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 next 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中获得了这种奇怪的行为，在Release中，行号是正确的。

Answer 1

我试过反编译程序集，看起来程序集在任一模式下都做了一些优化。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在调试和发布模式下告诉我方法的样子。如果您查看原始装配体，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Wiki，希望通过协作努力解决这个问题。

---

我做了一些测试。我已将ThrowSomeException（）函数移动到一个单独的类，并使其成为非静态的，并且没有任何改变。然后我稍微重写了一下，首先将异常分配给变量，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;

                }
        }

    }
}

以上代码在调试模式下具有以下输出：

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

在发布模式下，从第46行而不是第45行抛出第二个异常。对于所有版本的.NET框架和所有版本的VS，此行为都是一致的。接下来我将尝试使用VB项目来查看它是否有所作为。

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

问题不会发生且行号一致。

我还测试了输出直接生成的可执行文件，甚至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als似乎表明exception和throw语句之间的额外行（在这种情况下是console.writeline（）也会影响结果：

重写切换到：

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;                    
            }
    }

从VS发出此版本输出：

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

并从命令行输出：

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

和VS的这个Debug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

来自命令行的输出：

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 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