C# Tips: Be specific when handling Exception

Our program is great only when we handle exceptions appropriately.
We all know that we can catch different type of Exceptions in C# with try/catch, but we always forget to be a bit more specific.

There are several interesting example in official docs, so I pick up one to explain how this works.

See this document for more detail.

Sample code

Let's create sample code as console app.

using System;

namespace ExceptionFilter
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] array = { 1, 2, 3 };
            int index = -1;

            try
            {
                int result = array[index];
            }
            catch (IndexOutOfRangeException e) 
            {
                Console.WriteLine("IndexOutOfRangeException", e);
            }
            catch(Exception e)
            {
                Console.WriteLine(e.Message);
                Console.WriteLine("something went wrong!");
            }
        }
    }
}

When I run the program, I see IndexOutOfRangeException as expected.

However, what if I want distinguish when user put negative value and when user put larger size than the array length? Then I can use when exception filter like below.

using System;

namespace ExceptionFilter
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] array = { 1, 2, 3 };
            int index = -1;

            try
            {
                int result = array[index];
            }
            catch (IndexOutOfRangeException e) when (index < 0)
            {
                Console.WriteLine("Parameter index cannot be negative.", e);
            }
            catch (IndexOutOfRangeException e)
            {
                Console.WriteLine(e.Message);
                Console.WriteLine("Parameter index cannot be greater than the array size.");
            }
            catch(Exception e)
            {
                Console.WriteLine(e.Message);
                Console.WriteLine("something went wrong!");
            }
        }
    }
}

That's it! It may sound stupid, but in real case life, we had to do if/else statement inside catch several years ago :D