C# – difference between “throw” and “throw ex”

cexceptionexception handlingnet

There are some posts that asks what the difference between those two are already.
(why do I have to even mention this…)

But my question is different in a way that I am calling "throw ex" in another error god-like handling method.

public class Program {
    public static void Main(string[] args) {
        try {
            // something
        } catch (Exception ex) {
            HandleException(ex);
        }
    }

    private static void HandleException(Exception ex) {
        if (ex is ThreadAbortException) {
            // ignore then,
            return;
        }
        if (ex is ArgumentOutOfRangeException) { 
            // Log then,
            throw ex;
        }
        if (ex is InvalidOperationException) {
            // Show message then,
            throw ex;
        }
        // and so on.
    }
}

If try & catch were used in the Main, then I would use throw; to rethrow the error.
But in the above simplied code, all exceptions go through HandleException

Does throw ex; has the same effect as calling throw when called inside HandleException?

Best Answer

Yes, there is a difference;

throw ex resets the stack trace (so your errors would appear to originate from HandleException)

throw doesn't - the original offender would be preserved.

static void Main(string[] args)
{
    try
    {
        Method2();
    }
    catch (Exception ex)
    {
        Console.Write(ex.StackTrace.ToString());
        Console.ReadKey();
    }
}

private static void Method2()
{
    try
    {
        Method1();
    }
    catch (Exception ex)
    {
        //throw ex resets the stack trace Coming from Method 1 and propogates it to the caller(Main)
        throw ex;
    }
}

private static void Method1()
{
    try
    {
        throw new Exception("Inside Method1");
    }
    catch (Exception)
    {
        throw;
    }
}

This is the style that Microsoft tends to use in their examples.

It appears that the guidance in this area may have changed, as StyleCop now enforces the use of the C# specific aliases.

C# – the difference between const and readonly in C#

Apart from the apparent difference of

having to declare the value at the time of a definition for a const VS readonly values can be computed dynamically but need to be assigned before the constructor exits.. after that it is frozen.
const's are implicitly static. You use a ClassName.ConstantName notation to access them.

There is a subtle difference. Consider a class defined in AssemblyA.

public class Const_V_Readonly
{
  public const int I_CONST_VALUE = 2;
  public readonly int I_RO_VALUE;
  public Const_V_Readonly()
  {
     I_RO_VALUE = 3;
  }
}

AssemblyB references AssemblyA and uses these values in code. When this is compiled:

in the case of the const value, it is like a find-replace. The value 2 is 'baked into' the AssemblyB's IL. This means that if tomorrow I update I_CONST_VALUE to 20, AssemblyB would still have 2 till I recompile it.
in the case of the readonly value, it is like a ref to a memory location. The value is not baked into AssemblyB's IL. This means that if the memory location is updated, AssemblyB gets the new value without recompilation. So if I_RO_VALUE is updated to 30, you only need to build AssemblyA and all clients do not need to be recompiled.

So if you are confident that the value of the constant won't change, use a const.

public const int CM_IN_A_METER = 100;

But if you have a constant that may change (e.g. w.r.t. precision).. or when in doubt, use a readonly.

public readonly float PI = 3.14;

Update: Aku needs to get a mention because he pointed this out first. Also I need to plug where I learned this: Effective C# - Bill Wagner

Best Answer

Related Solutions

C# – the difference between String and string in C#

This is the style that Microsoft tends to use in their examples.

C# – the difference between const and readonly in C#

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