VB.NET 预处理器指令 [英] VB.NET Preprocessor Directives

问题描述

为什么 #IF Not DEBUG 不能像我在 VB.NET 中期望的那样工作?

Why doesn't #IF Not DEBUG work the way I'd expect in VB.NET?

#If DEBUG Then
   Console.WriteLine("Debug")
#End If

#If Not DEBUG Then
   Console.WriteLine("Not Debug")
#End If

#If DEBUG = False Then
   Console.WriteLine("Not Debug")
#End If
' Outputs: Debug, Not Debug

但是，手动设置的 const 可以:

But, a manually set const does:

#Const D = True
#If D Then
   Console.WriteLine("D")
#End If

#If Not D Then
   Console.WriteLine("Not D")
#End If
' Outputs: D

当然，C# 也有预期的行为:

And, of course, C# has the expected behavior as well:

#if DEBUG
    Console.WriteLine("Debug");
#endif

#if !DEBUG
    Console.WriteLine("Not Debug");
#endif
// Outputs: Debug

推荐答案

事实证明，损坏的并不是 VB.NET 的全部 - 只是 CodeDomProvider(ASP.NET 和 Snippet Compiler 都使用它)).

Turns out, it's not all of VB.NET that's broken - just the CodeDomProvider (which both ASP.NET and Snippet Compiler use).

给定一个简单的源文件:

Given a simple source file:

Imports System
Public Module Module1
    Sub Main()
       #If DEBUG Then
          Console.WriteLine("Debug!")
       #End If

       #If Not DEBUG Then
          Console.WriteLine("Not Debug!")
       #End If
    End Sub
End Module

使用 vbc.exe 版本 9.0.30729.1 (.NET FX 3.5) 编译:

Compiling with vbc.exe version 9.0.30729.1 (.NET FX 3.5):

> vbc.exe default.vb /out:out.exe
> out.exe
  Not Debug!

这是有道理的...我没有定义 DEBUG，所以它显示Not Debug！".

That makes sense...I didn't define DEBUG, so it shows "Not Debug!".

> vbc.exe default.vb /out:out.exe /debug:full
> out.exe
  Not Debug!

并且，使用 CodeDomProvider:

And, using CodeDomProvider:

Using p = CodeDomProvider.CreateProvider("VisualBasic")
   Dim params As New CompilerParameters() With { _
      .GenerateExecutable = True, _
      .OutputAssembly = "out.exe" _
   }
   p.CompileAssemblyFromFile(params, "Default.vb")
End Using

> out.exe
Not Debug!

好的，再说一遍——这是有道理的.我没有定义 DEBUG，所以它显示Not Debug".但是，如果我包含调试符号怎么办?

Okay, again - that makes sense. I didn't define DEBUG, so it shows "Not Debug". But, what if I include debug symbols?

Using p = CodeDomProvider.CreateProvider("VisualBasic")
   Dim params As New CompilerParameters() With { _
      .IncludeDebugInformation = True, _
      .GenerateExecutable = True, _
      .OutputAssembly = "C:\Users\brackett\Desktop\out.exe" _
   }
   p.CompileAssemblyFromFile(params, "Default.vb")
End Using

> out.exe
Debug!
Not Debug!

嗯...我没有定义 DEBUG，但也许它为我定义了它?但如果是这样，它一定将其定义为1"——因为我无法用任何其他值来获得这种行为.ASP.NET，使用 CodeDomProvider，必须以同样的方式定义.

Hmm...I didn't define DEBUG, but maybe it defined it for me? But if it did, it must have defined it as "1" - because I can't get that behavior with any other value. ASP.NET, using the CodeDomProvider, must define it the same way.

看起来 CodeDomProvider 正在绊倒 VB.NET 愚蠢的伪逻辑运算符.

Looks like the CodeDomProvider is tripping over VB.NET's stupid psuedo-logical operators.

故事的寓意?#If Not 对 VB.NET 来说不是一个好主意.

Moral of the story? #If Not is not a good idea for VB.NET.

现在该源可用，我可以验证它确实按照我的预期将它设置为等于 1:

And now that source is available, I can verify that it does actually set it equal to 1 as I expected:

if (options.IncludeDebugInformation) {
      sb.Append("/D:DEBUG=1 ");
      sb.Append("/debug+ ");
}

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