如果finally块抛出异常会发生什么？

Question

如果finally块抛出异常,究竟会发生什么？

具体来说,如果在finally块的中途抛出异常会发生什么.是否调用了此块中的其余语句(之后)？

我知道异常会向上传播.

Answer 1

如果finally块抛出异常,究竟会发生什么？

该异常传播出来,并且(可以)在更高级别处理.

您的finally块将不会在抛出异常之外完成.

如果在处理早期异常期间执行finally块,则第一个异常将丢失.

C#4语言规范§8.9.5:如果finally块抛出另一个异常,则终止当前异常的处理.

Answer 2

对于这些问题,我通常在Visual Studio中打开一个空的控制台应用程序项目并编写一个小示例程序:

using System;

class Program
{
    static void Main(string[] args)
    {
        try
        {
            try
            {
                throw new Exception("exception thrown from try block");
            }
            catch (Exception ex)
            {
                Console.WriteLine("Inner catch block handling {0}.", ex.Message);
                throw;
            }
            finally
            {
                Console.WriteLine("Inner finally block");
                throw new Exception("exception thrown from finally block");
                Console.WriteLine("This line is never reached");
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine("Outer catch block handling {0}.", ex.Message);
        }
        finally
        {
            Console.WriteLine("Outer finally block");
        }
    }
}

运行程序时,您将看到执行catch和finally执行块的确切顺序.请注意,抛出异常后finally块中的代码将不会被执行(事实上,在此示例程序中,Visual Studio甚至会警告您已检测到无法访问的代码):

Inner catch block handling exception thrown from try block.
Inner finally block
Outer catch block handling exception thrown from finally block.
Outer finally block

补充说明

正如Michael Damatov指出的那样,try如果你不在(内部)catch块中处理它,那么块中的异常将被"吃掉" .实际上,在上面的示例中,重新抛出的异常不会出现在外部catch块中.为了更清楚地看一下下面稍微修改过的样本:

using System;

class Program
{
    static void Main(string[] args)
    {
        try
        {
            try
            {
                throw new Exception("exception thrown from try block");
            }
            finally
            {
                Console.WriteLine("Inner finally block");
                throw new Exception("exception thrown from finally block");
                Console.WriteLine("This line is never reached");
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine("Outer catch block handling {0}.", ex.Message);
        }
        finally
        {
            Console.WriteLine("Outer finally block");
        }
    }
}

从输出中可以看出,内部异常是"丢失"(即忽略):

Inner finally block
Outer catch block handling exception thrown from finally block.
Outer finally block

Answer 3

如果存在异常挂起(当try块具有finally但不存在时catch),则新异常将替换该异常.

如果没有异常挂起,它就像在finally块外抛出异常一样.

Answer 4

异常被传播。

Answer 5

保存“原始异常”（在try块中抛出）并牺牲“最终异常”（在finally块中抛出）的快速（且相当明显）片段，以防原始异常对您更重要：

try
{
    throw new Exception("Original Exception");
}
finally
{
    try
    {
        throw new Exception("Finally Exception");
    }
    catch
    { }
}

执行上述代码时，“原始异常”向上传播调用堆栈，而“最终异常”丢失。