Difference between Catch(Exception) and Catch(Exception ex)

Question

What is the difference between Catch(Exception) and Catch(Exception ex) . I can see both giving me expected output. Then what is the actual difference ? Which one is recommended ?

Suppose the code is below.

int a = 1, b = 0;
try
{
    int c = a / b;
    Console.WriteLine(c);
}

Which of the below catch block is recommended to use ? What is the actual difference between those ?

catch (Exception ex)
{
    Console.WriteLine(ex.Message);
}

OR

catch (Exception)
{
    Console.WriteLine("Oh NO!!");
}

Answer 1

Well, catch(Exception ex) is just the same as catch(Exception) with one difference only: in catch(Exception ex) we have an access to the exception class (error cause) instance. Usually you need an exception class instance to print out the original message:

  try {
    ...
  }
  catch (AppServerException e) {
    Console.WriteLine("Application server failed to get data with the message:");
    Console.WriteLine(e.Message); // <- What's actually got wrong with it
  }

If you don't need the exception class instance, e.g. you plan just to consume the exception, the catch(Exception ex) syntax is excessive and catch(Exception) is prefferable:

  try {  
    c = a / b;
  }  
  catch (DivideByZeroException) {
    c = Int.MaxValue; // <- in case b = 0, let c be the maximum possible int
  }

Finally. Do not catch a general Exception class without re-throwing:

  try {
    int c = a / b;
  }
  catch (Exception) { // <- Never ever do this!
    Console.WriteLine("Oh NO!!");
  }

Do you really want to code "whatever error (green fume from CPU included) had happened just print out 'Oh No' and continue"?

The pattern with Exception class is something like this:

  tran.Start();

  try {
    ...
    tran.Commit();
  }
  catch (Exception) {
    // Whatever had happened, let's first rollback the database transaction
    tran.Rollback();

    Console.WriteLine("Oh NO!");

    throw; // <- re-throw the exception
  }