是否有理由两次抛出异常？

Question

Debugging production code I came across something I had not seen before and am not aware of a valid purpose. In several methods of one of our controllers we have try-catch blocks. The interesting part is there are 2 throw statements in one of the catches.

Is there any reason to have 2 throw statements? If so, in what circumstance(s) does that make sense?

        try
        {
           //statements
        }
        catch (SoapException se)
        {
            //Log statement
            return null;
        }
        catch (Exception ex)
        {
            //Log statement
            throw;
            throw;
        }

Answer 1

No there is no reason to throw twice. The second throw will never be reached.

It is also similar to having

public int GetNumber()
{
    return 1;
    return 2; // Never reached
}

Update

Resharper is a great tool to check things like this.

In this case it will grey out the second throw and tell you it is unreachable.

Answer 2

There is absolutely no purpose in throwing an exception twice in a row. The second throw can never be reached, and it is most likely a typo, or code that was edited, but never completed and since forgotten about.

Answer 3

In the example you showed, there would be no purpose to the two throw statements. As soon as the first one is hit it starts to work its way back up the call stack until it is caught. The only way for two to make any differance is if the first one was conditional or caught before he second one was hit.

    try
    {
       //statements
    }
    catch (SoapException se)
    {
        //Log statement
        return null;
    }
    catch (Exception ex)
    {
        //Log statement
        if (condition)
            throw;
        throw;
    }

or

    try
    {
       //statements
    }
    catch (SoapException se)
    {
        //Log statement
        return null;
    }
    catch (Exception ex)
    {
        //Log statement
        try
        {
             throw;
        }
        catch (Exception)
        {
             //Handle first thrown exception.
        }
        throw;
    }