Resuming execution of code after exception is thrown and caught

Question

Hi,

How is it possible to resume code execution after an exception is thrown?

For exampel, take the following code:

namespace ConsoleApplication1
{

    class Test
    {

        public void s()
        {
            throw new NotSupportedException();
            string @class = "" ;
            Console.WriteLine(@class);
            Console.ReadLine();
        }

    }

    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                new Test().s();
            }

            catch (ArgumentException x)
            {

            }

            catch (Exception ex) {   }


        }
    }
}

After catching the exception when stepping through, the program will stop running. How can I still carry on execution?

EDIT: What I specifically mean is the line Console.WriteLine(@class); does not seem to be hit, because when I run to it when in debug mode, the program exits from debug mode. I want to run to this line and stop at it.

Thanks

Answer 1

Execution is still carying on but there is no code after the exception is caught. If you want to repeatedly call s then consider wrapping the try/catch block in a while loop.

Answer 2

Well, you don't have any code after the catch blocks, so the program would stop running. Not sure what you're trying to do.

The following should be proof that the program doesn't simply "stop" after the catch blocks. It will execute code after the catch blocks if there is code to be executed:

    static void Main(string[] args)
    {
        try
        {
            new Test().s();
        }

        catch (ArgumentException x)
        {
            Console.WriteLine("ArgumentException caught!");
        }

        catch (Exception ex) { 
            Console.WriteLine("Exception caught!");
        }

        Console.WriteLine("I am some code that's running after the exception!");
    }

The code will print the appropriate string depending on the exception that was caught. Then, it will print I am some code that's running after the exception! at the end.

UPDATE

In your edit you asked why Console.WriteLine(@class); does not seem to be hit. The reason is that you are explicitly throwing an exception in the very first line of your s() method; anything that follows is ignored. When an exception is encountered, execution stops and the exception is propagated up the call stack until the appropriate handler can handle it (this may be a catch block that corresponds to the try that wraps the statement in question within the same method, or it may be a catch block further up the call-stack. If no appropriate handler is found, the program will terminate with a stacktrace [at least in Java - not sure if the same happens in C#]).

If you want to hit the Console.WriteLine line, then you shouldn't be explicitly throwing an exception at the beginning of the method.

Answer 3

The program stops running because there is no following code to be executed in the Main() method! You can add the following line to your code to keep the program running until there is a console input:

Console.ReadLine();

Answer 4

For that code, you can't. If you break the tasks up to smaller chunks, you can resume at the next chunk. But normally it's easier to have a different mechanism than exceptions to report non-fatal errors, such as a callback function which returns whether or not to continue.

Answer 5

If you're worried that an exception will be thrown in the method but you want the method to continue, add an error handler inside the method.

class Test 
    { 

        public void s() 
        { 


           try
           {
               // Code that may throw an exception
              throw new NotSupportedException();
           } 
           catch(Exception ex)
           {
          // Handle the exception - log?, reset some values?
           }
           string @class = "" ; 
           Console.WriteLine(@class); 
           Console.ReadLine(); 
        } 

    } 

You could also return a bool or some other value to indicate the state.

Good luck,

Patrick

Answer 6

You can use the "step-over" feature in debugging to achieve this on a per-run basis.

Answer 7

Disclaimer: I am not suggesting that you actually do this.

You can mimic the old VB style On Error Resume Next with the following code.

public static class ControlFlow
{
  public static Exception ResumeOnError(Action action)
  {
    try
    {
      action();
      return null;
    }
    catch (Exception caught)
    { 
      return caught;
    }
  }
}

And then it could be used like the following.

public static void Main()
{
  ControlFlow.ResumeOnError(() => { throw new NotSupportedException(); });
  ControlFlow.ResumeOnError(() => { Console.WriteLine(); });
  ControlFlow.ResumeOnError(() => { Console.ReadLine(); });
}

Answer 8

It sounds like you're wanting resumeable exceptions. C# doesn't do resumeable exceptions, and I'm doubtful that CLR supports them.

The purpose of throwing an exception is to abort a function and an entire operation (call stack) if/when something in the call environment (parameters, object state, global state) makes the function's operation impossible or invalid. Passing a zero param to a function that needs to divide a quantity by that param, for example. Division by zero won't produce a meaningful result, and if that's the sole purpose of the function, then the function can't return a meaningful result either. So, throw an exception. This will cause execution to jump to the nearest catch or finally block on the call stack. There is no returning to the function that threw the exception.

If you want to step into your code in the debugger to trace the Console.WriteLine() calls, you need to remove the throw new NotSupportedException() line from your code and recompile.