堆栈跟踪中的错误行号,用于在switch语句中抛出异常

Question

如果在switch语句中抛出异常,我注意到异常堆栈跟踪中的行号有奇怪的行为.

这是一个例子(格式当然是因为行号):

using System;
class Program {
    static void Main(string[] args) {
        for (int i = 0; i < 3; i++) {
            try {
                ThrowSomeException(i);
            } catch (Exception exc) {
                Console.WriteLine(exc);
            }
        }
    }
    private static void ThrowSomeException(int arg) {
        Console.WriteLine("arg = {0}", arg);
        switch (arg) {
        case 0:
            throw new Exception("Line number = 16");
        case 1:
            throw new Exception("Line number = 18");
        default:
            throw new Exception("Line number = 20");
        }
    }
}

堆栈跟踪中报告的行是switch语句中下一个异常的行.上面的程序产生了这个结果(注意异常文本中的行号与堆栈跟踪中的行号不匹配):

arg = 0
System.Exception: Line number = 16
   at Program.ThrowSomeException(Int32 arg) in x:\test\Program.cs:line 18
   at Program.Main(String[] args) in x:\test\Program.cs:line 6
arg = 1
System.Exception: Line number = 18
   at Program.ThrowSomeException(Int32 arg) in x:\test\Program.cs:line 20
   at Program.Main(String[] args) in x:\test\Program.cs:line 6
arg = 2
System.Exception: Line number = 20
   at Program.ThrowSomeException(Int32 arg) in x:\test\Program.cs:line 20
   at Program.Main(String[] args) in x:\test\Program.cs:line 6

为什么会这样？

注意:我在VS 2012和2013上都试过这个,在.NET 3.5和4.5上都进行了编译,得到了相同的结果.

调试与发布:令人惊讶的是,我只在Debug中遇到这种奇怪的行为,在Release中,行号是正确的.

Answer 1

我尝试过反编译程序集，似乎程序集在任一模式下都进行了一些优化。特别是第二种方法发生了变化：

private static void ThrowSomeException(int arg)
{
    Console.WriteLine("arg = {0}", arg);
    switch (arg)
    {
        case 0:
        {
            throw new Exception("Line number = 16");
        }
        case 1:
        {
            throw new Exception("Line number = 18");
        }
    }
    throw new Exception("Line number = 20");
}

这就是 Telerik JustDecompile 告诉我该方法在调试和发布模式下的样子。如果您查看原始程序集，很可能会进一步解释为什么存在这种差异。

我不知道如何继续这个，但我认为这是一个非常有趣的问题。我将把我的答案标记为社区维基，希望通过协作努力可以解决这个问题。

我做了更多测试。我已将 ThrowSomeException() 函数移至一个单独的类并使其成为非静态的，但这并没有改变任何内容。然后我稍微重写了它，首先将异常分配给一个变量，然后单独抛出它。

internal class Program
{
    private static void Main()
    {
        Test test = new Test();
        for (int i = 0; i < 3; i++)
        {
            try
            {
                test.ThrowSomeException(i);
            }
            catch (Exception exception)
            {
                Console.WriteLine(exception);
            }
        }
    }


}

public class Test
{
    public void ThrowSomeException(int arg)
    {

        Console.WriteLine("arg = {0}", arg);
        switch (arg)
        {
            case 0:
                {
                    Exception ex = new Exception("Line number = 36");
                    throw ex;
                }
            case 1:
                {
                    Exception ex = new Exception("Line number = 41");
                    throw ex;
                }
            default:
                {
                    Exception ex = new Exception("Line number = 46");
                    throw ex;

                }
        }

    }
}

上面的代码在调试模式下有以下输出：

arg = 0
System.Exception: Line number = 36
   bij linenumbertest.Test.ThrowSomeException(Int32 arg) in c:\Users\nate\Docume
nts\Visual Studio 2012\Projects\linenumbertest\Program.cs:regel 40
   bij linenumbertest.Program.Main() in c:\Users\nate\Documents\Visual Studio 20
12\Projects\linenumbertest\Program.cs:regel 14
arg = 1
System.Exception: Line number = 41
   bij linenumbertest.Test.ThrowSomeException(Int32 arg) in c:\Users\nate\Docume
nts\Visual Studio 2012\Projects\linenumbertest\Program.cs:regel 45
   bij linenumbertest.Program.Main() in c:\Users\nate\Documents\Visual Studio 20
12\Projects\linenumbertest\Program.cs:regel 14
arg = 2
System.Exception: Line number = 46
   bij linenumbertest.Test.ThrowSomeException(Int32 arg) in c:\Users\nate\Docume
nts\Visual Studio 2012\Projects\linenumbertest\Program.cs:regel 47
   bij linenumbertest.Program.Main() in c:\Users\nate\Documents\Visual Studio 20
12\Projects\linenumbertest\Program.cs:regel 14

在Release模式下，第二个异常是从第46行而不是第45行抛出的。此行为对于所有版本的.NET框架和所有版本的VS都是一致的。接下来我将尝试使用 VB 项目来执行此操作，看看是否会有所不同。

编辑：在 VS 2012 中使用以下 VB 项目：

Module Program
Sub Main()
    Dim test As New Test()
    For i As Integer = 0 To 2
        Try
            test.ThrowSomeException(i)
        Catch exception As Exception
            Console.WriteLine(exception)
        End Try
    Next
End Sub
End Module

Public Class Test
Public Sub ThrowSomeException(arg As Integer)

    Console.WriteLine("arg = {0}", arg)
    Select Case arg
        Case 0
            If True Then
                Dim ex As New Exception("Line number = 22")
                Throw ex
            End If
        Case 1
            If True Then
                Dim ex As New Exception("Line number = 27")
                Throw ex
            End If
        Case Else
            If True Then
                Dim ex As New Exception("Line number = 32")
                Throw ex

            End If
    End Select

End Sub
End Class

没有出现该问题，并且行号一致。

我还测试了直接输出生成的可执行文件，发现了更奇怪的结果。这是调试 exe 的输出：

arg = 0
System.Exception: Line number = 36
   bij linenumbertest.Test.ThrowSomeException(Int32 arg) in c:\Users\nate\Docume
nts\Visual Studio 2012\Projects\linenumbertest\Program.cs:regel 40
   bij linenumbertest.Program.Main() in c:\Users\nate\Documents\Visual Studio 20
12\Projects\linenumbertest\Program.cs:regel 14
arg = 1
System.Exception: Line number = 41
   bij linenumbertest.Test.ThrowSomeException(Int32 arg) in c:\Users\nate\Docume
nts\Visual Studio 2012\Projects\linenumbertest\Program.cs:regel 45
   bij linenumbertest.Program.Main() in c:\Users\nate\Documents\Visual Studio 20
12\Projects\linenumbertest\Program.cs:regel 14
arg = 2
System.Exception: Line number = 46
   bij linenumbertest.Test.ThrowSomeException(Int32 arg) in c:\Users\nate\Docume
nts\Visual Studio 2012\Projects\linenumbertest\Program.cs:regel 47
   bij linenumbertest.Program.Main() in c:\Users\nate\Documents\Visual Studio 20
12\Projects\linenumbertest\Program.cs:regel 14

这是发布模式 exe 的输出：

arg = 0
System.Exception: Line number = 36
   bij linenumbertest.Test.ThrowSomeException(Int32 arg) in c:\Users\nate\Docume
nts\Visual Studio 2012\Projects\linenumbertest\Program.cs:regel 41
   bij linenumbertest.Program.Main() in c:\Users\nate\Documents\Visual Studio 20
12\Projects\linenumbertest\Program.cs:regel 14
arg = 1
System.Exception: Line number = 41
   bij linenumbertest.Test.ThrowSomeException(Int32 arg) in c:\Users\nate\Docume
nts\Visual Studio 2012\Projects\linenumbertest\Program.cs:regel 42
   bij linenumbertest.Program.Main() in c:\Users\nate\Documents\Visual Studio 20
12\Projects\linenumbertest\Program.cs:regel 14
arg = 2
System.Exception: Line number = 46
   bij linenumbertest.Test.ThrowSomeException(Int32 arg) in c:\Users\nate\Docume
nts\Visual Studio 2012\Projects\linenumbertest\Program.cs:regel 37
   bij linenumbertest.Program.Main() in c:\Users\nate\Documents\Visual Studio 20
12\Projects\linenumbertest\Program.cs:regel 14

这与使用调试器运行它的结果不同。

快速测试似乎表明异常和 throw 语句之间的额外行（在本例中 console.writeline() 也会影响结果：

改写为：

switch (arg)
    {
        case 0:
            {
                Exception ex = new Exception("Line number = 37");
                Console.WriteLine("case 0");
                throw ex;
            }
        case 1:
            {
                Exception ex = new Exception("Line number = 43");
                Console.WriteLine("case 1");
                throw ex;
            }
        default:
            {
                Exception ex = new Exception("Line number = 49");
                Console.WriteLine("case default");
                throw ex;                    
            }
    }

给出 VS 的 Release 输出：

arg = 0
case 0
System.Exception: Line number = 37
   bij linenumbertest.Test.ThrowSomeException(Int32 arg) in c:\Users\nate\Docume
nts\Visual Studio 2012\Projects\linenumbertest\Program.cs:regel 43
   bij linenumbertest.Program.Main() in c:\Users\nate\Documents\Visual Studio 20
12\Projects\linenumbertest\Program.cs:regel 15
arg = 1
case 1
System.Exception: Line number = 43
   bij linenumbertest.Test.ThrowSomeException(Int32 arg) in c:\Users\nate\Docume
nts\Visual Studio 2012\Projects\linenumbertest\Program.cs:regel 49
   bij linenumbertest.Program.Main() in c:\Users\nate\Documents\Visual Studio 20
12\Projects\linenumbertest\Program.cs:regel 15
arg = 2
case default
System.Exception: Line number = 49
   bij linenumbertest.Test.ThrowSomeException(Int32 arg) in c:\Users\nate\Docume
nts\Visual Studio 2012\Projects\linenumbertest\Program.cs:regel 51
   bij linenumbertest.Program.Main() in c:\Users\nate\Documents\Visual Studio 20
12\Projects\linenumbertest\Program.cs:regel 15

以及命令行的输出：

arg = 0
case 0
System.Exception: Line number = 37
   bij linenumbertest.Test.ThrowSomeException(Int32 arg) in c:\Users\nate\Docume
nts\Visual Studio 2012\Projects\linenumbertest\Program.cs:regel 43
   bij linenumbertest.Program.Main() in c:\Users\nate\Documents\Visual Studio 20
12\Projects\linenumbertest\Program.cs:regel 15
arg = 1
case 1
System.Exception: Line number = 43
   bij linenumbertest.Test.ThrowSomeException(Int32 arg) in c:\Users\nate\Docume
nts\Visual Studio 2012\Projects\linenumbertest\Program.cs:regel 45
   bij linenumbertest.Program.Main() in c:\Users\nate\Documents\Visual Studio 20
12\Projects\linenumbertest\Program.cs:regel 15
arg = 2
case default
System.Exception: Line number = 49
   bij linenumbertest.Test.ThrowSomeException(Int32 arg) in c:\Users\nate\Docume
nts\Visual Studio 2012\Projects\linenumbertest\Program.cs:regel 39
   bij linenumbertest.Program.Main() in c:\Users\nate\Documents\Visual Studio 20
12\Projects\linenumbertest\Program.cs:regel 15

VS 的调试输出：

arg = 0
case 0
System.Exception: Line number = 37
   bij linenumbertest.Test.ThrowSomeException(Int32 arg) in c:\Users\nate\Docume
nts\Visual Studio 2012\Projects\linenumbertest\Program.cs:regel 42
   bij linenumbertest.Program.Main() in c:\Users\nate\Documents\Visual Studio 20
12\Projects\linenumbertest\Program.cs:regel 15
arg = 1
case 1
System.Exception: Line number = 43
   bij linenumbertest.Test.ThrowSomeException(Int32 arg) in c:\Users\nate\Docume
nts\Visual Studio 2012\Projects\linenumbertest\Program.cs:regel 48
   bij linenumbertest.Program.Main() in c:\Users\nate\Documents\Visual Studio 20
12\Projects\linenumbertest\Program.cs:regel 15
arg = 2
case default
System.Exception: Line number = 49
   bij linenumbertest.Test.ThrowSomeException(Int32 arg) in c:\Users\nate\Docume
nts\Visual Studio 2012\Projects\linenumbertest\Program.cs:regel 51
   bij linenumbertest.Program.Main() in c:\Users\nate\Documents\Visual Studio 20
12\Projects\linenumbertest\Program.cs:regel 15

命令行的输出如下：

arg = 0
case 0
System.Exception: Line number = 37
   bij linenumbertest.Test.ThrowSomeException(Int32 arg) in c:\Users\nate\Docume
nts\Visual Studio 2012\Projects\linenumbertest\Program.cs:regel 42
   bij linenumbertest.Program.Main() in c:\Users\nate\Documents\Visual Studio 20
12\Projects\linenumbertest\Program.cs:regel 15
arg = 1
case 1
System.Exception: Line number = 43
   bij linenumbertest.Test.ThrowSomeException(Int32 arg) in c:\Users\nate\Docume
nts\Visual Studio 2012\Projects\linenumbertest\Program.cs:regel 48
   bij linenumbertest.Program.Main() in c:\Users\nate\Documents\Visual Studio 20
12\Projects\linenumbertest\Program.cs:regel 15
arg = 2
case default
System.Exception: Line number = 49
   bij linenumbertest.Test.ThrowSomeException(Int32 arg) in c:\Users\nate\Docume
nts\Visual Studio 2012\Projects\linenumbertest\Program.cs:regel 51
   bij linenumbertest.Program.Main() in c:\Users\nate\Documents\Visual Studio 20
12\Projects\linenumbertest\Program.cs:regel 15