VS 2017开发人员命令提示中的语言版本

问题描述：

我创建了以下程序

public class Program
{
    static void Main()
    {
        System.Console.WriteLine("Hello, World!");
    }
}

在命令提示符下编译代码时（ c：\Windows\Microsoft.NET\Framework\v4.0.30319\csc hello.cs ），返回

When compiling the code in the command prompt (c:\Windows\Microsoft.NET\Framework\v4.0.30319\csc hello.cs) which returns

Microsoft (R) Visual C# Compiler version 4.7.3056.0
for C# 5
Copyright (C) Microsoft Corporation. All rights reserved.

This compiler is provided as part of the Microsoft (R) .NET Framework, but only supports language versions up to C# 5, which is no longer the latest version. For compilers that support newer versions of the C# programming language, see http://go.microsoft.com/fwlink/?LinkID=533240

程序仍然可以编译，所以我认为没什么大不了的。根据其他搜索，我似乎认为这则消息仅供参考。

The program still compiles so I thought no big deal. Based on other searches I've done I it seemed as if this message is only informational.

但是，对于该程序

public class Program
{
    static void Main()
    {
        System.Console.WriteLine(DateTime.Now.DayOfWeek);
    }
}

返回值为

Microsoft (R) Visual C# Compiler version 4.7.3056.0
for C# 5
Copyright (C) Microsoft Corporation. All rights reserved.

This compiler is provided as part of the Microsoft (R) .NET Framework, but only supports language versions up to C# 5, which is no longer the latest version. For compilers that support newer versions of the C# programming language, see http://go.microsoft.com/fwlink/?LinkID=533240

hello.cs(5,28): error CS0103: The name 'DateTime' does not exist in the current context

根据复数视频我应该可以正常工作跟着。经过一些搜索后，许多答案都涉及更改项目中使用的C＃版本，但似乎无法将其转换为在命令提示符下工作。需要更改什么？

which should work fine according to the pluralsight videos I'm following along with. After some searches many of the answers refer to changing the version of C# being used in the project but can't seem to translate that to working in the command prompt. What needs to change?

答

系统上有几种版本的C＃编译器（csc.exe）。因此，

There are several versions of C# compiler (csc.exe) available on the system. So you have

Microsoft编译器作为框架的一部分，例如 c：\Windows\Microsoft.NET \Framework\v4.0.30319\csc.exe

作为Visual Studio一部分的Microsoft编译器（Roslyn），例如 C ：\Program Files（x86）\Microsoft Visual Studio\2017\Professional\MSBuild\15.0\Bin\Roslyn\csc.exe

Microsoft Compilers as Part of The Framework, like c:\Windows\Microsoft.NET\Framework\v4.0.30319\csc.exe
Microsoft Compilers (Roslyn) as Part of Visual Studio, like C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\MSBuild\15.0\Bin\Roslyn\csc.exe

使用

c：\Windows\Microsoft .NET\Framework\v4.0.30319\csc

c:\Windows\Microsoft.NET\Framework\v4.0.30319\csc

您正在使用.NET Framework附带的C＃编译器，并且此编译器仅支持 C＃5.0 的语言功能。

You are using the C# compiler that shipped with .NET Framework, and this compiler only supports language features up to C# 5.0.

例如，它无法编译以下程序，该程序使用新的C＃6.0语言功能在catch / finally块中等待。

For example, it cannot compile the following program which uses the new C# 6.0 language feature Await in catch/finally blocks.

class Program
{
    static void Main(string[] args)
    {
    }

    async Task<int> GetVAsync()
    {
        try
        {
        }
        catch
        {
            //gives error CS1985: Cannot await in the body of a catch clause
            await Task.Delay(1000); 
        }            
        return 3;
    }
}

警告消息的含义 >，

您选择使用的编译器（.NET Framework附带的编译器）无法使用编译C＃5.0之后引入的新功能。如果不使用任何新功能（如您的示例），则编译可能会成功。但是，最好使用Visual Studio附带的 new 编译器-Roslyn-来充分利用编译器的全部功能。

the compiler you choose to use (the one shipped with .NET Framework) is not capable of compiling new features introduced after C# 5.0. The compilation may succeed if don't use any new feature, just like your example. But you have better use the newer compilers - Roslyn that shipped with Visual Studio - to take advantage of the full power of the compiler.

解决方案

在命令行中使用它（路径可能因VS版本而异）

Use this in your command line (the path may differs based on your VS edition)

C：\Program Files（x86）\Microsoft Visual Studio\2017\Professional\MSBuild\15.0\Bin\Roslyn\csc.exe你好.cs

C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\MSBuild\15.0\Bin\Roslyn\csc.exe hello.cs

参考

*用户Lex Li在这篇文章。

* user Lex Li gave an excellent explanation on the versioning history of the C# compilers in this post.

VS 2017开发人员命令提示中的语言版本

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