How To Deal With Nested Exceptions In C# & .NET

In yesterday’s post, “How To Deal With Aggregate Exceptions In C# & .NET”, we looked at how to deal with AggregateExceptions that may be thrown by the runtime.

In this post, we will look at how to handle nested Exceptions.

What is a nested Exception?

An Exception object has a property, InnerException, that itself could be another Exception. Which, in turn, could also have an InnerException that is another Exception.

In this fashion, we get a nested Exception.

Take this example:

try
{
  throw new Exception("This is the level 1", new Exception("This is the level 2", new Exception("This is the level 3")));
}
catch (Exception ex)
{
  Console.WriteLine(ex.Message);
}

Let us take a look at the caught Exception in the debugger.

We can see here that:

1. This is the Exception that was actually caught, Level 1
2. This is Level 2, the InnerException for Level 1
3. This is Level 3, the InnerException for Level 2

Suppose you wanted to print the Message for Exception ex (Level 1).

It will read as follows:

This is the level 1

This presents a problem when you want to print the details of all the Exceptions.

One way would be to write a recursive loop that visits all the Exceptions.

try
{
  throw new Exception("This is the level 1",
new Exception("This is the level 2", new Exception("This is the level 3")));
}
catch (Exception ex)
{
  StringBuilder sb = new();
  Console.WriteLine(GetMessage(ex, sb));
}

string GetMessage(Exception ex, StringBuilder sb)
{
  sb.AppendLine(ex.Message);
  if (ex.InnerException is not null)
  {
    GetMessage(ex.InnerException, sb);
  }

  return sb.ToString();
}

This will print the following, as expected.

This is the level 1
This is the level 2
This is the level 3

TLDR

Exceptions can have any level of nested InnerExceptions. Always be sure to check

The code is in my GitHub.

Happy hacking!