如何抛出异常

Question

What are the best practices for choosing between throw; and throw ex; ? Is there any at all? Regarding -for example- this simple snippet:

try{
    // some code
} catch (Exception ex) {
    // some catcher code
    // throw; ?
    // or
    // throw ex; ?
    // how to decide which one?
}

UPDATE: I know the difference between the tow above. Question is how to decide to use one of them? Is there any best practice to making a better choice?

Answer 1

You should either use throw; to re-throw the original exception (with the original stack trace) or use throw new MyException(..., ex); to throw your own exception that may provide additional information AND set inner exception to ex.

If you don't have any additional information just use throw;

If you only catch the exception to do cleanup, then use try {...} finally {...} instead.

Answer 2

It's very simple .

Do you want to keep stack trace to see exactly where exception occurs? Then use throw , this will be like if you don't use catch at all.

Do you only care about current method debug info? Then throw ex .

To demonstrate:

static void Main(string[] args)
{
    try
    {
        Test();
    }
    catch (Exception e)
    {
        Console.WriteLine(e);
    }
}

static void Test()
{
    try
    {
        // long lambda chain
        new Action(() => new Action(() => new Action(() => { throw new InvalidOperationException(); })())())();
    }
    catch (Exception ex)
    {
        //throw;
        //throw ex;
    }
}

throw will keep stack trace:

System.InvalidOperationException: Operation is not valid due to the current state of the object.
    at ConsoleApplication.Program.<>c.<Test>b__1_2() in ConsoleApplication\Program.cs:line 22
    at ConsoleApplication.Program.<>c.<Test>b__1_1() in ConsoleApplication\Program.cs:line 22
    at ConsoleApplication.Program.<>c.<Test>b__1_0() in ConsoleApplication\Program.cs:line 22
    at ConsoleApplication.Program.Test() in ConsoleApplication\Program.cs:line 26
    at ConsoleApplication.Program.Main(String[] args) in ConsoleApplication\Program.cs:line 13

throw ex will reset stack trace:

System.InvalidOperationException: Operation is not valid due to the current state of the object.
    at ConsoleApplication.Program.Test() in ConsoleApplication\Program.cs:line 27
    at ConsoleApplication.Program.Main(String[] args) in ConsoleApplication\Program.cs:line 13

As for best practices - the choice is usually throw , as developer you want to get as much information as you can, throw ex is a counterpart - some information is hidden, but maybe you want to hide it, who knows?