != null)
    {
        file.Close();
    }
}

Challenge

Easy

Create a method named ProcessData that:

Takes a string parameter representing a filename
Attempts to open the file and read its contents
Writes the contents to the console
Properly cleans up resources using a finally block
Handles FileNotFoundException and IOException

If the file can't be found, print: "ERROR: File not found: [filename]"

If another IO error occurs, print: "ERROR: Could not read the file: [error message]"

Always print "File operation completed." in the finally block, whether an exception occurred or not.

Cheat sheet

The finally block contains code that always executes, whether an exception occurs or not, even if there's a return statement in the try or catch blocks.

Basic try-catch-finally structure:

try
{
    // Code that might throw an exception
    int result = 10 / 2;
    Console.WriteLine("Result: " + result);
}
catch (DivideByZeroException ex)
{
    // Code that handles the exception
    Console.WriteLine("Cannot divide by zero: " + ex.Message);
}
finally
{
    // Code that always executes
    Console.WriteLine("This always executes");
}

The finally block is useful for cleanup tasks like closing files or database connections:

System.IO.StreamReader file = null;
try
{
    file = new System.IO.StreamReader("data.txt");
    string content = file.ReadToEnd();
    Console.WriteLine(content);
}
catch (System.IO.FileNotFoundException)
{
    Console.WriteLine("File not found.");
}
finally
{
    // Always close the file, even if an exception occurred
    if (file != null)
    {
        file.Close();
    }
}

Try it yourself

using System;
using System.IO;

class Program
{
    public static void ProcessData(string filename)
    {
        // Write your code here
    }
    
    static void Main(string[] args)
    {
        string filename = Console.ReadLine();
        ProcessData(filename);
    }
}