When is finally run if you throw an exception from the catch block?

Question

try {
   // Do stuff
}
catch (Exception e) {
   throw;
}
finally {
   // Clean up
}

In the above block when is the finally block called? Before the

Answer 1

After reading all of the answers here it looks like the final answer is it depends:

• If you re-throw an exception within the catch block, and that exception is caught inside of another catch block, everything executes according to the documentation.

• However, if the re-trown exception is unhandled, the finally never executes.

I tested this code sample in VS2010 w/ C# 4.0

static void Main()
    {
        Console.WriteLine("Example 1: re-throw inside of another try block:");

        try
        {
            Console.WriteLine("--outer try");
            try
            {
                Console.WriteLine("----inner try");
                throw new Exception();
            }
            catch
            {
                Console.WriteLine("----inner catch");
                throw;
            }
            finally
            {
                Console.WriteLine("----inner finally");
            }
        }
        catch
        {
            Console.WriteLine("--outer catch");
            // swallow
        }
        finally
        {
            Console.WriteLine("--outer finally");
        }
        Console.WriteLine("Huzzah!");

        Console.WriteLine();
        Console.WriteLine("Example 2: re-throw outside of another try block:");
        try
        {
            Console.WriteLine("--try");
            throw new Exception();
        }
        catch
        {
            Console.WriteLine("--catch");
            throw;
        }
        finally
        {
            Console.WriteLine("--finally");
        }

        Console.ReadLine();
    }

Here is the output:

Example 1: re-throw inside of another try block:
--outer try
----inner try
----inner catch
----inner finally
--outer catch
--outer finally
Huzzah!

Example 2: re-throw outside of another try block:
--try
--catch

Unhandled Exception: System.Exception: Exception of type 'System.Exception' was thrown.
at ConsoleApplication1.Program.Main() in C:\local source\ConsoleApplication1\Program.cs:line 53

Answer 2

It would be called after e is re-thrown (i.e. after the catch block is executed)

editing this 7 years later - one important note is that if e is not caught by a try/catch block further up the call stack or handled by a global exception handler, then the finally block may never execute at all.

Answer 3

Why not try it:

outer try
inner try
inner catch
inner finally
outer catch
outer finally

with code (formatted for vertical space):

static void Main() {
    try {
        Console.WriteLine("outer try");
        DoIt();
    } catch {
        Console.WriteLine("outer catch");
        // swallow
    } finally {
        Console.WriteLine("outer finally");
    }
}
static void DoIt() {
    try {
        Console.WriteLine("inner try");
        int i = 0;
        Console.WriteLine(12 / i); // oops
    } catch (Exception e) {
        Console.WriteLine("inner catch");
        throw e; // or "throw", or "throw anything"
    } finally {
        Console.WriteLine("inner finally");
    }
}

Answer 4

A simple way to tell also is to debug your code and notice when finally is called.

Answer 5

Your example would behave identically to this code:

try {
    try {
        // Do stuff
    } catch(Exception e) {
        throw e;
    }
} finally {
    // Clean up
}

As a side note, if you really mean throw e; (that is, throw the same exception you just caught), it is much better to just do throw;, since that will preserve the original stack trace instead of creating a new one.

Answer 6

If there is an unhandled exception inside a catch handler block, the finally block gets called exactly zero times

  static void Main(string[] args)
  {
     try
     {
        Console.WriteLine("in the try");
        int d = 0;
        int k = 0 / d;
     }
     catch (Exception e)
     {
        Console.WriteLine("in the catch");
        throw;
     }
     finally
     {
        Console.WriteLine("In the finally");
     }
  }

Output:

C:\users\administrator\documents\TestExceptionNesting\bin\Release>TestExceptionNesting.exe

in the try

in the catch

Unhandled Exception: System.DivideByZeroException: Attempted to divide by zero. at TestExceptionNesting.Program.Main(String[] args) in C:\users\administrator\documents\TestExceptionNesting\TestExceptionNesting.cs:line 22

C:\users\administrator\documents\TestExceptionNesting\bin\release>

I got asked this question today at an interview and the interviewer kept going back "are you sure the finally doesn't get called?" I was uncertain if it was meant a trick question or the interviewer had something else in mind and wrote the wrong code for me to debug so I came home and tried it (build and run, no debugger interaction), just to put my mind at rest.