C# compiler options

This section describes the options interpreted by the C# compiler. Options are grouped into separate articles based on what they control, for example, language features, code generation, and output. Use the table of contents to navigate amongst them.

How to set options

There are two different ways to set compiler options in .NET projects:

  • In your *.csproj file

    You can add MSBuild properties for any compiler option in your *.csproj file in XML format. The property name is the same as the compiler option. The value of the property sets the value of the compiler option. For example, the following project file snippet sets the LangVersion property.

    <PropertyGroup>
  <LangVersion>preview</LangVersion>
</PropertyGroup>

    For more information on setting options in project files, see the article MSBuild properties for .NET SDK Projects.

  • Using the Visual Studio Property pages

    Visual Studio provides property pages to edit build properties. To learn more about them, see Manage project and solution properties - Windows or Manage project and solution properties - Mac.

.NET Framework projects

Important

This section applies to .NET Framework projects only.

In addition to the mechanisms described above, you can set compiler options using two additional methods for .NET Framework projects:

  • Command line arguments for .NET Framework projects: .NET Framework projects use csc.exe instead of dotnet build to build projects. You can specify command line arguments to csc.exe for .NET Framework projects.
  • Compiled ASP.NET pages: .NET Framework projects use a section of the web.config file for compiling pages. For the new build system, and ASP.NET Core projects, options are taken from the project file.

The word for some compiler options changed from csc.exe and .NET Framework projects to the new MSBuild system. The new syntax is used throughout this section. Both versions are listed at the top of each page. For csc.exe, any arguments are listed following the option and a colon. For example, the -doc option would be:

-doc:DocFile.xml

You can invoke the C# compiler by typing the name of its executable file (csc.exe) at a command prompt.

For .NET Framework projects, you can also run csc.exe from the command line. Every compiler option is available in two forms: -option and /option. In .NET Framework web projects, you specify options for compiling code-behind in the web.config file. For more information, see <compiler> Element.

If you use the Developer Command Prompt for Visual Studio window, all the necessary environment variables are set for you. For information on how to access this tool, see Developer Command Prompt for Visual Studio.

The csc.exe executable file is usually located in the Microsoft.NET\Framework\<Version> folder under the Windows directory. Its location might vary depending on the exact configuration of a particular computer. If more than one version of .NET Framework is installed on your computer, you'll find multiple versions of this file. For more information about such installations, see How to: determine which versions of the .NET Framework are installed.