Error Invalid option '6' for /langversion; must be ISO-1, ISO-2, 3, 4, 5 or Default

Question

I am trying to target .NET 4.6 and also take advantage of the latest C# version by changing the C# language version to 6.

However during compilation I got this error:

Error Invalid option '6' for /langversion; must be ISO-1, ISO-2, 3, 4, 5 or Default

If I update the /langversion:6 in Web.Config setting to 5 it works,

  <system.codedom>
    <compilers>
      <compiler language="c#;cs;csharp" extension=".cs" type="Microsoft.CSharp.CSharpCodeProvider, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" warningLevel="4" compilerOptions="/langversion:6 /nowarn:1659;1699;1701">

But how do I resolve this without resorting to lower language version?

I am using Visual Studio 2015 Community Edition, and I have also installed .NET Framework 4.6 manually just in case it was not installed by default by Visual Studio 2015.

The project is a standard ASP.NET MVC template project created by Visual Studio 2015.

Answer 1

注意编译器＆＃34;输入＆＃34;在Web.Config文件中，更改Framework版本时：

表示4.5和C＃5 -

type="Microsoft.CSharp.CSharpCodeProvider...

表示4.6和C＃6 -

type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"

More info in this forum post

Answer 2

更新以下NuGet软件包（以安装者为准）解决问题：

• Microsoft.CodeDom.Providers.DotNetCompilerPlatform
• Microsoft.Net.Compilers

Answer 3

1.转到Project并选择您的项目属性。

2选择Build并单击Advanced Button。

3.选择语言版本默认。

4.Save。

https://youtu.be/IP8feQeWqkk

Answer 4

如果项目未完全升级到VS2015，我遇到了这样的行为。如果您在2015年在VS2013中打开解决方案 - 您将收到此错误

Answer 5

打开NuGet软件包管理器控制台并运行以下命令

更新包Microsoft.CodeDom.Providers.DotNetCompilerPlatform -r

Answer 6

查看 ASP.NET strange compilation error! 的答案。

将您的C＃语言降级为5只会掩盖问题，只要有人使用C＃6功能，您的网站/项目就会中断，您仍然会花时间再次修复它。尝试链接中的解决方案。

Answer 7

当我第一次在Visual Studio 2019中加载应用程序时，我遇到了类似的问题。将“ Microsoft.CodeDom.Providers.DotNetCompilerPlatform” nuget更新到更高版本对我来说很成功。